Identifying toxicity bioassays

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. 

The emphasis in this chapter is on the use of animal tests, or bioassays as they are sometimes called, to identify toxicity. Epidemiology has been important in uncovering the effects of subchronic and chronic exposures to some very important chemicals, including those capable of causing cancer. Carcinogens are a special breed of chronic... 

Bioassays can be used for cost-effective biomonitoring and rapid screening of environmental samples to detect the presence of mixtures of toxic chemicals and to identify hot spots. 

Toxic nephropathy of the type seen after inhalation exposure of rats (see Section 2.2.1.2) was not identified in rats or mice in the NCI (1978) gavage bioassay of 1,2-dibromoethane. 

The test is repeated for all identifiable effects and for a number of different rates of exposure. Standard 2x2 contingency tables(2 ) are used to determine the odds of observing the bioassay outcome if the null hypothesis is true using Fisher s exact test. For all adverse effects, including cancer, the first rule of the strategy for deciding whether a substance is toxic is to ... 

Some sophisticated guessing goes into dose selection. Knowledge of the minimum acutely toxic dose helps the toxicologist pick the highest dose to be used it will be somewhere below the minimum lethal dose. There is usually little basis for deciding the lowest dose it is often set at some small fraction of the high dose. Whether it turns out to be a NOAEL will not be known until the experiment is completed. Sometimes bioassays have to be repeated to identify the NOAEL. 

Let us skip by the question of the adequacy of the animal tests used to identify these agents. The general quality of the animal test is obviously of great importance in the overall evaluation and these questions cannot be ignored in the case of cancer bioassays any more than they can in any other type of toxicity test. But the more interesting questions arise when we move beyond the question of study quality. 

During the 1950 s, when the phytotoxic components of the photochemical-oxidant complex were not known, plants were used extensively as a bioassay of many simulated reaction mixtures to indicate toxicity. - - Plants were also used to help in identifying specific components of photochemical reaction products, such as PAN and its analogues. ... 

The third health effect bioassay employed utilizes acute toxicity in whole animals (rats). Since the major objective of the Level 1 biological testing procedure is to identify toxicology problems at minimal cost, a two-step approach is taken to the initial acute in vivo toxicology evaluation of unknown compounds. The first is based on a... 

Five isobutylamides were isolated as insect growth inhibitors and toxicants from Fagara macrophylla and identified from their spectroscopic and chemical data. Synthesis and bioassay of the five natural products plus four analogs showed pellitorine to be the most active against a variety of insects, but not against a species of snail. 

The mangrove plant Heritiera littoralis (Stercullaceae) has been utlized by natives of the Philippines as a fish poison. The hexane extract of this plant has shown toxicity to fish (Tilapia nllotlca). A novel sesquiterpene which was assigned the name heritianin has been identified as one of the compounds with ichthyotoxicity. The structure elucidation of heritianin and other compounds in the hexane extract of Heritiera littoralis is presented with bioassay data. 

B. Measurement of Toxicants and Toxicity. These important aspects deal primarily with analytical chemistry, bioassay, and applied mathematics they are designed to provide the methodology to answer certain critically important questions. Is the substance likely to be toxic What is its chemical identify How much of it is present How can we assay its toxic effect, and what is the minimum level at which this toxic effect can be detected A number of important fields are included ... 

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