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Ecotoxicology - What is it?

Of all the definitions of ecotoxicology that I have found the simplest is that ecotoxicology is "the study of the harmful effects of chemicals upon ecosystems" (Walker et al, 1996). The thorny question of what exactly ecotoxicology is is tackled in more detail below. More information about the highlighted terms can be found in the Definitions section.

Ecotoxicology is a young discipline, it was first defined by René Truhaut in 1969, and it attempts to combine two very different subjects: ecology ("the scientific study of interactions that determine the distribution and abundance of organisms" Krebs 1985) and toxicology ("the study of injurious effects of substances on living organisms", usually man). In toxicology the organisms sets the limit of the investigation whereas Ecotoxicology aspires to assess the impact of chemicals not only on individuals but also on populations and whole ecosystems.

It was after World War II that increasing concern about the impact of toxic discharges on the environment led Toxicology to expand from the study of impacts on man to that of impacts on the environment. This became known as Environmental Toxicology. The major tools of Environmental Toxicology were: detection of toxic residues in the environment or in individual organisms and testing for the toxicity of chemicals on animals other than man. It was however, a very big jump from a fish in a jar or a rat in a cage to a complex, multivariate environment and ECOTOXICOLOGY developed from the need to measure and predict the impact of pollutants on populations, communities and whole ecosystems rather than on individuals.

There are three main objectives in ecotoxicology (Forbes & Forbes 1994):

  • obtaining data for risk assessment and environmental management.
  • meeting the legal requirements for the development and release of new chemicals into the environment.
  • developing empirical or theoretical principles to improve knowledge of the behaviour and effects of chemicals
  • in living systems.

In order to achieve these objectives, the main areas of study are:

  • the distribution of POLLUTANTS in the environment, their entry, movement, storage and transformation within the environment.
  • the effects of pollutants on living organisms.
  • At an individual level, TOXICANTS may disrupt the biochemical, molecular and physiological structure and function which will in turn have consequences for the structure and function of communities and ecosystems.
  • At the population level it may be possible to detect changes in the numbers of individuals, in gene frequency (as in resistance of insects to insecticides) or changes in ecosystem function (e.g. soil nitrification) which are attributable to pollution.
  • it may be possible to use BIOMARKERS to establish that a natural population has been exposed to pollution and these can provide a valuable guide to whether or not a natural population is at risk or in need of further investigation.
  • For the purposes of the Regulation and Registration of chemicals the toxicity of individual chemicals is principally investigated via TOXICITY TESTING, the main tool of which is the Standard Toxicity Test (STT) which usually tests the DOSE or CONCENTRATION of a particular chemical that is toxic to under controlled, laboratory conditions. Toxicity tests are mainly carried out using individual animals although there has been a move towards the use of more complex systems known as MESOCOSMS. In some situations, particularly in the case of pesticides, it may be possible to carry out FIELD TRIALS to assess toxicity.
  • Toxicity data are used to make assessments of the HAZARD and the RISK posed by a particular chemical.

A more complete definition of Ecotoxicology comes from Forbes & Forbes 1994 " the field of study which integrates the ecological and toxicological effects of chemical pollutants on populations, communities and ecosystems with the fate (Transport, transformation and breakdown) of such pollutants in the environment".

There is an on-going debate as to the exact scope and definition of ecotoxicology and several books have been written recently which discuss this in some depth, these include:

Forbes, V E & Forbes T L (1994) Ecotoxicology in Theory and Practice. Chapman & Hall Ecotoxicology Series 2: London.
Cairns, J Jr & Niederlehner B R (1994) Ecological Toxicity Testing. CRC Press Inc: Boca Raton
Walker C H, Hopkin S P, Sibly R M & Peakall, D B (1996) Principles of Ecotoxicology. Taylor & Francis: London

Toxicity testing and regulation of release of toxic chemicals

As ecotoxicology largely arose from toxicology and the need to regulate the introduction of potentially toxic chemicals into the environment remains central to it today. Most toxicity testing for pollutants is still based on tests on individual organisms in artificial test situations. These tests are cheap, reliable and easy to perform but there is much debate about the relevance of many standard toxicity tests to 'real life'.

Initially in the early days of environmental toxicology the concept of the 'most sensitive species' was used to relate the results of toxicity tests to the 'real world'. Certain species in a particular community were assessed as being 'most sensitive' to pollutants. The logic was that if a pollutant was non-toxic to the 'most sensitive' species then it would be safe for the rest of the community.

Essentially, this logic remains today - the results of tests on single species, in artificial situations are extrapolated to predict the effects of pollutants on whole communities or ecosystems. It is assumed that if you have enough information about the effects of a pollutant on the parts of an ecosystem, then you can assemble the effects on the whole.

There is however, some question about the usefulness of extrapolating from simple, highly artificial, single-species toxicity tests to complex, multi-variate ecosystems. Forbes & Forbes (1994) argue that "understanding and predicting the consequences of pollutant-induced effects on ecosystems requires that the effects be examined at the level of interest" ie. the population, community or ecosystem.

This debate has been the source of much division in ecotoxicology, between the Applied, often Industrial, Ecotoxicologists concerned with the practicalities of chemical registration and testing and the Pure or Academic Ecotoxicologists who regard many toxicity testing regimes as inappropriate or at worst useless. Unfortunately, never the twain shall meet and the level of communication between the two camps has not been great. A fictional exchange makes the point well (from Forbes & Forbes 1994):

  • "Academic Ecotoxicologist: Single species acute toxicity tests are too simplistic and have no connection with what is really going on out in nature. These standard tests are not only irrelevant and a waste of time, they may in fact do more harm than good if they lead us to believe that we can use them to adequately protect the environment when in fact we cannot.
  • Industrial Ecotoxicologist: These tests may be oversimplified, but they are also cost-efficient, easy to perform, the procedures have been worked out, and the fact is they are required by government. We have absolutely no incentive to do more than is required by law, and, frankly, you have given us little hard evidence that current test procedures do fail to protect the environment adequately.
  • Government Ecotoxicologist: Do you have any idea of the number of new chemicals that we have to assess each year? We can't tell industry to stop producing new chemicals and we can't wait until we understand the whole system before we try to protect it. If you think current procedures fail, then come up with some better tests - which must of course be simple, cheap and fast.
  • Academic Ecotoxicologist: (Pause) ... Well, it's very complex, and of course I'll need much more data before I can give you an answer. But those single-species acute tests are oversimplified and have no connection with what is really going on out in the field ...
  • Government Ecotoxicologist: We need tests! Give us tests!"

The way forward for Ecotoxicology must be to integrate its two halves much more fully. Toxicity testing, using single species, do provide useful information and will almost certainly remain central to the regulation and registration of toxic chemicals but much can be done to expand the scope of toxicity testing, to add tests that apply to higher levels of organisation and so increase their relevance to the communities and ecosystems that are being protected.