Environmental Diseases Notes

Environmental Diseases

Some of the important factors which have led to alarming environmental degradation are as under:

1. Population explosion
2. The urbanisation of rural and forest land to accommodate the increasing numbers
3. Accumulation of wastes
4. Unsatisfactory disposal of radioactive and electronic waste
5. Industrial effluents and automobile exhausts.

Read And Learn More: General Pathology Notes

But the above atmospheric pollutants appear relatively minor compared with voluntary intake of three pollutants—use of tobacco, consumption of alcohol and intoxicant drugs.

The WHO estimates that 80% of cases of cardiovascular disease and type 2 diabetes mellitus, and 40% of all cancers are preventable through ‘three pillars of prevention’: avoidance of tobacco, healthy diet, and physical activity.

The WHO has further determined that about a quarter of the global burden of diseases and 23% of all deaths are related to modifiable environmental factors.

Infant mortality related to environmental factors in developing countries is 12 times higher than in developed countries.

Attempts at prohibition of alcohol in some states in India have not been quite effective due to difficulty in implementation. Instead, prohibition has only resulted in an off-and-on catastrophe of ‘hooch tragedies’ in some parts of this country due to illicit liquor consumption.

The present discussion on environmental is covered under the following major headings:

1. Environmental pollution:
   • Air pollution
   • Environmental chemicals
   • Tobacco smoking
2. Chemical and drug injury:
   • Therapeutic (iatrogenic) drug injury
   • Non-therapeutic toxic agents (For example, Alcohol, Lead, Carbon monoxide, Drug abuse)
   • Environmental chemicals
3.  Injury by physical agents:
   • Thermal and electrical injury
   • Injury by ionising radiation

Environmental Pollution

The environment is air we collectively breathe and share with others at all places—outside, inside homes and at work place.

Pollution is the contamination of the natural environment which determines adverse effects on health. Any agent—chemical, physical or microbial, that alters the composition of the environment is called a pollutant.

In addition, our personal environment gets affected by smoking of tobacco, water we drink and the food we eat.

Thus, the subject of environmental pollution is briefly reviewed below under 3 headings:

• Air pollution
• Environmental chemicals and
• Tobacco smoking.

Air Pollution

For the survival of mankind, it is important to prevent the depletion of the ozone layer (O₃) in the outer space from pollutants such as chlorofluorocarbons and nitrogen dioxide.

• Produced in abundance by day-to-day activities on our planet earth due to industrial effluent and automobile exhausts.
• A vast variety of pollutants are inhaled daily, some of which may cause trivial irritation to the upper respiratory pathways, while others may lead to acute or chronic injury to the lungs, and some are implicated in the causation of lung cancer.
• Whereas some pollutants are prevalent in certain industries (such as coal dust, silica, and asbestos), others are general pollutants present widespread in the ambient atmosphere (for example Sulphur dioxide, nitrogen dioxide, and Carbon monoxide).
• The latter group of environmental pollutants is acted upon by sunlight to produce secondary pollutants such as ozone and free radicals capable of oxidant cell injury to respiratory passages.
• In highly polluted cities where coal consumption and automobile exhaust accumulate in the atmosphere, the air pollutants become visible as ‘smog’.
• It has been reported that 6 out of 10 largest cities in India have such severe air pollution problem that the annual level of suspended particles is about three times higher than the WHO standards.
• An estimated 50,000 persons die prematurely every year due to high levels of pollution in these cities.

The adverse effects of air pollutants on lung depend upon a few factors that include:

• Longer duration of exposure
• Total dose of exposure
• Impaired ability of the host to clear inhaled particles, and
• Particle size of 1-5 µm capable of getting impacted in the distal airways to produce tissue injury.

Pneumoconiosis—the group of lung diseases due to occupational over-exposure to pollutants.

 Environmental Chemicals

Our environment gets affected by long-term or accidental exposure to certain man-made or naturally-occurring chemicals.

