On ranking chemicals for environmental hazard

A formal vectorial approach for partial ordering was used to rank 34 organic chemicals according to seven criteria related to their bioaccumulation and degradation characteristics. Three basic assumptions were used, namely that bioaccumulation made the chemical more hazardous, degradation decreased the hazard of chemicals with their toxicity. Four levels of ranking were obtained using seven criteria. Reduction in the number of components increased the discriminatory levels. A smaller set of test compounds, the chlorobenzenes, were ranked according to their toxicity to fish, bacteria and zooplankton, and according to their environmental fate. The ranking was displayed using Hasse diagrams. Based on seven criteria, 2,4-dichlorobiphenyl, 2,4,6,2'-tetrachlorobiphenyl, pentachlorobenzene and hexachlorobenzene were environmentally the most hazardous of the 34 chemicals. Using only five criteria, hexachlorobenzene was ranked the most hazardous.