Sewage hardness and mortality from cancer and cardiovascular disease

Data on sewage hardness (reflective of municipal drinking water hardness) and its major determinants, cadmium and magnesium, were obtained from analyses of sewage and sludge conducted in 1979-80 in 25 Standard Metropolitan Statistical Areas in the U.S.A. Mortality and population statistics on cancer and cardiovascular disease in these areas related to 1970. Simple correlation analysis used for preliminary screening was followed by multiple regression analyses using confounding variables as covariates. Statistics revealed positive associations between sewage hardness characteristics and death from arteriosclerosis (both sexes) and ischaemic heart disease (males only). Sewage hardness characteristics were negatively associated with death rates for leukaemia and prostate cancer in males, and total cancer in both sexes. However, employment in manufacturing industry, smoking, education and the percentage of non-whites in the population were also important variables in cancer correlations. The water hardness variable could be merely coincidental. Higher cancer mortality rates tended to occur in populations from urban and industrial areas with a higher proportion of non-whites.