• A large number of chemicals are found as contaminants in the ecosystem, food and water supply and find their way into the food chain of man.
• These substances exert their toxic effects depending upon their mode of absorption, distribution, metabolism and excretion. Some of the substances are directly toxic while others cause ill effects via their metabolites.
• Environmental chemicals may have slow damaging effects or there may be sudden accidental exposure such as the Bhopal gas tragedy in India due to accidental leakage of methyl isocyanate (MIC) gas in December 1984.

Some of the common examples of environmental chemicals are given below:

• Agriculture chemicals:  Modern agriculture thrives on pesticides, fungicides, herbicides and organic fertilisers which may pose a potential acute poisoning as well as long-term hazard.
  • The problem is particularly alarming in developing countries like India,
  • China and Mexico where farmers and their families are unknowingly exposed to these hazardous chemicals during aerial spraying of crops.
  • Acute poisoning by organophosphate insecticides is quite well known in India as an accidental or suicidal poison by inhibiting acetylcholinesterase and sudden death.
  • Chronic human exposure to low-level agricultural chemicals is implicated in cancer, chronic degenerative diseases, congenital malformations and impotence but the exact cause-and-effect relationship is lacking.
  • According to the WHO estimates, about 7.5 lakh people are taken ill every year worldwide with pesticide poisoning, half of which occur in the developing countries due to ready availability and indiscriminate use of hazardous pesticides which are otherwise banned in developed countries.
  • Pesticide residues in food items such as in fruits, vegetables, cereals, grains, pulses etc. is of greatest concern.
• Volatile organic solvents: Volatile organic solvents and vapours are used in industry quite commonly and their exposure may cause acute toxicity or chronic hazard, often by inhalation than by ingestion. Such substances include methanol, chloroform, petrol, kerosene, benzene, ethylene glycol, toluene etc.
• Metals: Pollution by occupational exposure to toxic metals such as mercury, arsenic, cadmium, iron, nickel and aluminium are important hazardous environmental chemicals.
• Aromatic hydrocarbons: The halogenated aromatic hydrocarbons containing polychlorinated biphenyl which are contaminants in several preservatives, herbicides and antibacterial agents are a chronic health hazard.
• Cyanide: Cyanide in the environment is released by the combustion of plastic, and silk and is also present in cassava and the seeds of apricots and wild cherries. Cyanide is a very toxic chemical and kills by blocking cellular respiration by binding to mitochondrial cytochrome oxidase.
• Environmental dusts: These substances causing pneumoconioses while others are implicated in cancer.

Tobacco Smoking

Habits:

Tobacco smoking is the most prevalent and preventable cause of disease and death. The harmful effects of smoking pipe and cigar are somewhat less.

• Long-term smokers of filter-tipped cigarettes appear to have 30-50% lower risk of development of cancer due to reduced inhalation of tobacco smoke constituents.
• Cigarette smoking is a major health problem all over the world. In India, a country of over 1.30 billion people, a quarter (about 330 million) are tobacco users in one form or the other
• Smoking bidis and chewing pan masala, zarda and gutka are more widely practised than cigarettes.
• The habit of smoking chute (a kind of indigenous cigar) in which the lighted end is put in mouth is practised in the
• The Indian state of Andhra Pradesh is associated with higher incidence of squamous cell carcinoma of the hard palate.

Another habit prevalent in the Indian states of Uttar Pradesh and Bihar is chewing of tabacco alone or mixed with slaked lime as a bolus of paan kept in the mouth for long hours which is the major cause of cancer of the upper aerodigestive tract and oral cavity.

Hookah smoking, in which tobacco smoke passes through a water-filled chamber which cools the smoke before it is inhaled by the smoker, is believed by some reports to deliver less tar and nicotine than cigarettes and hence fewer tobacco-related health consequences.

