Ministry of Environmental Protection of The People`s Republic of China

Q&A about national general survey on soil contamination in China


MEP and MLR announced the report on the national general survey on soil contamination today, and the survey results showed the general condition of the soil environment across the country not optimistic; some areas are suffering from bad soil pollution, the environmental quality of the arable land is worrying, and there are pressing soil environmental problems in industrial and mining deserted lands.To help get a comprehensive and correct understanding of the report, officials with MEP and MLR answered questions raised by journalists.

Q: What is the significance of the survey?

A: It is the first general survey onnationwide soil environment quality, which fillsin a gap in this area. The survey has got a preliminary understanding of the general conditions and changing trends of the soil environment quality across the country and of the type, extent, and distribution of the soil contamination nationwide; figured out the contamination situations of typical land masses and theirperimeters; and established a soil sample bank and survey database.

The survey helps build up the soil environment monitoring capacity of local areas and lays a solid foundation for establishing a national monitoring network for soil environment, for better distributing the monitoring sites, and for carrying out the routine soil environment qualitymonitoring. The data from the survey provide a scientific basis for improving the national standards for soil environment quality, for carrying out soil environment functional zoning and planning, for identifying priority areas for soil remediation, and for tightening the regulation and control of soil pollution risks. The results of the survey are very important for stepping up the country’s soil conservation and remediation, rationally utilizing and preserving land resources, guiding agricultural production, safeguarding farm produce quality and public health, and promoting sustained economic and social development.

Q: Whatpollutant indicatorsdoes the survey include?

A: The kinds of pollutants to be surveyed are decided as follows: a. pollutants affecting the yield and quality of farm produce; b. pollutants constituting public health hazards. Accordingly, theindicators include 13 kinds of inorganic pollutants (arsenic, cadmium, cobalt, chromium, copper, fluorine, mercury, manganese, nickel, lead, selenium, vanadium, and zinc) and 3 kinds of organic pollutants (C6H6Cl6, DDT, and PAHs). However, for comparative study on soil environment background, another 61 elements including antimony and molybdenum are also considered in addition to the above indicators.

Q: Why is the soil sampling depth set between 0 and 20cm?

A: Generally, topsoil is where the roots of most farm crops sprawl and it isalso the cultivated horizonin agricultural production. What’s more, the soil pollutants are concentrated in topsoil. So, the sampling depth in this survey is set from 0 to 20 cm.

Q: What is the basis for evaluating soil environmental quality?

A: A regulatory document Technical Specifications for Evaluation of Soil Contamination Conditions has been developed specifically for this survey, however, wehave applied the followingongoing standardsin principle during the evaluation of data, which include Soil environment quality standards (GB15618-1995), Farmland environmental quality evaluation standards for edible agricultural products (HJ332-2006) and Environmental quality evaluation standard for farmland of greenhouse vegetables production (HJ333-2006). Indicators not specified by the above standards, such as manganese, cobalt, and PAHs, are evaluated in accordance with overseas standards of relevance.

Q: There is no data availableon the total area of contaminated soils, why is that?

A: Soil contaminationis non-linear pollution as opposed to water and air pollution. Moreover, pollutants move around slowly in soils, so it is difficult to get an accurate picture of the geographical distribution of soil contamination. This is a preliminary and generic survey which aims to grasp the general situation of soil contamination. The survey sites are distributed sparsely due to limited objective conditions. Taking the farmland for example, the data of one site on every8km×8kmgrid (6,400 ha., i.e., 96,000 mu) can only reflect thegeneral condition of soil environment of farmlands. So, we use the non-attainment rate of those sites to describe the soil pollutionsituation. It is really hard to get an accurate data on the total area of polluted soils. 
Q: What is soil environment background value?

A: Soil environment background value refers to the inherent content of a chemical element or compound in soils under no or very little impact of human activities.

China highly values the study on soil environment background value. A total of 4,095 typical soil profiles were collected across the country during the seventh Five-Year Plan period from 1986 to 1990 through whichthe soil environment background value of arsenic, cadmium, chromium, copper, cobalt, fluorine, mercury, manganese, nickel, lead, selenium, vanadium, and zinc was determined.

Q: What are the changes to the soil contamination situations?

A: To get a clear picture of the changes to the soil contamination situations, the survey also carried out comparativestudy on the sites covered by the survey on soil environment background value during the seventh Five-Year Plan period according to the coordinates of those sites. The results indicate significant elevationof the contents of inorganic pollutants in topsoil. Among others, the content of cadmium elevated on a national scale, by over 50 percent in southwestern and coastal regions and from 10 percent to 40 percent in north China, east China, and western China.

Q: Can you describe the features of soil contamination as opposed to water and air pollution?

