The accumulation of cadmium by vegetables grown on soils contaminated from a variety of sources

Abstract

The accumulation of cadmium by four crops (cabbage, carrot, lettuce and radish) grown on soils contaminated from a variety of sources was investigated in greenhouse pot experiments. Stepwise multiple regression analyses of the data revealed that, out of the 23 soil variables determined, only eight were significantly related to cadmium accumulation in the edible plant tissues. The most frequently occurring soil parameter was total cadmium, which was inversely related to plant cadmium accumulation (CdPlant tissue/CdSoil). This implies that, for the heterogeneous group of soils used, as the concentration of cadmium in the soil increases the proportion available to the plant decreases. This may be due to the presence of metallic ore particles and/or the high sorptive capacity of the most contaminated soils. When the data were divided into two groups: sewage sludge amended soils and inorganically contaminated soils, the R-squared values were usually enhanced and some differences occurred in the variables included in the multiple regression equations; this may be indicative of the differences in speciation. Cadmium accumulation by plants grown on sewage sludge amended soils was lower than that for the inorganically contaminated soils. The heterogeneity of the inorganically contaminated group of soils resulted in lower R-squared values for the multiple regression equations; this group of soils exhibited a wide range of soil variables, such as pH, and had been contaminated by a variety of means, such as atmospheric deposition from metal smelters and the dumping of mine wastes.