Cadmium accumulation in soil and risk prediction in the Qaidam Basin

This study characterized and mapped the spatial distribution of total and available cadmium in original land and farmland soils in the Qaidam basin，China，using geostatistical methods. 22 soil samples from original land (native soil that had never been farmed) and 50 soil samples from farmland (that had been farmed for 50 years) were analyzed cadmium content of soil at Nuomuhong farm in the Qaidam basin. In the original land soil，the mean cadmium content was 0.30 mg/kg，two times the background level (0.14 mg/kg). This met both the pollution-free food (0.60 mg/kg) and the green food (0.40 mg/kg) standards. In the farmland soil，the mean cadmium content was 0.43 mg/kg，three times the background level. This was lower than the pollution-free food standard，but higher than the green food standard. Irrigation water from river cadmium content was 0.0036 ng/kg. 15 kinds of pesticides，fungicides，herbicides and plant hormones were detected and found to carry 17.17 mg/ha of cadmium to the soil per year. 7 kinds of fertilizer contributed 3444 mg/ha of cadmium to the soil per year. The most serious source of pollution was chicken manure，which contributed 2025 mg/ha per year. This was followed by compound fertilizer (576 mg/ha per year)， Diammonium Phosphate（DAP） (432 mg/ha per year)，and organic fertilizer (360 mg/ha per year). Fertilization is thus a major source of cadmium pollution in the soil. About pH 8 adsorption of cadmium alkaline soils are highly difficult to drain，if agricultural practices at the Nuomuhong farm do not change，the original land cadmium contents will exceed the green food standards upper limit of 0.4 mg/kg after 76.3 years.