Effects of metal mixtures on human health and aquatic life: Similarities and differences

Metals and other chemicals of potential concern in ecological and human health risk assessments rarely occur singly and mostly occur as mixtures. Concerns are often heard from the public, some scientists, and some regulators about the possibility of synergistic human health and ecological effects from mixtures, while antagonistic (i.e., less-than-additive effects), have also been reported. The public and many regulators wand a highly conservative, e.g., worst-case, approach to risk assessments with mixtures, while the regulated community generally wants to be assured that risk assessment methodologies are not more conservative than necessary to protect human health and the environment. Most ecological risk assessment methodologies assume that the effects of multiple metals are independent or additive, while human health methods assume additivity, unless contrary information is available. The authors review and contrast the chemical, biochemical, physiological, and toxicological evidence for independent, additive, synergistic, and antagonistic effects of mixtures of metals to humans and aquatic biota. Then, they summarize (1) the weight-of-evidence in support of independent, additive, synergistic, and antagonistic effects for mixtures of metals to humans and aquatic life, and (2) the extent to which such information from either human toxicology or aquatic toxicology can and cannot be extrapolated between the twomore » disciplines.« less