Chronic bioassays, assessment

Toxicity Bioassay. Ninety-six hour acute toxicity tests were conducted on the effluent streams of major industries. A static renewal procedure was used in which waste waters of various dilutions were renewed at 24 hour intervals over a 96 hour period. Rainbow trout was used as the test organism. Tests were conducted at 13°C in 20 liter aquaria according to standard procedures (22), Results are summarized in Table 8. Chemical and toxicity test results indicate that the trace element quantities identified in Table 8 are not acutely toxic under the prevailing conditions and unlikely to pose an acute threat to aquatic life. In this case a chronic toxicity assessment would require additional research. 

Among their multiple uses, acute and chronic bioassays have served, for example, to rank and screen chemicals in terms of their hazardous potential, to undertake biomonitoring studies, to derive water quality criteria for safe release of single chemicals into aquatic bodies and to assess industrial effluent quality in support of compliance and regulatory statutes. 

Martinez-Madrid, M., Rodriguez, P. and Perez-Iglesias, J.I. (1999) Sediment toxicity bioassays for assessment of contaminated sites in the Nervion River (Northern Spain). I. Three-brood sediment chronic bioassay of Daphnia magna Straus, Ecotoxicology 8, 97-109. 

Ziehl, T.A. and Schmitt, A. (2000) Sediment quality assessment of flowing waters in South-West Germany using acute and chronic bioassays, Aquatic Ecosystem Health and Management 3 (3), 347-357. 

Secondary sources report the following oral LDso s in rats 725 mg/kg (RTECS 1988) and 14.1 g/kg (Grayson 1978). Since these values were obtained from secondary sources, no details were available to assess the quality of these data. Survival was poor in both treated and control rats and mice in the chronic bioassay conducted by NCI (1977), but a significant dose-related trend for mortality was noted in the male rats and mice. The deaths could not be attributed to cancer or any other non-neoplastic lesions, though pneumonia was observed in a large percentage of the rats, and this was thought to be related to the increased mortality (NCI 1977). 

Preliminary effect assessment. Three acute or chronic bioassays from different taxonomic groups are prescribed. Three cut-off effect levels are discerned, i.e. 

Refined effect assessment. The results from four acute or chronic bioassays of different taxonomic groups are expressed in a concentration factor where 50% effect is measured (EC50). These data then are used to construct a sensitivity distribution (De Zwart and Sterkenburg, 2002). The potentially affected fraction (PAF) is determined for the 100% sample (the as is sample). The negligible effect level is at a value for PAF = 5%. 

Genetically modified mice have been useful to show the relationships between the key events in the PPARa MOA. PPARa-null mice provided critical evidence establishing the rodent MOA for PPARa activator-induced hepatocarcinogenesis. Evidence that a particular compound induces key events in wild-type mice but not in mice lacking PPARa would be considered strong support for a PPARa MOA for that particular compound. To date, three chronic bioassays have been conducted in these mice (Hays et al. 2005 Ito et al. 2007 Peters et al. 1997). A greater body of data exists in which precursor events for cancer have been assessed in wild-type and PPARa-nuU mice after acute or subacute exposures. 

Since persistence in sediments is longer than that in the water column, the relevant toxicity studies are those that consider longer term, chronic exposures. A number of standard tests have been developed for assessing sediment toxicity and the bioassay of field collected sediments (e.g., [16-24]). The most commonly tested freshwater species are arthropods, including the amphipod shrimp // azteca and chironomid midge larvae, both Chironomus dilutus (formerly C. tentans) and C. riparius. Water-only studies have demonstrated that II. azteca are particularly sensitive to SPs (see Sect. 3) and in the published literature, this is the most commonly tested species for assessing the sediment toxicity of SPs. 

Table 8. Average experts judgements on the adequacy of bioassays and other parameters in term of their usefulness for effluent toxicity assessment. Each expert had to rank usefulness as an integer value between 1 (least useful) to 5 (most useful) and they were also allowed to suggest other tests or parameters deemed useful. Some experts recommended tests without numerical ranking (Lemna minor and chronic Daphnia magna).

The pT-index allows the assessment and comparison of the toxic potential of sediments and dredged material. It is one example of an integrated bioassay-battery approach developed for the purpose of environmental management. This sediment assessment index relies on the use of an appropriate battery of bioassays at different trophic levels (decomposers, primary producers, and consumers) allowing the measurement of various types (acute, chronic) and levels (lethal, sublethal) of toxicity. 

Thus far, quality objectives for chemical substances are derived from the most sensitive organisms in acute and chronic toxicity test batteries that determine NOEC values for different trophic levels. The pT-method similarly determines specific sample dilution levels that are devoid of adverse effects toward (micro)organisms of a standardized test battery. Common to both approaches is the more frequent use of water-column test organisms as opposed to benthic-dwelling organism that reflect more intimate contact with sediment. This practice is primarily based on the fact that standardized bioassays capable of appraising sediment porewaters and elutriates are presently more numerous than solid-phase tests for whole-sediment assessment. As more of these latter tests become developed and standardized (see Chapters 12 and 13, volume 1 of this book on amphipod and chironomid tests), their more frequent use will contribute to a better understand of the toxic effects of sediment-bound contaminants. 

Bioassay herein describes a chronic feeding study for the assessment of the potential of a chemical to produce carcinogenic effects. 

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