Environmental Problems


Can environmental problems cause cancer?
Yes.
More and more indicators are pointing to this tragic fact.

A BRIEF HISTORY

  • Within 6 years of the discovery of x-rays – A relationship between skin cancer and radiation exposure was established.
  • An association between leukemia and radiation was suspected a few years later.
  • In 1931, Martland first suspected induction of cancers in humans by ingested radio nuclides, from a study of radium dial painters.

Radiation protection standards in pioneering days were based largely on early effects, such as skin reaction, but the risk of cancer induction is now the dominant factor that determines occupational exposure limits.

 

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Other Hazards

What are the other environmental hazards which can lead to cancer?
Physical factors in the development of occupational cancer
Ionizing radiation:

  • Life on Earth has evolved against a background of ionizing radiation arising from cosmic rays & from radioactivity in the Earth.
  • In addition, the human population is now exposed to various human made or human enhanced sources.
  • Radiation is said to be ionizing if it has sufficient energy to eject one or more orbital electrons from an atom or molecule.
  • The important characteristic of ionizing radiation is the local release of large amounts of energy, sufficient to break strong chemical bonds that are biologically important.
  • Electromagnetic.
    • X-rays
    • Gamma rays
  • Particulate
    • Alpha particles
    • Beta particles
    • Charged particles
      • Electrons
      • Protons
  • Various sources of radiation:
    • RADON 55 %.
    • COSMIC 8 %.
    • TERRESTIAL 8 %.
    • INTERNAL 11 %.
    • MEDICAL X RAYS 11 %.
    • NUCLEAR MEDICINE 4 %.
    • CONSUMER PRODUCTS 3 %.
    • OTHERS 1 %.
  • Radon – what is it?
    • Only a recent discovery.
    • The home & the work place are the main sources.
    • It is a naturally occurring radioactive gas which emanates from the ground.
    • In the home & the work place, it decays to short lived radioactive progeny that attach to aerosol particles & which are      deposited in the tracheo-bronchial tree (the airways).
    • It’s progeny, Polonium 218 & 214, are the main concerns; they produce alpha particles which cause lung cancer
  • EVEN MORE DANGEROUS - THORON?
    • Very serious.
    • In the USA, number of lung cancer cases due to radon range from 4,000 to 50,000 per year.
    • In India, no studies or statistics are available.
    • The Environmental Protection Agency (EPA) recommends an annual average dose of 4pCi/L of air as the levels at home at which remedial measures have to be taken.
    • By these levels, number of factory workers & domestics likely to be hit by radon / thoron in this country – 8 to 12 %

Physical factors in the development of cancer.

  • Ultraviolet radiation carcinogenesis
    • The most common cancers in the world are skin cancers.
    • 500,000 cases diagnosed annually in India alone.
    • Solar ultraviolet rays are DNA damaging.
    • Skin cancer due to ultraviolet ray exposure at work has reached epidemic proportions.
    • Ozone depletion has also led to this phenomenon
  • Asbestos
    • Broad commercial term for a group of naturally occurring hydrated mineral silicates that crystallize in a fibrous habit.
    • Cancers caused by asbestos.
      • Lung cancer.
      • Mesothelioma – almost path gnomonic of fiber induced carcinogenesis
      • City dwellers also breathe in lot of asbestos fiber from shredding car brakes.
      • Mesothelioma killed 24 asbestos workers in USA in 1960; in 1980, it killed 3000.
      • The amphibole variety of asbestos is the main culprit.
      • It is a non genotoxic carcinogen which directly attacks the cells.
  • Electric & magnetic fields
    • Not enough scientific evidence is available.
    • Field interactions are too weak.
    • Unlike X rays, power frequency fields do not break chemical bonds.
    • Unlike microwaves, power frequency fields cannot cause significant tissue heating
    • On the flip side are the pigeons, the eels & the whales, generating homing signals form electromagnetic impulses.
    • There is obviously a yet unknown area of the brain which is exquisitely sensitive to these fields.
  • Hyperthermia & erythema abigne
    • Hyperthermia refers to the phenomenon of over exposure to heat.
    • Erythema ab igne is a macular reticulated skin discoloration (flat and lined) seen after heat exposure, either      conductive or radiative.
    • Commonly seen on the anterior aspects of the legs of older people who sit close to fires for a long time or use hot      water bottles or heating pads or spend a lot of their life close to boilers & furnaces.
    • It is a highly premalignant condition which must be monitored closely.
    • In India, it is commonly seen amongst Kangri hill folk of Himachal Pradesh, who frequently develop a skin cancer called 'Kangri Cancer'. They develop it in the region of the mid abdomen, which gets exposed to the severe heat being generated from the Kangri, which they carry around to ward off heat.

