Environmental Toxicology Environmental Toxicology Definition Environmental toxicology refers

Environmental Toxicology

Environmental Toxicology Definition “ Environmental toxicology”: refers to study of the direct effects of environmental chemicals on human beings specifically, whereas "Ecotoxicology" refer their effects on other species and ecosystem.

Ecotoxicology n It is concerned with the harmful effects of chemicals upon ecosystems. That include the chronic effects of anthropogenic chemicals, chemical mixtures, and natural substrates on organisms, structures within ecosystems. Also on diversity of organisms, populations, and communities.

Anthropogenic n Anthropogenic effects, processes or materials are those that are derived from human activities, as opposed to those occurring in natural environments without human influence.

Ecosystems n n n It is the space where all the microorganisms, plants, animals, and humans live. It includes the air close to the ground, the soil where the roots of plants are present, caves, and all surfacewater systems, including depths of oceans. Ecosystems are part of the biosphere and are connected to each other by immense transfers of mass and substrates.

n The biosphere is divided into aquatic, terrestrial systems and air in the lower part of the atmosphere, in which flying animals are prevalent and where substrates are transferred by the wind. Simple ecosystem model

Pollution of ecosystems n Sources of ecosystem pollution It is usually arises from either: a) Natural sources b) Anthropogenic sources or

a) Natural sources These sources include: n n Metallic ions Mycotoxins Soil nutrients Volcanic activities

b) Anthropogenic sources They include: n n n Industry and agriculture activities. Botany (alteration of plants by breeding, selection, and genetic engineering). Mining, deforestation, transportation and construction. Habitations (waste products, sewage, and debris). Military activities (radiation, chemical warfare agents).

The pollution of ecosystem is divided into: 1 - Air pollution 2 - Terrestrial pollution 3 -Aquatic pollution

Air pollution Sources of air pollution n 1. 2. 3. 4. 5. Pollutants are discharged into the atmosphere in gaseous state from Combustion of fuel. Open fires. Industrial processing of metals. Gasoline synthetic chemicals. The domestic energy supply.

Types of pollutants 1. 2. 3. 4. 5. 6. Carbon monoxide (Co) and carbon dioxide (Co 2). Sulfur dioxide (SO 2). Oxides of nitrogen (NO 2). Volatile organic compounds such as benzene, and toluene. Polycyclic aromatic hydrocarbons such as benzopyrene, hydrogen fluoride and chlorofluorocarbons. Metals, non metals and other suspended particulate matter.

Classification of air pollutants I- Depending on the release (i) Primary air pollutants: n The pollutants which are directly released in atmosphere in enough concentrations without modification e. g. CO, hydrocarbons, particulate matter, SO 2 and nitrogenous compounds (NO, NO 2). (ii) Secondary air pollutants: n The pollutants which interact with each other in the presence of certain compounds, particularly energy sources, e. g. nitrogenous compounds, ozone, proxy-acetyl nitrate (PAN).

II- Depending on the chemical nature (i) Reducing type of pollution: n As SO 2 and smoke are due to incomplete combustion of coal, fog and cool temperatures. (ii) Oxidizing type of pollution or photochemical air pollution: n Pollution due to hydrocarbons, oxides of nitrogen and automobile exhaust, where intense sunlight causes photochemical reactions in polluted air masses.

n Acute Hazards due to exposure to high concentration of pollutants (e. g. Bhopal gas tragedy due to methyle-isocyanate). n Chronic Hazards due to long term exposure to low levels of pollutants. Respiratory aliments are common in animals or people living in urban areas than those in village as air pollution is precipitating factor.

Toxic effects to some pollutants Carbon monoxide n n It is highly toxic as it has high affinity for haemoglobin (Hb), thus displaces Hb-bound oxygen and increases carboxy-haemoglobin (Co-Hb) concentration with the current decrease in oxygencarrying capacity of blood and thus causing dyspnoea. Affinity of Hb for Co is 220 times greater than oxygen; therefore, Co is dangerous even at very low concentrations.