A: There are five features, a) soil contamination is underlying and lagged.Air and water pollution are more visual and perceivable, while soil pollution can only be determined by analysis of soil samples, testing of farm crops, and study on its effects on human and livestock health. There is a long spell of time between the generating of soil pollution to the identification of its hazards. 
b) Soil contamination is a cumulative process. It is more difficult for pollutants to move, diffuse, or dilute in soils than in air or waters. Therefore, pollutants tend to accumulate in soils.

c) Soil contamination is non-linear. The nature of differentsoils variessignificantly, added by chronic movement of pollutants aroundsoils, the pollutants distribute non-uniformly and varysignificantly in geographical distribution.

d) Soil contamination is irreversible. Heavy metals are non-degradable,accordingly, their contamination to soils is an irreversible process. Besides, it takes a long time for even many organic pollutants to degrade in soils.

e) Soil remediation is a very challenging task. Once contaminated, it takes more than cutting off pollution source to restore the soils. In general, soil remediation is expensive, chronic, and difficult.

Q: What are the main causes of soil contamination in China?

A: The soil contamination in our country is a cumulative process during the economic and social development over a long period of time, and the main causes include,

1) The waste gas, water, and residues from the operations of industrial and mining companies are the main causes of soil pollution in their vicinity. Stockpiled solid wastes such as tailings and hazardous wastes also pollute nearby soils. Vehicle exhausts lead to soil contamination by lead, zinc and other heavy metals, as well PAHs along traffic routes. 
2) Agricultural activities are the important causes of farmland contamination. Sewage irrigation plus irrational application of chemical fertilizers, pesticides, agro-films, and other agricultural inputs, plus livestock and poultry breeding result in farmland pollution. 
3) High national background value is one of the causes why some regions and watersheds fail to attain soil quality standards in terms of heavy metals.

Q: What is the connection between how much heavy metalsare therein soil and the geological background?

A: How much elements including heavy metals are there in soil is a result of natural background and human activities. The natural background hinges on multiple factors including soil parent materials, climate, topography, life-forms, and time.

Parent materials are the material foundation for the formation of soil. The mineral components and chemical composition of parent materials (geologic body) decide to a large extent the content of an element in soil. Basic-rock regionscontain high-level iron, manganese, magnesium, and calcium in soil, acid rock regions contain high-level silicon, sodium, and kalium in soil, and non-ferrous metal deposits such as sulfide deposits, coal beds, and black rock series contain high-level cadmium, lead, chromium, nickel, tungsten, and stannum in soil. The reason is, the soil formed in-situ from the weathering of a geologic body rich in heavy metal elements inherits the mineral components and chemical composition ofits parent materials, and accordingly, the content of such heavy metals is generally high.

In addition, when there is a geologic body rich in cadmium, lead, chromium, and other heavy metals in the upstream catchment of a river, and the clasts from the physical, chemical, and biological weathering of rocks are flushed by water down to the downstream andsedimented there, the sediments and the soils formed thereof inherit the high-level cadmium, lead, and other heavy metals from the geologic body in the upstream catchment. Normally, the enrichment of heavy metals in soil formed through geologic body weathering and river transportation can happen at a very large scale.

It is notable that soil formation is also one of the causes of high-level heavy metals in soil. For example, carbonate rock is the parent rock of the karst area in southwestern China, during the soil formation, the main chemical component of the rock, which is calcium carbonate, is dissolved and leached, leading to the intensive enrichment of arsenic, cadmium, lead, and mercury which is at a very low level in the parent rock, then the content of those elements in soil formed thereof can be 10 to 20 times of the content in the parent rock. As a result, the karst area in southwestern China becomes one of the regions rich in cadmium, chromium, mercury, and other toxic elements in soil.

Heavy metals in soil come from different sources, thismeans heavy metals exist in varied forms in soil and have differed biological availabilities, thus leading to significance variation of their ecological risks. Normally, the high-level heavy metals in soils formed from a geologic body and soil formation have lower ecological hazards.

Q: What hazards can be caused by soil contamination?

A: a. Soil contamination can affect the yield and quality of farm produce. It can affect the growth of crops and reduce the yields. The crops may absorb and enrich certain pollutants, which affect the quality of the produce and cause enormous economic losses to the agricultural production. Long-term consumption of contaminated farm produce may seriously harm one’s health.

b. Soil contamination can pose a safety threat to living environment. The contaminated residential, business, and industrial sites may harm public health through eating, breathing, and exposure. The development activities of contaminated sites without any remediation may harm a certain population for a long period of time.

c. Soil contamination can pose a safety threat to the ecological environment. Soil contamination affects the growth and reproduction of plants, soilanimals (e.g., earthworm), and microorganisms (e.g., rhizobia), threatens the normal ecological process and ecosystem service of soils, is unfavorable for soil nutrient conversion and fertility maintenance, and affects the normal functions of soil. The pollutants in soil may transform and move into surface water, groundwater, and atmosphericenvironment, affect other environmental media, and compromise source waters.

Q: Grain may contain excessive heavy metals, why is that?

