STUDY OBJECTIVES: To investigate whether exposure to tap water contaminated in a major river pollution incident with 2 ethyl 5,5 dimethyl 1,3 dioxane (EDD) and 2 ethyl 4 methyl 1,3 dioxolane (EMD) was associated with an increase of self reported symptoms. To assess the extent of association between noticing the water had an unusual taste or odour and self reported symptoms. DESIGN: Retrospective cohort study. SETTING: A city and two nearby towns in a semi-rural area of England, UK. PARTICIPANTS: A total of 3861 people who replied to a postal questionnaire asking about symptoms and water consumption sent to a sample of 1000 households in each of three areas--one area supplied with contaminated water (study group) and two control areas that were unaffected (control groups). MAIN RESULTS: The household response rates were 65% for the study group and 56% and 57% for the two control groups. Self reporting of 10 individual symptoms was significantly increased in the study group compared with controls. Within the study group, reporting of one or more symptoms was significantly higher in subjects who consumed contaminated water but not among subjects who used it to wash or cook. Subjects who drank contaminated water showed a dose-response relationship for self reporting of one or more symptoms and for seven individual symptoms. Within the study group, however, only 62% (867 of 1398 subjects) noticed that the water had an unusual taste or odour. Among subjects who did not notice that the water had an unusual taste or odour, no association was found between drinking contaminated water and reporting one or more symptoms, or between drinking contaminated water and reporting of individual symptoms, although a dose-response relationship was shown between the amount of water consumed and self reporting of nausea. Among subjects who noticed the water had an unusual taste or odour, both an association and a dose-response relationship were found between consumption of contaminated water and the self reporting of six symptoms--diarrhoea, nausea, headache, stomach pains, skin irritation, and itchy eyes. CONCLUSIONS: Higher rates of symptom reporting were associated with the water contamination incident. Reported symptoms seemed, however, to be associated with the ability to detect an unusual taste or odour in the water. Because concentrations of the contaminants would be expected to be evenly distributed in the tap water in the affected area, irrespective of taste or odour, and because of the known toxicity of the parent compounds of EMD and EDD, it is concluded that the increase in self reported symptoms in the study group respondents was associated with noticing the unpleasant taste or odour of the tap water and not with the chemical contamination. It is concluded that the observed increase in reporting of nausea with increasing water consumption was due to public anxiety caused by the incident but did not pose a serious risk to the public's health. The increase in self reported symptoms in the area affected by the contamination was an important reminder of the wider health implications of "health scares".
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