Sulfur dioxide n n It is a mild respiratory irritant and predominantly acts on the upper respiratory tract and causes bronchoconstriction. It increase mucous secretion due to proliferation of goblet cells and finally produces bronchitis. It also impairs macrophages-dependant host defense mechanism.

n n Sulfuric acid comes on the earth in the form of acid rain. Sulfuric acid is also respiratory system irritant. It induces bronchoconstriction by causing hyperplasia of airway mucousecretory cells and in chronic and prolonged exposure, it induces bronchitis. Sulfur dioxide when comes in contact with oxygen or water in air in the presence of moisture is oxidized to sulfur trioxide, sulfuric acid.

Hydrocarbons n n n Different hydrocarbons formed are low molecular weigh aliphatic, olefinic and aromatic compounds. The olefinic and aromatic hydrocarbon vapours are more irritating to mucous membrane and systemic injury occurs on inhalation of aromatic vapours. The hydrocarbon air pollutants promote the formation of photochemical smog. Some polycyclic aromatic hydrocarbons (PAHs) are potent carcinogens and mutagens.

Particulate materials n n n It include both organic or inorganic particulate materials of different diameters all metals are found in some concentration in the atmospheric particles. The most common metal released with oils and coal combustion are lead, mercury, copper, manganese, chromium, cadmium, beryllium, iron, magnesium, nickel. The general toxicity of most of the common metals is discussed in details previously.

Nitrogen oxides n n Nitrogen dioxide is a deep lung irritant and it penetrates to alveolar capillary membranes where it converted to nitric acid and produce lung oedema. This pollutant is of particular risk to farmers because very high amounts of No 2 are liberated from ensilage. Silo filler's disease due to NO 2 and CO poisoning is well documented.

Photochemical oxidants n n n They arise from a series of complex atmospheric reactions between hydrocarbons and nitrogen oxides. Ozone is one of the most important constituents of this group. The mixture of ozone, peroxyacetyl nitrate (PAN), aldehydes and ketones for a haze which is termed as photochemical smog (a reddish brown haze in the atmosphere).

Ozone n n n Ozone is respiratory toxin. It penetrates deep into the bronchioles and alveoli of lungs and deposited in the acinar region of the lungs, damages respiratory system and produces pulmonary oedema and emphysema. Ozone produces morphological, functional, immunological and biochemical alterations. Pulmonary injury by ozone may be to formation of reactive free radical intermediates by its interaction with sulfhydryl groups.

Green house effects Carbon dioxide n n n Carbon dioxide and water vapours are responsible for maintaining earth's temperature. About 50% of the solar energy is absorbed by earth and rest by the atmosphere after reflection. Carbon dioxide, water vapours and other gases in atmosphere absorbed large part of energy and emit it towards the ground where it warms the surface of earth and referred as natural green house effect.

n n More is the production of carbon dioxide, more is its concentration in the atmosphere, more is the earth temperature. Carbon dioxide is the main green house gas contributing about 49% toward green house effect. Other gases are methane (18%), N 2 O (6%), chlorofluorocarbons (14%) and others (13%).

Aquatic pollution Sources of water pollution 1 -Natural 2 -Anthropogenic Point sources of water pollution Discharges of municipal sewage, industrial units, cooling systems, electricity generating plants are added to rivers, lakes, pipes or channels.

Non-point sources of water pollution n n Agricultural land run- offs containing pesticides, fertilizers, nutrient, phosphorous, nitrates, salinity, acidity. Urban run- offs containing municipal sewage, industrial effluents, run-offs of city streets and land fills.

Types of water pollutants and their hazards n Depending on the nature water pollutants have been divided into three types: (i) Physical pollutants (ii) Chemical pollutants (iii) Biological pollutants

Physical pollutants n Water may be polluted with mud, grit, stone lime, ash, mining wastes, aquatic fauna or heatthermal pollution. Thermal pollution due to absorption of solar energy, release of industrial cooling or power plants water discharges. These result to increased ambient temperature of water and decreased solubility of oxygen in water which will have adverse effects on aquatic flora and fauna.

Chemical pollutants 1 -Mineral salts and metallic ions n n A large number of mineral salts and metallic ions find their ways into drinking water e. g. carbonates bicarbonates, sulfates and chlorides of calcium, magnesium and sodium. Lead, iron, arsenic, manganese, cadmium, fluorides present in the water and precipitate down stream into the sediment of the rivers, produce severe toxicity in consumers.