In view of serious health hazards of tobacco, the WHO launched Tobacco Free Initiative in 2002. India enacted a law in 2008 banning smoking at all public places, imposing the world’s biggest smoking ban which is showing favourable results.

In the US, Canada and most European countries, health awareness by people has resulted in a decline in tobacco smoking by about 20%.

Besides the harmful effects of smoking on active smokers themselves, involuntary exposure of smoke to bystanders (passive smoking) is also injurious to health, particularly to infants and children.

Dose and Duration:

Tobacco contains several harmful constituents which include nicotine, many carcinogens, carbon monoxide and other toxins).

• The harmful effects of smoking are related to a variety of factors, the most important of which is dose of exposure expressed in terms of pack years.
• For example, One pack of cigarettes daily for 5 years means 5 pack years. It is estimated that a person who smokes 2 packs of cigarettes daily at the age of 30 years reduces his life by 8 years than a non-smoker.
• On cessation of smoking, the higher mortality slowly declines and the beneficial effect reaches the level of non-smokers after 20 or more of smoke-free years.

Tobacco-related Diseases:

Tobacco contains numerous toxic chemicals having adverse effects varying from minor throat irritation to carcinogenesis. Some of the important constituents of tobacco smoke with adverse effects are given in table. Overall, about 30% of all cancer cases in India are tobacco-related.

The relative risk of major diseases in tobacco smokers compared from non-smokers and accounting for higher mortality include the following (in descending order of frequency):

• Cancer of the lung: 12 to 23 times.
• Chronic obstructive pulmonary disease (COPD): 10-13 times.
• Cancers of the upper aerodigestive tract (larynx, pharynx, lip, oral cavity, oesophagus): 6 to 14 times.
• Aortic aneurysm: 6-7 times.
• Other cancers by systemic effects (kidneys, pancreas, urinary bladder, stomach, cervix): 2-3
  times.
• Cerebrovascular accidents (CVA): 2-4 times.
• Coronary heart disease: 2 to 3 times relative risk.
•  Sudden infant death syndrome: 2 times.
• Buerger’s disease (thromboangiitis obliterans).
• Peptic ulcer disease with 70% higher risk in smokers.
• Early menopause in smoker women.

Major constituents of tobacco smoke with adverse effects:

• In smoking pregnant women, higher risk of lower birth weight of the foetus, higher perinatal mortality and intellectual deterioration of the newborn.

Environmental Pollution:

The adverse effects of air pollutants on lung depend upon the duration of exposure, the total dose of exposure, the impaired ability of the host to clear inhaled particles and particle size of 1-5 µm.

The effects may range from trivial upper respiratory irritation to pneumoconiosis.

• Our environment gets affected by long-term or accidental exposure to certain man-made or naturally-occurring chemicals for example, Pesticides, volatile organic solvents, toxic metals, aromatic hydrocarbons, cyanide and several environmental dusts.
• Cigarette smoking is a major health problem all over the world. Its effects depend upon the dose and duration.
• Smoking is strongly implicated in many cancers (lung, upper aerodigestive tract, kidneys, pancreas, urinary bladder, cervix) and there is an increased incidence of certain non-neoplastic diseases (coronary artery disease, cerebrovascular accidents, Buerger’s disease, COPD, peptic ulcer)

Chemical And Drug Injury

During life, each one of us is exposed to a variety of chemicals and drugs.

These are broadly divided into the following two categories:

1. Therapeutic (iatrogenic) agents for example Drugs, which when administered indiscriminately are associated with adverse effects.
2. Non-therapeutic agents for example Alcohol, Lead, Carbon monoxide, Drug abuse.

1. Therapeutic (Iatrogenic) Drug Injury:

Though the basis of patient management is rational drug therapy, nevertheless adverse drug reactions do occur in 2-5% of patients. In general, the risk of adverse drug reactions increases with increasing number of drugs administered.

Adverse effects of drugs may appear due to:

• Overdose
• Genetic predisposition
• Exaggerated pharmacologic response
• Interaction with other drugs; and
• Unknown factors.

