Ecotoxicological evaluation of xylenes: an integrated approach

In this paper we present a critical review of the ecotoxicological risk ass ociated to xylenes in Canada. The objectives are: 1) To describe Canadian p roduction and consumption of xylenes. 2) To relate physico-chemical propert ies of xylenes to sources, fate and toxicities of xylenes. 3) To integrate the danger associated with xylenes to the real exposure to xylenes in air, water, soil and organisms. 4) To index the ecotoxicological risk of xylenes and the daily acceptable dose for humans in Canada. 5) To assess suitable bioindicators for xylenes. Xylenes are flammable liquids belonging to the v olatile organic compounds (VOCs) family. In Canada, they are mainly used in petrochemical and chemical industries. Xylenes enter the environment via s ources including mainly combustion, solvents, liquid spills and both their volatilization and soil infiltration. As volatile compounds, xylenes have a n abiotic degradation. They are listed as emissions to be reduced because t hey are precursors of the tropospheric ozone. In the environment, xylenes' biodegradation is influenced by oxygen presence, salinity, pH, diversity an d abundance of the microorganisms occurrence in ecosystems of concern. This biodegradation which allows a biological detoxification of the environment inspires biological treatments for air emissions contaminated with xylenes . In this paper we review the most significative bioassays towards xylenes' toxicity. Xylenes' concentrations found in wild populations as well as in laboratory studies indicate that both vegetal and animal species are concer ned by xylenes' ecotoxicity: xylenes can be used as biological controls for pathogen plants and insects. In humans, xylenes are concentrated in lipids where they are susceptible to biotransformation and/or biodegradation. Acc ording to Environment Canada (1993), the daily acceptable dose for humans i s 144 mu g.kg(-1). Various dimensions of xylenes' ecotoxicity indicate that xylenes are air, water, soil and organisms pollutants. Nevertheless the pa ramount xylenes emissions are atmospheric via combustion and domestic or in dustrial volatilization. Finally, the eel A. japonica can be used as a poll ution indicator for xylenes in aquatic media and lichens can be used as xyl enes' bioindicators for terrestrial environments.