Abstract
Bioassays, consisting of a diverse selection of organisms, aid in assessing the ecotoxicological status of aquatic ecosystems. Daphnia pulex and Hydra vulgaris are commonly used test organisms belonging to different trophic levels. The current study focused on comparing the sensitivity of H. vulgaris to D. pulex when exposed to geometric dilutions of two different water sources, the first (Site 1) from a source containing agricultural run-off and the second (Site 2), acid mine drainage. These sources were selected based on the contribution that the agricultural and mining sectors make to water pollution in South Africa. The bioassay method followed in this study was a modified version of the method described by the USEPA and additional peer-reviewed methods. The mortalities as well as morphological changes ( H. vulgaris ) were analysed using Microsoft Excel. The LC 50 -values were statistically determined using the EPA Probit Analysis Model and the Spearman-Karber analysis methods. Prior to being used, analysis of the physico-chemical properties, nutrients and metals of both water samples was performed. These results showed a relationship to the results obtained from the D. pulex and H. vulgaris bioassays, as Site 1 (lower concentration of contaminants) was less hazardous to both test organisms than Site 2 (higher concentration of contaminants). Both organisms can be used for ecotoxicity testing, with D. pulex being a more sensitive indicator of toxicity with regards to water sampled from the acid mine drainage site. Due to the sensitivities of sub-lethal endpoints observed over time, H. vulgaris may be used for chronic toxicity testing and D. pulex for acute toxicity testing. Keywords: Hydra, Daphnia , toxicity, ecotoxicity, definitive toxicity test
Highlights
Man’s production and use of chemicals and minerals, and his dependence thereon, has led to valuable products and services, and to the release of numerous hazardous substances into the natural environment (Wharfe, 2005)
The current study focused on comparing the sensitivity of H. vulgaris to D. pulex in 96 h bioassays when exposed to geometric dilutions of water samples collected from a source containing agricultural run-off (Site 1) and a source containing acid mine drainage (Site 2)
Advances in ecotoxicology have led to the development of various bioassays utilising a diverse selection of organisms belonging to different trophic levels
Summary
Man’s production and use of chemicals and minerals, and his dependence thereon, has led to valuable products and services, and to the release of numerous hazardous substances into the natural environment (Wharfe, 2005). The agricultural and mining sectors have grown in South Africa. These sectors provide economic profits, the activities have resulted in increased pollution of South African water sources (Bezuidenhout, 2013). Irrigation and surface run-off water has been found to contain pesticides, fertilisers, harmful chemicals and/or pathogenic microorganisms (Britz and Sigge, 2012). The aims of ecotoxicology have evolved over the years, from establishing the concentrations at which chemicals exert adverse effects, estimating environmental risk based on measured toxicity endpoints, and predicting environmental concentrations for specific chemicals, to defining toxicant concentrations harmful for specific organism groups and/or for assemblages of species (Blaise and Fèrard, 2005)
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