Environmental Toxicology Essay Example

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.

During the early years, 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 in understanding from an experimental animal to a complex, multivariate environment and the subject of ECOTOXICOLOGY developed from the need to measure and predict the impact of pollutants on populations, communities and whole ecosystems rather than on individuals.

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. [pic] Significant Issues with Chemicals that have driven the development of Ecotoxicology [pic] 1. DDT – around the world 2. Cadmium in Japan 3. Mercury in Japan 4. PCBs in Japan and Taiwan 5.

Dioxins – various 6. The contamination of pristine environments (eg Arctic) by atmospheric transport of organohalogens Most workers in the field of ecotoxicology refer to the publication of Rachel Carson’s Silent Spring (1962) as a landmark in the public’s awareness of potential damage to human and environmental health from man-made toxic substances. According to Rodricks (1992), Carson’s book “almost single-handedly created modern society’s fears about synthetic chemicals in the environment and, among other things, fostered renewed interest in the science of toxicology”.

Certainly the consolidation of academic and related pursuits into the study of toxic substances in the environment dates from about the same time as the publication of Silent Spring. Prior to the 1960s, there were no coordinated programmes in research, in education or in regulation that systematically addressed toxic

substances in the environment. Considerable progress has been made in all these areas during the past four decades. Fate of chemicals in the environment and within organisms As ecotoxicologists we are concerned with the movement and fate of toxic chemicals at both the organism level and that of the whole ecosystem.

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" i. e. 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. Testing methodologies An extensive range of ecotoxicological and biodegradation tests are required for the chemical, agrochemical and pharmaceutical industries.