Because heavy metals and metalloids in soils are derived from both natural and anthropogenic sources, it is not straightforward to determine if a soil is contaminated. In the recent MEP/MLR soil contamination survey, the status of soil contamination was determined by comparing the total concentration of a contaminant to the benchmark values of the Chinese environmental quality standard for soils issued by the MEP in 1995. The standard specifies three classes of benchmark values for eight heavy metals or metalloids and two pesticides 4.
Class I values are considered to represent the natural background, to be used in the protection of regional natural ecosystems from contamination. Class II is set up to protect agricultural production and human health via the food chain, and can be applied to agricultural, orchard and pasture land.
The Class II values are dependent on soil pH and land use. In the recent MEP and MLR soil contamination survey, a soil is considered to be contaminated if a heavy metal or metalloid is above the class II value; the degree of contamination is designated as light, medium, or severe when the concentration is 1−3, 3−5, or >5 times the benchmark value, respectively.
Class III is for the protection of crops or forests from phytotoxicity and may also be used where the natural background is elevated.
Go through the bellow article, you will find more details.
https://www.researchgate.net/publication/279895584_Heavy_Metal_Pollution_in_Soils_in_China_Status_and_Countermeasures [accessed May 29 2019]. https://www.researchgate.net/publication/279895584_Heavy_Metal_Pollution_in_Soils_in_China_Status_and_Countermeasures
Dear J. C. Tarafdar Karanveer Singh Mohammad Neaz Morshed ,
Thank You you all for your helpful answers.
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