The partitioning of fenvalerate to natural dissolved organic matter

Abstract

The degree of association of the pyrethroid insecticide fenvalerate to dissolved organic matter (DOM) was measured with the reverse-phase partition coefficient ( K rp) using Sep-Paks. Natural DOM of four size fractions ranging from 1 K molecular weight up to 1 μm was isolated from Jack Lake and Luther Marsh in Ontario, Canada, and compared to the commercial DOM substitute Aldrich humic acid (AHA). A generator column method to produce fenvalerate-saturated DOM solutions necessary for determining K rp was compared to the standard method of mixing the components in a bottle until equilibrium was reached. Using the bottle method, the association of fenvalerate to DOM was not significantly different (α = 0.05) for any of the DOM. With the generator column-produced solutions, the mean K rp of the smallest fraction (1 K < DOM < 10 K) was significantly lower (2.2 × 10 3 litres/kg, p < 0.00001) than the mean of each of the three larger fractions and AHA, which were not different from each other (8.0 × 10 4 to 3.0 × 10 5 litres/kg). Jack Lake DOM had higher K rp values than Luther Marsh, which predominantly contained lower molecular weight DOM. The generator column method produced more precise K rp measurements between fenvalerate and DOM than the bottle method; however, the use of Sep-Paks to measure DOM association with hydrophobic chemicals which exhibit high breakthrough, such as fenvalerate, may produce questionable results.