In a similar study, Swiss Webster mice were exposed to styrene for 3 minutes ( Alarie 1973). The test substance was solubilized in polyethylene glycol and aerosols were prepared. An RD50 of 666 µ g/ l ( 156 ppm) ( 95 % conf. limit 574   758 µ g/ l; 134   177 ppm) was determined. In a further study by the same author ( cited in Bos et al. 1992), Swiss Webster mice were exposed for 10 minutes and an RD50 of 980 ppm ( 85 % conf. limit 826   1297 ppm) was determined.

Behavioral studies Behavioral changes in a " despair swimming test" were studied in Swiss OF1 mice ( de Ceaurriz et al. 1983). Groups of 10 male animals were exposed to analytically ( gas chromatography) confirmed concentrations of 413, 610, 807, or 851 ppm styrene or air in 200 L chambers for 4 hours. Immediately afterwards, total duration of immobility during a 3 minute period in a " despair swimming test" was determined. Immobility was defined as cessation of struggling to get out of the water. Exposure to solvents including styrene caused a dose dependent decrease in duration of immobility as compared to the corresponding controls. In case of styrene, the mean duration of immobility decreased significantly by 28, 60, 77, or 83 % of control at the concentrations noted above. An ID50 ( 50 % decrease in immobility) of 549 ppm ( 95 % confidence interval 522   573 ppm) was calculated.

Immunological effects It is reported that female BALB/ c mice ( 6 per group) exposed to 300 ppm but not to 200 or 100 ppm styrene showed an increase in IgM response of lung associated lymph nodes in an anti SRBC ( sheep red blood cells) assay. Furthermore, the ex vivo release of   interferon from lung associated lymph nodes decreased with increasing concentration of styrene but was higher than control values at all styrene concentrations. No effects were seen in the spleen ( Ban et al. 2003). An evaluation of the results is not possible since the duration of exposure is not reported.

Studies with repeated inhalation exposure Pulmonary toxicity was studied in CD 1 mice ( Green et al. 2001b). Groups of 5 female and 5 male mice were exposed " whole body" in 3.4 m ³ chambers to analytically ( gas chromatography) controlled concentrations of 0, 40 or 160 ppm styrene for 6 hours. At 40 ppm, in mice killed immediately after exposure, there was evidence of necrosis and loss of cells, believed to be Clara cells, from large bronchioles, Styrene NAC: 02/ 2004 29 while Clara cells in the terminal bronchioles were not overtly affected. At 160 ppm, no significant effect was seen at this time point. In animals killed 18 hours after exposure, minimal necrosis but treatmentrelated focal loss of cytoplasm from non ciliated cells was observed, predominantly at the terminal bronchiolar area. Females seemed slightly more affected than males. The lesions observed at this time point were similar at both styrene concentrations. In mice that had received 5 bromo 2 deoxyuridine 3 days prior to sacrifice, no evidence of an increase in cell replication in the alveoli, terminal or large bronchioles was observed after one day of exposure to styrene.

In a further study of the authors, the toxicity of styrene to the nasal epithelium was studied in male CD 1 mice. 20 mice per dose group were exposed to analytically ( gas chromatography) confirmed concentrations of 0, 40 or 160 ppm styrene for 6 hours/ day for 3 days. Mice were killed 17 hours after the last exposure. At 160 ppm, degenerative, mostly focal changes in the olfactory tissue were observed in all mice. Most obvious was the presence of cellular and serious fluid exudate in the airways of the nasal passages in the olfactory epithelium of the dorsal meatus. Atrophy of the olfactory mucosa with loss of cellular organisation and focal decrease of Bowman ´ s glands were also observed. At 40 ppm, animals were largely unaffected, only one mouse showed minimal atrophy of the olfactory mucosa ( Green et al. 2001a).

Effects on the nasal passages and the lung were also investigated by Cruzan et al. ( 2001). Groups of 55 male CD 1 mice were exposed to analytically ( gas chromatography) confirmed concentrations of 0, 40 or 80 ppm styrene in 2.43 m ³ inhalation chambers for 6 hours/ day, 5 days/ week for up to 13 weeks. A subgroup of 5 mice was terminated after one exposure ( and further subgroups after repeated exposures). In the nasal olfactory epithelium, single cell necrosis was found after a single exposure to 80 ppm, but not to 40 ppm. No changes were observed in the lung at 40 or 80 ppm up to the end of the 13th week.

3.2.4 Guinea pigs In the study of Spencer et al. ( 1942), guinea pigs generally showed the same reactions to styrene exposure than rats: irritation of mucous membranes, CNS depression and pulmonary changes ( see 3.2.2). The effects occurred at the same concentrations, however, it was reported that under comparable conditions of exposure the pulmonary changes were more severe in guinea pigs than in rats.

Studies with repeated inhalation exposure In a study on ototoxicity of styrene, pigmented guinea pigs were exposed to 1000 ppm, 6 hours/ day, for 5 days. Cochlear function as tested by DPOAE ( distortion product otoacoustic emissions) was measured before exposure, immediately afterwards, and 2 and 4 weeks after exposure. In contrast to the observations made in rats similarily exposed in the same study ( see 3.2.2), no disruption of auditory function was observed in guinea pigs ( Lataye et al. 2003).

3.2.5 Rabbits Studies with repeated inhalation exposure In the study of Spencer et al. ( 1942), 2 rabbits ( strain, sex, and further experimental details not reported) received up to 126 exposures to 2000 ppm for 7.5   8 hours/ day, 5 days/ week The rabbits were reported not to be affected by these exposures. In contrast, rats and guinea pigs showed marked eye and nose irritation during the exposures. Styrene NAC: 02/ 2004 30 3.3 Developmental/ Reproductive Toxicity Data are available from studies with rats, mice, rabbits, and hamsters ( for review, see Brown 1991; 2000; IARC 2002).

3.3.1 Rats No studies were identified concerning the effects of a single inhalation exposure to styrene on developmental or reproductive toxicity.

Studies with non inhalation exposure Sprague Dawley rats were treated on the 11th day of gestation with a single dose of 300 mg/ kg styrene in corn oil by gavage ( Daston et al. 1991). The dose led to maternal toxicity ( decreased body weight, reduced food intake) but no effects on pre and postimplantation losses, malformations and variations were observed on gestation day 20.

In a carcinogenicity study ( Ponomarkov and Tomatis 1978), female BD IV rats were given 1350 mg/ kg b. w. styrene in olive oil by gavage on day 17 of gestation ( followed by weekly treatment of the offsprings with 500 mg/ kg b. w. after weaning). Preweaning mortality in offsprings from styrene treated dams was non significantly higher ( 10 %) than in the control group ( 2.5 %). There was no effect on litter size at birth, postweaning survival, or body weight development.

Studies with repeated inhalation exposure A " segment II" developmental toxicity study was conducted by Murray et al. ( 1978). Female Sprague Dawley rats were exposed to 0, 300 or 600 ppm for 7 hours/ day during day 6   15 of gestation. Both styrene concentrations were maternally toxic ( decreased body weight gain and decreased food consumption). A greater incidence of skeletal variations but no other embryo or fetal developmental effects were observed in offsprings of styrene treated dams compared to controls. The authors reported that the observed incidence was within the range ( number not reported) of historical controls.

Postnatal neurochemical changes, growth, and physical landmarks of development were studied in offsprings of female Wistar rats that had been treated with 0, 50 or 300 ppm 6 hours/ day during gestation day 6   20 ( Katakura et al. 2001). To adjust for nutritional effects, pair fed and ad libitum controls were included. Food consumption of dams was decreased at 300 ppm, but maternal weight gain was not significantly different from that of both control groups. Litter size, birth weight and sex ratio were found to exhibit no effects within the variation range studied. At 300 ppm, an increased neonatal death rate was observed compared to the pair fed control group. Postnatal development ( incisor eruption, eye opening, air righting reflex) was also delayed at 300 ppm compared to both control groups. Furthermore, neurochemical alterations were observed as indicated by a significantly decreased 5 hydroxytryptamine concentration in the cerebrum at postnatal day 21 in offspring exposed in utero to 300 ppm styrene. These results suggest that the offspring were susceptible to the effects of styrene on a few developmental landmarks and the results support previous findings of alterations in postnatal development in offsprings of styrene treated dams ( Kishi et al. 1992; 1995).

Studies with non inhalation exposure In the study of Murray et al. ( 1978) ( see above), pregnant rats were also treated with 90 or 150 mg/ kg b. w. styrene by gavage twice daily from the 6th to 15th day of gestation. Compared to non treated Styrene NAC: 02/ 2004 31 controls, maternal weight gain was reduced and the incidence of skeletal variation was higher in styreneexposed groups. However, the authors reported that the observed incidences were within the range ( numbers not reported) of historical controls.

In a further segment II teratology study, albino rats were treated orally with 250 or 400 mg/ kg b. w. styrene in peanut oil on gestation days 6   15 ( Srivastava et al. 1990). At 400 mg/ kg b. w., maternal toxicity ( severe reduction in weight gain), increased pre and postimplantation losses and reduction in fetal weight was observed but no gross or structural defects. No maternal toxicity and embryo/ fetotoxic or developmental effects were seen at 250 mg/ kg b. w.

Maternal toxicity ( severe reduction in body weight, but no deaths) were also seen in a further study in which Sprague Dawley rats were administered 1147 mg/ kg b. w. styrene on gestation day 6   15 ( Chernoff et al. 1990). No differences compared to control were observed with respect to fetal weight, embryo/ fetal death, and skeletal or soft tissue malformations or variations.

Interactions of styrene exposure with protein malnutrition were studied by Khanna et al. ( 1991). Rats were given a diet of 20 % casein or 8 % casein throughout pregnancy and lactation, with or without 100 mg/ kg b. w. of styrene given orally from day 6 of gestation onward. Low casein diet alone led to a reduction in postnatal weight gain and a delay in development ( eye opening, behavioral responses). These effects were more pronounced in pups of dams that were treated with styrene and receiving the low casein diet. These pups also showed a decrease in brain enzyme activities. No such effects were seen in offsprings of dams that were given the normal casein diet.

In a three generation reproductive toxicity study, female and male rats were continuously exposed to 125 or 250 ppm styrene in drinking water ( 7   10 mg/ kg b. w. or 14   21 mg/ kg b. w., respectively). Water consumption was reduced in both groups. In high dose females, body weight gain was slightly reduced but no consistent treatment related effects on pup survival, pup body weights, or developmental parameters could be observed ( Beliles et al. 1985).

3.3.2 Mice In a carcinogenicity study ( Ponomarkov and Tomatis 1978), female O20 and C57Bl mice were given styrene in olive oil by gavage on day 17 of gestation ( O20: 1350 mg/ kg b. w.; C57Bl: 300 mg/ kg b. w. each followed by weekly treatment of the offsprings with the same dose after weaning). In O20 mice, the maximum tolerated dose was exceeded. There was no effect on litter size at birth or on body weight gain but survival prior to weaning was decreased in the offspring of treated animals. In C57Bl mice, no effects on maternal mortality, litter size or preweaning mortality was observed.

