Question

Risk is defined as toxicity * exposure. For effects on human health, the toxicity component of this equation is determined differently if there is a threshold than if there is no threshold for toxic effects. Compare and contrast the cancer slope factor with a reference dose as measures of toxicity used in equations of risk.

Answer 1

In compare and contrast to the cancer slope factor with a reference dose with a measures of toxicity used in equation determins the relationship between dose and incidence of effects in humans. There are normally two major extrapolations required. The procedures used to extrapolate from high to low doses are different for assessing carcinogenic effects and non -carcinogenic effects. Carcinogenic effects are not considered to have a threshold and mathematical models are generally used to provide estimates of carcinogenic risk at very low dose levels, whereas non carcinogenic are considered to have dose thresholds below which the effects doesn't occur.

While the agency for toxic substances and disease registry doesn't conduct cancer risk assessments, it does derive MRLs which is defined as an estimate of daily human exposure to a substance that is likely to be without in a appreciable reisk of adverse effects over a specified duration of exposure.

When evaluating cancer risks of genotoxic carcinogens , theoretically an effect threshold cannot be estimated. For chemicals that are carcinogens, a two part of evolution to quantify risk is often employed in which the substance first is assigned a weight of evidence classification, and then a slope factor is calculated.

Risk at low exposure levels is difficult to measure directly either by animal experiments or by epidemiologic studeies, the development of a slope factor generally entails applying a model to the available data set and using the model to extrapolate from the relatively high doses administered to experimental analysis to the lower exposure levels expected for human contact in the environment. The cancer slope factor is used to derive the RSD for direct acting carcinogens agents, those that cause chemical changes in DNA. The formula to calculate the RSD for a chemical based on a one-in-a - million extra risk 10-6 risk is : RSD=0.000001/CSF.