120 Ecotoxicology associations with the roots of many plant species In fact plant roots have adapted specially to accommodate for these microorganisms Furthermore, microorganisms associated with the gut of animals provide essential vitamins that animals cannot synthesize themselves On the negative side, microorganisms are responsible for causing a wide variety of diseases in plants and animals Although this is negative from the viewpoint of the organism (or population) that is affected, disease causing organisms are important in ensuring that excessive population growth of particular populations is curtailed, thus ensuring the maintenance of an environment that contains a rich diversity of species The interdependence between microorganisms and higher life forms means that toxic effects that affect either group of organisms can have important consequences for the other Biotechnology Biotechnology is an applied science that aims to harness different life forms for the benefit of man Agriculture, antibiotic production, and bioremediation are examples of such applications Recent advances in molecular biology have given biotechnologists new tools to change the nature of life by genetic modification This technology has resulted in the creation of organisms that would very unlikely have arisen in nature via normal mating and exchange of genetic material It is now possible for humans to combine the genes of widely different organisms into one organism, giving this recombinant organism the means to express novel characteristics Such ‘‘novel characteristics’’ include resistance to diseases and pests, resistance to pesticides, or the means to produce products that are of commercial or medical value Whereas these organisms are of potential value to society, it is necessary to evaluate their environmental impact before they can be safely released into the environment Therefore, with the advance of biological science comes the responsibility for biotechnologists to ensure that the integrity of the environment is maintained by ensuring that the biological functions that allow life on this planet to thrive are not impaired Interestingly, recombinant technology has also opened the way to construct organisms that can be used to monitor the environmental impact of toxicants more sensitively An important interface of ecotoxicology with biotechnology arises in the use of such genetically modified organisms as biomonitoring tools However, the detection (and assay) of ecotoxicants can be achieved by a variety of methods An interesting example is the detection of carbon monoxide This can be achieved using a caged canary (that responds sensitively to carbon monoxide in coal mines) or using an enzyme-based detector electrode that functions as a biosensor for this gas A detailed account of biotechnological techniques for biomonitoring and bioremediation in relation to ecotoxicology can be found in the book by Lynch and Wiseman (1998) Ecology Ecology is the study of the interactions between organisms and their environment that determine the distribution and abundance of organisms These interactions can be studied at different levels of biological integration starting from individuals, which are part of populations, which are part of communities, which are part of ecosystems, which are part of the earth’s biosphere To gain a living from nature, humans have to understand the interactions that determine the abundance and distributions of organisms on which human life depends This is not only important for the harvest of species from natural ecosystems by hunting, fishing, and or gathering of plant products, but also where the aim is to modify the natural environment to yield predominantly products that are of economical value as is the case in agriculture and forestry Not only we need to understand how we can most efficiently use the environment, but also increasingly we need to be aware of the impact of human activities on ecosystem function in general Pollution of the environment by human activities (manufacturing, mining, waste disposal, transport, energy use, pesticide use, etc.) can have a large impact on ecosystem function via effects at all levels of biological integration Especially since the scale of human activities has increased so dramatically over the past century there is a real danger that human activity interferes significantly with the basic biological processes of sustained life, including our own Therefore, ecological knowledge applied to ecotoxicology aims to evaluate the consequences of human activity to ecosystem function, especially in relation to pollution caused by human activity Toxicology Important principles of toxicology that relate to ecotoxicology include the concepts of extent of exposure, persistence, and distribution of chemicals in the environment Subsequently predictions can be made on the toxicity of such chemicals to individual organisms or populations The starting point of such analysis is often the chemical structure of each toxin, which will allow some prediction of the behavior of the chemical in the environment to be made One of the best examples of this kind is the environmental impact assessment of the insecticide DDT DDT is almost completely insoluble in water but readily soluble in fat Furthermore, DDT and its degradation product DDE are highly persistent Its low solubility means that it is easily dispersed in aquatic environments (in the case of DDT it is found at low concentrations all over the globe) and only accumulates in places with a high fat content (i.e., living organisms) Once it has entered living organisms, it persists and accumulates in the fat tissues of organisms that are higher up the food chain resulting in toxicity For this reason, populations of both fish eating birds and bird eating raptors such as peregrines and hawks were badly affected by DDT, even in cases where they inhabited pristine environments Another aspect of toxicology is risk analysis This quantitative topic is most easily studied when death rates within a population can be quoted Whereas the rates can be determined experimentally for animals, plants, and microorganisms, the determination of the effects on the human population is inevitably more difficult to determine, and one of the few situations where effects are well known is the mutagenic effects of radionucleotides, resulting from