Studies with repeated inhalation exposure Pregnant female BMR/ T6T6 mice were exposed to an analytically ( infrared spectophotometry) controlled concentration of 250 ppm styrene or air ( control) for 6 hours/ day from the 6th to the 16th day of gestation and sacrificed the last day of exposure ( Kankaanpää et al. 1980). The number of dead or resorbed fetuses was higher in styrene exposed mice ( 26.9 %) compared to controls ( 18.2 5) but did not reach statistical significance ( 0.05 < p < 0.10). Among 94 live fetuses in the styrene exposed group, 3 were malformed ( rib fusion, extra rib), in the control group, among 76 live fetuses, one was malformed ( exteriorization of the liver). No statistical evaluation of these results was presented in the report, but it seems unlikely that the effect would have been significant. In preliminary experiments with exposure to 500 and 750 ppm, high maternal mortality was observed ( 250 ppm: 2/ 6; 750 ppm: 3/ 5 died before gestation day Styrene NAC: 02/ 2004 32 16). Surviving mice carried a high number of dead and resorbed fetuses ( fetal death rate at 250 ppm: 47 %; at 750 ppm: 95 %).

3.3.3 Rabbits Studies with repeated inhalation exposure A " segment II" developmental toxicity study was conducted by Murray et al. ( 1978). Female New Zealand white rabbits were exposed to 0, 300 or 600 ppm for 7 hours/ day during day 6   18 of gestation. No maternal toxicity, no embryo/ fetotoxicity and no teratogenic effects were evident in styrene exposed groups. Compared to the concurrent control, a higher incidence of a single skeletal variation was observed at 600 ppm. However, the authors state that the observed incidence was within the range of historical controls. It is reported ( Brown et al. 2000) that styrene is not maternally toxic to rabbits at concentrations up to 1000 ppm so the validity of the study seems to be limited.

3.3.4 Hamsters Studies with repeated inhalation exposure Pregnant Chinese hamsters were exposed to analytically ( infrared spectophotometry) controlled concentrations of 300, 500, 750, and 1000 ppm styrene or air ( control) for 6 hours/ day from the 6th to the 18th day of gestation and sacrificed the last day of exposure ( Kankaanpää et al. 1980). No fetal/ embryotoxic effects or malformations were seen at 300, 500, and 750 ppm. At 1000 ppm, the only effect seen was a significantly increased number of dead or resorbed fetuses ( 66 %) compared to 26.2 % in the control group.

3.4 Genotoxicity A large number of studies have been published in which genotoxic effects ( including DNAadducts of styrene were investigated in vitro and in vivo. These studies have been extensively evaluated and summarized in a number of reviews ( ATSDR 1992; Cohen et al. 2002; IARC 1994; IARC 2002; Scott and Preston 1994; Vodicka et al. 2002; WHO 1983; WHO 2000). Since a detailed description of the findings from these studies is beyond the scope of this TSD, results described in these reviews are summarized.

Styrene itself does not react with DNA or other nucleophiles in vitro in the absence of metabolic activation. The genotoxic potential of styrene depends on the ability of the in vitro or in vivo system to metabolize styrene to reactive elecrophiles. The main primary metabolite of styrene in mammals is styrene oxide ( SO), an electrophilic epoxide that is able to form covalent adducts with nucleophiles such as DNA. In accordance with this, SO binds to DNA and shows genotoxic activity in vitro and in vivo. The potency of styrene in metabolically active test systems is dependent on a number of additional factors, e. g., the ability to detoxify SO to non reactive metabolites and to repair initial DNA lesions.

In several studies with bacteria test systems ( different strains of Salmonella typhimurium), styrene was not mutagenic in the absence of exogenous metabolic activation system. In the presence of such activation system, in some but not all studies, mutagenic effects were observed. Styrene induced gene conversion and mitotic recombination in yeast cells in vitro and in a host mediated assay using mice as hosts. In Drosophila melanogaster, somatic mutations were only observed in insecticide resistant strains that have a high bioactivation capacity. Styrene NAC: 02/ 2004 33 In in vitro tests using rodent cells, styrene induced sister chromatid exchanges ( SCE) in a study using whole blood rat lymphocyte cultures. An increase in SCE was also observed in several studies with Chinese hamster ovary ( CHO) cells, mostly in the presence of exogenous metabolic activation ( S9 mix, human erythrocytes), and a further increase was observed by the addition of cyclohexane epoxide, an epoxide hydrolase inhibitor. Furthermore, styrene induced chromosomal aberrations ( CA) in Chinese hamster lung ( CHL) cells in the presence but not in the absence of exogenous metabolic activation.

In vivo assays with rodents were performed with rats, mice, and hamsters. Chromosomal aberrations ( CA) and polyploidy, but not aneuploidy, in bone marrow were observed in one inhalation study in which Wistar rats were exposed to 300 ppm styrene ( 6 hours/ day, 5 days/ week, 9 weeks). No increase in CA was observed in other inhalation studies in bone marrow of Sprague Dawley rats ( 600, 1000 ppm, 6 hours/ day, 5 days/ week, 12 months), in blood and spleen lymphocytes of B6C3F1 mice ( 124   491 ppm, 6 hours/ day, 14 days), and in bone marrow of Chinese hamsters ( 300 ppm, 6 hours/ day, 4 days or 5 days/ week for 3 weeks). Also, no increase in CA in bone marrow was observed following oral administration of styrene in CD 1 mice ( 1000 mg/ kg once; 500 mg/ kg for 4 days, 200 mg/ kg for 70 days) or i. p. administration in C57/ BL6 mice ( 50   1000 mg/ kg). Induction of micronuclei ( MN) in bone marrow occurred following i. p. treatment of C57BL6 mice ( 250   1500 mg/ kg), but not in blood erythrocytes and spleen lymphocytes of B6C3F1 mice following inhalation exposure ( 124   491 ppm, 6 hours/ day, 14 days) or in bone marrow of hamsters after i. p. administration ( 1000 mg/ kg). Sister chromatid exchanges ( SCE) were not observed in blood lymphocytes of F344 rats after inhalation of styrene ( 150   1000 ppm, 6 hours / day, 5 days/ week, up to 4 weeks). In mice, however, an increase in SCE in liver, bone marrow, alveolar macrophages, lung, blood and spleen lymphocytes was observed after single ( 922 ppm, 6 hours) or repeated ( 387 ppm, 6 hours/ day, 4 days) inhalation of styrene in BDF1 mice and in C57/ Bl6 and B6C3F1 mice after i. p. administration of styrene. In a recently published study that is not included in the reviews mentioned above, no evidence of clastogenicity in bone marrow of NMRI mice was observed following styrene inhalation exposure at 750 mg/ m ³ ( 175 ppm) or 1500 mg/ m ³ ( 350 ppm), 6 hours/ day, for 1, 3, 7, 14, or 21 consecutive days ( Engelhardt et al. 2003).

DNA strand breaks were detected in a comet assay in liver, kidney, lymphocytes, and bone marrow of C57/ Bl6 mice following single i. p. administration of 250 or 350 mg/ kg b. w. styrene.

DNA adducts of SO have been detected in several studies with rodents. In CD 1 mice and Sprague Dawley rats exposed by inhalation to 160 ppm 14C styrene for 6 hours, an increase of N7 guanine DNA adducts was found in lung in liver of both species 42 hours later. More recent studies use 32Ppostlabelling assays to detect and quantify different DNA adducts. A dose respondent increase in N7 and O6 guanine DNA adducts of SO could be detected 3 hours after a single i. p. administration of styrene ( up to 450 mg/ kg b. w.) to NMRI mice. The adduct level in the lungs was higher than that in liver. Similar results were obtained in a further study with NMRI in which animals were exposed by inhalation to 175 or 350 ppm styrene, 6 hours/ day, 7 days/ week, for 1   21 days. The adduct levels increased linearily with time.

Differences in adduct levels between rats and mice with respect to differences in carcinogenicity between these two species were studied by Otteneder et al.( 2002). In samples of liver tissue from CD rats treated with styrene via inhalation for 2 years, levels of O6 SO guanine adducts were above the limit of detection only in the highest dose group ( 1000 ppm). It was concluded that rat liver is able to tolerate a comparatively high level of styrene derived DNA adducts without a detectable increase of the tumor rate. Further, CD 1 mice were exposed 6 hours/ day, 5 days/ week, 2 weeks, to 0, 40, or 160 ppm styrene, CD rats were exposed to 0 or 500 ppm. No increase in O6 SO guanine adducts could be detected in any of the lung samples despite the observation from carcinogenicity studies that styrene increases the rate of lung tumors in mice but not in rats. The authors concluded that species and site specific tumor formation by Styrene NAC: 02/ 2004 34 styrene is not reflected by DNA adducts in tissues. However, this conclusion has been questioned because the expected levels of O6 SO guanine adducts may be far below the detection limit ( Vodicka et al. 2002).

3.5 Carcinogenicity No carcinogenicity studies with single inhalation exposure of animals have been found in the literature.

Studies with non inhalation exposure No increase in tumor incidence compared to " vehicle only" controls was observed in 40 female and 40 male Sprague dawley rats given a single subcutaneous dose of 50 mg styrene per animal in olive oil or four i. p. doses of 50 mg per animal in olive oil over a period of 4 months ( Conti et al. 1988).

Studies with repeated inhalation exposure Carcinogenicity studies with repeated inhalation or oral exposure were performed with different strains of rats ( TABLE 5) and mice ( TABLE 6). A detailed review with a critical comprehensive evaluation has recently been published ( Cohen et al. 2002).

Rats Sprague Dawley rats ( initially 96 females, 96 males) were exposed to 0, 600 or 1000  1200 ppm styrene in air for 6 hours/ day, 5 days/ week for 20.7 months ( females) or 18.3 months ( males). The higher concentration was reduced from 1200 ppm to 1000 ppm after 2 months because of excessive treatmentrelated effects ( decreased weight gain) in male rats ( Jersey et al. 1978). The authors observed an incidence ( 7/ 85 animals) of mammary adenocarcinoma at 600 ppm in females that was statistically higher compared to the corresponding control ( 1/ 85) but was within the range of historical controls ( 0   9 %). There was no significant association at 1000 ppm. The incidence of lymphosarcomas and leukemia in females was identical at both styrene exposures and was not statistically higher than in the corresponding control but exceeded that observed in historical controls.

In another inhalation study, Sprague Dawley rats ( 30 females and 30 males) were exposed to 25, 50, 100, 200 or 300 ppm styrene for 4 hours/ day, 5 days/ week for 52 weeks. The study was terminated when the survival rate reached 50% in at least one experimental group ( Conti et al. 1988). Inhalation exposure to styrene was associated with a higher incidence of overall mammary tumors ( benign and malignant combined, control: 57 %, exposed: 70   83 %) and of malignant mammary tumors alone ( control: 10 %, exposed: 13   40 %). However, in the colony of rats used the incidence of mammary tumors was quite high and fluctuating and there was no clear concentration response.

