Abstract
There are currently few suitable test systems for the chronic toxicity testing of aquatic macroinvertebrates under stream conditions. Therefore, a new test system mimicking running water conditions was developed for testing with lotic insects. This system uses small test cages, with 10 of these suspended inside each 25-L container and rotating at 0.1 m/s, to create a water flow for the individual organism inside each cage. To test the performance of the new exposure system, chronic effects (21 d) of the neonicotinoid imidacloprid were investigated with field-collected larvae of the stonefly Protonemura sp. Endpoints were survival, growth, and/or emergence (depending on the developmental stage of the larvae at the start of the exposure). Two experiments conducted 1 yr apart showed good reproducibility: growth 10% effect concentration (EC10) values were 15.3 and 18.5 μg/L and no-observed-effect concentration (NOEC) values were 30.3 and 21.5 μg/L. A third experiment, performed with further-developed larval instars, showed a significant effect of imidacloprid on emergence (with EC10 of 5.97 μg/L and NOEC of 2.89 μg/L) and a significant effect on survival (with median lethal concentration of 44.7 µg/L). The results of the present study show that the newly developed test system provides a suitable approach for toxicity testing with stonefly larvae and potentially for other lotic macroinvertebrate species. Environ Toxicol Chem 2021;40:2229-2239. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Highlights
Lentic test systems like ponds are typically used in the risk assessment of pesticides, even though lotic water bodies like creeks and small streams are more typical for agricultural landscapes (Kreuger 1998; Mohr et al 2012)
Imidacloprid concentrations remained relatively stable during the 1‐wk medium renewal intervals
There are several studies with stream insect larvae not performed under stream conditions but in conditions of a standing water body, for example, studies with stream insects performed by Kreutzweiser et al (2008)
Summary
Lentic test systems like ponds are typically used in the risk assessment of pesticides, even though lotic water bodies like creeks and small streams are more typical for agricultural landscapes (Kreuger 1998; Mohr et al 2012). Pesticides entering lotic water bodies can have significant effects on nontarget arthropods (Tisler et al 2009). Standard laboratory tests performed in still‐water bodies may not be sufficient to assess ecological risks because it is difficult to extrapolate these results to ecosystems with different natural conditions. Testing of lotic species under stream conditions is important for predictions of risks for nontarget species in realistic settings and to detect possible indirect effects. A few studies have used test systems simulating conditions of running water in a laboratory‐scale test design.
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