The partitioning of fenvalerate to natural dissolved organic matter

The degree of association of the pyrethroid insecticide fenvalerate to dissolved organic matter (DOM) was measured with the reverse-phase partition coefficient (Krp) 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 Krp 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 Krp of the smallest fraction (1 K < DOM < 10 K) was significantly lower (2.2 × 103 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 × 104 to 3.0 × 105 litres/kg). Jack Lake DOM had higher Krp values than Luther Marsh, which predominantly contained lower molecular weight DOM. The generator column method produced more precise Krp 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.