Effects of the pyrethroid insecticide gamma-cyhalothrin on aquatic invertebrates in laboratory and outdoor microcosm tests

The sensitivity of a range of freshwater lentic invertebrates to gamma-cyhalothrin (GCH), a single enantiomer of the synthetic pyrethroid lambda-cyhalothrin, was assessed in single species laboratory tests and an outdoor multi-species ecosystem test. The most sensitive species in the laboratory single species tests with GCH was Chaoborus obscuripes (96 h EC50: 3.8 ng/l). The species sensitivity distribution curve, based on the laboratory 96 h EC50 acute toxicity data for eight species, gave a median HC5 value for GCH of 2.12 ng/l. The NOECcommunity derived from the multi-species ecosystem test was 5 ng/l, and the insects Chaoborus sp. and Caenis sp. were identified as the most sensitive species. The results indicate that the median HC5, based on eight species selected to include those known to be sensitive to pyrethroids, provided a good estimation of the NOECcommunity for GCH. Furthermore, the results for GCH indicated that the endpoints typically used in higher-tier risk assessments for pesticides in Europe (HC5 and NOECcommunity) were consistent with expectations when compared to the equivalent endpoints for the racemate LC