Macro-invertebrate decline in surface water polluted with imidacloprid: A rebuttal and some new analyses

This paper challenges the findings of Van Dijk et al. 2013 by rebutting their assumptions that other pesticide residues that could be collinear with imidacloprid are not affecting macroinvertebrate abundance and that imidacloprid concentrations can be extrapolated over 160 days at a 1km spatial scale. The authors examined the 2009 pesticide monitoring data to explore trends. If a pesticide was not detected or was below the limit of detection, that was set at zero for their calculations (rather than assuming it was present below the detection limit). They extracted smaller data sets to test for collinearity between different pesticide detections, and determined that imidacloprid cannot be separated from other pesticides that may also be influencing toxicity. Detections of other compounds also commonly exceeded the water quality standards, so it is unlikely that imidacloprid was solely responsible for the declines in macroinvertebrates. However, imidacloprid did exceed the water quality standards frequently, so it may have had a relatively large impact on water quality. The authors conclude that imidacloprid is likely affecting water quality negatively, but that its effects cannot be singled out clearly as Van Dijk et al. 2013 propose.