Ecotoxicology is concerned with the toxic effects of chemical agents on living organisms, particularly on population and communities within a defined ecosystem.
It includes the transfer chain reactions of those toxic elements and their close relationships with the given environment. Ecotoxicology is different from classical toxicology in that it is a four-pronged subject. Any assessment of the ultimate impact of a pollutant on the ecosystem must consider each of the four distinct processes, viz.:
Image Source: 4.bp.blogspot.com
ADVERTISEMENTS:
(i) The chemical and physical form of the pollutant released into the environment and the medium into which it is released. The quantities, forms, types and sites of releases must be ascertained.
(ii) Changes effected in the pollutant by biotic and abiotic processes during the transit time, i.e. from the source of release to the receptor. The pollutants are transported geographically into different biotic phenomena and chemically transformed creating compounds with quite different toxic properties and environmental effects. The exact nature of these processes is not known for most of the pollutants and thus needs to be studied scientifically.
(iii) Quantitative metabolism of the transported pollutant and the receptor organism. This enables the calculation of accumulation of toxic agents in the available food chains and doses thereof to receptors. The identification of the nature of the target organism and the type of exposure to the transported pollutant is extremely important.
(iv) The effect of these doses or receptor individuals, populations and communities and the response of individual organism, population and community to specific pollutants over a given time scale has to be studied.
ADVERTISEMENTS:
History of Ecotoxicology
Environment contamination is not a new menace. The international efforts to initiate remedial measures probably originated from the widespread apprehensions caused by the atmospheric testing of nuclear weapons in the 1950s and 1960s.
The United Nations created the Scientific Committee on the Effects of Atomic Radiation in 1955. Its aim was to assess the magnitude of environmental radiation and its hazards to human population.
Later, individual environmentalists and some organisations studied and publicized the possible risks of large scale contamination by industrial chemicals either released intentionally in the form of pesticides, etc. or unintentionally during production processes.
ADVERTISEMENTS:
In 1968, the United Nations decided to hold an International Conference on Environment at Swedish capital, later called the Stockholm Conference. Addressing the Conference, India’s former Prime Minister stressed inter alia the need for adopting environment friendly ways and provide enough economic opportunities to tribals who live around forests so that they do not indulge in wanton deforestation.
The idea was to preserve the natural purification system of the atmosphere and keep the toxic effects to the minimum. Most of the present day international environmental activities are organised in the light of Stockholm Conference.
Scope
In the year 1969, the International Council of Scientific Unions (ICSU) formed the Scientific Committee on Problems of the Environment (SCOPE) to study the influence of human race on environment as well as the effects of environmental changes on human health and welfare. The Committee seeks to synthesise environmental information on the following aspects:
(i) Biochemical cycles,
(ii) Evolution of ecosystems and other dynamic changes,
(iii) Human settlements and environment,
(iv) Simulation modeling of environmental systems,
(v) Ecotoxicology,
(vi) Environment monitoring,
(vii) Communication of environmental and societal assessment and the response therefore..
Ecotoxicology is essentially a study of the effects of released pollutants on the environment and on the biota that inhabit it. Human beings are the most important of biotic atmosphere.
They not only alter the environment but also produce the pollutants and release them into the environment. Hence, the growing importance of ecosophy, i.e. concern for environmental and ecological matters. The history, scope and significance of ecotoxicology were also reviewed by Trupant in 1975.
Intake and Update of Pollutants
The entry of substance into the lungs, gastro-intestinal tract or subcutaneous regions of animals constitute intake. The rate of the taken material will be governed by the process of absorption. Uptake, on the other hand, is the absorption of the substance into extracellular fluid for systematic circulation. In this case, the fate of the taken material will be governed by the metabolic processes in the host.
In humans, the radio-nuclides are believed to be absorbed through skin. In an experiment, radioactive iodide applied to human skin, appeared in the thyroid gland. Oshorne, an eminent scientist showed in 1996 that in ‘workmen’, two-thirds of the total absorption of triturated water vapour took place through lungs and one third by way of skin.
When a substance is inhaled by a person, it may be deposited in the nasopharyngeal regions, trachea-bronchia or alveoli in the lungs. In all these regions, the substance is either absorbed into the extracellular fluids or transported to the pharynx from where it is swallowed into the digestive system. The most important site of absorption is the alveoli. Materials taken up from them either go to the blood stream or lymph.
Results of Experiments
The results of some experiments conducted to study the toxic effects on animals are given below:
Dichlorobiophenyl is rapidly absorbed from the upper gastrointestinal tract and is taken to liver for metabolism and excretion through intestines. Thus, liver and intestines are prone to infection.
Dieldrin is absorbed the same way. However, the metabolic conversion is much slower; only a part of the substance is metabolised and excreted while the remaining amount is redistributed into the storage depot of adipose tissue for a repetition of the process. This results in weakening of the digestive system of the organism.
Methyl mercury is absorbed by the aquatic animals like fish through their gills. The respiratory uptake depends on the rate of metabolism. Fish with higher metabolic rate have higher uptake and are more prone to be affected.
The knowledge of retention of a pollutant in the animal’s body is useful to determine toxic effects. It is obtained either by estimation or the measurement of total amount excreted per unit time. Values have been fixed for tritiated water, lead, cobalt, etc. in humans and methyl mercury in plants.
