Assessing effects of the pharmaceutical ivermectin on meiobenthic communities using freshwater microcosms

Ivermectin is a widely applied veterinary pharmaceutical that is highly toxic to several non-target organisms. So far, little is known about its impact on benthic freshwater species, although its rapid sorption to sediment particles and high persistence in aquatic sediments have raised concerns about the risk for benthic organisms. In the present study, indoor microcosms were used to assess the impact of ivermectin on freshwater meiobenthic communities over a period of 224 days. Microcosm sediments were directly spiked with ivermectin to achieve nominal concentrations of 0.9, 9, and 45 mu g kg(-1) dw. Initially measured ivermectin concentrations (day 0) were 0.6, 6.2, and 31 mu g kg(-1) dw. In addition to abundance of major meiobenthic organism groups, the nematode community was assessed on the species level, assuming a high risk for free-living nematodes due to their close phylogenetic relationship to the main target organisms of ivermectin, parasitic nematodes. Benthic microcrustaceans (cladocerans, ostracods) and nematodes showed the most sensitive response to ivermectin, while tardigrades profited from the presence of the pharmaceutical. The most pronounced effects on the meiofauna community composition occurred at the highest treatment level (31 mu g kg(-1) dw), leading to a no observed effect concentration (NOECcommunity) of 6.2 mu g kg(-1) dw. However, the nematode community was already seriously affected at a concentration of 6.2 mu g kg(-1) dw with two bacterivorous genera, Monhystera and Eumonhystera, being the most sensitive, whereas species of omnivorous genera (Tripyla, Tobrilus) increased in abundance after the application of ivermectin. Thus, a NOECcommunity of 0.6 mu g kg(-1) dw was derived for nematodes. Direct and indirect effects of ivermectin on meiobenthic communities could be demonstrated. The pharmaceutical is likely to pose a high risk, because its NOECs are close to predicted environmental concentrations (PECs) in sediments (0.45-2.17 mu g kg(-1) dw), resulting in worst case risk quotients (RQs) of 1.05-36.2. This observation lends support to efforts aimed at preventing the repeated entry of ivermectin in aquatic environments and thus its accumulation in sediments. Moreover, this study points out that model ecosystem studies should be part of environmental risk assessments (ERAs) of veterinary medicinal products (VMPs). (C) 2010 Elsevier B.V. All rights reserved.