Biological Monitoring of Exposure To Industrial Chemicals
Authors: Fiserova-Bergerova Vera , Mraz Jaroslav 
Published: August 2005

Abstract
Pollution of air, water, and soil by industrial chemicals presents a potential health risk to humans. Such chemicals can enter the human body by three routes, namely, by inhalation, dermal absorption, and ingestion. In the work place, pulmonary and dermal absorption are the main routes of entry, but poor personal hygiene and work habits can result in ingestion that contributes to the dose. Air monitoring provides reliable information on inhalation exposure, and patches can be used to estimate dermal exposure. Local adverse effects, such as skin and eye irritation, or nose and lung irritation, are closely related to the external exposure. Systemic adverse effects, on the other hand, are related to the absorbed amount (dose), or to the level of the pollutant or its metabolite in the target organ.
The actual dose—body burden—is determined by the difference between absorption and elimination rates of the pollutant. These rates, which are a function of time, are not easy to determine. The absorption rate (also called uptake rate) depends on the degree of external exposure. Both the absorption rate and the elimination rate depend on the chemical structure of the pollutant, on environmental factors such as temperature and humidity, and on physiological factors of the exposed subjects, such as pulmonary ventilation, cardiac output, tissue perfusion rate, and body surface. The need for assessment of internal exposure—i.e., assessment of actual exposure of the body tissues regardless of the route of absorption and of variables affecting the uptake and elimination—led to biological monitoring. Biological monitoring is based on the measurement of biological levels of the exposure indicators, also called biomarkers. They can be the pollutant itself (parent compound), its metabolite(s) and conjugate(s), adduct(s) with biological macromolecules, or induced reversible enzymatic and functional changes such as enzyme inhibition, or oxidation of oxyhemoglobin to methemoglobin. For the purposes of occupational exposure monitoring, epidemiological studies, and health risk assessment, the biomarkers are measured in urine, exhaled air, or blood. However, tissue bank samples can be used for retrospective studies of occupational and environmental exposures. In animals, biological levels of biomarkers in tissues are studied mainly for the purpose of elucidating the interaction of toxic agents with the body.
Exposure monitoring is an important tool in disease prevention in the work place. Thus, for example, the safety guidance values published for occupational exposure by the American Conference of Governmental Industrial Hygienists (ACGIH) for indicators of internal exposure (Biological Exposure Indices, BEIs) and the safety guidance values for airbornes (Threshold Limit Values for air contamination, TLVs) relate to each other on toxicokinetic bases.
Timing of sample collection in biological monitoring is critical for estimation of the degree of exposure. Toxicokinetics provide guidance on the relation between external and internal exposure and on timing for collection of biological samples. The reference values define the sampling time that must be maintained when reference values such as BEIs or BATs are used.
Some biomarkers correlate better with adverse health effects than with the external exposure.
Irreversible biochemical and functional changes are not recommended as biomarkers for exposure monitoring because abnormal values already indicate a health injury which is supposed to be prevented by the monitoring. This chapter will discuss those biomarkers that are suitable for monitoring of occupational exposure.