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

The sorption of seven pesticides in 10 Danish aquifer sediments has been studied. 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 out with metamitron, atrazine, isoproturon, mecoprop, 2,4-D, bentazone, and metsulfuron-methyl at an initial pesticide concentration of 0.25 mg L-1 in ground water. Generally, the sorption decreases in the order: metamitron, atrazine, isoproturon, mecoprop, 2,4-D, metsulfuron-methyl. The bentazone sorption 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 characteristics. Multivariate regression analyses demonstrate that : (i) metamitron sorption is enhanced by increasing content of iron silicates; by contrast the oxalate extractable iron oxides have no influence on the metamitron sorption; (ii) sorption of atrazine, mecoprop, and 2,4-D depends primarily 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 (iv) isoproturon sorption is primarily influenced by the specific surface area (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.