Overview of results from the WaterTox intercalibration and environmental testing phase II program: Part 1, statistical analysis of blind sample testing

Abstract

There is an urgent need to evaluate the presence of toxicants in waters used for human consumption and to develop strategies to reduce and prevent their contamination. The International Development Research Centre undertook an intercalibration project to develop and validate a battery of bioassays for toxicity testing of water samples. The project was carried out in two phases by research institutions from eight countries that formed the WaterTox network. Results for the first phase were reported in the special September 2000 issue of Environmental Toxicology. Phase II involved toxicity screening tests of environmental and blind samples (chemical solutions of unknown composition to participating laboratories) using the following battery: Daphnia magna, Hydra attenuata, seed root inhibition with Lactuca sativa, and Selenastrum capricornutum. This battery was also used to assess potential toxicity in concentrated (10x) water samples. Results are presented for a set of six blind samples sent to the participating laboratories over a 1-year period. Analyses were performed for each bioassay to evaluate variations among laboratories of responses to negative controls, violations of test quality control criteria, false positive responses induced by sample concentration, and variability within and between labs of responses to toxic samples. Analyses of the data from all bioassays and labs provided comparisons of false positive rates (based on blind negative samples), test sensitivities to a metal or organic toxicant, and interlaboratory test variability. Results indicate that the battery was reliable in detecting toxicity when present. However, some false positives were identified with a concentrated soft-water sample and with the Lactuca and Hydra (sublethal end-point) tests. Probabilities of detecting false positives for individual and combined toxic responses of the four bioassays are presented. Overall, interlaboratory comparisons indicate a good reliability of the battery.

Hydra, a model system for environmental studies

“…Bioassays with other invertebrates, such as daphnia (Daphnia magna) and Ceriodaphnia (C. affinis or C. dubia), are widely used to detect chronic toxicity (after 21-days exposure) of chemical solutions, environmental and waste waters (Viganò et al, 1996). In several studies the Hydra bioassay, particularly when chronic changes in morphology and reproduction rate were measured, was more sensitive than other bioassays undertaken with invertebrate, vertebrate and plant test organisms (Diaz-Baez et al, 2002;Ronco et al, 2002a;Arkhipchuk et al, 2006b;Oberholster et al, 2008). In particular, sub-lethal effects on Hydra morphology were found to be considerably more sensitive than lethal effects , closely matching the toxicity response of the fathead minnow (Fu et al, 1994) and are generally more sensitive than the Microtox test (Pardos et al, 1999).…”

“…The core battery of tests consisted of 2 animal assays (48 hour acute toxicity to D. magna (Dutka, 1989) and 96 hour exposure lethality to H. vulgaris, (Trottier et al, 1997) and a vascular plant bioassay (L. sativa 120 hour exposure inhibition of root elongation (Dutka, 1989). This program initially established quality control mechanisms for the bioassays used (Ronco et al, 2002b) followed by examining the sensitivity, applicability and reproducibility of selected battery to screen drinking water and drinking water sources of the presence of toxicants (Diaz-Baez et al, 2002). These bioassays have been subsequently used in several other studies (Arkhipchuk and Garanko, 2002;Oberholster et al, 2008) where Hydra was found to show good sensitivity.…”

Overview of results from the WaterTox intercalibration and environmental testing phase II program: Part 2, ecotoxicological evaluation of drinking water supplies

“…Given the different number and diversity of samples, results obtained are discussed in general terms and the toxicity is expressed as EC 50 /LC 50 /IC 50 (%, v/v) values. However, throughout this article the toxic responses for the Hydra test are reported in terms of lethality, given the variability observed with the sublethal end point during the blind sample testing control exercise (see Ronco et al, 2002).…”

Environmental legislation and aquatic ecotoxicology in Mexico: Past, present and future scenarios

“…This last bioassay was included based on a new protocol developed during the first phase of the WaterTox project. [23,24] Results showed that water samples produced a toxic response in 24% of the cases. Of seven treated drinking waters, four showed toxicity with at least one bioassay, raising the possibility that treatment processes were unable to remove toxic contaminants.…”