Tetrachlorobenzenes (of which there are 3 isomers: 1,2,4,5-, 1,2,3,5- and 1,2,3,4- tetrachlorobenzene) are not produced in Canada, and currently there is no commercial domestic demand for these substances. On the basis of limited data, the 2 most significant sources of entry of tetrachlorobenzenes into the Canadian environment are from spillage of dielectric fluids and long-range transport and deposition. Tetrachlorobenzenes have been detected in samples of air, surface water, rain, sediment and biota collected at various locations in Canada. Tetrachlorobenzenes are not persistent in air or surface water, but can persist under anaerobic conditions in buried soil or sediment.

The highest concentration of tetrachlorobenzenes detected in Canadian surface waters is approximately 8 500 times less than the effects threshold estimated for the most sensitive aquatic species identified. For wildlife, the estimated dietary intake of tetrachlorobenzenes by piscivorous mammals is approximately 500 times less than the estimated effects threshold based on studies in laboratory animals. Although significant exposure of benthic organisms to tetrachlorobenzenes in sediment may be occurring in specific aquatic ecosystems in Canada, adequate data on the toxicological effects on these organisms were not identified. It is therefore not possible to determine whether concentrations of these substances in sediments could result in harmful effects to these biota. Similarly, because of the lack of information on concentrations in ambient soils and on the toxicological effects on soil dwelling organisms, it is not possible to determine whether these organisms are adversely affected by exposure to the levels of tetrachlorobenzenes present in Canada.

Currently, the rates of release of tetrachlorobenzenes into the environment are low. Tetrachlorobenzenes are removed from the atmosphere by photooxidation and precipitation, and, therefore, are present in low concentrations in air. As such, they are 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 total average daily intakes for each of the isomers of tetrachlorobenzene by various age groups in the general population have been estimated. Except for the estimated intakes of breast-fed infants which are elevated for only a short period of their lifespan, these intakes are from 210 to > 34 000 times less than the tolerable daily intakes derived on the basis of the available longest term (sub-chronic) studies in laboratory animals. 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 available information is insufficient to conclude whether tetrachlorobenzenes are entering the environment in quantities or under conditions that may be harmful to the environment. It has been concluded, however, that tetrachlorobenzenes are not entering the environment in quantities or under conditions that may constitute a danger to the environment on which human life depends. It has been concluded that each of the isomers of tetrachlorobenzene is not entering the environment in quantities or under conditions that may constitute a danger in Canada to human life or health.

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