[Nitrates in drinking water and cancer].

Nitrates originating from food and particularly from water are supposedly precursors of carcinogenic N-nitroso compound (NOC) formed within the organism. According to Correa and al. these transformations could be a consequence of bacterial gastric pollution resulting from certain hypochlorhydric conditions. Much epidemiological research has tried to establish a relationship between exposure to nitrates in drinking water and cases of gastric cancer. The present article deals with research into this relationship in France, in a region where the rate of nitrates in water supplies is among the highest. Death statistics (from cancers of the digestive and urinal tracts) are issued by INSERM and these of the population by INSEE. Towns are classified according to nitrate concentration and the number of deaths is established according to tumour detection by sex and age. Research into death rate divergencies is found by chi 2 and the correlated coefficient. The average relative risk for any age group is calculated for all types of cancer. Research on frequency is carried out from tumour records. Comparative frequency rates are established by direct standardisation according to the structural age of any one European population. Results are analysed in relation to (1) mortality rates and (2) incidence rates. (1) None of the cancers studied, be they of the digestive or urinary systems, whatever the age on sex, is significantly linked to the quantity of nitrates in water supplies. When all these cancers are taken into account, the death rate does not vary significantly for increasing concentration of nitrates. Towns exceeding the maximum concentration permitted by law do not have a higher mortality rate than other towns. The overall can incidence rate in the Nord-Pas-de-Calais regions of France is 11.8 per 100,000 inhabitants. The average European rate is 18.3 per 100,000 for men in the Nord region and 20.5 in the Pas-de-Calais; for women, 5.9 and 7.2 respectively. These rates are comparable to those in other French regions. The incidence rate for gastric cancer is not significantly different for inhabitants of towns exposed to water containing more or less than 50 mg/l. The absence of links between cancer and nitrates water research into possible methodological expedients necessary. A certain number of factors (consumer habits, diet, population mobility) can, for the same concentration of nitrates, modify the actual quantity consumed, and so the corresponding long-term risk. However, no inverse effect of these factors which would be susceptible to counter the link to the extent of concealing it, is know for the moment.(ABSTRACT TRUNCATED AT 400 WORDS)