Thermodynamic activity and fugacity were used to describe the toxic effects concentrations of petroleum hydrocarbons (PHCs) across a range of PHCs and PHC mixtures in different media (water, sediment, soil, lipid), for a variety of effects (e.g., survival, growth) on a variety of species. There is a similar range in activity associated with PHC toxicity across chemicals, media, species, and effects, and PHC mixtures of varying composition. Therefore, the lower 5th percentile of all PHC toxicity data (activity = 0.003), or corresponding lipid-normalized concentration (4.36 mol/m3) or volume fraction (0.0008 m3/m3) calculated from activity at equilibrium can be applied to integrate a broad range of effects data into risk assessments and criteria development. When expressed as activity, the current PHC mixture criteria for sediment, soil, and water that are applicable in British Columbia overlap or exceed the range of activities associated with toxic effects, and therefore, these criteria may be underestimating environmental risks from PHC exposure.
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