Intestinal Effects of Sulfate in Drinking Water on Normal Human Subjects

Uncontrolled observations implicate sulfate indrinking water at concentrations exceeding 500-700mg/liter as a cause of diarrhea, but controlled studieshave not been reported. We conducted a controlled study in normal adults to determine the effectof various drinking water sodium sulfate concentrationson bowel function. Ten healthy subjects were given aconstant diet and fluid intake. Fluid consisted of 36 ml/kg/day of drinking water of variousknown sulfate concentrations and 500 ml of other fluid.In a dose-ranging study, four subjects received drinkingwater with sulfate concentrations of 0, 400, 600, 800, 1000, and 1200 mg/liters for sixconsecutive two-day periods. In a single-dose study, sixother subjects received water with sulfateconcentrations of 0 and 1200 mg/liter for twoconsecutive six-day periods. Stool mass, frequency, and consistencyand mouth-to-anus appearance time of colored markerswere measured. In the dose-ranging study, the onlysignificant linear trend was decreasing mouth-to-anus appearance time with increasing sulfateconcentrations. In the single-dose study, 1200 mg/litersulfate caused a significant but clinically mildincrease in mean stool mass per six-day pool from 621 gto 922 g (P = 0.03). When all 10 subjects wereused to compare effects of 0 mg/liter and 1200 mg/litersulfate, significant differences in stool consistency (P= 0.02) and transit time (P = 0.03) were observed. None of the subjects reported diarrhea orpassed more than three stools per day. In 10 normaladult subjects, sulfate in drinking water at aconcentration of 1200 mg/liter, which is higher thanreported to occur in US municipal water sources, causeda measurable but clinically insignificant increase instool mass and decrease in stool consistency andappearance time, but no change in stool frequency and no complaint of diarrhea.