Biomonitoring using benthic macroinvertebrates has been used to assess water quality in Europe since the early 20th century. Most methods use community-level measurements, and the use of single-species responses has been limited, despite their potential benefits as sensitive, early warning indicators. Here we evaluate a single-species in situ assay in which the response is feeding inhibition of the freshwater amphipod Gammarus pulex. The assay was deployed in uncontaminated reference sites to quantify background variability in feeding rates and to elucidate sources of this variation. The ability of the assay to detect impacts of point-source discharges was assessed and the ecological relevance of the assay determined by comparing assay responses to aspects of community structure and functioning. Water temperature accounted for 76% of the variation in the feeding rate of animals deployed at uncontaminated sites, and summer deployments had a >90% power to detect a 30% inhibition in feeding. Inhibition of the situ feeding rate of G. pulex deployed downstream of a variety of point-source discharges ranged from 27 to 99.6%. Gammarus pulex is an important detritivore in stream communities, and a strong positive correlation existed between in situ feeding rate measured over 6 d and leaf decomposition measured over 28 d. A positive correlation also existed between in situ feeding and macroinvertebrate diversity and a biotic index. The G. pulex in situ feeding assay is a short-term sublethal biomonitor of water quality that is indicative of community- and ecosystem-level responses occurring over longer time periods. It is robust, responsive, and relevant.

Abstract-Biochemical biomarkers are increasingly used for environmental assessment. Although the emphasis has been on vertebrate biomarkers, invertebrates biomarkers have been developed as well. This study evaluated the usefulness of biomarker responses of freshwater invertebrates by comparing the sensitivity and specificity of endpoints at three levels of biological organization: biochemical, physiological, and individual. The study focused on the epibenthic amphipod Gammarus pulex L., and the end points were cholinesterase (ChE) and glutathione-S-transferase (GST) activity, feeding inhibition, and mortality. Chemicals representing five major classes of toxic chemicals were assessed, including zinc, linear alkylbenzene sulphonate (LAS; surfactant), lindane (organochlorine), pirimiphos-methyl (organophosphorus), and permethrin (pyrethroid). Lethality was the least sensitive endpoint, with 96-h LC50 values ranging from 2.78 g/L for permethrin to 6.31 mg/L for LAS. Comparison of the biochemical biomarkers and the sublethal feeding rate assay indicated that whereas ChE inhibition was a specific indicator of organophosphate exposure, the biochemical assay was more than 13-fold less sensitive than the feeding rate assay. The GST biomarker performed with greater sensitivity but with lower specificity compared with the ChE biomarker. However, only on exposure to lindane did the GST biomarker marginally outperform the feeding rate assay in terms of sensitivity. Feeding inhibition is both a general and a sensitive (LC50, Ͻ3%) indicator for exposure to a range of chemicals. The Gammarus sp. ChE biomarker may have utility in providing a diagnostic and rapid indicator of organophosphate exposure, but evidence from this and other studies questions the sensitivity of this biomarker in predicting sublethal, higher-order effects. The GST biomarker may provide a rapid and sensitive indicator for toxicant exposure, but it has limited use as a diagnostic tool and provides only limited improvement in sensitivity over more ecologically relevant sublethal end points (e.g., feeding rate, growth rate).

Biomonitoring using benthic macroinvertebrates has been used to assess water quality in Europe since the early 20th century. Most methods use community-level measurements, and the use of single-species responses has been limited, despite their potential benefits as sensitive, early warning indicators. Here we evaluate a single-species in situ assay in which the response is feeding inhibition of the freshwater amphipod Gammarus pulex. The assay was deployed in uncontaminated reference sites to quantify background variability in feeding rates and to elucidate sources of this variation. The ability of the assay to detect impacts of point-source discharges was assessed and the ecological relevance of the assay determined by comparing assay responses to aspects of community structure and functioning. Water temperature accounted for 76% of the variation in the feeding rate of animals deployed at uncontaminated sites, and summer deployments had a >90% power to detect a 30% inhibition in feeding. Inhibition of the situ feeding rate of G. pulex deployed downstream of a variety of point-source discharges ranged from 27 to 99.6%. Gammarus pulex is an important detritivore in stream communities, and a strong positive correlation existed between in situ feeding rate measured over 6 d and leaf decomposition measured over 28 d. A positive correlation also existed between in situ feeding and macroinvertebrate diversity and a biotic index. The G. pulex in situ feeding assay is a short-term sublethal biomonitor of water quality that is indicative of community- and ecosystem-level responses occurring over longer time periods. It is robust, responsive, and relevant.

Abstract-Whole effluent toxicity (WET) tests are increasingly used to monitor compliance of consented discharges, but few studies have related toxicity measured using WET tests to receiving water impacts. Here we adopt a four-stage procedure to investigate the toxicity and biological impact of a point source discharge and to identify the major toxicants. In stage 1, standard WET tests were employed to determine the toxicity of the effluent. This was then followed by an assessment of receiving water toxicity using in situ deployment of indigenous (Gammarus pulex) and standard (Daphnia magna) test species. The third stage involved the use of biological survey techniques to assess the impact of the discharge on the structure and functioning of the benthic macroinvertebrate community. In stage 4, toxicity identification evaluations (TIE) were used to identify toxic components in the effluent. Receiving-water toxicity and ecological impact detected downstream of the discharge were consistent with the results of WET tests performed on the effluent. Downstream of the discharge, there was a reduction in D. magna survival, in G. pulex survival and feeding rate, in detritus processing, and in biotic indices based on macroinvertebrate community structure. The TIE studies suggested that chlorine was the principal toxicant in the effluent.

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