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Exposure pathways and monitoring

smog in Paris Pollutants enter the human body in three main different ways: by inhalation, ingestion or skin absorption. The amount of any given pollutant that is received is often termed the dose. The dose will be dependent on the duration and intensity of the exposure. organ dose refers specifically to the amount that reaches the human organ where the relevant effects can occur, e.g. the lung.

In many cases, exposure may occur simultaneously from many sources and through multiple routes. Pathways of exposures to lead, for example, include air pollution from traffic and industrial emissions, drinking water, food, tobacco smoking, dusts, paints and other industrially produced commodities and soil. Valid exposure assessment therefore typically requires detailed knowledge about the geographical distribution of the pollutants of concern, the temporal variations in pollution levels, and the processes of exposure.

People are often exposed to different pollutants simultaneously. Exposure to these may occur at different locations (e.g. in the workplace and/or at home) and at different times.

The full range of factors which therefore may need to be examined is potentially large. It may include many different environmental pollutants (including hazardous chemicals, radioactivity, dusts and particulates), from many different sources (including energy production, industry, pesticide use), released either continuously or sporadically, and either under controlled conditions (i.e. deliberate discharges) or accidentally.

In order to be able to draw up and implement an appropriate strategy for improving local air quality, local authorities should implement the necessary monitoring programmes to determine the levels of pollutants and identify the sources. The extent of monitoring will depend on the resources available though it is important to stress that adequate monitoring can be carried out using relatively inexpensive equipment.

Monitoring enables local authorities to confirm previous assumptions that pollution levels are unacceptably high; it also enables them to set priorities and for improvement according to the resources available and the cost and benefits of particular courses of action. Long-term monitoring programmes show the efficiency of the policies put in place thus enabling the re-allocation of resources if this is thought appropriate.

Biomarkers: an emerging indicator
Recent advances in molecular biology and analytic chemistry facilitate development of biomarkers as measures of dose. The aim is to characterise absorbed toxins in their most biologically relevant form. After absorption, transport, and metabolism, toxins initiate biological changes. Identifying the transformed toxin as close as possible to this point of initiation enhances accuracy in knowing the true biologically active dose. Biomarkers may also be used to characterise the early biological alterations, thereby increasing the fit between toxin and response. DNA- and protein-adducts have undergone recent intensive study as biomarkers in the study of cancer caused by environmental factors, for example.

New sampling and analytical technologies are being developed, including the use of automatic samplers, remote sensing and low-cost sampling devices (e.g. passive samplers). Gradually, improved awareness about the spatial and temporal variations in pollution is contributing to improved monitoring, for example, by sampling the micro environment where exposure principally occurs, including indoor environments (e.g. in living rooms and kitchens in the assessment of NO2 and radon). The use of total exposure monitoring, in which all potentially relevant micro environments are sampled, also offers opportunities to improve exposure estimates. In addition, personal exposure monitoring is being incorporated to some extent into environmental health assessment.

Local authorities should aim, as a minimum, to monitor the following pollutants, all of which can affect local air quality and human health: sulphur dioxide, particles, nitrogen dioxide, ground level ozone, carbon monoxide, and airborne lead (the latter is dealt with in the WHO pamphlet Lead and health).

Another pamphlet in this series, Monitoring of air quality, will describe the purpose of monitoring air pollution, the positioning of monitoring sites and networks, and types of equipment available.


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