Acute toxicity rating system

Quantitative estimation of ventilation by indirect methods in mussels requires four assumptions (16) a) reduction of concentration results from uptake, b) constant ventilation (pumping) rate, c) uptake of a constant percentage of concentration (first order process), d) homogeneity of the test solution at all times. Our transport studies have utilized antipy-rine (22, 23) a water soluble, stable chemical of low acute toxicity to mussels. It is readily dissolved in ocean water or Instant Ocean and is neither adsorbed nor volatilized from the 300 ml test system. Mussels pump throughout the 4 hour test period and this action is apparently sufficient to insure homogeneity of the solution. Inspection of early uptake and elimination curves (antipyrine concentration as a function of time) prompted use of Coughlan s equation (16) for water transport. 

Cumene has a potent narcotic action characterized by a slow induction period. It is a depressant to the central nervous system. The long duration of its action indicates a possible slow rate of elimination, meaning that cumulative effects must be considered. Cumene is thought to have a greater acute toxicity than either benz or toluene (Ref 4) Cumene is used in org synthesis as a solvent, diluent, and as an additive to aviation gasoline... 

The effects of pyrrolizidine alkaloids on the mixed-function oxidase enzyme system in rat liver have been studied.79,80 Dehydroheliotridine and heliotrine (at higher dose rates) have similar effects on pregnant rats and their embryos.81 The development of pulmonary hypertension and obstructive lesions in rats after administration of monocrotaline (48) has been studied.82 Butylated hydroxyanisole protects young mice against the acute toxicity of monocrotaline.83 Reduced levels of pyrrole metabolites were observed. 

The use of a rat study for developing an RfD for GA is complicated by the fact that rodents have a much lower RBC-AChE activity level compared to humans (Ellin, 1981). By itself, this could cause rats to be relatively more sensitive than humans to anticholinesterase compounds however, the lower RBC-AChE activity may be offset by the presence of ahesterases in the blood of rats. Aliesterases, which are not found in human blood plasma, are known to bind to and, therefore, reduce the toxicity of GB, and a similar mechanism may operate in the case of GA. Other species differences, such as in the rates of aging of the GA-ChE complex, in the rates of synthesis of plasma-ChE in the liver, and in the levels of AChE in the nervous system (see Ivanov et al., 1993) may also result in difference between species in sensitivity to GA. Data are insufficient to more fuUy evaluate these possibihties. There is httle human acute toxicity data that can be compared with the available rat data however, acute toxicity data for primates in general (see Table 2) suggests that humans are likely to be more sensitive than rats. Therefore, for the purpose of this assessment, the standard EPA method will be followed which assumes that humans can be as much as ten times more sensitive to a chemical than laboratory animals. 

The Microtox acute toxicity test is based upon measuring metabolic inhibition using a standard suspension of luminescent bacteria. Since bioluminescence is a direct measure of metabolic activity in these wganisms, measuring the rate of light output is a simple way to measure metabolic inhibition (toxicity). The test system has been in use for over 10 years and is the subject of many reports, reviews and application studies as well as being... 

The toxicity of a chemical also varies from one animal to the next. The LD50 for the common insecticide Diazinon is 300 to 400 mg/kg in rats, while in birds it is 2.75 mg/kg. Theobromine, a chemical found in chocolate, is toxic to dogs but not to rodents. Although largely extrapolated from animal tests, a rating system for acute chemical toxicity for humans has been devised and is presented in Table 1. 

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