Environmental cancer in the Indian context

Summary

There is increasing global concern on the upward trend of cancer attributable to environmental causes. This has found articulate expression in the intensive action programme initiated in developed countries to carry out systematic epidemiological surveillance studies on environmental based cancer, to conduct both short-term and long-term studies on experimental animals on the mechanism of induction and to search for preventive measures.

Of all environmental agents, chemicals which have been introduced by man have received the maximum attention on account of the fact that besides functioning per se as carcinogens, many chemicals can play roles of synergists, promotors, or procarcinogens. The total number of chemicals in wide use today will be more than a million but hardly a thousand of them has been subjected to the vigorous three animal safety evaluation according to Brigg.

Developmental programmes initiated in post-independence India in the last three decades include industrialisation and modernisation of agriculture. So far as industrialisation is concerned, the major units have grown round certain urban centres or in settlements which have become identifiable pockets of high levels of air and water pollution. Data on air pollution inventory provided by NEERI and other agencies indicate a high content of polycyclic hydrocarbons, including 3,4-benzpyrenes especially in Bombay and Calcutta. The marginal health surveys conducted in these metropolitan cities have attempted only correlation between high incidence of respiratory disorders to particulate or gaseous pollutants.

The modernisation of agriculture, particularly boosting of farm productivity, involves greater and greater use of past control chemicals and synthetic fertilisers. Chlorinated pesticides are also being used in massive quantities for controlling vector-borne epidemics. The evidence for an unusually high body burden of organochlorine pesticide residues in Indians has been documented. Many of them have been shown to be carcinogenic to experimental animals. Relatively high levels of residues of organochlorine have been detected in placentae, cord blood, and breast milk.

The presence of high levels of suspected particulate matter (SPM) made up of industrially released pollutant in industrial areas, or air-borne pollens and microbial or fungal spores or the minute fugitive dust particles is also a problem of concern to us in this country. Besides health effects caused by them per se, they can act as nuclei for absorption of NO₂ released from industrial activity or from bacterial reduction of nitrate fertilisers. Ideal matrices are formed for chain photochemical reaction triggered by solar or other cosmic irradiation giving rise to nitrosamines, free radicals, etc. Water used for potable purposes in some rural areas has been shown to contain relatively high nitrate and nitrite content.

Occupational exposure to carcinogenic chemicals has also received some attention. Sporadic surveys have been conducted for the ulceration of the nose and septum in workers handling chromate salts (valency vi) or bladder tumors in anthracene dyes. Detailed analysis of environment related morbidity and mortality data has not yet been attempted to build models for the purpose of predictive epidemiology. Welders are exposed to fumes of heavy metals including those of chromium and nickel. The intake of nickel through leafy vegetables and hydrogenated vegetable oils has been considered as one possible source of bioaccumulation of this carcinogenic metal.

In the absence of data banks or registry of reliable morbidity/mortality data in humans, the Industrial Toxicology Research Centre has made a partial survey of the dust load of lungs of food animals killed in abbatoirs in the industrial and mining areas of Bihar and West Bengal. Blocking of lymph nodes by dust has been observed in most of the animals and analysis of the dust collected from lung by X-ray fluorescence spectroscopy has revealed the presence of many toxic metals. The Outdoor Occupational Clinic run by the Industrial Toxicology Research Centre in ESI Hospital at Kanpur has recorded cases of skin allergy due to chromium.