Dmean Et4193

Several regression methods are also available, including nonlinear regression and maximum likelihood estimation. These have the advantage of producing not only the parameters but also a confidence interval for the dose-response curve predicted. The disadvantage of all the foregoing methods is that they may produce poor results if the data are not normally distributed or if the data do not cover the range of toxic effects well. That is, the data must include at least one dosage with essentially zero response and one with about 100% response. For example, if a bioassay on a wastewater produces 30% mortality at 100% concentration, these methods will not work.

TABLE 19.2 Qualitative Classification of Toxic Compounds

Classification

LD50 Range (mg/kg)

Example

LD5o of Example

Supertoxic Extremely toxic Highly toxic Moderately toxic Slightly toxic Practically nontoxic

50-500 500-5,000

5 or less 5-50

Strychnine in rat Ethanol in mouse

Parathion in goats DDT in rat

Dioxin in guinea pig

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