A：The reasons are threefold, a. The natural background value of cadmium and other heavy metals is high in soil. China’s southern region and central-southern region are rich in non-ferrous metal mineral resources, and the background value of cadmium and other heavy metals is high in soil. b. Traditional mining sites of non-ferrous metals have by far over 100 years of mining history in our country. The soil there was contaminated as a result of mining activities, metal smelting, and industrial waste water and residues containing heavy metals for a long period of time. Accordingly, the grain from the land contains excessive heavy metals as well. c. Climate change and environmental pollution bring more acid rain, and then soil acidification. With growing acidity, cadmium and other heavy metals in soil are more active and easily absorbed by paddy rice and other crops. Besides, certain paddy rice varieties in some regions, thanks to the natural adaptation, possess strong cadmium enrichment tendency.

Q: What is the connection between non-attainment farm produce and soil contamination?

A: Non-attainment farm produce refer to the farm produce which contains contaminants exceeding the upper limit allowed by ongoing standards (e.g., National food safety standard-Maximum levels of contaminants in foods (GB2762-2012)). Any contamination to the farm produce during the planting, processing, storage, packaging, and transportation process may break the limit.

The non-attainment contaminants in farm produce include heavy metals, nitrite, Benzopyrene, etc. Among others, excessive heavy metals are closely related to soil contamination. However, as the resistance to and absorbing ability of soil contaminants vary among different varieties of crops, plus the movement capacity of different contaminants in the soil-plant (crop) system is not the same, there is uncertainty between soil contamination and non-attainment farm produce.

Q: How does the soil contamination affect groundwater?

A: Groundwater pollution refers to the deterioration of groundwater qualitydue to human activities. Soil contamination is an important source of pollution toshallow groundwater. Certain pollutants in the soil are easily leached or permeated into groundwater, and as time goes by, deterioratingshallow groundwater, which ultimately causes pollution.

Q: Once contaminated, is there any fix? How many restoration methods are there?

A: Contaminated soil may be restored to reduce its risks or hazards and bring back soil functions. However, soil restoration normally takes considerable amount of money and time. Soil restoration refers to move, absorb, degrade and transform contaminants in soil through physical, chemical, and biological approaches, in order to bring the contaminants to acceptable levels or decontaminate toxic and hazardous contaminants. There are normally three approaches, i.e., biological, physical, and chemical restoration approaches. Sometimes a single approach is not enough and multipleapproaches are needed, due to the complexity of soil contamination.

Biological restoration techniquesstarted since the 1980s. The cardinal principle is to utilize the unique ability of a life-form to decompose toxic and hazardous substances to remove contaminants from soils. These include plant restoration technique, microorganism restoration technique, and biological joint restoration technique.

Physical restoration refers to the techniques used to remove or separate contaminants from soils through various physical processes. Among others, thermal processing technique is suitable for restoring soils contaminated by organic pollutants and has been applied to restore soils contaminated by benzene compounds, PAHs, PCBs, and dioxins.

Chemical restoration means adding chemical substances into soils, and through the absorption, oxidation and reduction, antagonistic action, and deposition of heavy metals and organic substances, reduce the biological availability or toxicity of contaminants in soil. They mainly include soil solidification, stabilization, leaching, oxidation and reduction, photocatalytic degradation, and electrodynamics.

Q: What will the State do to step up soil conservation and remediation, facing the status quo of soil contamination?

A: a. We will develop an action plan against soil contamination. As arranged by the State Council, MEP is working with relevant line ministries to map out an action plan against soil contamination as soon as possible. The overarching train of thought is to, with safeguarding safe farm produce and sound living environment as the starting point, the conservation and improvement of soil environment quality as the core, reform and innovation as the driving force, and legal building as the cornerstone, insist on pollution control at the source, exercise graded management and classification management, increase the S&T elements, give play to the market, and encourage public participation.

b. We will accelerate the legislation process for soil environmental protection. The Standing Committee of the 12th NPC already put soil environmental protection law on Category-A legislation agenda. MEP and relevant line ministries set up a leading team, working team, and expert panel for the drafting of this law. And a draft law has been enacted over two years’ work.

c. We will conduct the detailed survey on soil contamination. Building on the general survey, MEP will work with Ministry of Finance, MLR, Ministry of Agriculture, and National Health and Family Planning Commission to organize a detailed survey, in order to get a clear understanding of the soil environment conditions. A preliminary master plan of implementation has been formulated.

d. We will carry out a soil remediation projects. The State will carry out pilot projects and model projects on remediation of contaminated soils, establish a technological system for soil remediation step by step, and promote it on a planned and phased basis.

e. We will strengthen soil environment regulation. The State will strengthen its regulatory role and set up a life-long accountability mechanism for soil contamination; tighten the supervision and inspection on the performances of heavy metal polluters on processing of wastewater, gas, and residues; strictly control the misuse and abuse of agricultural inputs during the agricultural production activities; and set standards for the collection, storage, transfer, transportation, and processing of hazardous wastes, in order to prevent new contamination.


Customer comments

  1. By Ken Glick (EEI) on

    I know this survey is only preliminary, but I somehow doubt that the Chinese government is going to seriously use it to remediate their soil contamination problems. After all, they have shown a remarkable resistance to enacting any meaningful type of legislation that would force Chinese industry to make significant changes in how they approach pollution/waste management