In order to determine the extent of environmental exposure to a chemical, it is necessary to evaluate that chemical’s environmental fate. While the amount and frequency of a chemical’s release, as well as the environmental medium — air, water, or soil — into which it’s released are important considerations, environmental fate is determined by what happens after the chemical has been released into the environment.

Environmental fate, then, is based on three main factors:

• the partitioning of the chemical between environmental media
• the transport properties of the media
• the transformation rate of the chemical into other substances

The tendency of a substance to partition to — or concentrate in — a particular part of the environment can be determined from the physical and chemical properties of the substance. These can be measured or estimated.

The tendency for environmental transport of a substance depends on the transport properties of the medium into which the substance is released or partitions. It also depends on its lifetime in the medium. Substances that migrate to environmental media that enhance transport will be more widely distributed.

Environmental transformation describes a chemical’s lifetime in the environment until it is converted to substances naturally found in the environment, or until its fate can be described in some other way. Environmental transformation is highly dependent on the medium. In air, transformation is by abiotic chemical reactions; in soil and water, biodegradation may predominate. Substances that persist in the environment will build to higher concentrations and may be more widely distributed.

In order to evaluate potential hazardous effects of chemicals on environmental species, environmental toxicologists study representative species in the laboratory and extrapolate the results to the vast number of species in the environment.¹