In the most recently conducted inhalation study, groups of 60 female and 60 male CD ( Sprague Dawley derived) rats were exposed to 0, 50, 200, 500 or 1000 ppm styrene for 6 hours/ day, 5 days/ week for 104 weeks ( Cruzan et al. 1998). In female rats, there was no increase of any tumor or in the number of tumor bearing rats in the exposed groups compared to controls; there was a decrease in pituitary adenomas and mammary adenocarcinomas. In males, a significant trend for an increase in the incidence of interstitial cell testicular adenomas was observed ( control: 3.3 %, exposed 3.3   11.5 %). However, all rates were within the range of historical controls ( 0   13.5 %), none of the incidences were significantly different from controls by pairwise comparison, and no treatment related increase in histological alterations ( cell hyperplasia, seminiferous tubular atrophy) typically associated with chemically induced interstitial cell Styrene NAC: 02/ 2004 35 tumors was observed. Therefore, the authors judged the observed effect to be incidental and not related to styrene exposure.

TABLE 5: SUMMARY OF RESULTS ON STUDIES OF CANCER IN RATS TREATED WITH STYRENE *

Exposure Strain Route Concentration or dose Duration Tumor incidence statistically elevated, type of tumor Reference SD Inhalation 600, 1000  1200 ppm 6 hours/ day, 5 days/ week f: 18.3 months, m: 20.7 months Yes, for mammary adenocarcinoma Jersey et al. 1978 SD Inhalation 25, 50, 100, 200, 300 ppm 4 hours/ day, 5 days/ week 52 weeks Yes, for combined mammary tumors and for malignant mammary tumors only Conti et al. 1988 CD ( SDderived Inhalation 50, 200, 500, 1000 ppm 6 hours/ day, 5 days/ week 104 weeks Yes, for testicular tumors Cruzan et al. 1998 SD Gavage 50, 250 mg/ kg b. w. 4 or 5 days/ week No Conti et al. 1988 SD Drinking water 125, 250 ppm a 2 years No Beliles et al. 1985 SD Drinking water 15   19 mg/ animal x day 561 days No Oettel and Schulze 1962 F 344/ N Gavage 500 mg/ kg b. w.

1000, 2000 mg/ kg b. w. 5 days/ week; 103 weeks 5 days/ week, 78 weeks No NCI 1979b F 344/ N Gavage 175, 350, 700 mg/ kg b. w. 3 days/ week, 79 weeks No NCI 1979a BDIV Gavage 500 mg/ kg b. w. once a week b No Ponomarkov and Tomatis 1978 * Table from Cohen et al. ( 2002), modified and supplemented; a: doses at 125 ppm were 7.7 mg/ kg b. w. in males and 12 mg/ kg b. w. in females, at 250 ppm, 14 mg/ kg b. w. in males and 21 mg/ kg b. w. in females; b: Dams were administered 1350 mg/ kg b. w. styrene on day 17 of gestation, offspring received 500 mg/ kg b. w. after weaning once weekly for lifetime.

Studies with non inhalation exposure Six studies were performed in which rats were exposed orally by gavage or via drinking water to styrene ( Beliles et al. 1985; Conti et al. 1988; NCI 1979b; Oettel and Schulze 1962; Ponomarkov and Tomatis 1978) or to a mixture of 70 % styrene and 30 % ß nitrostyrene ( NCI 1979a). None of these studies Styrene NAC: 02/ 2004 36 did show an association between exposure to styrene and the development of tumors. However, it must be noted that none of these studies are fully acceptable under current standards ( number of animals, maximum tolerated dose not reached, low survival, exposure to mixture, or only weekly dosing).

Mice With mice, only one carcinogenicity study was performed in which the animals were exposed to styrene via inhalation. In this study, 50 female and 50 male CD 1 mice per group were exposed to 0, 20, 40, 80 or 160 ppm styrene for 6 hours/ day, 5 days/ week for 98 weeks ( females) or 104 weeks ( males). An increased incidence for lung tumors was observed in male and female mice. The incidence of bronchioalveolar adenomas was significantly increased in males at all except the lowest concentration of styrene, and in females at 20, 40, and 160 ppm. In males, the incidence of bronchio alveolar carcinomas in the styrene treated group was not significantly increased compared to the control. In females exposed to 160 ppm, the incidence of bronchio alveolar carcinomas was higher than in controls. In interim sacrifices after 12 and months, respectively, did not reveal lung tumors in male or female mice. Since the lung tumors observed after 2 years in styrene exposed and in control mice showed no difference in intensity of immunostaining, tumor location and type of tumor, the authors concluded that styrene increased the number of tumors seen spontaneously in this strain of mice ( Cruzan et al. 2001a).

Studies with non inhalation exposure In three studies, mice were exposed orally by gavage to styrene ( NCI 1979b; Ponomarkov and Tomatis 1978) or to a mixture of 70 % styrene and 30 % ß nitrostyrene ( NCI 1979a). It must be noted that none of these studies is fully acceptable under current standards ( number of animals too low, exposure to mixture, or only weekly dosing).

In the NCI study with styrene ( NCI 1979b), 50 female and 50 male B6C3F1 mice per styrene dose group ( 20 females, 20 males for control receiving vehicle only) received 150 or 300 mg/ kg b. w. styrene in corn oil for 5 days/ week for 78 weeks followed by a 27 week postexposure observation period. No treatment induced effect on the incidence of tumors was seen in female mice. In males, an increase in the combined incidence of lung adenomas and carcinomas was observed. The incidence in the low dose group ( 13.6 %) was clearly higher than in the corresponding control ( 0 %) but about as high as in historical controls ( 12 %, range 0   20 %). In the high dose group, the incidence ( 20.9 %) exceeded that observed in historical controls. In the NCI study using a mixture of styrene and ß nitrostyrene ( NCI 1979a), no increase in the incidence of any tumor was observed.

In the study of Ponomarkov and Tomatis ( 1978), 29 pregnant O20 mice were treated with 1350 mg/ kg b. w. in olive oil on day 17 of gestation. Offsprings ( 39 females, 45 males) received 1350 mg/ kg b. w. in olive oil once a week for 16 weeks when exposure was ended due to high mortality with hepatic necrosis, lung congestion, and spleen hypoplasia ( 20 % of females and 50 % of males had died). Controls ( 22 females, 20 males) received vehicle only. Animals were sacrificed after 120 weeks. The combined incidence of lung adenomas and carcinomas was significantly higher in the group of styrenetreated animals. No treatment related effects were described with respect to other tumors. It must be noted that the maximum tolerated dose had been exceeded.

Ponomarkov and Tomatis ( 1978) also exposed 15 pregnant C57 mice and their offspring ( 27 females, 27 males) to styrene similarly as described above but to a lower dose of only 300 mg/ kg b. w. There were no effects of styrene on survival, growth or the incidence of any tumor in this experiment. Styrene NAC: 02/ 2004 37 In a further study with i. p. administration, groups of 25 female A/ J mice received a total amount of 200 µ mol styrene ( 20.8 mg) in olive oil 3 times a week for a total of 20 injections ( Brunnemann et al. 1992), 25 control animals received vehicle only. 20 weeks after the last dose, three treated animals and one control animal had lung adenoma, the difference was not statistically significant. No lung adenocarcinomas were found in any animal. It must be noted that the total dose applied was very low.

Taking together, these studies provide evidence of an increase of lung tumors in styrene treated mice.

TABLE 6: SUMMARY OF RESULTS ON STUDIES OF CANCER IN MICE TREATED WITH STYRENE *

Exposure Strain Route Concentration or dose Duration Tumor incidence statistically elevated, type of tumor Reference CD 1 Inhalation 20, 40, 80, 160 ppm 6 hours/ day, 5 days/ week f: 98 week, m: 104 weeks Yes, for lung tumors Cruzan et al. 2001a O20 Gavage 1350 mg/ kg b. w. once a week a Yes, for lung tumors Ponomarkov and Tomatis 1978 C57 Gavage 300 mg/ kg b. w. once a week b No Ponomarkov and Tomatis 1978 B6C3F1 Gavage 150, 300 mg/ kg b. w. 5 days/ week, 78 weeks Yes, for lung tumors NCI 1979b B6C3F1 Gavage 200, 400 mg/ kg b. w. 3 days/ week, 78 weeks c No NCI 1979a A/ J I. p. total: 200 µ mol ( 20.8 mg) 3 days/ week, 20 injections No Brunnemann et al. 1992 * Table from Cohen et al. ( 2002), modified. a: Dams were administered 1350 mg/ kg b. w. styrene on day 17 of gestation, offspring received 1350 mg/ kg b. w. after weaning once a week for lifetime. b: Dams were administered 300 mg/ kg b. w. styrene on day 17 of gestation, offspring received 300 mg/ kg b. w. after weaning once a week for lifetime. c: Mice were given a mixture of 70 % styrene wih 30 % ß nitrostyrene.

3.6 Summary Lethality data were available for rats, mice, and guinea pigs. Mice were much more sensitive than the other species as death in this but not in the other species was observed in a number of studies with single or short term repeated 6 hour exposures to 250 and 500 ppm ( Cruzan et al. 1997b; Mahler et al. 1999; Morgan et al. 1993c; Morgan et al. 1993a; Sumner et al. 1997). In contrast, no death occurred in rats upon subchronic daily 6 hour exposures to 1500 ppm ( Cruzan et al. 1997b). Guinea pigs could be more sensitive than rats as indicated by the lethality data provided by Stewart et al. ( 1942), but the data base is too limited to allow firm conclusions. Limited data for monkeys ( 4 animals, species not reported; Stewart et Styrene NAC: 02/ 2004 38 al. 1942) that were exposed in a subchronic study at 1300 ppm of styrene for 7 8 hours/ day do not provide any evidence that monkeys may be more sensitive to styrene than rats.

In studies with rats, the reported lethality data ( LC0; LC50; LC100) show considerable differences between individual studies:

10,000 ppm 1 hour LC0 ( Spencer et al. 1942) 5000 ppm 1 hour LC0 ( Niklasson et al. 1993) 5000 ppm 2 hours LC0 ( Spencer et al. 1942) 10,000 ppm 3 hours LC100 ( Spencer et al. 1942) 2761 ppm 4 hours LC50 ( Shugaev 1969) 2700 ppm 4 hours LC50 ( Jaeger et al. 1974; abstract only) 6410 ppm 4 hours LC50 ( BASF 1979b) 7769 ppm 4 hours LC0 ( Lundberg et al. 1986) 1500 ppm 6 hours LC0 ( Cruzan et al. 1997; repeated exposure) 4618 ppm 6 hours LC50 ( Bonnet et al. 1982) 2500 ppm 8 hours LC0 ( Spencer et al. 1942) 7769 ppm 8 hours " LC40" ( Lundberg et al. 1986) 5000 ppm 8 hours LC100 ( Spencer et al. 1942)

Most notable, the 4 hour LC50 reported in two studies ( Jaeger et al. 1974; Shugaev, 1969) was lower than the LC50 in a third study ( BASF 1979b) and only 1/ 3 of the 4 hour LC0 in another study ( Lundberg et al. 1986). Also, it must be noted that these two " low" 4 hour LC50 were even lower than the 6 hour LC50 in another study ( Bonnet et al. 1982b) and similar to an 8 hour LC0 in a further study ( Spencer et al. 1942). Furthermore, the 4 hour LC50 of BASF ( 1979b) and the 6 hour LC50 are lower than the 8 hour concentration which caused death in 4/ 10 animals (" LC40") ( Lundberg et al. 1986).

