Exposure assessment
Exposure assessment is a branch of environmental science and occupational hygiene that focuses on the processes that take place at the interface between the environment containing the contaminant of interest and the organism being considered.
These are the final steps in the path to release an environmental contaminant, through transport to its effect in a biological system.
For example, even for an extremely toxic (high hazard) substance, the risk of an adverse outcome is unlikely if exposures are near zero.
Conversely, a moderately toxic substance may present substantial risk if an individual or a population is highly exposed.
Once a contaminant has been proved to reach people, exposure analysts work backwards to determine its source.
It is highly important to use both regulatory and non-regulatory approaches in order to decrease people's exposure to contaminants.
For example, exposure to byproducts of water chlorination can obviously occur by drinking, but also through the skin, while swimming or washing, and even through inhalation from droplets aerosolized during a shower.
Therefore, the equation in the previous section is correct in a strict mathematical sense, but it is a gross oversimplification of actual exposures, which are the sum of the integrals of all activities in all microenvironments.
[citation needed] The point of contact approach indicates the total concentration reaching the host, while biological monitoring and the use of biomarkers infer the dosage of the pollutant through the determination of the body burden.
[6] An advantage of the direct approach is that the exposures through multiple media (air, soil, water, food, etc.)
In general, direct methods tend to be more accurate but more costly in terms of resources and demands placed on the subject being measured and may not always be feasible, especially for a population exposure study.
The indirect approach measures the pollutant concentrations in various locations or during specific human activities to predict the exposure distributions within a population.
Examples of indirect methods include environmental water, air, dust, soil or consumer product sampling coupled with information such as activity/location diaries.
Such information can be combined with contaminant concentrations from ad-hoc studies or monitoring network to produce estimates of the exposure in the population of interest.
In the case of lifetime average daily dose, variability pertains to the distribution and range of LADDs amongst individuals in the population.
The uncertainty, on the other hand, refers to exposure analyst's lack of knowledge of the standard deviation, mean, and general shape when dealing with calculating LADD.
The U.S. Environmental Protection Agency's Exposure Factors Handbook[4] provides solutions when confronting variability and reducing uncertainty.
The general points are summarized below: Occupational exposure limits are based on available toxicology and epidemiology data to protect nearly all workers over a working lifetime.
