Pentachlorobenzene is not produced in Canada and currently there is no domestic commercial demand for this substance. On the basis of limited data, the 2 most significant sources of entry of pentachlorobenzene into the Canadian environment result from spillage of dielectric fluids and from long-range transport and deposition. Pentachlorobenzene has been detected in samples of air, surface water, rain, sediment and biota collected at various locations in Canada. Pentachlorobenzene is removed from air and surface water by degradation processes, such as photo-oxidation and biodegradation, but can persist and accumulate under anaerobic conditions in buried sediments and soils.

The highest concentration of pentachlorobenzene detected in Canadian surface waters was over 10 000 times less than the effects threshold estimated for the most sensitive aquatic species identified. For wildlife, the dietary intake of pentachlorobenzene estimated for piscivorous mammals under worst-case conditions was more than 400 times less than the effects threshold estimated on the basis of studies in laboratory mammals. Although significant exposure of benthic organisms to pentachlorobenzene in sediments may be occurring in specific aquatic ecosystems in Canada, adequate data on the toxicological effects on these organisms were not identified. Therefore, it is not possible to determine whether concentrations of this substance in sediments could result in harmful effects to these biota.

Currently, the rates of release of pentachlorobenzene into the environment are low. Pentachlorobenzene is removed from the atmosphere by photo-oxidation and precipitation and, therefore, is present in low concentrations in air. As such, it is not expected to contribute significantly to global warming or to depletion of stratospheric ozone.

Based on limited available data on concentrations in ambient air, drinking water and food, the average total daily intakes of pentachlorobenzene for various age groups in the general population have been estimated. These average daily intakes are less (by approximately 250 to 1 000 times) than the tolerable daily intake derived on the basis of studies in laboratory animals. For breast-fed infants whose intakes are elevated for only a short period of their life-span, the estimated average total daily intake is 5 times less than the tolerable daily intake. The tolerable daily intake is the intake to which it is believed that a person can be exposed daily over a lifetime without deleterious effect.

Based on these considerations, it has been determined that there is insufficient information to conclude whether pentachlorobenzene is entering the environment in quantities or under conditions that may be harmful to the environment. It has been concluded, however, that pentachlorobenzene is not entering the environment in quantities or under conditions that may constitute a danger to the environment on which human life depends, or to human life or health.

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