Expression of Risk

Depending on the purposes of a particular risk assessment, the risk may be expressed in different terms. Common measures include the number of additional cases of cancer, the percentage increase in cancer incidence, the number of additional cancer deaths, or the percentage increase in cancer mortality in a population. The loss of life expectancy in the population (in person-years) or the average loss of life expectancy per capita (in minutes, hours, or days) also are helpful measures, because the term life expectancy conveys the statistical nature of a risk. The number of working days lost (total per population, or average 

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In risk characterization, the toxicology and exposure data are combined to obtain a quantitative or qualitative expression of risk. 

Risk characterization is tlie process of estimating tlie incidence of a healtli effect under tlie various conditions of human or animal exposure as described in the exposure assessment. It evolves from both dose exposure assessment and toxicity response assessment. The data are then combined to obtain qualitative and quantitative expression of risk. 

Finally, it is hoped that this book will facilitate the broadening of perspective in the domain of safety research, for example, to enable research of the correlations existing between quantitative expression of risk and recorded aocidents. 

These types of expressions of risk are more familiar to people, but they mean roughly the same thing as those described earlier for the risks of toxicity from chemical exposure - with at least one exceedingly important difference. 

According to the WHO (WHO/IPCS 1994, 1999 WHO 1996, 2000), it should be noted that cmde expression of risk in terms of excess incidence or numbers of cancers per unit of the population at doses or concentrations much less than those on which the estimates are based may be inappropriate, owing to the uncertainties of the quantitative extrapolation over several orders of magnitude. Estimated risks are therefore considered to represent only the plausible upper bounds and vary depending upon the assumptions on which they are based. 

Several different expressions of risk may be quoted in an analysis, e.g., a risk averaged ov a whole population, an age-spedfic risk, or a risk for a particularly susceptible individual or subgroup. Such an individual or subgroup might be more susceptible because of genetic predisposition, exposine to another risk factor, e.g., cigarette smoke, or other reasons. 

Thus, the excretory pattern of fecal secondary bile acids observed in these studies correlated with colon tumor incidences in animal models. These studies also suggest that high dietary intake of certain types of fat may be necessary for the full expression of risk for colon cancer. 

Convergence to a common expression of risk (i.e. comparing exposme to an established AOEL or providing scenario-specific MOEs) is feasible and wonld promote harmonization. 

Common expression of risk (i.e. AOELs versus MOEs). 

The difficulty with such an analysis is that it is a qualitative expression of risk without regard to the probability distributions of the chemical concentrations or the effects. The distribution of each concentration can be plotted and the distribution of expected effects calculated. In this example, although... 

People are more familiar with expressions of risk associated with various activities than they are with risks associated with chemical exposures. We speak, for example, of the annual risks of dying as a result of certain activities. The annual chance of dying in automobile accidents for people who drive the average number of miles is about... 

Notice that the ADI is not a direct expression of risk. Risk, recall, is a probability the ADI is a very low risk intake, or dose, with very low undefined. If there were some means to estimate the fraction of the population having thresholds lower than the ADI (the potentially at risk group), then a measure of the risk associated with the ADI could be obtained. No means exist to do this except for a few agents, particularly those such as the common air pollutants (ozone, carbon monoxide, sulfur and nitrogen oxides) that cause readily observable damage to human health. 

Conversely, the opposite can be said about the methods as far as the notion of risk is concerned in SMA the risk is contained implicitly, whereas the result of seismic PSA is an explicit expression of risk. 

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