It is beyond the scope of this book to delve into the list of drugs with their harmful effects which forms a separate subject of study. However, some of the common forms of iatrogenic drug injury and the offending drugs are listed in Table.

2. Non-Therapeutic Toxic Agents

1. Alcoholism:

• Chronic alcoholism is defined as the regular imbibing of an amount of ethyl alcohol (ethanol) that is sufficient to harm an individual socially, psychologically or physically.
• It is difficult to give the number of ‘drinks’ after which the diagnosis of alcoholism can be made because of differences in individual susceptibility.
• However, adverse effects acute as well as chronic, are related to the quantity of alcohol content imbibed and duration of consumption.
• Generally, 10 gm of ethanol is present in:
  • One can of beer (or half a bottle of beer);
  • 120 ml of neat wine; or
  • 30 ml of 43% liquor (small peg).
• A daily consumption of 40 gm of ethanol (4 small pegs or 2 large pegs) is likely to be harmful; intake of 100 gm or more daily is certainly dangerous.
• Daily and heavy consumption of alcohol is more harmful than moderate social drinking having gap periods, because the liver where ethanol is metabolised, gets time to heal.

Metabolism:

Absorption of alcohol begins in the stomach and small intestine and appears in blood shortly after ingestion. Alcohol is then distributed to different organs and body fluids proportionate to the blood levels of alcohol.

About 2-10% of absorbed alcohol is excreted via urine, sweat and exhaled through breath, the last one being the basis of breath test employed by law-enforcement agencies for alcohol abuse.

Metabolism of alcohol 646); In brief alcohol is metabolised in the liver by the following 3 pathways:

1. The major rate-limiting pathway of alcohol dehydrogenase (ADH) in the cytosol, which is then quickly destroyed by aldehyde dehydrogenase (ALDH), especially with low blood alcohol levels.
2. Via microsomal P-450 system (microsomal ethanol oxidising system, MEOS) when the blood alcohol level is high.
3. Minor pathway via catalase from peroxisomes.

Iatrogenic drug injury:

In any of the three pathways, ethanol is biotransformed to toxic acetaldehyde in the liver and finally to carbon dioxide and water by acetyl coenzyme A.

Harmful Effects of Alcoholism:

Alcohol consumption in moderation and socially acceptable limits is practiced mainly for its mood-altering effects. Heavy alcohol consumption in unhabituated person is likely to cause acute mill-effects on different organs.

Though the diseases associated with alcoholism are discussed in respective chapters later, the spectrum of ill-effects is outlined below.

• Acute Alcoholism The acute effects of inebriation are most prominent on the central nervous system but it also injures the stomach and liver.
  • Central nervous system:  Alcohol acts as a CNS depressant; the intensity of effects of alcohol on the CNS is related to the quantity consumed and duration over which consumed, which are reflected by the blood levels of alcohol:
    1. Initial effect of alcohol is on subcortical structures which is followed by disordered cortical function, motor ataxia and behavioural changes.
    2. These changes are apparent when blood alcohol level does not exceed 100 mg/dl which is the upper limit of sobriety in drinking as defined by law-enforcing agencies in most Western countries while dealing with cases of driving in drunken state.
    3. Blood level of 100-200 mg/dl is associated with depression of cortical centres, lack of coordination, impaired judgement and drowsiness.
    4. Stupor and coma supervene when blood alcohol level is about 300 mg/dl.
    5. Blood level of alcohol above 400 mg/dl can cause anaesthesia, depression of medullary centre and death from respiratory arrest.
    6. However, chronic alcoholics develop CNS tolerance and adaptation and, therefore, can, withstand higher blood levels of alcohol without such serious effects.
    7. Stomach:  Acute alcohol intoxication may cause vomiting, acute gastritis and peptic ulceration.
    8. Liver:  Acute alcoholic injury to the liver is explained.

