Uptake of DDT and related compounds from soils into forage crops

Abstract

The uptake of DDT and related compounds ( p, p′-DDT, p, p′-DDE, p, p′-TDE and o, p′-DDT, hereafter expressed as DDTR, in alfalfa, maize, sugarbeet, mangold, potato and ryegrass was studied in field trials on loamy soils that had previously been used for fruit trees. Residues in these soils result from repeated use of DDT in these orchards over the last 20 years. Contents of DDTR in soil ranged from 0.7 to 2.5 mg/kg dry soil. The value of the quotient “content of DDTR in crop/content of DDTR in soil” (both contents expressed on a dry matter basis) for the foddered part of alfalfa and maize and for sugarbeet and mangolds was less than 0.03. The highest values were found for potatoes with an average quotient for all sizes of 0.09. The DDTR residues in the tubers were mainly in the peelings; residues in peeled potatoes were below limits of determination. Ryegrass also took up measurable amounts of DDTR residues from soil. The value of the quotient content in crop/content in soil for the grass blades from the first three cuts after sowing was lower than 0.05. For grass, mown during a whole season on a permanent pasture, an average value of 0.044 for p, p′-DDE was found. In most instances, no significant differences in the uptake of the four compounds were found. Contamination of crops with soil during harvesting can considerably enhance contents of DDTR, thus decreasing usability for animal feeding.