Water contamination in North Cornwall: a retrospective cohort study into the acute and short-term effects of the aluminum sulphate incident in July 1988.

IN JULY 1988 the drinking water supply of part of Cornwall was contaminated with 20 tons of aluminum sulphate solution. Emergency measures ensured that aluminum sulphate levels in most parts of the water distribution system were rapidly reduced, but residents were supplied with water containing raised concentrations of aluminum and other metals for at least a few days. A retrospective cohort study compared 480 individuals in the exposed area with 532 individuals resident in an area served by a different water supply. The exposed group were more likely to complain of all 18 symptoms in the questionnaire enquiry. They had a significantly higher relative risk of experiencing painful joints. These symptoms were reported by less than a quarter of the respondents exposed to contaminated water. This may represent a previously unrecognised acute effect of water contamination with aluminum sulphate, but the study does not exclude the possibility that the threshold for symptom reporting was lowered by anxiety and by the publicity associated with the incident. The overall response rate of the study was low (45%) and reflects the difficulties in both carrying out and interpreting environmental epidemiological studies of acute incidents.