 In order to obtain TWA concentrations the sampler must first be calibrated in the laboratory so as to ascertain the uptake rate (usually measured as the volume of water cleared per unit time i.e.L/h for the analyte) of the pollutant of interest.Chemcatcher® has been used in a range of aquatic environments; however, most work to date has been in monitoring the TWA concentrations of priority and emerging pollutants surface waters.