Mitigation of polar pesticides across a vegetative filter strip. A mesocosm study.

Vegetated filter strips (VFSs) are planted at the edge of agricultural fields to reduce pesticide run-off and its consequent potential toxicological effects on ecosystem biota; however, little attention has been paid to date to the attenuation of highly polar and ionisable pesticides such as phenoxyacid herbicides. This study assesses the effect of soil moisture, run-off flow and vegetation on the attenuation of MCPA, mecoprop, dicamba, dichlorprop, fenitrothion, atrazine and simazine by VFSs. Reactors measuring 5 m long by 0.1 m wide were each filled with 60 kg of soil from a real field VFS. VFSs planted with Phragmites australis and unvegetated control reactors were assessed. After a simulated rainfall event of 50 mm, two hydraulic loading rates (HLRs) were assessed (1 and 2 cm h). These results were compared to those from the same systems under water-saturated conditions. The results show that VFSs reduced the peak inlet concentration and pesticide mass by more than 90 % and that the presence of vegetation increased that attenuation (82-90 % without vegetation and 90-93 % with vegetation, on average). The laboratory-scale study showed that such attenuation was due to sorption into the soil. The toxicity units of pesticides fell by more than 90 % in all cases, except under the water-saturated conditions, in which the decrease was lower (16 vs 54 %, for unvegetated and vegetated reactors). Therefore, the presence of vegetation was shown to be effective for reducing mass discharge of ionisable and highly polar pesticides into surface-water bodies.