Abstract
In order to assess interaction among multiple pollutants, over-content ratio rj=xj/Aj and equation Σrj1/μ=r01/μ are proposed, where xj and Aj are content of Pollutant j in a polluted material and the control value of the pollutant, respectively, and μ and r0 are positive constants. The interaction is expressed by μ (say interaction index) as follows: independent (i.e. no) at μ → 0, somewhat independent and somewhat complementary (or negative) at 0<μ<1, completely complementary at μ=1, and stronger than the complementary case (or positive) at μ>1. The control value of dioxins is given on the assumption that the interaction among chemicals belonging to the dioxins is completely complementary. In lung cancer relating to asbestos exposure and cigarette smoking, the death rate is given by r={rA1/3+rC1/3}3, where rA and rC are over-content ratios (= death rates in this example) of only asbestos and only cigarette. This equation shows that the death rate of both asbestos and cigarette (ca. 600) is 12 times of the death rate of only asbestos (ca. 50), and 6 times of the death rate of only cigarette (ca. 100). The equation suggests that environmental assessments may cause risks that hazardous cases are assessed to be safe or that safe cases are assessed to be hazardous, if control values are given not taking account of interaction among pollutants. When an interaction index indicating degree of combined pollution is not known, it may be the most adequate that the interaction is assumed to be completely complementary.
