posted on 2019-09-25, 19:45authored byJakob Wolfram, Sebastian Stehle, Sascha Bub, Lara L. Petschick, Ralf Schulz
Although
pesticide contamination in agricultural surface waters
is a common phenomenon, large-scale studies dealing with the responsible
drivers are rare. We used data from 259 publications reporting 5830
individual water or sediment concentrations of 32 insecticides and
their metabolites in 644 US surface waters to determine the factors
driving insecticide risks, that is, exceedance of regulatory threshold
levels (RTLs). Multiple linear regressions (R2 adj. = 49.6–76.5) revealed that toxicity-normalized
agricultural insecticide use (i.e. use divided by toxicity) was the
most important driver. Burst rainfall erosivity and irrigation practices
also had risk-promoting effects, whereas time, catchment size, and
sampling interval had risk-demoting effects. A regression model (R2 adj. = 62.2, n = 1833) for
small, medium, and large running waters was validated and used for
risk mapping at the national scale, highlighting multiple regions,
where the comparison of predicted insecticide concentrations with
their RTLs indicate adverse conditions for aquatic organisms. Particularly
in smaller streams, risks were most pronounced with an average RTL
exceedance frequency of 27.7% in all grid cells (n = 9968). Finally, mixture toxicity was mainly (about 76.7%) explained
by the most toxic compound in the mixture, causing ∼95.7% of
RTL exceedances. Identifying the factors, which drive exposure for
all relevant insecticide classes, and subsequently mapping these risks
for surface waters of various sizes across the U.S., will support
future risk management.