• Chronic Alcoholism: Chronic alcoholism produces widespread injury to organs andsystems.
  • Contrary to the earlier belief that chronic alcoholic injury results from nutritional deficiencies.
  • It is now known that most of the alcohol-related injury to different organs is due to toxic effects of alcohol and accumulation of its main toxic metabolite, acetaldehyde, in the blood.
  • Other proposed mechanisms of tissue injury in chronic alcoholism are free-radical mediated injury and genetic susceptibility to alcohol-dependence and tissue damage.
  • Some of the more important organ effects in chronic alcoholism are as under:

1. 1. 1. Liver:  Alcoholic liver disease and cirrhosis are the most common and important effects of chronic alcoholism.
      2. Pancreas:  Chronic calcifying pancreatitis and acute pancreatitis are serious complications of chronic alcoholism.
      3. Gastrointestinal tract:  Gastritis, peptic ulcer and oesophageal varices associated with fatal massive bleeding may occur.
      4. Central nervous system:  Peripheral neuropathies and Wernicke-Korsakoff syndrome, cerebralatrophy, cerebellar degeneration and amblyopia (impaired vision) are seen in chronic alcoholics.
      5. Cardiovascular system:  Alcoholic cardiomyopathy and beer-drinkers myocarditis with consequent dilated cardiomyopathy may occur. Level of HDL (atherosclerosis-protective lipoprotein), however, has been shown to increase with moderate consumption of alcohol.
      6. Endocrine system:  In men, testicular atrophy, feminisation, loss of libido and potency, and gynecomastia may develop. These effects appear to be due to lowering of testosterone levels.
      7. Blood:  Haematopoietic dysfunction with secondary megaloblastic anaemia and increased red blood cell volume may occur.
      8. Immune system:  Alcoholics are more susceptible to various infections.
      9. Cancer:  There is higher incidence of cancers of upper aerodigestive tract in chronic alcoholics but the mechanism is not clear.

2. Lead Poisoning

Lead poisoning may occur in children or adults due to accidental or occupational ingestion.

• In children: Children following are the main sources of lead poisoning:
  • Chewing of lead-containing furniture items, toys or pencils.
  • Eating lead paint flakes from walls.
• In adults: Adults the sources are as follows:
  • Occupational exposure to lead during spray painting, recycling of automobile batteries (lead oxide fumes), mining, and extraction of lead.
  • Accidental exposure by contaminated water supply, house freshly coated with lead paint and sniffing of lead-containing petrol (hence unleaded petrol introduced as fuel).
  • Lead is absorbed through the gastrointestinal tract or lungs.

The absorbed lead is distributed in two types of tissues :

1. Bones, teeth, nails and hair representing relatively harmless pool of lead.  About 90% of absorbed lead accumulates in the developing metaphysis of bones in children and appears as areas of increased bone densities (‘lead lines’) on X-ray. Lead lines are also seen in the gingiva.
2. Brain, liver, kidneys and bone marrow accumulate the remaining 10% lead which is directly toxic to these organs. It is excreted via kidneys.

Lead toxicity occurs in the following organs predominantly:

• Nervous system:  The changes are as under:
  • In children, lead encephalopathy; oedema of the brain, flattening of gyri and compression of ventricles.
  • In adults, demyelinating peripheral motor neuropathy typically affects radial and peroneal nerves resulting in wrist-drop and foot-drop respectively.

• Haematopoietic system:  The changes in the blood are quite characteristic:
  • Microcytic hypochromic anaemia is due to the inhibition of two enzymes: delta-aminolevulinic acid dehydrogenase required for haem synthesis, and through inhibition of ferroketolase required for incorporation of ferrous iron into the porphyrin ring.
  • Prominent basophilic stippling of erythrocytes.
• Kidneys:  Lead is toxic to proximal tubular cells of the kidney and produces lead nephropathycharacterised by an accumulation of intranuclear inclusion bodies consisting of lead-protein complex in the proximal tubular cells.
• Gastrointestinal tract:  Lead toxicity in the bowel manifests as acute abdomen presenting as lead colic.