2 -Petrochemicals n n They are another type of chemical pollutants due to large spills from the tankers or near the shores, e. g aromatic hydrocarbons, phenols, sodium chloride washed into streams, hydrogen sulfide, inorganic compounds, fuels, heavy metals , nitrate, nitrites, pesticides, fungicides, soil nutrients, fertilizers and air born pollutants/acid rains. All these chemicals are standing on the surface and in the ground waters.

Acid rain n n It leaches calcium, sodium, magnesium and potassium out of the soil into the ground water and thus results into deficiency of these metals/ions into the soil and making the soil infertile. Acidification in aquatic communities may have a dramatic effect on fish population, phytoplankton and zooplankton communities. Juveniles are generally more sensitive than adults. Fishless lakes have been observed in highly polluted areas such as Scandinavian lacks.

Salinization n n Excessive levels of these salts in water results in Salinization of soil and inhibit the plant growth. Air borne toxins e. g. metals, pesticides, organic chemicals ect. Are carried by air to distant places come to earth with rains or snow and pollute soil and water.

Bioaccumulation and Biomagnification n n Residues levels of persistent organochlorine compounds have been observed in organisms of almost all trophic levels and all most in all places. There is a strong relationship between the concentrations of the residues and the trophic level of the organisms. The lowest levels are in plants (brown algae) and the highest are in predators of trophic levels 4 and 5. The bioaccumulation and biomagnification occur at every stage of the food chain.

n n n Fish–eating birds bioaccumulate substantial levels of persistent organochlorine compounds because the have low activities of the mono-oxygenase system, which is mainly responsible for the detoxification. A deficiency in the detoxification system and the high contamination of prey favors bioaccumulation. Persistent polychlorinated biphenyls (PCBs), polychlorinated dibezo-dioxines(PCDDs), and polychlorinated dibenzofuranes (PCDDs) have been shown to bioaccumulate substantially, especially in aquatic food chain.

n n n Lipophilic compounds, which are extensively metabolized and have relatively short half-lives, don't pass along the food chain. Some invertebrates of the lower trophic level bioconcentrate them, because the rate of the degradation by metabolism is low. On the other hand, individuals of the next trophic level, such as fish, birds, and mammals, metabolize them rapidly via the mono-oygenase system. A consequence of this may be metabolic activation toward genotoxic and carcinogenic intermediates.

Biological pollutants n n Aquatic fauna, planktons including saprophytic, holozoic and chlorophyllous forms of life, sponges, worms, algae, creepers like snails or insects. In addition to certain bacteria, fungi, parasites and viruses also contaminate water and theses may become potential threat to human and animal on prolonged consumption of such polluted water.

Terrestrial pollution Sources of pollution n The contamination of the land may be due to: 1) Domestic wastes 2) Industrial activities

Domestic wastes: n n n The disposable of wastes at landfill sites, municipal waste including detergents and heavy metals. The control of pests or vectors during farming including nitrates, phosphorus, insecticides and herbicides. The use of sewage sludge as a fertilizer on agricultural lands.

Industrial activities: n n Metalloferous deposits of metals from mining activity. Synthetic organic chemicals are aroused as industrial waste. Inorganic material such as arsenite, copper and silver comes from smelting work. The extensive use of leaded gasoline has led to widespread of urban soil.

The major types of pollutant in the soil n n n Nitrates, phosphorous Biocides (atrazine herbicide), pesticides, fungicides and chlorophenols Metals (lead, copper, zinc and cadmium) Detergents and synthetic chemicals Organic, inorganic chemicals and oil Radionucleotide

The toxic effect of some pollutants n Soil organisms such as earthworms, woodlice and millipedes are absent in cadmium contamination. This effect leads to reduction in the decomposition rate of dead vegetation and dead organic matter accumulates on the surface in thick layer preventing the normal aeration in the soil. n The acidification of the soil decreases the binding of essential elements which leached to lower soil layers. Thus, the uptake of these elements (e. g. , magnesium) by the roots of trees my be impeded.

n High input of nitrogen compounds lead to serious stress on trees lending to forest dieback. n Chemical stable lipophilic compounds have long half-lives in soil and metabolized very slowly. Thus, the highest concentrations are found in organisms at contaminated areas of the soil. These compounds may be interring the food chain.