Experimental differences between the studies are likely to have affected the outcomes of the studies. In the study of BASF ( 1979b), animals were observed for 14 days after the exposure, and delayed deaths that were observed up to 3 days after exposure were taken into account. In contrast, Lundberg et al. ( 1986) counted the number of deaths only 24 hours after start of the inhalation exposure but not at later time points. Therefore, delayed deaths will have been missed in this study. Niklasson et al. ( 1993) obviously observed no death during the neurological studies they performed in rats, but it cannot be deduced from their data whether the rats exposed to the highest concentration were observed for one week after exposure or not.

The data of Jaeger et al. ( 1974) only were published in an abstract lacking any experimental details. Shugaev ( 1969) also did not report important data, especially, the number of animals and of dose groups used were not given. In addition to data for rats, Shugaev ( 1969) also reported a 2 hour LC50 of 4914 ppm for an unspecified strain of mice. Interestingly, this value is much higher than the LC50 for rats although it is clear from a vast number of studies that mice are more susceptible to styrene than rats. Furthermore, whereas the LC50 reported by Shugaev ( 1969) for rats is much lower than the LC50 determined in other studies, the opposite is true fot the LC50 for mice in Shugaev ( 1969); this value is much higher than others reported in other studies, even when the different exposure times are taken into account ( BASF 1979a; Bonnet et al. 1979b; Izmerov et al. 1982). Although it cannot be ruled out that differences in the susceptibility of different strains of mice to styrene could play some role, it is tempting to speculate that the LC50 for rats and mice could have been erroneously mixed up with each other in the publication of Shugaev ( 1969). Styrene NAC: 02/ 2004 39 In the study of Spencer et al. ( 1942), the concentration of 10,000 ppm may be doubted in view of the observation of Lundberg et al. ( 1986) that 7769 ppm was the highest attainable ( analytically confirmed) vapor concentration of styrene. Therefore, it seems possible that in the study of Spencer et al. ( 1942) some condensation of styrene vapor at the highest concentration used had occurred ( leading to a lower vapor concentration but possibly to additional dermal exposure).

The studies of BASF ( 1979b) and Bonnet et al. ( 1982a) both reported the experimental conditions in detail ( especially, number of animals and dose groups, analytically determined vapor concentrations, and consideration of delayed deaths during post exposure period). These studies thus provide the most reliable and relevant acute lethality data for rats.

Following i. p. treatment of rats with styrene, no differences in LD50 and the corresponding confidence limits were observed when deaths were counted 24 days and 14 days after the injection ( Lundberg et al. 1986). This indicates that the delayed deaths observed after inhalation exposure are not due to a systemic effect but probably are related to the local toxic effects that are observed in the lung of animals dying some days after styrene exposure.

Very limited data from one study are available for styrene toxicity in monkeys ( species not reported) ( Spencer et al. 1942). In this study, none of 4 animals died during subchronic exposure to 1300 ppm styrene, 7   8 hours/ day, 5 days/ week. It was further reported that there were no signs of irritation or intoxication and no pathological findings in inner organs or in hematology compared to 3 control animals.

At non lethal concentrations, rats showed CNS depression. Animals were in state of deep narcosis after 1 hour of exposure to the 4 hour LC50 ( reported to be 2761 ppm, but see discussion above) ( Shugaev 1969) and lost consciousness at 2000 ppm after 5 hours ( Withey and Collins 1979). Reduced attention was described to occur at 6 hours of exposure to 1500 ppm ( Jarry et al. 2002), and an inability to supress nystagmus in an optokinetic test were seen at 1730 ppm after about 30 minutes of exposure ( Niklasson et al. 1993). Animals were mostly recumbent at 12 hours of exposure to 600 ppm ( Mäkitie et al. 2003), this may also indicate CNS depression. In mice, signs of CNS depression that occurred during a 4 hour exposure included staigered gait at 1420 ppm and apathy and finally narcosis at higher concentrations ( 2983 and 3766 ppm) ( BASF 1979a).

In rats, immediate sensory irritation occurred at 1300 ppm ( Spencer et al. 1942). Cruzan et al. ( 1997b, 1998) observed a concentration dependent increase of irritation reaching from closed eyes at 200 ppm to salivation and rubbing of paws and chin at higher concentrations ( 500, 100, 1500 ppm). Signs of sensory irritation were also observed at 500 ppm during initial exposure in one study ( Jarry et al. 2002), but in another study, no clear signs of eye, skin or mucous membrane irritation could be observed at 600 ppm ( Mäkitie et al. 2003). In mice, RD50 for sensory irritation of 156 ppm ( 3 minutes), 586 ppm ( 5 minutes) and 980 ppm ( 10 minutes) were reported ( Alarie 1973; de Ceaurriz et al. 1981; Bos et al. 1992).

In rats, pulmonary lesions at acute exposure only were observed at concentrations that also caused severe and mostly lethal CNS effects. Mice were more sensitive to styrene than rats. At 250 ppm and 500 ppm, upper respiratory tract and lung toxicity, liver lesions and sometimes death were observed following one or few exposures, and differences in sensitivity between strains were observed; B6C3F1 were most sensitive ( Morgan et al. 1993a, c; Mahler et al. 1999; Cruzan et al. 1997; Sumner et al. 1997).

Ototoxicity of styrene was observed in rats after repeated exposure. Exposure for 6 hours/ day, 5 days/ week, for 4 weeks to 850 ppm and higher concentrations caused a permanent increase in auditory Styrene NAC: 02/ 2004 40 threshold, at 500 ppm, no effect was observed ( Loquet et al. 1999). In another study, no effect was seen immediately after exposure to 1000 ppm, 6 hours/ day, for 5 days, but tests indicated a disruption of cochlear auditory function 2 and 4 weeks after the end of exposure. In the same study, no effects were detected in similarily exposed guinea pigs ( Lataye et al. 2003). Histological lesions of the cochlea and worsening of the electrophysiological results after the end of exposure were also described in another publication of the same group after exposure of rats to 1000 ppm, 6 hours/ day, 5 days/ week, for up to 4 weeks ( Campo et al. 2001). No hearing impairment was detected in rats exposed to 100 or 300 ppm styrene for 12 hours/ day, 5 days/ week, for 4 weeks; at 600 ppm, a hearing loss of ~ 3 dB was observed only at the highest test frequeny of 8 kHz, and cytocochleograms showed a substantial loss of the outer hair cells of the cochlea from these animals ( Mäkitie et al. 2003).

No studies were available concerning effects of a single inhalation exposure to styrene on reproductive or developmental toxicity. A single oral administration of 300 mg/ kg b. w. of styrene on day 11 of gestation caused maternal toxicity in rats, but had no developmental or fetotoxic effects ( Daston et al. 1991). In another study with rats and mice that were treated orally with styrene on gestation day 17, 1350 mg/ kg b. w. styrene had no significant effect on preweaning mortality, litter size at birth, or body weight development in BD IV rats. In O20 mice, survival prior to weaning was reduced after 1350 mg/ kg b. w., no effect was seen in C57Bl mice given 300 mg/ kg b. w. ( Ponomarkov and Tomatis 1978).

Following repeated 6 hour exposure of rats to 300 ppm during gestation day 6   20, an increased neonatal death rate was observed compared to pair fed controls ( that were included to control for a styreneinduced reduction of food intake; maternal weight gain was not affected). Postnatal development ( incisor eruption, eye opening, air righting reflex) also was delayed. No effects were seen at 50 ppm ( Katakura et al. 2001). These findings supported those from earlier studies in which similar effects were described but no pair fed controls were used ( Kishi et al. 1992; 1995). In a study with hamsters, the number of dead or resorbed fetuses was increased in the group exposed to 1000 ppm 6 hours/ day from gestation day 6  18, but not at 750 ppm or lower concentrations ( Kankaanpää et al. 1980). In other studies with repeated oral or inhalation exposure of rats, mice, and rabbits, no significant developmental effects were seen ( Murray et al. 1978; Srivastava et al. 1990; Chernoff et al. 1990; Beliles et al. 1985; Kankaanpää et al. 1980).

Styrene is genotoxic in vitro, provided there is sufficient activation to styrene oxide ( SO), and in vivo. Data from laboratory animals indicate that styrene exposure may lead to the formation of DNAadducts sister chromatid exchange, and chromosomal aberrations.

With respect to carcinogenicity, no clear effect was observed in rats. In mice, the studies provide evidence for an increase of lung tumors. IARC recently has re evaluated the data on carcinogenicity of styrene and concluded that there is " limited evidence" in experimental animals for the carcinogenicity of styrene. In the overall evaluation, it was concluded that styrene is " possibly carcinogenic to humans ( Group 2B)" ( IARC 2002). Styrene is being reassessed under the IRIS Program of the US EPA, no quantitative carcinogenicity assessment for lifetime exposure is currently proposed ( US EPA 1998). US EPA ´ s Office of Research and Development has updated previous assessments on the carcinogenic potential of styrene and concluded that styrene is appropriately classified as a Group C, possible human carcinogen ( US EPA 2003). Styrene NAC: 02/ 2004 41 4 SPECIAL CONSIDERATIONS 4.1 Toxicokinetics The toxicokinetics of styrene both in humans and laboratory animals has been reviewed ( e. g. ATSDR 1992; Bond 1989; Cohen et al. 2002; Engelhardt et al. 2003; Government Canada 1993; Linhart 2001; Sherrington and Routledge 2001; Sumner et al. 2001).

Uptake and distribution In studies with human volunteers and occupationally exposed workers, retention of styrene was about 70 % of the inhaled dose. E. g., in two studies on male healthy volunteers who were exposed to 300 mg/ m ³ ( 70 ppm) of styrene during light exercise, the average uptake of styrene was 68 % of the amount supplied; the percentage of uptake was nearly constant during the whole exposure period ( 0   30 minutes: 71.0 %; 90   120 minutes: 66.7 % ( Wigaeus et al. 1983; Wigaeus et al. 1984).

Experimental and simulation studies suggest a washin washout effect for styrene in the upper respiratory airways of humans ( Jonsson and Johanson 2002). In rats and mice, styrene has been shown to be taken up and metabolized in surgically isolated upper respiratory tract preparations; uptake amounted to about 10 % of styrene at 200 ppm ( Morris 2000).