3. Carbon Monoxide Poisoning:

Carbon monoxide (CO) is a colourless and odourless gas produced by incomplete combustion of carbon. Sources of CO gas are:

• Automobile exhaust
• Burning of fossil fuel in industries or at home; and
• Tobacco smoke.

CO is an important cause of accidental death due to systemic oxygen deprivation of tissues. This is because haemoglobin has about 200 times higher affinity for CO than for O₂ and thus varying amount of carboxyhaemoglobin is formed depending upon the extent of CO poisoning.

Besides, carboxyhaemoglobin interferes with the release of O₂ from oxy-haemoglobin causing further aggravation of tissue hypoxia. Diagnosis of CO poisoning is, therefore, best confirmed by carboxy-haemoglobin levels in the blood.

CO poisoning may present in 2 ways:

1. Acute CO poisoning in which there is sudden development of brain hypoxia characterised by oedema and petechial haemorrhages.
2. Chronic CO poisoning presents with nonspecific changes of slowly developing hypoxia of the brain.

4. Drug Abuse:

Drug abuse is defined as the use of certain drugs for the purpose of ‘mood alteration’ or ‘euphoria’ or ‘kick’ but subsequently leading to habit-forming, dependence and eventually addiction.

Some of the commonly abused drugs and substances are as under:

• Marijuana or ‘pot’:  Is the psychoactive substance most widely used. It is obtained from the leaves of the plant Cannabis sativa and contains tetrahydrocannabinol (THC). It may be smoked or ingested.
• Derivatives of opium:  Include heroin and morphine. Opioids are derived from the poppy plant. Heroin and morphine are self-administered intravenously or subcutaneously.
• CNS depressants: Include barbiturates, tranquilisers and alcohol.
• CNS stimulants: For example, Cocaine and amphetamines.
• Psychedelic drugs:  (Meaning enjoyable perception-giving) for example, LSD.
• Inhalants:  For example, Glue, Paint thinner, Nail polish remover, Aerosols, and Amyl nitrite.

It is beyond the scope of the present discussion to go into the pharmacologic actions of all these substances. However, apart from the pharmacologic and physiologic actions of these street drugs.

The most common complication is the introduction of infection by the parenteral use of many of these drugs. Sharing of needles by the drug-addicts accounts for the high risk of most feared viral infections in them, AIDS and viral hepatitis (HBV and HCV).

Following are a few common drugs abuse-related infectious complications:

1.  At the site of injection—cellulitis, abscesses, ulcers, thrombosed veins
2. Thrombophlebitis
3. Bacterial endocarditis
4.  High risk for AIDS
5.  Viral hepatitis and its complications
6.  Focal glomerulonephritis
7. Talc (foreign body) granuloma formation in the lungs.

Chemical and Drug Injury:

• Harmful chemicals and drugs can be broadly divided into 2 groups:
  1. Therapeutic (iatrogenic) agents (for example, Drugs, which when administered indiscriminately are associated with adverse effects) and
  2. Non-therapeutic agents (for example Alcohol, Lead, Carbon monoxide, drug abuse).
• Alcoholism may produce acute and chronic effects on the body. The most prominent ill-effect of acute alcoholism is on the central nervous system; other acute effects are on the stomach and liver.
• Chronic alcoholism causes alcoholic liver disease, pancreatitis, and other systemic adverse manifestations pertaining to CNS, CVS, endocrines, blood, and the immune system.
• Lead poisoning may occur in children by eating lead-contaminated items and in adults from occupational or accidental exposure.
• The adverse effects pertain to the nervous system and blood.
• Carbon monoxide poisoning may cause accidental death or may produce chronic effects.
• Drug abuse from marijuana, opium, barbiturates, cocaine, inhalants etc may cause a variety of local and systemic effects.