Pergamon Chemosphere, Vol. 38, No. 8, pp. 1777-1796,1999 6© 1999Elsevier Science Ltd.All rightsreserved 0045-6535/99/$ - see frontmatter PH: S0045-6535(98)00394-4 AN ASSESSMENT OF THE ENVIRONMENTAL FATE AND EXPOSURE OF BENZENE ANDTHECHLOROBENZENESINCANADA Matthew MaeLeod and Don Mackay* Environmental and Resource Studies Trent University, P~erborough, Ontario, Canada K9J 7B8 (Received in Germany 22 June 1998;accepted 16 July 1998) Abstract Systematic modelling of the fate of benzene and the chlorobenzenes is presented which follows a four-stage process of chemical classification, quantifying discharge rates and environmental concentrations, evaluative assessment of fate and regional mass balance modelling has been carried out for the southern Ontario region. The EQC model was applied to determine the principal transport and transformation processes experienced by this group of chemicals, which vary considerably in volatility and hydrophobicity. Observed environmental concentrations are in satisfactory agreement with the predictions of the steady state Level HI ChemCAN model of chemical fate. A multiple pathway human exposure model which estimates intake of contaminants by residents of suuthern Ontario has been developed and applied to these chemicals. A novel method of deducing maximum tolerable environmental concentrations is presented. Results suggest that benzene and 1,4- dichlorobenzene are present in the environment at levels sufficient to cause exposures near allowable daily intake (ADI) levels for the general population, but the other substances are present at levels which result in exposure ranging from 1/10 to 1/1000 of the ADI. © 1999 Elsevier ScienceLtd. All fights reserved Introduction In this study the environmental fate of benzene and the series of chiorobenzenes is evaluated using a Level III multimedia mass balance model, and the resulting human exposure by a variety of routes is assessed. The objectives were to: (A) provide a systematic evaluation of how the changing physical chemical properties of this series (notably volatility and hydrophobicity) affect their fate and exposure, (B) ascertain if the predictions of the ChenaCAN model used in this context are consistent with observed fate and (C) provide an example of an evaluation procedure which can be applied to other chemicals or series of chemicals. In a series of papers on this general topic, Mackay et al. [1,2,3] advocated a five stage assessment process involving chemical classification, acquisition of discharge data, and evaluative assessment of chemical fate, followed by regional far field, then local near field evaluations. The assessment described here is an example of the first four steps 1777