Cadmium in soil solutions from a transect of soils away from a fertiliser bin

The effects of high inputs of phosphate fertiliser on Cd concentrations wer e studied in soil solutions extracted from topsoils. Soils were sampled alo ng a transect at distances of 1-100 m away from a fertiliser bin. The trans ect was sampled four times during 1 year. Soil solutions wire analysed for Cd, pH, major cations and anions, and other heavy metals (As, Cr, Cu, Pb). For one of the transect samplings, soil total Cd. Cr, Cu, Pb and P were als o measured. Cd speciation in the soil solutions was calculated by the GEOCH EM-PC computer program. Chemical composition varied substantially along the transect, and also between samplings, indicative of seasonal effects and t he influence of a fresh application of superphosphate fertiliser during the year. Application of fertiliser decreased soil solution pH and increased t he levels of heavy metals in soil solution. Generally, soil total Cd, Cr, C u, Pb, and P decreased with increasing distance from the fertiliser bin. Co rrelations between P and the four heavy metals were: P and Cd (R-2 = 0.978) , P and Cr (R-2 = 0.712), P and Pb (R-2 = 0.538), P and Cu (R-2 = 0.267). L ess than 1% of the total Cd in the soil samples was found in the soil solut ion. The free metal ion Cd2+ accounted for 55-90% of solution Cd. Of the co mplexed species of Cd, the chloride and sulphate complexes were usually the most important, even when nitrate and phosphate concentrations were relati vely high. The presence of As, Cr, Cu and Ph had no effect on Cd speciation . (C) 2001 Elsevier Science Ltd. All rights reserved.