For styrene, a high in vitro blood: air partition coefficient at equilibrium of 32 was reported by Astrand ( 1975). Even higher coefficients of 40 for rats and mice and 52 for humans were reported by Ramsey and Andersen ( 1984). In controlled human studies in vivo, the blood: air coefficient was found to depend on the work load during exercise: At 50 and 150 ppm styrene, the coefficient of the concentration of styrene in alveloar air: blood was 15 at rest and increased to 50, 85, and 105 at work loads of 50 W, 100 W, and 150 W during subsequent 30 minute exposure periods, respectively ( Astrand 1975).

Concentrations of styrene determined in blood of humans and rats and in rat brain are summarized in TABLE 7. In humans exposed to 69 ppm for two hours during light physical exercise ( 50 W), the concentration of styrene in arterial blood rose steeply during the first 30 minutes and reached a plateau at about 60 minutes ( FIGURE 3) ( Wigaeus et al. 1984). Controlled studies further show that the concentration of styrene in blood depends on the intensity of physical work load. When volunteers were exposed at 154 ppm styrene for consecutive 30 min periods with increasing intensity of physical exercise ( 0, light exercise: 50 W, 100 W, heavy exercise: 150 W), the arterial blood concentration increased with increasing exercise activity and was approximately 3fold higher at 50 W, 5fold higher at 100 W, and 10fold higher at 150 W than at rest ( Astrand 1975). However, care must be taken when interpreting these observations since a 30 minute exposure period ( at 154 ppm) is not sufficient to reach a plateau level of styrene in blood. Thus, the experimental condition in the study of Astrand ( 1975) leads to an overestimation of the effect of work load.

At higher inhalation concentrations, no constant styrene concentration in blood is reached ( data for humans see FIGURE 4, Löf and Johanson 1993). In rats exposed to 520, 1274, and 2850 ppm styrene by inhalation for up to 5 hours, the level of styrene in jugular venous blood rose continuously. After about 90 minutes, a nearly linear increase was observed at the three higher concentrations and no equilibrium was reached during exposure. At 45 ppm, no marked increase with continuing exposure was observed ( FIGURE 5, Withey and Collins 1979). Styrene NAC: 02/ 2004 42 FIGURE 3: STYRENE CONCENTRATION IN ARTERIAL BLOOD OF HUMANS DURING AND AFTER A 2 HOUR EXPOSURE TO 69 PPM STYRENE IN AIR ( Human volunteers ( n = 5) were exposed to 69 ppm styrene ( open symbols) or a mixture of 70 ppm styrene and 520 ppm acetone ( closed symbols) during a work load of 50 W ( light exercise) ( Graph from Wigaeus et al. 1984). 1 µ M = 104 µ g/ l.).

FIGURE 4: OBSERVED ( CIRCLES) AND SIMULATED CONCENTRATIONS OF STYRENE IN ARTERIALIZED CAPILLARY BLOOD FROM TWO HUMAN VOLUNTEERS ( 2 hours of exposure during light ( 50 W) exercise. Continuous line: PBPK model simulation with a linear model ( nonsaturable metabolism in liver); broken lines: same model with saturable metabolism. The study did not indicate which of the values were determined in the female and the male volunteer. Graph from Löf and Johanson ( 1993)). Styrene NAC: 02/ 2004 43 FIGURE 5: STYRENE CONCENTRATION IN BLOOD OF RATS DURING A 5 HOUR EXPOSURE TO DIFFERENT CONCENTRATIONS OF STYRENE IN AIR ( Animals were exposed to the styrene vapor concentrations indicated and styrene was determined in blood from jugular vein at different time points by means of an indwelling cannula fixed prior to exposure. Graph from Withey and Collins 1979.)

Styrene is widely distributed throughout the body. From its high lipophilicity, the highest concentrations may be expected in lipid rich tissues. However, it must be taken into account that the distribution of styrene is affected by its rapid metabolic clearance ( see below). Thus, at low exposure concentrations ( 54 ppm), the concentration of styrene in rat brain was lower than in blood. At higher concentrations (  470 ppm) where metabolic clearance approaches saturation ( see below), the concentration in rat brain was 1.17   1.89 fold higher than in blood. Similar effects were observed in heart, lung, liver, and spleen, but not in kidney where the styrene concentration was higher than in blood at all concentrations. Concentrations at least 10fold higher than in every other tissue were observed in perirenal fat ( Withey and Collins 1979). In humans, the ratio between the styrene concentration in subcutaneous adipose tissue ( from the gluteal region) and arterial blood reached 3 at the end of a 2 hour exposure to 70 ppm styrene. This value is far below the value in equilibrium that can be calculated from the oil: air ( about 5.5) and blood: air partition ( 52) coefficient of styrene indicating that styrene in adipose tissue does not reach equilibrium under the condition of the study. Taking into account the long half life of styrene in subcutaneous adipose tissue ( 2.2   5.2 days), the authors further estimated that several days of continuous exposure would be necessary to reach 90 % of steady state ( Wigaeus et al. 1983). Styrene NAC: 02/ 2004 44 TABLE 7: EXPOSURE CONCENTRATIONS AND BLOOD LEVEL OF STYRENE IN HUMANS AND RATS Exposure time Conc. in air ( ppm) Concentration in blood ( mg/ L) or brain( mg/ kg) Remarks Reference Humans 50 min 87 139 2.7 Exposure at light physical exercise ( 50 W) Ödkvist et al. 1982 55 min 1 h 55 min 3 h 30 min 51.4 116.7 116.7 99 0.2   0.7 ( vb) 1.7 ( vb) 2.7 ( vb) 0.9   1.4 ( vb) Exposure at rest Stewart et al. 1968 30 min 1 h 2 h 69 1.8 ( ab) 2.1 2.2 Exposure with light physical exercise ( 50 W) Wigaeus et al. 1983; 1984 30 min 154 ~ 2 ( ab) ~ 6 ~ 9 ~ 16 Exposure at rest 50 W exercise 100 W exercise 150 W exercise; all values estimated from figure Astrand 1975 2 h 69 1.6 ( ab) Exposure with light physical exercise ( 50 W); study with occupationally exposed workers Löf et al. 1984 6 h 80 0.92 ( vb) Exposure at rest Ramsey et al. 1980 2 h 26 77 201 386 ~ 0.7/ 0.7 ( acb) ~ 2/ 3.1 ~ 6.2/ 8.3 ~ 15/ 21 Values for 2 volunteers exposed with light physical exercise ( 50 W); values estimated from figure Löf and Johanson 1993 Rats 2 h 520 1274 2850 ~ 24 ~ 73 ~ 100 Values estimated from graph Withey and Collins 1979 5 h 45 520 1274 2800 < 2 ( vb) ~ 43 ~ 149 ~ 198 Values estimated from graph Withey and Collins 1979 5 h 54 470 1018 1522 2144 2240 0.65 ( vb)/ 0.2 ( brain) 2 31.8 / 43 65.3 / 76 72.8 / 105 173.7 / 302 135.5 / 256 Withey and Collins 1979 > 75 ( ab) i. v. exposure; effects on vestibular system as indicated by changes in nystagmus Tham et al. 1982 6 h 80 1.0 ( wb) Ramsey and Styrene NAC: 02/ 2004 45 TABLE 7: EXPOSURE CONCENTRATIONS AND BLOOD LEVEL OF STYRENE IN HUMANS AND RATS Exposure time Conc. in air ( ppm) Concentration in blood ( mg/ L) or brain( mg/ kg) Remarks Reference 1200 63 Andersen 1984 6 h 50 200 500 1000 0.43/ 0.29 ( m/ f) 2.8/ 1.95 12.5/ 9.5 33.2/ 29.7 Values determined in week 95 of chronic study Cruzan et al. 1998 4 h 1 h 2760 *

2760 * 250 ( brain)

218 ( brain) 222 ( brain) 177 ( brain) 86 ( brain) 0  max. 44 ( brain) Exposure to LC50 End of exposure, animal in deep narcosis 15 min after end of exposure 30 min after end of exposure 60 min after end of exposure 90 min after end of exposure Shugaev 1969 6 h + 4 h1 1750 37.5 ( ab) 68 ( brain) At end of exposure Campo et al. 1999 ab: arterial blood; acb: arterialized capillary blood; vb: venous blood; wb: whole blood; m/ f: values for males/ females; 1: 6 hours on 1st and 4 hours on 2nd day; 2: approximate concentration, calculated from values presented as brain concentration relative to blood in original reference. * see section 3.6 for discussion of validity of data from this study.

Metabolism The metabolism of styrene was compared in male Sprague Dawley rats and B6C3F1 mice. In both species, the rate of metabolism of inhaled styrene was found to increase linerarily with concentration up to about 300 ppm. In this concentration range, delivery of styrene to the site of metabolism but not metabolic capacity was the rate limiting step for metabolism. Above 300 ppm, the rate of metabolism at steady state became more and more limited by metabolic parameters. Metabolism approached nearly saturation at about 700 ppm in rats and 800 ppm in mice; exposure concentrations at half maximum rates of metabolism were 190 ppm in rats and 270 ppm in mice, respectively. Repeated exposure for 6 hours/ day on 5 consecutive days to 150 or 500 ppm caused no detectable changes in the rates of styrene metabolism ( Filser et al. 1993). However, evidence for an induction of styrene metabolism in male rats following preexposure to styrene was observed in another study in which prior exposure to styrene ( 1000 ppm, 6 hours/ day, 4 days) increased Vmax about twofold. Significant induction of styrene metabolism was observed in 24 hr continuous exposure to 400, 600, or 1200 ppm. Calculations using a physiological model of styrene inhalation kinetics to estimate the dynamics of the induction indicated that induction at 1200 ppm began 4.6 hr after the start of exposure and reached 4.4 times the Vmax of naive rats. No induction occurred in 48 hr exposure to 200 ppm ( Andersen et al. 1984).

In humans, evidence from controlled studies indicates that saturation of metabolic capacity to clear styrene becomes noticeable at concentrations around 200 ppm. In one study, one female and one male volunteer were exposed to analytically confirmed concentrations of 26, 77, 201 and 386 ppm styrene vapor for 2 hours with light exercise ( 50 W). During the 2 h exposure, the concentration of styrene in blood Styrene NAC: 02/ 2004 46 reached a plateau at the lower concentrations in both individuals. At 386 ppm, the arterial styrene concentration only approached a plateau in one individual but continued to increase steadily in the other ( FIGURE 4); it was not indicated in the study which of the values were determined in the male and in the female volunteer). This non linear relationship between the level of exposure to styrene and the concentration of styrene in arterial blood ( and also the 0   5 hours cumulative excretion of mandelic acid, see below) indicated metabolic saturation. A physiologically based pharmacokinetic model was used to estimate metabolic parameters. According to the model, transition to metabolic saturation is seen at about 100 ppm ( at 50 W physical activity) and at about 200 ppm at rest ( Löf and Johanson 1993). Previous studies also provided evidence that styrene metabolism in rats, mice and humans becomes saturated at concentrations exceeding 200 ppm. At lower concentrations, the ratio of styrene concentration in blood to inhaled air is controlled by perfusion limited metabolism, while at higher concentrations, the ratio is controlled by the blood: air coefficient ( Ramsey and Andersen 1984).

