Ecotoxicology and Environmental Fate

Introduction
Ecotoxicology is concerned with adverse effects caused by chemicals on large numbers of species, i.e. populations, communities and also ecosystems. It involves the direct study of the toxic effects on the organism of interest. By contrast, toxicological studies examine the adverse health effects of chemicals on the individual using animals or cell cultures as surrogates.

When considering environmental effects it is important to be specific with respect to what is being affected, or at risk of being affected. Therefore it is useful to think of the environment as being made up of different compartments (or media). These are usually taken as being air, water, sediment/soil and biota.

Environmental transport and fate
Before a chemical can cause an effect it needs to get into one of the compartments. However they do not always stay in the same compartment because natural phenomena, such as wind, or even human activities mean that they can be transported elsewhere. This can either occur within the same compartment or between different compartments.

The fact that there is constant change in this way can make life very difficult when trying to predict where chemicals will end up in the environment. That is, their environmental fate. However there are certain intrinsic properties of chemicals that can be used to help predict their potential movement, concentration and fate in the environment. These properties include water solubility, volatility, bioaccumulation potential and biodegradability.

Although these intrinsic properties will influence the movement of chemicals and their fate in the environment, transport within the environment will, to a large extent, depend on the mobility of the medium into which the chemical was introduced. Therefore, any chemicals present in air and water will be transported further than those remaining within the soil or sediment. As a result attention from environmental agencies world wide is focused on chemical pollution of both air and water media.

A well known example of a problem resulting from chemical movement within the environment is that involving sulphur dioxide emissions from the United Kingdom being transported to countries such as Scandinavia. This as caused acidification of both water (lakes) and soil as a result of the gas being washed out of the air by water which then falls as “acid rain”.