Influence of Various Filters on the Concentration of Pesticides Dissolved in Water

Abstract

Many studies on the fate and transport of pesticides as well as analytical procedures such as solid/liquid extraction and flow injection analysis include a filtration step. However, the influence of filtration on the dissolved concentrations of pesticides is poorly documented. The objective of this study was therefore to quantify the changes in the dissolved concentrations of 17 pesticides when filtered through a 0.45 μm pore diameter cellulose ester (CE) filter, a 0.45 μm polyvinylidene fluoride (PVDF) filter, and a 0.7 μm nominal pore size glass-fiber filter (GF/F). Seventeen pesticides added at concentrations between 0.5 and 2.0 M to a synthetic mineralized water were studied: atrazine, simazine, cyanazine, deethylatrazine, alachlor, metolachlor, chlortoluron, diuron, isoproturon, dinoseb, dinoterb, bentazone, lindane, dieldrin, p,p‘-DDT, malathion, and parathion. Liquid/liquid extraction, under either acidic or neutral conditions, was followed by GC/MS or HPLC/UV with a diode array detector. The detection limit was 0.05 μg/L for each molecule. Significant differences (least significant difference test, α ≤ 0.01) between unfiltered and filtered water, and between different filters, were observed only for p,p‘-DDT, about 30% of which was lost during filtering, regardless of the filter, and for dieldrin, about 20% of which was lost with the CE and PVDF filters. The fact that significant loss was observed only for P,P‘-DDT and dieldrin might be related to their aqueous solubility, the lowest among the 17 compounds investigated here. For the molecules with aqueous solubility >1 mg/L studied here, the filtering of water samples can therefore be carried out with no significant effect on the dissolved concentrations. When filtration is required, the choice of filter will depend on the desired filtration rate and resistance to clogging, both of which are highest for glass-fiber filters.