Cancer is a real force to reckon with in many occupations (including our own) & comes in many disguises.

Screening of the susceptible & education of the industries is the major battle ahead.

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Chemical and Industrial Pollution

  • The extent to which chemical exposures contribute to cancer incidence was not fully appreciated until population based studies documented differing organ specific cancer rates among geographically different populations.
  • Changes in cancer frequency among migrating ethnic groups, high cancer rates associated with specific occupations & the high risk of smoking associated cancers confirmed that environmental, lifestyle & occupational exposures were major determinants of human cancer risk.
  • Individual genetic factors influence cancer risk in several ways. The general public carries hereditary susceptibility genes (genes inherited from parents which are susceptible to development of cancer) that increase cancer risk for particular occupational exposures.
  • Thus most human cancer is not simply a genetically determined sequelae of aging; rather they are the manifestations of     personal & cultural behavior, superimposed on individually determined hereditary susceptibility.
  • Although a wide variety of chemicals can cause cancer in humans, the processes involved are very specific.
  • Most chemicals are not carcinogenic (cancer causing), & within chemical classes themselves, even stereo isomers(chemicals with almost mirror image structures) may vary widely in carcinogenecity.

 

Types of carcinogens.
Genotoxic carcinogens

These have high chemical reactivity. DNA , the basic content in genetic material is the ultimate target for most such carcinogens. Common examples.

  • N – nitroso compounds.
  • Aliphatic epoxides.
  • Aflatoxin.
  • Mustards.
  • Polycyclic aromatic hydrocarbons.
  • Combustible fossil fuel products.
  • Combustible vegetable products.
  • Aryl aromatic amines.
  • Amino azo dyes.
  • Heterocyclic aromatic amines.

 

Non genotoxic carcinogens.
Require high doses and prolonged exposure. Mechanism of action is controversial Cause toxic cell death & regenerative hyperplasia (cells do regrow after damage, but in a normal, healthy manner). Also believed to have hormonal effects, effecting hormone dependent tissue directly. Act as modifiers in concert with genotoxic agents Some examples.

 

  • Herbicides.
  • Pesticides.

Known /suspected chemical carcinogens in humans.

 

Target organ Agent(s) Industry Tumor type
Bladder 4 amino biphenyl,
benzidine, 2-napthylamine
Magenta manufacture TCC (transitional cell carcinoma)
Prostate Cadmium compounds Auramine manufacture, paints, heavy metals Adenocarcinoma
Skin Arsenic, benzo(a)pyrene, coal tar pitch, mineral oils, soot Coal gasification, coke production Squamous carcinoma Basal cell carcinoma
Bone marrow Benzene, ethylene oxide Rubber workers Leukemia
Lung Smoke, arsenic, asbestos, crystalline silica, benzo(a)pyrene, bis(chloro)methyl ether, 1,3, butadiene, chromium6 compounds, coal tar & pitch products, nickel compounds, soots, mustard gas Aluminium, coal gasification, coke production, hematite mining, painters Mesothelioma
Oral cavity Smoke, nickel compounds Boot / shoe production, furniture manufacturers, isopropyl alcohol production Squamous carcinoma
Stomach Smoked, salted & pickled food Rubber industry Adenocarcinoma.
Colon Heterocyclic amines, asbestos Pattern makers Adenocarcinoma.
Liver Vinyl chloride Paints & plastics Hepatocellular carcinoma, Hemangiosarcoma

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