Contaminant Fate & Transport Definition

Fate and Transport refers to the way chemicals move through organisms, through the environment, their ultimate destinations and how they arrive. Defining the fate and transport for any single contaminant is often complex.

Chemical Origins

• Fate and transport begins with a source point. A chemical's initial release into the environment and environmental conditions are important for determining its free moving lifespan and ultimate destination. For instance, a small oil spill might be cleaned up and disposed of right away on a sunny day, but if that same spill happens during a rainstorm, the oil might spread out, leach into the soil, and penetrate the ground water table.

Chemical Persistence

• Chemical persistence, or the chemical's stability in the environment, strongly influences the fate and transport of contaminants. Chemical persistence is a measure of how quickly a contaminant will break down into other chemicals through biological metabolism or exposure to salinity, sunlight and other natural influences. The infamous chemical DDT did not become dangerous to most animals until it was metabolized into DDE.

Movement and Transport

• Many chemicals can be dispersed according to wind, tidal action and oceanic currents. Chemicals that do not dissolve in water or bind readily to substrates such as soil flow freely and can be roughly tracked by models for their methods of dispersion. Biological vectors are also a means of transport, and even of concentration. The contaminants in an insect with a short lifespan and small range of movement could spread far if that insect was consumed by a bird with a much larger range.

Binding to Substrates

• Many chemicals have an affinity for binding to certain substrates. PCBs, chemicals now banned but previously used as industrial lubricants and thermal insulators, are fond of organic tissues such as fat, and even the organic components of soil. Binding to a substrate can make the fate and transport story very short, like PCBs bound to dirt which is collected and disposed of as hazardous waste, or very long if that same contaminated dirt washed out into a bay.

Final Destination

• One chemical's story might end as soon as it breaks down in the sunlight a few weeks after release. A much more persistent chemical such as a PCB molecule might spend 30 years slowly making its way from a factory on the U.S. Gulf Coast to polar bear populations at the Arctic Circle.