INTESTINAL EFFECTS OF SULFATE IN DRINKING-WATER ON NORMAL HUMAN-SUBJECTS

Uncontrolled observations implicate sulfate in drinking water at conce ntrations exceeding 500-700 mg/liter as a cause of diarrhea, but contr olled studies have not been reported. We conducted a controlled study in normal adults to determine the effect of various drinking water sod ium sulfate concentrations on bowel function. Ten healthy subjects wer e given a constant diet and fluid intake. Fluid consisted of 36 ml/kg/ day of drinking water of various known sulfate concentrations and 500 ml of other fluid. In a dose-ranging study, four subjects received dri nking water with sulfate concentrations of 0, 400, 600, 800, 1000, and 1200 mg/liters for six consecutive two-day periods. In a single-dose study, six other subjects received water with sulfate concentrations o f 0 and 1200 mg/liter for two consecutive six-day periods. Stool mass, frequency, and consistency and mouth-to-anus appearance time of color ed markers were measured. In the dose-ranging study, the only signific ant linear trend was decreasing mouth-to-anus appearance time with inc reasing sulfate concentrations. In the single-dose study, 1200 mg/lite r sulfate caused a significant but clinically mild increase in mean st ool mass per six-day pool from 621 g to 922 g (P = 0.03). When all 10 subjects were used to compare effects of 0 mg/liter and 1200 mg/liter sulfate, significant differences in stool consistency (P = 0.02) and t ransit time (P = 0.03) were observed. None of the subjects reported di arrhea or passed more than three stools per day. In 10 normal adult su bjects, sulfate in drinking water at a concentration of 1200 mg/liter, which is higher than reported to occur in US municipal water sources, caused a measurable but clinically insignificant increase in stool ma ss and decrease in stool consistency and appearance time, but no chang e in stool frequency and no complaint of diarrhea.