Antagonistic chemical mixture

From Environmental Technology

Humans are exposed to many chemicals and other potentially toxic agents in the environment, but toxicity testing and regulations generally focus on one chemical at a time, often just in air, water, or food. Most risk assessments evaluate the toxicity of or risk associated with individual chemicals and then combine them by simple addition to estimate risk related to chemical mixtures. However, adding risks ignores potential synergistic or antagonistic interactions that could lead to underestimation or overestimation of total risk, respectively. Knowledge of mechanisms of action can guide judgments of whether risks related to combinations of particular chemicals will be additive or independent.

reference

http://www.riskworld.com/Nreports/1996/risk_rpt/html/nr6aa008.htm