|
|
|
|
|
Environmental toxicology is a young field that has developed rapidly over the past 40 years. Environmental toxicology involves the studying of sources, pathways, transformations, and effects of chemicals that are harmful in the environment. The study of these harmful effects extends from individuals and populations of organisms to the ecosystem level. The study of the toxic effects of environmental contaminants really began in the 1960's, evolving from the traditional field of human or classical toxicology. (reference)
The first writings of toxicology relate back to prehistoric times when various chemicals, or mixtures of chemicals, were used as both tonics and poisons, with particular references to arsenic and mercury based compounds. Historically, most of the positive applications of arsenic and mercury were overshadowed by their 'usefulness' as a poison to resolve various personal or political problems.
The first students of toxicology were physicians and alchemists. The Swiss physician Paracelsus (1499-1541) was particularly well-known for the formulation of the dose-response relationship. Paracelsus observed that some chemicals administered to patients at low concentrations had a therapeutic effect, whereas high concentrations produced toxic effects. One of the next major advances in toxicology came from the Spanish physician Mattieu Orfila (1787-1853). Orfila published a comprehensive paper on the toxicity of natural substances, which identified a relationship between the toxic symptoms of the patients (pathology) and the chemical content of the tissues.
Orfila further studied the action of antidotes and proposed that the human body has mechanisms for eliminating poisons. This lead to the work of the French physiologist Claude Bernard (1813-1878), who introduced a more strategic approach to toxicology by performing controlled experiments on animals. The findings and theories produced by Orfila and Bernard over a one hundred year span highlight the foundation of toxicology as a science. With the mid nineteenth century came the chemical revolution, with a rapid expansion in the extraction of natural chemicals and production of new synthetic compounds. Toxicology developed concurrently, still focusing on the two base themes:
Testing of new pharmaceutical products, and
The identification of potentially harmful effects from the new natural and synthetic compounds.
This era marked the beginning of occupational toxicology, with direct links between the workplace and employee health being proposed and tested.It was during the chemical revolution that an awareness of animal toxicology evolved in Europe and North America, as it was confirmed that a variety of chemical contaminants were causing wildlife deaths. Environmental contamination was recognized as a serious issue by the British government, and a royal commission was established to assess the potential contaminants in industrial wastewater.
However, it was not until 1962 with the release of Rachel Carson’s book ‘Silent Spring’, that a true public awareness of environmental toxicity was established. ‘Silent Spring’ was written for the lay-person and clearly describes the impacts of harmful chemicals on wildlife, namely the disappearance of birds from waterways.
In the late 1960's Réné Truhaut used the term ‘ecotoxicology’ to describe the study of environmental toxicity. Truhraut defined ecotoxicology as a branch of toxicology that focuses on the toxic effects caused by both natural and artificial substances on living organisms. Truhraut went on to formally distinguish between classical toxicology and ecotoxicology, describing the study of ecotoxicity as a multi-step process, which includes:
The entry, distribution and fate of pollutants within the environment;
The entry and fate of pollutants in living organisms of the ecosystem; and
The harmful effects of the chemical pollutants on the constituents of ecosystems (which include man).
Each of these steps is complicated by potential biological or abiotic transformations of the parent pollutant. It was during the mid 1970’s that scientists began to realize that the environmental monitoring of toxic substances from anthropogenic sources was producing a growing inventory of data on the quantities of substances in the terrestrial and aquatic environments.
Kovach stated that before this information could be used to evaluate the biological effects, knowledge was required of the chemical form of the pollutants, the mechanisms by which the pollutants enter and move through organisms, the abiotic and bio-transformations of the parent compound, the nature of the toxic reactions within biological tissues, and the changes in physiological and physical behavior of the contaminated individual. This was the time when many scientists acknowledged that quantification, in itself, was not sufficient to define and describe toxicological problems.
Interest in developing physicochemical models of contaminant behavior in the environment also expanded in the 1970’s. Various physical and chemical parameters (such as pH, temperature, dissolved oxygen) were known to govern contaminant speciation in the environment, and attempts to predict contaminant species, and hence the potential toxicity of the environment, were made through modeling. Thirty years on and these models are still being refined, and are the focus of many environmental toxicity studies.
An abiotic system is one which is free of biological organisms. Abiotic transformations are those brought about by a non-biological mechanism. Thus, the modification of a chemical through heating or by the absorption of radiation is, strictly, an abiotic transformation or process.
Abiotic factors are essentially non-living components that effect the living organisms of the freshwater community for example. When an ecosystem is barren and unoccupied, new organisms colonizing the environment rely on favorable environmental conditions in the area to allow them to successfully live and reproduce. These environmental factors are abiotic factors. When a variety of species are present in such an ecosystem, the consequent actions of these species can affect the lives of fellow species in the area, these factors are deemed biotic factors. (reference)
Rachel Carson's Silent Spring is now nearly fifty years years old. Written over the years 1958 to 1962, it took a hard look at the effects of insecticides and pesticides on songbird populations throughout the United States, whose declining numbers yielded the silence to which her title attests. "What happens in nature is not allowed to happen in the modern, chemical-drenched world," she writes, "where spraying destroys not only the insects but also their principal enemy, the birds. When later there is a resurgence of the insect population, as almost always happens, the birds are not there to keep their numbers in check." The publication of her impeccably reported text helped change that trend by setting off a wave of environmental legislation and galvanizing the nascent ecological movement. It is justly considered a classic, and it is well worth rereading today.