Pesticide sorption by low organic carbon sediments: a screening for seven herbicides

The sorption of seven pesticides in 10 Danish aquifer sediments has been st udied. These sediments all have a total organic carbon (TOC) content below 1 g kg(-1), and include carbonate-bearing and carbonate-free Quatenary sand deposits and a Cretaceous chalk aquifer. Batch experiments were carried ou t with metamitron, atrazine, isoproturon, mecoprop, 2,4-D, bentazone, and m etsulfuron-methyl at an initial pesticide concentration of 0.25 mg L-1 in g round water. Generally, the sorption decreases in the order: metamitron, at razine, isoproturon, mecoprop, 2,4-D, metsulfuron-methyl. The bentazone sor ption was found to be insignificant. For a specific pesticide the sorption covers a range of K-d values (L kg(-1)) reflecting the different sediment c haracteristics. Multivariate regression analyses demonstrate that : (i) met amitron sorption is enhanced by increasing content of iron silicates; by co ntrast the oxalate extractable iron oxides have no influence on the metamit ron sorption; (ii) sorption of atrazine, mecoprop, and 2,4-D depends primar ily on pH; the sorption is high at low pH (<6.7) compared with sorption at higher pH (>7.4); (iii) metsulfuron-methyl only sorbs at pH below 5; and (i v) isoproturon sorption is primarily influenced by the specific surface are a (SSA) and TOC. The present results illustrate the importance of choosing sediments of different geological origin in order to describe the influence of sediment properties on pesticide sorption.