An overview of the pathways of styrene metabolism is presented in FIGURE 6. The major metabolic pathway starts with the formation of styrene 7,8 oxide ( SO) by cytochrome P450 dependent monoxygenases. SO is either conjugated with glutathione ( GSH) to finally produce mercapturic acids or it is hydrolyzed by epoxide hydrolase to styrene glycol that is subsequently oxidized to mandelic and phenylglyoxylic acid. Phenylacetic acid and benzoic acid or rather hippuric acid, its glycine conjugation product, are also found in urine.

Different CYP isozymes are involved in the oxidation of styrene to SO. Based on in vitro studies, CYP2B6 and CYP2E1 seem most important in liver and CYP2F2 in lung, but other isozyms also seem to play a role. In mice devoid of CYP2E1 activity ( Cyp2e1 null mice), the amount of metabolites derived from SO was higher and that derived from phenylacetaldehyde was lower as compared to control mice. The excretion of total urinary metabolites was higher in " null mice" than in wild type controls. These data indicate that CYP2E1 may not be a major isozyme involved in the metabolism of styrene to SO in mice ( Sumner et al. 2001). In humans with individual differences in xenobiotic metabolism capacity determined with enzyme specific substrates for CYP2E1, CYP1A2, and CYP2D6, no correlation was found between the blood clearance of styrene and the metabolic capacity as measured by urinary excretion of mandelic and phenylglyoxylic acid. Under the experimental conditions ( 24 and 84 ppm styrene, 1 hour exposure, light exercise), the apparent blood clearance of styrene ( 1.4 l/ min) was similar to the hepatic blood flow ( IARC 2002). These data further support the assumption that styrene metabolism at low concentrations is limited by perfusion and not by the capacity of the metabolism.

Qualitatively, styrene metabolism is similar in humans and rodents ( FIGURE 6), and in both, humans and animals, more than 90 % of styrene taken up is metabolized. However, there are quantitative differences between rats and humans, and, more pronounced, humans and mice. With respect to the metabolism of styrene in the liver, the experimental data indicate that the order of the oxidation rate of styrene to SO is mice > rats > humans, while the order for microsomal epoxide hydrolase activity of the liver is humans > rats > mice ( Mendrala et al. 1993). However, enzymatic activities in tissues other than in liver may be different ( Vodicka et al. 2002). In humans, conversion of SO preceeds predominantly via oxidation to styrene glycol, whereas conjugation with GSH and formation of mercapturic acid is important in mice and, to a much lesser extent, in rats. Furthermore, in mice up to 30 % of styrene metabolism leads to the formation of phenylaceturic acid. This pathway likely involves the formation of phenylacetaldehyde as a reactive intermediate that is able to react with proteins. In rats and humans, this pathway is of minor impotance ( rats: 5 %; humans: less than 5 %) ( Sumner et al. 2001). Styrene NAC: 02/ 2004 47 FIGURE 6: PATHWAYS FOR THE METABOLISM OF STYRENE IN HUMANS AND RODENTS ( modified from IARC 2002; main pathways are illustrated by arrows in bold)

Nasal metabolism of styrene is thought to be related to olfactory epithelium toxicity that is pronounced in mice and less or marginal in rats ( Cruzan et al. 2002). The metabolism of styrene in nasal epithelia of rats, mice, and humans was studied by Green et al. ( 2001a). Pretreatment of mice with 5 phenyl 1 pentyne, an inhibitor of CYP2F2 and CYP2E1, prevented the development of nasal lesions upon


[Federal Register: March 12, 2010 (Volume 75, Number 48)]
[Notices]
[Page 11974-11975]
[DOCID:fr12mr10-177]

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SECURITIES AND EXCHANGE COMMISSION

[Release No. 34-61659; File No. SR-CBOE-2010-023]

Self-Regulatory Organizations; Chicago Board Options Exchange,
Incorporated; Notice of Filing and Immediate Effectiveness of a
Proposed Rule Change To Amend the CBSX Fees Schedule To Adopt a
Document Request Fee and Transaction Fees for Cross Trades That Settle
Non-Regular-Way

March 5, 2010.
    Pursuant to Section 19(b)(1) of the Securities Exchange Act of 1934
(``Act'') \1\ and Rule 19b-4 thereunder,\2\ notice is hereby given that
on February 26, 2010, the Chicago Board Options Exchange, Incorporated
(``Exchange'' or ``CBOE'') filed with the Securities and Exchange
Commission (``Commission'') the proposed rule change as described in
Items I, II, and III below, which Items have been prepared by the
Exchange. The Commission is publishing this notice to solicit comments
on the proposed rule change from interested persons.
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    \1\ 15 U.S.C. 78s(b)(1).
    \2\ 17 CFR 240.19b-4.

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I. Self-Regulatory Organization's Statement of the Terms of Substance
of the Proposed Rule Change

    The Exchange proposes to amend the CBSX Fees Schedule to adopt a
document request fee and non-Regular-way cross frees [sic]. The text of
the proposed rule change is available on the Exchange's Web site
(http://www.cboe.org/legal), at the Exchange's Office of the Secretary,
and at the Commission.

II. Self-Regulatory Organization's Statement of the Purpose of, and
Statutory Basis for, the Proposed Rule Change

    In its filing with the Commission, the self-regulatory organization
included statements concerning the purpose of and basis for the
proposed rule change and discussed any comments it received on the
proposed rule change. The text of those statements may be examined at
the places specified in Item IV below. The Exchange has prepared
summaries, set forth in sections A, B, and C below, of the most
significant parts of such statements.

A. Self-Regulatory Organization's Statement of the Purpose of, and the
Statutory Basis for, the Proposed Rule Change

1. Purpose
    CBSX proposes to modify its Fees Schedule to add transaction fees
for cross trades that are marked for cash and next-day settlement. Such
settlements are permissible pursuant to Rule 51.7.\3\ Because these are
non-Regular Way settlements, CBSX deems it appropriate to charge more
for these crosses than for ``traditional'' settlement crosses.\4\
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    \3\ See CBOE Rule 51.7(a) and (b).
    \4\ The Exchange proposes to modify the CBSX fee schedule to add
transaction fees for cross trades that are marked for cash and next-
day settlement. As proposed, next-day settlement cross trades would
be charged $0.0025 per share with a minimum rate of $1 per trade and
a maximum rate of $30 per trade. Cash settlement cross trades would
be charged $0.0025 per share with a minimum rate of $1 per trade and
a maximum rate of $50 per trade. The Exchange is proposing a higher
cap for cash settlement cross trades because cash settlement is a
more expedited settlement time frame than next-day settlement.
Because cash settlement presumably satisfies a more pressing need
for the user, the Exchange believes the market will bear a higher
cap for cash settlement cross trades. See e-mail from Angelo
Evangelou, Assistant General Counsel, Legal Division, CBOE, to Steve
L. Kuan, Special Counsel, Division of Trading and Markets,
Commission, on March 5, 2010.
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    CBSX also proposes to add a Document Request Fee of $100.00 per
monthly billing statement. This fee would be imposed upon any person or
organization that requests that CBSX deliver printed hard-copy versions
of the person's or organization's monthly billing statements. Current
CBSX practice is to e-mail such statements, and the practice of
printing and delivering such statements is costly and time-consuming
because the statements are quite voluminous.
    The fee changes will become effective on March 1, 2010.
2. Statutory Basis
    The proposed rule change is consistent with Section 6(b) of the
Securities Exchange Act of 1934 (``Act''),\5\ in general, and furthers
the objectives of Section 6(b)(4) \6\ of the Act in particular, in that
it is designed to provide for the equitable allocation of reasonable
dues, fees, and other charges among CBOE members and other persons
using its facilities.
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    \5\ 15 U.S.C. 78f(b).
    \6\ 15 U.S.C. 78f(b)(4).
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B. Self-Regulatory Organization's Statement on Burden on Competition

    CBOE does not believe that the proposed rule change will impose any
burden on competition not necessary or appropriate in furtherance of
the purposes of the Act.

C. Self-Regulatory Organization's Statement on Comments on the Proposed
Rule Change Received From Members, Participants, or Others

    No written comments were solicited or received with respect to the
proposed rule change.

III. Date of Effectiveness of the Proposed Rule Change and Timing for
Commission Action

    The proposed rule change is designated by the Exchange as
establishing or changing a due, fee, or other charge, thereby
qualifying for effectiveness on filing pursuant to Section
19(b)(3)(A)(ii) \7\ of the Act and subparagraph (f)(2) of Rule 19b-4
\8\ thereunder.
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    \7\ 15 U.S.C. 78s(b)(3)(A)(ii).
    \8\ 17 CFR 240.19b-4(f)(2).
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    At any time within 60 days of the filing of the proposed rule
change, the Commission may summarily abrogate such rule change if it
appears to the Commission that such action is necessary or appropriate
in the public interest, for the protection of investors, or otherwise
in furtherance of the purposes of the Act.

IV. Solicitation of Comments

    Interested persons are invited to submit written data, views, and
arguments concerning the foregoing, including whether the proposed rule
change is consistent with the Act. Comments may be submitted by any of
the following methods:

Electronic Comments

     Use the Commission's Internet comment form (http://
www.sec.gov/rules/sro.shtml); or
     Send an e-mail to<EMAIL_ADDRESS>Please include
File Number SR-CBOE-2010-023 on the subject line.

Paper Comments

     Send paper comments in triplicate to Elizabeth M. Murphy,
Secretary, Securities and Exchange Commission, 100 F Street, NE.,
Washington, DC 20549-1090.

All submissions should refer to File Number SR-CBOE-2010-023. This file
number should be included on the subject line if e-mail is used. To
help the Commission process and review your comments more efficiently,
please use only one method. The Commission will post all comments on
the Commission's Internet Web site (http://www.sec.gov/rules/
sro.shtml). Copies of the submission, all subsequent amendments, all
written statements with respect to the proposed rule change that are
filed with the Commission, and all written communications relating to
the proposed rule change between the Commission and any person, other
than those that may be withheld from the public in accordance with the
provisions of 5 U.S.C. 552, will be available for Web site viewing and
printing in the Commission's Public Reference Room, 100 F Street, NE.,
Washington, DC 20549, on official business days between the hours of 10
a.m. and 3 p.m. Copies of such filing also will be available for
inspection and copying at the principal office of the Exchange. All
comments received will be posted without change; the Commission does
not edit personal identifying information from submissions. You should
submit only information that you wish to make available publicly. All
submissions should refer to File Number SR-CBOE-2010-023 and should be
submitted on or before April 2, 2010.

