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Critical variables are discussed that occur in the culture and testing of Cladocerans that are responsible for the failure to obtain acceptable results in interlaboratory comparisons. The variables in question include diet, ambient medium, health of the test species, characteristics and purity of the compounds tested, and, finally, whether nominal or measured concentrations are utilized to estimate the results of static acute toxicity tests. Available data indicate that diet, ambient medium, health of the test organism, and the physical and chemical characteristics of the test compound and how the latter is measured seriously affects the comparability of the results of round-robin tests.
Some recommendations are offered that might improve results from interlaboratory studies. These include procedures to be instituted to ascertain the health of the test organism. In addition, careful consideration should be accorded the selection of test compounds. Test compounds that are nontoxic or slightly toxic, have a high solubility in water, are of low molecular weight, have a low boiling point, a high vapor pressure, and few chlorine atoms within their structure will provide better precision than those compounds that have characteristics distinct from those just mentioned. In addition, measured test concentrations will improve interlaboratory comparisons over results obtained with nominal test concentrations.
aquatic toxicology, Daphnia magna, D. pulex, round-robin testing, interlaboratory comparison, static acute tests, physical characteristics, test compounds, chemical characteristics, test organism health
Associate environmental consultant, Dow Chemical U.S.A., Midland, MI