The environmental risks associated with toxicants in leachate emissions from 43 Finnish waste sites were analysed and prioritized by site-aggregating procedures using various linear models and indices based on statistics of observed concentration distributions, on available data concerning volatilization and decay, on flux estimates and on toxic values to humans and to aquatic organisms. Considering only concentrations (90% fractiles of distributions) and effect criteria, 1,2-dichloroethane, 2,4,6-trichlorophenol and trichloroethene were the most important toxicants in terms of drinking water standard violation, while PCBs and Cr along with 1,2-dichloroethane displayed the values of carcinogenic risk index, and Cu, PCBs, toluene and endrin ranked highest in terms of aquatic ecotoxicity. The distributions of ecotoxicity indices reached rather consistently more alarming levels than those of health risk indices. When sinks were accounted for, the persistent and nonvolatile dieldrin and lindane emerged as the key toxicants for both human health and aquatic organisms. Considering estimated fluxes (by flow-weighted concentrations), hexachlorobenzene gained the highest values of health risk, Cu topping the list of substance-specific ecotoxic risk fluxes. The procedures for treatment of nondetects and for the estimation of distribution statistics considerably affected the rank orders particularly in the case of ecotoxicity and flux indices and for substances with low detection frequencies and high maxima relative to critical values (e.g., neutral pesticides). The methodological basis and development possibilities of risk indices were critically evaluated.
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