Control mortality, toxicity testing

Since toxicity is a necessary but not sufficient quality of a rodenticide, the next phase of the testing was conducted to determine the acceptability of the treated diet to rats and mice. The test consisted of twenty rats per treatment level with at least twenty control animals. The tests were run from three to ten days, with the feed consumption data and necropsy data recorded for each animal. The desirable candidate compounds should comprise at least 30% of the total diet of the rats and should have a mortality of 90% or more. 

The no-observed-effect concentration of silver nitrate in a 28 day toxicity test using a marine invertebrate Americamysis bahia) was 34pgl. The 96 h LC50 value was 260 pgl. In a 21 day toxicity study using the freshwater invertebrate Daphnia magna, 5 pg Agl (as silver nitrate) under static conditions, 20% mortality was noted (0% in controls). Silver caused a significant reduction of reproductive performance (14% decrease in the number of neonates). Silver caused a 65% decrease in whole body sodium concentration and a 60% increase in whole body Na, K + -ATPase activity. 

There are two basic types of aquatic single-species toxicity tests acute and chronic. Acute toxicity tests have been the workhorse of aquatic toxicologists for many years. These tests are relatively simple, take little time, and are cost-effective. A large historical database exists for many chemicals and effluents. Acute toxicity tests are most often used to quickly screen toxicity or to determine the relative sensitivities of different test species. Mortality is the effect monitored during the test duration of 48 h (invertebrates) or 96 h (fish). In a typical acute toxicity test, 5-10 organisms are exposed under static conditions in glass test beakers to five test concentrations. A control is included. The experiments with test concentrations and control are conducted in triplicate. Daily observations are made on survival, and dead organisms are removed. 

Toxicity tests were conducted according to the standard procedures (ASTM 1980) and have been described in detail previously (Broderius and Kahl 1985). Briefly, juvenile fathead minnows (Pimephales promelas) were placed in continuous-flow diluters having five treatment concentrations and a control for each test. Mortalities were recorded daily, and the estimated median lethal concentration (LC50) was determined after 96 hours. Binary mixtures of chemicals were tested at ratios of 5 0, 4 1,2 1,1 1,1 2,1 4, and 0 5. The 96-hr LC50 of these binary mixtures were used to construct isoboles (Loewe 1953, 1928) of joint toxic action. The procedures used to analyze results by concentration or response addition models are according to those proposed by Finney (1971) and Anderson and Weber (1975). 

Similar results for rats were reported by Crowder et al. (1980). Oral administration of 1 mg/kg/day of methyl parathion (99.9% purity) in com oil on days 7-15 of gestation resulted in increased mortality in pups, relative to controls. Significant difference from controls in a maze transfer test was observed in pups from the treated group. However, use of a single-dose level precluded the assessment of dose-response, and several other behavioral end points were not affected. Furthermore, no information was presented regarding body weights or signs of toxicity in the treated dams. 

Death. Occupational mortality studies of pesticide workers exposed to heptachlor have not revealed an excess number of deaths in these cohorts compared to the general U.S. population. This may possibly be explained as a healthy worker effect. The ERA has described human case reports in which convulsions and death were reported following suicidal ingestion of technical-grade chlordane, which typically contains 6-30% heptachlor, but these effects cannot be attributed to heptachlor or heptachlor epoxide. There are no controlled, quantitative human data for any route of exposure. Acute lethality data were located for animals exposed via the oral and dermal routes. Both heptachlor and heptachlor epoxide may be considered very toxic via the oral route on the basis of acute animal data in rats and mice. Intermediate oral exposure to these compounds also caused up to 40% and 100% mortality in rats and mice, respectively. There appear to be differences in sensitivity in males and females in some species with the males being most sensitive. Heptachlor epoxide is more toxic than heptachlor. Heptachlor may be considered very toxic to extremely toxic via the dermal route on the basis of acute lethality data in rats and mice. The severity of acute effects may possibly depend upon the extent of formation of heptachlor epoxide and the species tested. 

The test organisms are exposed for 24, 48, and 96 hours to different concentrations of testing water. After the exposure period the number of dead organisms is counted. Each test sample container is examined and the number of dead organisms counted (looking for the absence of swimming movements). A test is regarded as valid if the mortality in the control is <10%. Toxicity is calculated as ... 

In Ireland, compliance with toxicity limits for selected industries is ascertained by annual or biannual test on representative samples of effluent. The test species most commonly used is the rainbow trout (Salmo gairdneri). Control authorities normally require results from 96-hour tests. The toxicity values are expressed as the minimum acceptable proportion of effluent (as a percentage) in a test resulting in 50% fish mortality after 96 hours of exposure. The toxic units (TU) are defined as the maximum number of times an effluent may be diluted to produce the test criteria (TU = 100/96-hour LC50, with LC50 expressed as the percentage of effluent in the test) (Fig. 5). 

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