    For the Commission, by the Division of Trading and Markets,
pursuant to delegated authority.\9\
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    \9\ 17 CFR 200.30-3(a)(12).
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Florence E. Harmon,
Deputy Secretary.
[FR Doc. 2010-5301 Filed 3-11-10; 8:45 am]
BILLING CODE 8011-01-P


[Federal Register Volume 83, Number 240 (Friday, December 14, 2018)]
[Rules and Regulations]
[Pages 64249-64250]
[FR Doc No: 2018-26801]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 71

Docket No. FAA-2018-0883; Airspace Docket No. 18-ANE-5]
RIN 2120-AA66

Amendment of Class E Airspace; Bethel, ME

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: This action amends Class E airspace extending upward from 700
feet above the surface at Bethel Regional Airport, Bethel, ME, to
accommodate new area navigation (RNAV) global positioning system (GPS)
standard instrument approach procedures serving this airport.
Controlled airspace is necessary for the safety and management of
instrument flight rules (IFR) operations at this airport. This action
also updates the geographic coordinates of this airport to be in
concert with the FAA's aeronautical database.

DATES: Effective 0901 UTC, February 28, 2019. The Director of the
Federal Register approves this incorporation by reference action under
Title 1 Code of Federal Regulations part 51, subject to the annual
revision of FAA Order 7400.11 and publication of conforming amendments.

ADDRESSES: FAA Order 7400.11C, Airspace Designations and Reporting
Points, and subsequent amendments can be viewed online at http://www.faa.gov/air_traffic/publications/. For further information, you can
contact the Airspace Policy Group, Federal Aviation Administration, 800
Independence Avenue SW, Washington, DC 20591; telephone: (202) 267-
8783. The Order is also available for inspection at the National
Archives and Records Administration (NARA).
    For information on the availability of FAA Order 7400.11C at NARA,
call<PHONE_NUMBER>, or go to https://www.archives.gov/federal-register/cfr/ibr-locations.html.
    FAA Order 7400.11, Airspace Designations and Reporting Points, is
published yearly and effective on September 15.

FOR FURTHER INFORMATION CONTACT: John Fornito, Operations Support
Group, Eastern Service Center, Federal Aviation Administration, 1701
Columbia Avenue, College Park, GA 30337; telephone<PHONE_NUMBER>.

SUPPLEMENTARY INFORMATION:

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is
found in Title 49 of the United States Code. Subtitle I, Section 106
describes the authority of the FAA Administrator. Subtitle VII,
Aviation Programs, describes in more detail the scope of the agency's
authority. This rulemaking is promulgated under the authority described
in Subtitle VII, Part A, Subpart I, Section 40103. Under that section,
the FAA is charged with prescribing regulations to assign the use of
airspace necessary to ensure the safety of aircraft and the efficient
use of airspace. This regulation is within the scope of that authority
as it amends Class E airspace at Bethel Regional Airport, Bethel, ME,
to support IFR operations at this airport.

History

    The FAA published a notice of proposed rulemaking in the Federal
Register (83 FR 50050, October 4, 2018) for Docket No. FAA-2018-0883 to
amend Class E airspace at Bethel Regional Airport, Bethel, ME, to
support IFR operations at this airport.
    Interested parties were invited to participate in this rulemaking
effort by submitting written comments on the proposal to the FAA. Two
comments supporting this action were received.
    Class E airspace designations are published in paragraph 6005, of
FAA Order 7400.11C dated August 13, 2018, and effective September 15,
2018, which is incorporated by reference in 14 CFR part 71.1. The Class
E airspace designation listed in this document will be published
subsequently in the Order.

Availability and Summary of Documents for Incorporation by Reference

    This document amends FAA Order 7400.11C, Airspace Designations and
Reporting Points, dated August 13, 2018, and effective September 15,
2018. FAA Order 7400.11C is publicly available as listed in the
ADDRESSES section of this document. FAA Order 7400.11C lists Class A,
B, C, D, and E airspace areas, air traffic service routes, and
reporting points.

The Rule

    This amendment to Title 14 Code of Federal Regulations (14 CFR)
part 71 amends Class E airspace extending upward from 700 feet or more
above the surface within an 8.6-mile radius (increased from a 6-mile
radius) of Bethel Regional Airport, Bethel, ME, providing the
controlled airspace required to support the new RNAV (GPS) standard
instrument approach procedures for IFR operations at Bethel Regional
Airport. The geographic coordinates of the airport are amended to
coincide with the FAA's aeronautical database.

Regulatory Notices and Analyses

    The FAA has determined that this regulation only involves an
established body of technical regulations for which frequent and
routine amendments are necessary to keep them operationally current.
It, therefore: (1) Is not a ``significant regulatory action'' under
Executive Order 12866; (2) is not a ``significant rule'' under DOT
Regulatory Policies and Procedures (44 FR 11034; February 26, 1979);
and (3) does not warrant preparation of a regulatory evaluation as the
anticipated impact is so minimal. Since this is a routine matter that
only affects air traffic procedures and air navigation, it is certified
that this rule, when promulgated, does not have a significant economic
impact on a substantial number of small entities under the criteria of
the Regulatory Flexibility Act.

Environmental Review

    The FAA has determined that this action qualifies for categorical
exclusion under the National Environmental Policy Act in accordance
with FAA Order 1050.1F, ``Environmental Impacts: Policies and
Procedures,'' paragraph 5-6.5a. This airspace action is not expected to
cause any potentially significant environmental impacts, and no
extraordinary circumstances exist that warrant preparation of an
environmental assessment.

Lists of Subjects in 14 CFR Part 71

    Airspace, Incorporation by reference, Navigation (air).

Adoption of the Amendment

    In consideration of the foregoing, the Federal Aviation
Administration amends 14 CFR part 71 as follows:

PART 71--DESIGNATION OF CLASS A, B, C, D, AND E AIRSPACE AREAS; AIR
TRAFFIC SERVICE ROUTES; AND REPORTING POINTS

0
1. The authority citation for part 71 continues to read as follows:

    Authority: 49 U.S.C. 106(f), 106(g); 40103, 40113, 40120; E.O.
10854, 24 FR 9565, 3 CFR, 1959-1963 Comp., p. 389.

Sec.  71.1  [Amended]

0
2. The incorporation by reference in 14 CFR 71.1 of Federal Aviation
Administration Order 7400.11C, Airspace Designations and Reporting
Points, dated August 13, 2018, and effective September 15, 2018, is
amended as follows:

Paragraph 6005 Class E Airspace Areas Extending Upward From 700
Feet or More Above the Surface of the Earth.

ANE ME E5 Bethel, ME [Amended]

Bethel Regional Airport, ME
    (Lat. 44[deg]25'31'' N, long. 70[deg]48'36'' W)

    That airspace extending upward from 700 feet above the surface
within an 8.6-mile radius of Bethel Regional Airport.

    Issued in College Park, Georgia, on December 4, 2018.
Ryan W. Almasy,
Manager, Operations Support Group, Eastern Service Center, Air Traffic
Organization.
[FR Doc. 2018-26801 Filed 12-13-18; 8:45 am]
BILLING CODE 4910-13-P


[Federal Register: May 19, 2008 (Volume 73, Number 97)]
[Notices]
[Page 28846-28847]
[DOCID:fr19my08-96]

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SECURITIES AND EXCHANGE COMMISSION

[Release No. 34-57812; File No. SR-ISE-2008-28]

Self-Regulatory Organizations; International Securities Exchange,
LLC; Notice of Filing of Amendment No. 1 to the Proposed Rule Change
and Order Granting Accelerated Approval of Proposed Rule Change, As
Modified by Amendment No. 1 Thereto, Relating to the Exposure of Public
Customer Orders

May 12, 2008.

I. Introduction

    On March 18, 2008, the International Securities Exchange, LLC (the
``Exchange'' or the ``ISE'') filed with the Securities and Exchange
Commission (``Commission''), pursuant to Section 19(b)(1) of the
Securities Exchange Act of 1934 (``Act''),\1\ and Rule 19b-4
thereunder,\2\ a proposal to expose public customer orders that are not
executable on the Exchange before sending an order through the
intermarket linkage system (a ``Linkage Order'') on behalf of the
public customer. The proposed rule change was published for comment in
the Federal Register on March 31, 2008.\3\ The Commission received one
comment letter regarding the proposal.\4\ ISE filed Amendment No. 1 to
the proposed rule change on May 7, 2008.\5\ The Commission is
publishing this notice to solicit comments on the proposed rule change,
as modified by Amendment No. 1, from interested persons and is
simultaneously approving the proposed rule change, as modified by
Amendment No. 1, on an accelerated basis.
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    \1\ 15 U.S.C. 78s(b)(1).
    \2\ 17 CFR 240.19b-4.
    \3\ See Securities Exchange Act Release No. 57551 (March 25,
2008), 73 FR 16917.
    \4\ See letter from Lisa J. Fall, General Counsel, Boston
Options Exchange (``BOX''), to Nancy M. Morris, Secretary,
Commission, dated May 2, 2007 (``BOX Comment'').
    \5\ In Partial Amendment No. 1, the Exchange: (1) Amended the
rule text to add subsection (e) to Supplementary Material .02 to
Rule 803 to state that a ``pattern or practice of submitting
unrelated orders that cause an exposure period to conclude early
will be deemed conduct inconsistent with just and equitable
principles of trade and a violation of Rule 400 and other Exchange
Rules''; and (2) confirmed that the obligation of primary market
makers under existing Rule 803(c)(2)(ii) to address public customer
orders that are not automatically executed because there is a better
price on another exchange includes the handling of the balance of an
order that initially receives a partial execution on the Exchange.
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II. Description of the Proposal

