Microbiological and chemical analyses of indoor swimming pools and virucidal effect of chlorine in these waters

: Virological and bacteriological examinations and chemical analysis were made of 24 water samples from 6 public indoor swimming pools in Aichi Prefecture. In 3 of these swimming pools, sodium hypochlorite was used as a disinfectant and in the remainder trichloroisocyanurates. All samples were negative for adenovirus per 20 liters. Coliform group was detected in one sample with 26.7 mg/l cyanuric acid. Total plate counts ranged from 0 to 1 per ml in the swimming pools treated with sodium hypochlorite and 0 to 51 in those with trichloroisocyanurates. Turbidity, pH and potassium permanganate concentrations in the samples were within allowable limits. Seven of 24 samples did not meet the recommended value of 0.4 mg/l for free chlorine residuals. Ammonium nitrogen was detected in one pool water with trichloroisocyanurates. In 11 of 12 water samples of swimming pools using sodium hypochlorite, poliovirus 1 (2 x 10(4) PFU/0.2 ml) was inactivated within 1 min under the condition of 1.0 mg/l free available chlorine and 25 degrees C. In 11 of 12 water samples of 3 swimming pools using trichloroisocyanurates, poliovirus type 1 survived after 2 min contact while in 5 samples poliovirus type 1 survived after 5 min contact. This shows that the risk of viral infection is greater in swimming pool water treated with chlorinated isocyanurics than that with sodium hypochlorite. The operator of the swimming pool should pay special attention to the control of water quality and free residual chlorine value.