| The current Soil Environmental Quality Standard of China(GB 15617-1995) which was promulgated in 1995, has made great contribution to the evaluation and management of soil environmental quality in China. However, due to the limited research data and scientific knowledge at the time, the standard did not fully consider great variations of different area, different agricultural land use and too few pollutants were contained. Therefore the standard was not scientific enough to meet the requirements of current soil environmental quality management. The standard of specific pollutants adopted unified national standard value. In the course of implementation, some local soils exceeded the standard in the north and the agricultural products did not exceed the standard, while the soil in the south did not exceed the standard but the agricultural products exceeded the standard. Because it did not fully consider the influence of soil properties, crop species and cultivars, the speciation of heavy metals. Environmental quality standards "across the country" can not scientifically and effectively guide the cumulative assessment of farmland soil pollution, crop suitability evaluation and the division of production areas and other practical problems. Considering the large variations of soil types, soil physical and chemical properties and spatial variation of crop type, it is necessary to carry out zoning and classification of soil environmental benchmarks and standards. The Action Plan for the Prevention and Control of Soil Pollution(Article 10) was issued by the end of May 2016 and the Soil Environmental Quality Standard for Agricultural Land will be issued by the end of 2017. The regions can formulate local standards which are stricter than national standards.Guizhou Province is located in the southwest of China. It is a main karst mountainous area with a per capita arable land area of less than 0.5 mu. It is a famous mineral resource province with a high geological background, a long history of mining and primitive techniques. With the groundwater system, migration intertwined pollution, seriously heavy metal contamination problems exist in Guizhou Province. Lead and zinc smelting area ofBijie district, Guizhou province is located in the "two rivers" upstream. Lead-zinc deposits have been the main source of cadmium smelting. "Three wastes" discharged by all around lead and zinc smelting contains a lot of lead and zinc cadmium. Risk to the soil environment is high and the pollution form is special of Bijie district, Guizhou province.In this study, six main soils(yellow soil, yellow brown soil, red soil, lime soil, purple soil and paddy soil) were selected to study the ecological toxicity of lead and cadmium. The toxicity of lead and cadmium to plants in main soils of Guizhou Province was studied by means of root elongation test of main crop wheat in Guizhou Province. The acute toxicity test of Eisenia fetida was carried out to study the toxicity of semi- Lead and Cadmium Ecological Toxicity Threshold at the End of Test. And a model for predicting cadmium accumulation in earthworms in four main soils of Guizhou Province was established. This paper can provide reference data for the development of lead and cadmium soil environmental benchmarks and standards in Guizhou Province.The main findings are as follows:(1) The effects of lead on the root elongation of wheat seeds in different types of soils were studied. The inhibition rate of lead to the root elongation of wheat was significantly different in different soils. The ability of lead inhibition on root elongation of wheat seeds was: yellow soil> red soil> limestone soil> purple soil> paddy soil> yellow brown soil in which lead concentration is 5000 mg · kg-1 in six soils. The EC10 values of soils purple soil, paddy soil, yellow brown soil, yellow soil,red soil and limestone soil were741, 2570,1349,447,1349 and 955 mg · kg-1, respectively. The results showed that the effect of cadmium on root elongation of wheat seed was significantly different in different soil types in the test of the effects of exogenous cadmium on seed root elongation of six main soils in Guizhou Province.The ability of Cadmium inhibition on root elongation of wheat seeds was: paddy soil> purple soil> red soil>> yellow brown soil limestone soil>yellow soilin which lead concentration is 1000 mg · kg-1 in six soils. The EC10 values of soils in purple soil, paddy soil,yellow brown soil, yellow soil,red soil and limestone soil were 309, 98,79, 437,229 and 174 mg · kg-1.(2) For the six main soils in Guizhou Province, the ecological toxicity threshold of lead was determined based on the ecotoxicity threshold LC50 of earthworm acute toxicity. The order was yellow soil> lime soil> red soil> purple soil> yellow brown soil>paddy soil.Threshold of LC50(14d) were 2517?2761?3184?3343?3581?3652 mg · kg-1, respectively. Based on the ecological toxicity threshold of cadmium, the toxicity of cadmium was determined by LC50. The order of toxicity was cadmium> yellow brown> lime> red> yellow> purple. LC50(14d) were 871, 931, 988, 1037, 1161 and 1292 mg · kg-1, respectively.(3) For the 4 types of main soils( lime soil, purple soil, red soil, yellow brown soil), according to the calculation value of the soil biological enrichment coefficient(BSAF) shows that the enrichment ability of earthworms on the absorption of Cd in the 4 types of uncontaminated soils red soil > lime soil > yellow brown soil> purple soil. For these 4 types of soils, at the soil cadmium exposure concentration of 0 ~ 2000mg·kg-1, the concentration of Cd in the earthworm body was 2.69 ~ 643.67mg·kg-1. The prediction model lg[Cdworm]=0.648lg[Cdtotal]-0.290[pH]+2.621,(R2=0.882) predict cadmium accumulation in earthworms of the 4 main soils in Guizhou Province.(4)The European Commission or recommended by the U.S. Environmental Protection Agency, calculated based on earthworm soil lead / cadmium can be predicted no effect concentration PNECsoil, purple soil, paddy soil, yellow brown soil, yellow soil, red soil, lime soil, Lead PNECsoil were 3.34, 3.65, 3.58, 2.52, 3.18, 2.76 mg·kg-1; Cadmium the PNECsoil were 1.29, 0.87, 0.93, 1.16, 1.04, 0.99 mg·kg-1. |
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