Last changed: 25/01/11
There are various ways of investigating the impact of the environment on human health.
In the first instance it is a matter of establishing which influences people (or, as the case may be, animals, organs, or cell systems) are exposed to, to what degree, and for how long (exposure estimation). Human biomonitoring investigates the concentration of substances in body fluids (blood, urine, or saliva) or other body structures (hair or organ tissue samples). By this means the “internal exposure” is determined - in other words, which foreign substances have been ingested.
In a further step, any changes (e.g. symptoms, illnesses, or deaths) which have arisen as a result of the exposure need to be established (determination of effects).
In the third step, relationships between the exposure and the effects are investigated. Epidemiology observes what occurs under which conditions in the population at large. It is the role of toxicology to investigate the effect of hazardous substances under controlled laboratory conditions, mostly by means of animal experiments or on isolated organs, cell structures, or individual cells.
In this procedure statistical methods are used to identify the relationship between a particular incidence of exposure and the observed effects, to describe it, and to determine its extent (dose-effect relation). It thus becomes possible to state the probability of observed relations being purely a matter of coincidence, without real significance. This probability is usually abbreviated to “p” and given as a decimal fraction. Depending on the type of enquiry, the permissible probability of error is set at 5% (p = 0.05) or less.
For the purpose of risk analysis, the uncertainties on all levels – that is, in the determination of exposure, its effects, and the dose-effect relation – must be taken into account.