Toxicologists and risk assessment experts are confronted with demands to respond to this situation by weighing whether exposures to multiple chemicals are associated with risks to human health, wildlife, and ecosystems. However, established risk assessment procedures, with their focus on dealing with environmental and human health risks on a chemical-by-chemical basis, are ill-equipped to deal with these challenges (Office of Emergency and Remedial Response 1991). Nevertheless, awareness is growing among experts that this is a genuine problem worthy of serious attention. In approaching the topic from a scientific viewpoint, a number of issues can be distinguished:

Can the effects of mixtures be predicted from the toxicity of individual components?

Are risks to be expected from exposure to multiple chemicals at low doses?

How likely is it that chemicals interact with each other, leading to synergistic effects, and which factors determine the potential for synergisms?