The retention sometimes varies with the body weight. In experiments, specific values have been obtained for tritiated water, lead, cobalt and strontium for human beings and for methyl mercury in aquatic plants like Elodea and Utricularia.
Variations in retention time of caesium have been found in mammals depending upon their body weight. The organ or tissue of the body which is most affected by the uptake of a toxicant is called the critical organ.
Sometimes, the concentration of heavy metals in hair is measured to calculate the concentration in the body. For instance, the concentration of methyl mercury in the hair is 300 times more than in blood.
Absorption of Toxicants by Plants
Plants absorb toxicants either from soil or water through roots, or directly from the atmosphere. The usual pathway of absorption of gaseous pollutants is through the leaves. Other chemicals present in the atmosphere as particulate forms may be impacted into leaf surface but rarely reach the stomata.
Such toxicants include: zinc, cadmium, lead, copper and nickel. Lead is known to gather on plants and trees that grow alongside highways in proportion to the flow and density of traffic. Sedimentation from atmosphere also contaminates soil and vegetation.
Lead in the topsoil along roadside may be as high as 30 times that in the non-roadside soil. The introduction of lead-free petrol and CNG is therefore a welcome step for the health of greenery.
Warfare and Ecology
Humanity got its first taste of destruction by an atomic weapon when America dropped atom bombs on Hiroshima and Nagasaki in August 1945. War in Europe was scientific enough with pilotless planes and rockets but the devastation caused in the Japanese cities were unheard of. A single bomb had killed as many, wounded as many, as a mass said of 279 huge aircrafts laden to capacity with bombs striking at a city ten times as populous.
The effects on those who were removing from immediate injury were also large. Many of them contracted wasting diseases where the corpuscles of the blood diminished. Surface wounds, grazes, abrasions and scratches closed and for no reason reopened. The red blood count and white blood count lost proportion.
Incalculable damage was done to environment and nature strived for years to re-establish her equilibrium.
Gulf War I and II
During Gulf War I, heavy atmospheric clouds were formed over the skies of Arabian pennisula making US military operations difficult even during day time.
The dense fog covering the entire area was in fact emission of oil soot that had wafted from over six hundred environmentally destructive oil well fires throughout Kuwait and drifted through the air for up to a radius of 1000 miles.
The fires skewed million tons of carbon in the air resulting in the largest oil spill in history. It took fire crews nine months to put out the blazes. The intake and uptake of such large quantities of toxins by human, animals and vegetation was consequently huge and manifested themselves in various diseases, endangering and even extinction of certain prone species.
The United Nations Environment Programme (UNEP) and ecological experts have agreed that the ecological disaster brought by hi-tech Gulf War II will be even more astonishing.
Immediate Effects
(i) The Iraq and Arabian Peninsula will witness change of surface and desert species affecting Iraqi tribes which are solely dependent on them. Hundreds of birds and sea species have already been killed by layers of thick, black oil spills.
(ii) An extensive damage has been caused to Mesopotanian marshes, an area of connected lakes and floodplains along the Tigers and Euphrates.
(iii) About six million to eight million barrels of oil dumped into Indian Ocean created catastrohic oil slicks for sea animals. The oil also coated the shoreline and destroyed natural habitats for several species of reptiles.
(iv) Iraq is a major transit spot for migrant birds between European and African continents. Large groups of birds migrate to this place over land and sky every spring and autumn.
The vast expanse of wetland and marshes in the south of Iraq are natural sanctuaries for tens of thousands of water birds. The modern weapons like depleted uranium, high-energy microwave and clustered bombs used by the US and allied armed forces are doing incalculable harm to these natural habitats and the species.
According to experts, nearly 40 species of rare water birds, crustaceans and mammals extirpated from the land of Iraq during Gulf War I.
It is apprehended that current war may take a toll of over 70 types and sub-types due to toxic effects, surface contamination and destruction of natural habitats due to heavy bombardment, tank movement, landmines and other military operations.
Experts are of the opinion that the Gulf War Syndrome was caused mainly by the leakage of chemical and biological preparations and environmental pollution due to flagrant oil well burning and depleted uranium bombs dropped by US army.
Long-Term Ecological Damage
The research data indicate that the micro granules produced after the explosion of the depleted U-bombs will cause a long term damage to the ecological environment, ‘here will be an obvious increase in the number of patients suffering from carcinoma, cardio-vascular and neurological borders, cataract, hematopoietic problems and decrease in fertility.
The French experts who conducted a study of Gulf Wars I and II for comparative analysis said that the frequent use of the depleted U-bombs by the US armed forces in 1991 and the recent use of research type of chemicals and explosives is sure to cause new disasters in the Middle East.
It is apprehended that in the recent Gulf War II, the Arabian Peninsula is likely to witness a climate change. The desert temperature has already increased by 2°C.
The war is also threatening Iraq’s agriculture and river in a major way since Saddam Hussain’s troops had used ferrying of missiles and other war equipments through the river systems that attracted US attacks leading to massive dumping of missiles and explosives into river waters.
The large scale use of mines in river and sea waters by Saddam’s forces has also led to water pollution and destabilisation.
The recent study by the United Nations Environment Programme (UNEP) suggests that Iraq, Kuwait, Jordan and the Arabian Peninsula will witness massive new human health hazards unknown to medical experts.
The natural course for civilised minds which we think we would have been to decry all war and any of its manifestations particularly those which are instrumental in the devastation of environment.