Fate of pollutants in ecosystems n The fate of the pollutants in ecosystem depends mainly on: (i) The pollutant n Local concentrations of pollutants in air, soil or water are strongly dependent on many parameters:

n n Type of release as gaseous compounds from chimneys, leakage from waste deposits, and washout from agricultural land. The amounts of pollutants were released. The frequency of the release which it may be permanently, periodically or by acute incidents. Physicochemical features as volatility, affinity of absorption, and partition coefficient between phases of ecosystem.

(ii) The ecosystem There are many factors related to ecosystem itself and affect deeply on the fate of the pollutants as: n Temperature, PH. n Reduction –oxidation conditions. n Density of the particles. n Sedimentation and the type of nutrient cycling.

The final termination of chemicals in ecosystems occurred by: Abiotic transformation n Molecular modifications of environmental pollutants occur in ecosystems by abiotic transformation due to photolysis, hydrolysis and redox reactions (oxidation and reduction).

Biotic transformation In most cases the pollutants deactivated by molecular biotic transformation but there are many examples where, the transformation reactions produce species that more active as following:

1 - Biotic methylation of metals raises the toxic activity of mercury and lead. Inorganic Hg (low toxic) Methyl Hg (high toxic) Soil bacteria

2 - Dechlorination of organochlorine compounds as DDT to DDE produce a metabolite that still active and persists even longer in ecosystem than the mother substrate. DDT (low toxic) by water plankton DDE (high toxic and more persistent).

3 -Oxidation of the organophosphorous insecticides leads to production of reactive metabolites, such dimethoate, diazinon, malathion, parathion and disulfoton. Parathion (inactive) Paraxon (active) liver oxidation

4 - Oxidation of benzo (a) pyrene, aflatoxin, and vinyl chloride lead to production of carcinogens. Aflatoxin by hepatic microsomal mixed function oxidases reactive epoxide which forms covalent adducts with DNA (Genetic Carcinogen)

5 -Hydrolysis of some pollutants is associated sometimes with their transformation to higher toxic products. It is strongly dependent on the PH. water PH is toxicity of inorganic pollutants is such as cyanides, metal cyanides, and H 2 S. While the toxicity of the nitrogen compounds ammonia and ammonium ions is increased with high level PH. Ammonia (NH 3) increase in water PH less toxic Ammonia ions (NH 4+) more toxic

6 - Metabolic biotransformation of some compounds in the body of organisms as the effect of stomach HCL or ruminal microflora on the toxicity of some pollutants. Urea by HCL Ammonia Zinc phosphide by GIT microflora phosphin gas Nitrite Stomach HCL Nitrosamines

7 - Biological magnification of organochlorine compounds through the different trophic levels of organisms. DDT in Planktons (+) Fish (++) Birds eating fish (+++) animal (++++) Human (+++++)

8 - Industrial magnification of organochlorine compounds in contaminated dairy products. Ration has about 7 -8 ppm Lactating animal Milk has 3 ppm DDT by industrial manufacturing butter has 65 ppm DDT.

Risk assessment of environmental pollution The basic concepts of toxicity elicted by chemicals demand the data be provided on: n The quantity of chemical to which the organism is exposed. n The dose-response relation ship. n The nature of the toxic effects. n The individual sensitivity of the organisms within ecosystem.

The strategies for recognizing environmental risks It involve several methods or levels as following: 1 -Screening tests n These tests evaluate the fate and action of chemicals in different compartments of the ecosystem. 2 -On-line monitoring of the concentrations of certain battery of pollutants n It is an important method of recognizing hazards early and offers insight into the extent of pollution for a limited number of compounds at the place from which the sample was taken.

3 -Identifying biomarkers for pollution in ecosystems n The biomarker approach aims to measure a biological response to a chemical as a parameter that provides information on exposure and on adverse effects that sometimes happen. n Examples to different levels of biomarkers are TCDD binding to Ah receptor and induction of mono-oxygenases.

4 -Biological monitoring n n n It attempts to analyze various parameters of natural populations that reflect the situation in the field. The approaches involve the description of the community (e. g. number and species composition). The concentrations of pollutants in indicator organisms. The assessment of the effects on the concentration -effect basis. The detection of genetically different strains in which the resistance has evolved.

5 -Modeling of data from population study n n Finally, in population dynamic, an effort is made to interpret data on the number and development of populations with respect to cause and effect. This demands complex modeling of data using parameters and information that are generated from the other levels of toxicity testing, field observations, and the natural development of populations in the environment.