    As described in the proposal, the ISE will not automatically
execute a customer's options order when the ISE's best bid or offer
(``BBO'') is inferior to the national best bid or offer (``NBBO'').\6\
Under ISE Rule 803(c)(2)(ii), the primary market maker (``PMM'') is
obligated to address public customer orders that are not automatically
executed because there is a better price on another exchange.\7\ Rule
803(c) specifies that the PMM can either execute the order or send a
Linkage Order to any other exchange displaying the best price in an
attempt to get the better price for the public customer.\8\ Under the
current procedure, if the PMM does not execute the public customer
order, it sends a Linkage Order(s) to a competing exchange(s) even
though there may be other ISE market makers who would be willing to
execute the public customer order at the better price.\9\
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    \6\ See ISE Rule 714.
    \7\ The Exchange noted in Amendment No. 1 that this obligation
of the PMM to address these public customer orders includes the
handling of the balance of an order that initially receives a
partial execution on ISE.
    \8\ ISE Rules, Chapter 19 (Intermarket Linkage Rules).
    \9\ When a PMM sends a Linkage Order to another exchange, it is
charged the other exchange's execution fee.
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    Under the proposal, before the PMM sends a Linkage Order on behalf
of a public customer, the public customer order will be exposed at the
NBBO price for a period established by the Exchange not to exceed one
second.\10\ During the exposure period, Exchange market makers may
enter responses up to the size of the order being exposed in the
regular trading increment applicable to the option. If at the end of
the exposure period, the order is executable at the then-current NBBO
and ISE is not quoting at the then-current NBBO, the order will be
executed against responses that equal or better the then-current
NBBO.\11\ The exposure period will be terminated if the exposed order
becomes executable on the ISE at the prevailing NBBO or if the Exchange
receives an unrelated order that could trade against the exposed order
at the prevailing NBBO price.\12\ If, after an order is exposed, the
order cannot be executed in full on the Exchange at the then-current
NBBO or better, and it is marketable against the then-current NBBO, the
PMM will send a Linkage Order on the customer's behalf for the balance
of the order as provided in Rule 803(c)(2)(ii). If the balance of the
order is not marketable against the then-current NBBO, it will be
placed on the ISE book.
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    \10\ The Exchange will issue a Circular to inform members of the
time period. The Exchange clarified in Amendment No. 1 that this
exposure process will apply to the balance of an order that received
a partial execution on ISE. See supra note 7.
    \11\ Executions will be allocated pro-rata based on size (i.e.,
the percentage of the total number of contracts available at the
same price that is represented by the size of a market maker's
response).
    \12\ The order will be executed against orders and quotes on the
book and responses received during the exposure period in price
priority. At the same price, customer orders will be executed first
in time priority and then all other interest (orders, quotes and
responses) will be allocated pro-rata based on size.
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    Immediate-or-cancel orders are cancelled if they cannot be executed
on the ISE upon entry. Therefore, such orders are not handled by the
PMM under Rule 803(c)(2)(ii) and will not be exposed under this
proposal.
    The Commission received one comment letter regarding the proposed
rule change.\13\ The commenter believes that ISE's proposal is not
consistent with Rule 602 of Regulation NMS (``Quote Rule''),\14\ which
``requires a responsible broker-dealer to execute an order at its quote
when that order is presented.'' \15\ Specifically, the commenter
believes that, if a PMM or CMM is at the ISE best bid or offer on the
opposite side of the market at the time the public customer order is
received, that public customer order has been ``presented'' to the PMM
or CMM under the Quote Rule.\16\ As a result, the commenter concludes
that the proposal is inconsistent with the Quote Rule because it would
permit public customer orders to be executed after the exposure period
at a price or size inferior to the price or size on ISE at order
presentment.\17\ The commenter also requests clarification of the
handling of the balance of a public customer order, a portion of which
is automatically executed on ISE at the NBBO. In that scenario, the
commenter was unclear whether the balance of the order would be routed
as Linkage Orders or handled under the proposed exposure period. In
this regard, ISE

confirmed in Amendment No. 1 that the exposure period will apply to the
balance of a public customer order that has received partial execution
on ISE.
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    \13\ See BOX Comment, supra note 4.
    \14\ 17 CFR 242.602.
    \15\ See BOX Comment, supra note 4, at 2.
    \16\ See generally BOX Comment, supra note 4, at 2 to 6.
    \17\ Id at 6.
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III. Solicitation of Comments

    Interested persons are invited to submit written data, views, and
arguments concerning the foregoing, including whether the proposed rule
change, as modified by Amendment No. 1, is consistent with the Act.
Comments may be submitted by any of the following methods:

Electronic Comments

     Use the Commission's Internet comment form (http://
www.sec.gov/rules/sro.shtml); or
     Send an e-mail to<EMAIL_ADDRESS>Please include
File Number SR-ISE-2008-28 on the subject line.

Paper Comments

     Send paper comments in triplicate to Nancy M. Morris,
Secretary, Securities and Exchange Commission, 100 F Street, NE.,
Washington, DC 20549-1090.

All submissions should refer to File Number ISE-2008-28. This file
number should be included on the subject line if e-mail is used. To
help the Commission process and review your comments more efficiently,
please use only one method. The Commission will post all comments on
the Commission's Internet Web site (http://www.sec.gov/rules/
sro.shtml). Copies of the submission, all subsequent amendments, all
written statements with respect to the proposed rule change that are
filed with the Commission, and all written communications relating to
the proposed rule change between the Commission and any person, other
than those that may be withheld from the public in accordance with the
provisions of 5 U.S.C. 552, will be available for inspection and
copying in the Commission's Public Reference Room, 100 F Street, NE.,
Washington, DC 20549, on official business days between the hours of 10
a.m. and 3 p.m. Copies of such filing also will be available for
inspection and copying at the principal office of ISE. All comments
received will be posted without change; the Commission does not edit
personal identifying information from submissions. You should submit
only information that you wish to make available publicly. All
submissions should refer to File Number SR-ISE-2008-28 and should be
submitted on or before June 9, 2008.

IV. Discussion and Commission Findings

    After carefully considering the proposal and the comment submitted,
the Commission finds that the proposed rule change, as modified by
Amendment No. 1, is consistent with the requirements of the Act and the
rules and regulations thereunder applicable to a national securities
exchange.\18\ In particular, the Commission finds that the proposal is
consistent with Section 6(b)(5) of the Act,\19\ which requires, in
part, that the rules of a national securities exchange be designed to
prevent fraudulent and manipulative acts and practices, to promote just
and equitable principles of trade, to remove impediments to and perfect
the mechanism of a free and open market and a national market system,
and, in general, to protect investors and the public interest.
Specifically, the proposal will expose public customer orders that are
not executable on the Exchange before sending a Linkage Order on behalf
of the public customer. The Commission notes that exposing public
customer orders before the PMM sends a Linkage Order on the public
customer's behalf will give additional ISE participants an opportunity
to provide public customer orders an execution at the NBBO (or better)
on ISE and may reduce PMM costs by reducing the number of Linkage
Orders sent to other exchanges. Thus, the Commission believes that the
exposure rules outlined above will allow ISE to provide more efficient
and competitive executions for these orders, subject to priority
principles.
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    \18\ In approving this proposed rule change, the Commission has
considered the proposed rule's impact on efficiency, competition,
and capital formation. 15 U.S.C. 78c(f).
    \19\ 15 U.S.C. 78f(b)(5).
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    The Commission also believes that the proposal is consistent with
the Quote Rule.\20\ The Quote Rule, among other things, requires a
responsible broker or dealer to execute orders presented to it by
another broker or dealer, at a price at least as favorable as the
responsible broker or dealer's published bid or offer, unless an
exception applies. The Commission believes that when an order is
received on ISE that a responsible broker or dealer is not permitted to
execute pursuant to ISE's rules or the Linkage Plan,\21\ and the
submitting member has chosen to allow ISE to expose the order to other
additional interest rather than submitting an immediate-or-cancel
(``IOC'') order,\22\ the order is not ``presented'' under the Quote
Rule. The Commission therefore does not believe it is necessary for ISE
to ``stop'' a public customer order against the existing best priced
quotes and orders on ISE's book at the beginning of the exposure period
to comply with the Quote Rule.
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    \20\ 17 CFR 242.602.
    \21\ The Plan for the Purpose of Creating and Operating an
Options Intermarket Linkage and ISE's rules contain provisions
restricting the ability of an ISE member to trade-through certain
prices on away markets. ISE has represented that it does not
automatically execute a customer's order when ISE is not at the
NBBO. In addition, public customer orders will be exposed under
ISE's proposal only when ISE is not at the NBBO.
    \22\ ISE has represented that IOC orders are cancelled if they
cannot be executed on ISE upon entry, and are not handled by the PMM
under Rule 803(c)(2)(ii) and will not be exposed under this
proposal. Therefore, public customers may avoid the proposed
exposure period by submitting IOC orders.
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    The Commission finds good cause to approve the proposal prior to
the thirtieth day after the proposal was published for comment in the
Federal Register. The Commission believes that the change made in
Amendment No. 1 generally strengthens the proposal. In Amendment No. 1,
ISE made explicit that a pattern or practice of submitting unrelated
orders that cause an exposure period to conclude early will be deemed
conduct inconsistent with just and equitable principles of trade and a
violation of ISE Rule 400 and other Exchange rules. This addition will
provide guidance to market participants regarding compliance with the
requirements of ISE's rules, and is consistent with the rules of
another options exchange.\23\ Further, this provision will help limit
potential ``gaming'' of the exposure period. For these reasons, the
Commission finds good cause, consistent with Section 19(b)(2) of the
Act,\24\ to grant accelerated approval of the proposed rule change, as
modified by Amendment No. 1.
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    \23\ See CBOE Rule 6.14.01.
    \24\ 15 U.S.C. 78s(b)(2).
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V. Conclusion

    It is therefore ordered, pursuant to Section 19(b)(2) of the
Act,\25\ that the proposed rule change (File No. SR-ISE-2008-28), as
modified by Amendment No. 1, is approved on an accelerated basis.
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    \25\ 15 U.S.C. 78s(b)(2).

    For the Commission, by the Division of Trading and Markets,
pursuant to delegated authority.\26\
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    \26\ 17 CFR 200.30-3(a)(12).
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Florence E. Harmon,
Deputy Secretary.
 [FR Doc. E8-11035 Filed 5-16-08; 8:45 am]

BILLING CODE 8010-01-P


[Federal Register Volume 86, Number 138 (Thursday, July 22, 2021)]
[Notices]
[Page 38731]
[FR Doc No: 2021-15625]

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DEPARTMENT OF HOMELAND SECURITY

Federal Emergency Management Agency

[Internal Agency Docket No. FEMA-4512-DR; Docket ID FEMA-2021-0001]

Virginia; Amendment No. 5 to Notice of a Major Disaster
Declaration

AGENCY: Federal Emergency Management Agency, Homeland Security (DHS).

ACTION: Notice.

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SUMMARY: This notice amends the notice of a major disaster declaration
for the Commonwealth of Virginia (FEMA-4512-DR), dated April 2, 2020,
and related determinations.

DATES: This change occurred on July 6, 2021.

FOR FURTHER INFORMATION CONTACT: Dean Webster, Office of Response and
Recovery, Federal Emergency Management Agency, 500 C Street SW,
Washington, DC 20472,<PHONE_NUMBER>.

SUPPLEMENTARY INFORMATION: The Federal Emergency Management Agency
(FEMA) hereby gives notice that pursuant to the authority vested in the
Administrator, under Executive Order 12148, as amended, MaryAnn
Tierney, of FEMA is appointed to act as the Federal Coordinating
Officer for this disaster.
    This action terminates the appointment of Janice P. Barlow as
Federal Coordinating Officer for this disaster.

    The following Catalog of Federal Domestic Assistance Numbers
(CFDA) are to be used for reporting and drawing funds: 97.030,
Community Disaster Loans; 97.031, Cora Brown Fund; 97.032, Crisis
Counseling; 97.033, Disaster Legal Services; 97.034, Disaster
Unemployment Assistance (DUA); 97.046, Fire Management Assistance
Grant; 97.048, Disaster Housing Assistance to Individuals and
Households In Presidentially Declared Disaster Areas; 97.049,
Presidentially Declared Disaster Assistance--Disaster Housing
Operations for Individuals and Households; 97.050, Presidentially
Declared Disaster Assistance to Individuals and Households--Other
Needs; 97.036, Disaster Grants--Public Assistance (Presidentially
Declared Disasters); 97.039, Hazard Mitigation Grant.

Deanne Criswell,
Administrator, Federal Emergency Management Agency.
[FR Doc. 2021-15625 Filed 7-21-21; 8:45 am]
BILLING CODE 9111-23-P