Biological monitoring: State of the art

Exposure to chemical agents can be assessed either by measuring the concentration of the agent in the air by stationary or personal sampling (ambient monitoring), or by measuring some biological variables (biological monitoring). The term biomarker that has been proposed for a few years is used in a broad sense to include almost any measurement reflecting an interaction between a biological system and an environmental agent, which may be chemical, physical, or biological. However, there is still some debate about the definition of the term and it is clear that interpretation of the term varies between authors. Strictly speaking, biological monitoring of exposure to chemical agents means measurement of a substance or its metabolites in various biological media. Sometimes, the concept of biological monitoring is extended to include the detection of early reversible non- adverse effects (biological monitoring of effect). The detection of an adverse effect-for example, increased proteinuria-indicates that exposure is or has been excessive and therefore such a measurement is more logically included in a programme of early detection of health impairment due to industrial chemicals rather than in a biological monitoring programme for evaluating exposure. In view of differences between people in susceptibility to xenobiotics, the detection of increased susceptibility to a chemical hazard might also be considered. This implies the use of biological markers able to detect endogenous acquired or inherent limitation of an organism to respond to a challenge of exposure to a specific xenobiotic substance or a group of such substances (biological monitoring of susceptibility).