RADIATION HAZARDS AND TOXICITY Sources of radiation: Radioactive materials n n are being increasingly used in: Medicine. Industry. Agriculture. Power generating reactors.

Sources of environmental radiation pollution may be: a) Natural pollution 1 -- Cosmic rays from the space and the external terrestrial radionuc 1 ides composed mainly of the emission from 238 uranium, 235 uranium and 232 thorium in the geochemical environment. 2 --Solar radiation.

b) Anthropogenic pollution 1 -- Nuclear reactors. 2 -- Nuclear explosions. 3 -- Industrial units using radioactive materials. 4 --Medical units using radioisotopes for diagnosis and cancer chemotherapy. 5 -- Research units handling radioisotopes.

Mechanism and pathogenesis: n n Radiation toxicity represents a dynamic interaction with matter by direct or indirect processes to form ion pairs. These ion pairs rapidly interact with themselves and surrounding molecules to produce free radicals (OH and H) which react with cellular macromolecules or with each other to form hydrogen peroxide, a strong oxidizing agent. n The interaction of these free radicals or H 2 O 2 with cellular macromolecules such as nucleic acids, amino acids, proteins; lipids, thiols or carbohydrates leads to a variety of damages. As

1. 2. DNA strands break, point mutation and chromosomal aberrations and subsequent loss of those gene products. If these gene products are required by the cell to maintain itself, it will eventually result in cell death. The rate of chromosomal aberrations is directly related to radiation dose. Chromosomal aberrations are still evident in the lymphocyte chromosomes of Japan's atomic bomb survivors or in uranium miners.

Radiation toxicity Depending on the level of the exposure the radiation toxicity is divided into: Acute radiation toxicity: Direct and acute exposure to high doses of irradiation results in radiation sickness which is characterized by: n n Signs of acute irritation of the alimentary tract resulting in intense and refractory diarrhea, dehydration and death in some cases, Redness of skin, lot of thirst, weakness, recumbency, rapid respiration, fainting, profuse and bloodstained nasal discharge in others.

n n n Almost after one week, there is severe depression of bone marrow as reflected by lymphopenia and depression of granulocytes and thrombocytes. Blood c 1 otting and antibody production is impaired, followed by anemia and necrosis of gastrointestinal tract wall, hair start falling , ulceration of skin, secondary bacterial infections, degenerative changes in lens of eye (cataract). High rate of mutations, tumors mostly of haemopoietic system, particularly leukemia. Death in a few days due to dehydration and salt depletion. Most of the deaths in acute and sub- acute cases occur in, 1 -4 weeks of irradiation.

Sub-acute radiation toxicity Following exposure to median doses of radiation, there is initial phase of radiation sickness which is characterized by: n Anorexia, vomition, depression and weakness, lasting for several hour to several days. n It is followed by fever, swelling of legs, diarrhoea, dysentery, polydipsia, recumbency and hyperirritability. n Severe anaemia and septicemia in terminal stages and death in about 3 weeks time.

n n Fetal death and resorption, teratogenesis, decreased survival of the young ones born alive and stunted growth are observed. Other signs in the survivors are alopecia, sterility, tumors, especially of the haemopoietic system and skin injury.

Chronic radiation toxicity n It is generally due to continuous contamination of pasture with the fall out of radioactive material. Effects depend on the level of concentration of the radioactive material consumed. n The effects differ depending on the radioactive material e. g. radioactive iodine damages thyroid glands, strontium bone tissues etc.

n n Both these are excreted in the milk of animals and sometimes, their levels are too high. Consumption of milk and meat of such animals in turn adversely affects human health. Alopecia, sterility, tumors of haemopoietic system (leukemia), thyroid, breast and lungs and teratogenesis and stunted growth are the main clinical signs of chronic exposure.

General post mortem findings: (i) Haemorrhagic to ulcerative gastroenteritis. (ii) Ulceration of pharyngeal mucosa. (iii) Pulmonary oedema. (iv) Extravasations of fluids. (v) Fibrinous pneumonia and pericarditis. (vi) Degeneration of bone marrow and lymphoid tissues.

Diagnosis: (i) History of exposure to irradiation or radioactive materials. (ii) Clinical signs. (iii) Post mortem lesions.

Prevention: n Prevention is the best strategy. Treatment: n No specific treatment is available. Give only the symptomatic treatment long with supportive therapy.