Disinfection byproducts: chloroform
Some disinfection byproducts, such as trihalomethane chloroform, are suspected carcinogenic.
Trihalomethane concentration depends upon total organic carbon, the number of swimmers and the water temperature.
Chloroform is the most important reaction product. Additionally other trihalomethanes, dichloromethane, tetrachloromethane, trichloroethene, bromodichloromethane and other chlorobromo hydrogen carbons can be found.
Chloroform and similar substances are volatile. Some part escapes from water and swimmers are exposed through inhalation. Chloroform concentrations in swimming pools vary a lot. Chloroform concentrations are highest just above the water. The suggested health standard for chloroform 100 mg/m3, this concentration is found in indoor swimming pools.
Swimming is one of the main sources of non-professional exposure to chloroform (over 70% percent after one hour of swimming). In outdoor swimming pools exposure is lower, because the wind ventilates the air above the water.
Exposure to chloroform can be measured in blood plasma of swimmers. Swimmers that swim for a long time with great physical effort (competitive swimmers) take up most chloroform. Chloroform concentrations in air is the main factor that determines the amount of chloroform that is absorbed. The time interval, the number of swimmers and the chloroform concentration in water are less important factors.