Instances of soil and crop heavy metal contamination in China

Both general and specific investigations of soil and crop heavy metal conta mination were carried out across China. The former was focused mainly on Cd , Hg, As, Pb, and Cr in soils and vegetables in suburbs of four large citie s; the latter investigated Cd levels in both soils and rice or wheat in con taminated areas throughout 15 provinces of the country. The results indicat ed that levels of Cd, Hg, and Pb in soils and some in crops were greater th an the Governmental Standards (Chinese government limits for soil and crop heavy metal contents). Soil Cd ranged from 0.46 to 1.04 mg kg(-1), on avera ge, in the four cities and was as high as 145 mg kg(-1) in soil and 7 mg kg (-1) in rice in the wide area of the country. Among different species, tuberous vegetables seemed to accumulate a larger portion of heavy metals than leafy and fruit vegetables, except celery. For both rice and wheat, two staple food crops, the latter seemed to hav much higher concentrations of Cd and Pb than the former grown in the same area. Furthermore, the endosperm of both wheat and rice crops had the highest por tion of Cd and Cr. Rice endosperm and wheat chaff accumulated the highest P b, although the concentrations of all three metals were variable in differe nt parts of the grains. For example, 8.3, 6.9, 1.4, and 0.6 mg kg(-1) of Pb were found in chaff, cortex, embryo, and endosperm of wheat compared with 0.11, 0.65, 0.71, and 0.19 mg kg(-1) in the same parts of rice, respectivel y. Untreated sewage water irrigation was the major cause of increasing soil an d crop metals. Short periods of the sewage water irrigation increased indiv idual metals in soils by 2 to 80% and increased metals in crops by 14 to 20 9%. Atmospheric deposition, industrial or municipal wastes, sewage sludge i mproperly used as fertilizers, and metal-containing phosphate fertilizers p layed an important role as well in some specific areas.