Thresholds for the Effects of Pesticides on Invertebrate Communities and Leaf Breakdown in Stream Ecosystems

Abstract

We compiled data from eight field studies conducted between 1998 and 2010 in Europe, Siberia, and Australia to derive thresholds for the effects of pesticides on macroinvertebrate communities and the ecosystem function leaf breakdown. Dose-response models for the relationship of pesticide toxicity with the abundance of sensitive macroinvertebrate taxa showed significant differences to reference sites at 1/1000 to 1/10,000 of the median acute effect concentration (EC50) for Daphnia magna, depending on the model specification and whether forested upstream sections were present. Hence, the analysis revealed effects well below the threshold of 1/100 of the EC50 for D. magna incorporated in the European Union Uniform Principles (UP) for registration of single pesticides. Moreover, the abundances of sensitive macroinvertebrates in the communities were reduced by 27% to 61% at concentrations related to 1/100 of the EC50 for D. magna. The invertebrate leaf breakdown rate was positively linearly related to the abundance of pesticide-sensitive macroinvertebrate species in the communities, though only for two of the three countries examined. We argue that the low effect thresholds observed were not mainly because of an underestimation of field exposure or confounding factors. From the results gathered we derive that the UP threshold for single pesticides based on D. magna is not protective for field communities subject to multiple stressors, pesticide mixtures, and repeated exposures and that risk mitigation measures, such as forested landscape patches, can alleviate effects of pesticides.

Guidance on tiered risk assessment for plant protection products for aquatic organisms in edge‐of‐field surface waters

“…In South Africa, Dabrowski et al (2001) identified pesticide effects on a stream. A recent meta-study of Schäfer et al (2012) identified pesticide effects in eight data sets comprising exposure data and effect data.…”

A catchment scale evaluation of multiple stressor effects in headwater streams

“…an increase in the number of mixture components has been suggested to lead to a decrease in the range of deviation from toxic additivity (the Funnel hypothesis) (Warne and Hawker, 1995). For log max TU D.magna the suggested threshold for effects of pesticides in the field is at least -3 (Schäfer et al, 2012b).…”

Pesticides reduce regional biodiversity of stream invertebrates

“…The only exceptions are two studies that addressed effects of salinity (8,9). Hence, although chemical contaminants are well known as an important driver for biodiversity loss (1,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28), there is scarce empirical evidence to support such opinion for the large-scale taxonomic pools.…”

“…Essentially, it remains unknown whether, to what degree, and at what concentrations pesticides cause the species losses at the regional scale. However, there are many investigations showing the effects on the local biodiversityrelated parameters in both freshwater (16)(17)(18)(19)(20)(21)(22)(23) and terrestrial systems (14,15,(24)(25)(26)(27). Thus, the previous studies with freshwater invertebrates reliably measured the aquatic pesticide concentrations and identified local (site-scale) changes in the abundance of the taxa specifically vulnerable to pesticides and structural community alterations, e.g., using the species-at-risk (SPEAR) pesticides indicator (16)(17)(18)(19)(20)(21), or the abundance of separate species (22) (for different taxonomic groups, see ref.…”