Miljøprojekt, 1078 – Sundhedsmæssig vurdering af frit og bundet klor og trihalomethaner i bassinvandet i svømmebade

Sundhedsmæssig vurdering af frit og bundet klor og trihalomethaner i bassinvandet i svømmebade

Summary and conclusions

Chlorine as molecular, gaseous chlorine or sodium chlorite is used in Denmark for disinfection the water in public swimming pools. These chemical substances react with other chemicals in the pool water, i.a. pollutants from the users (e.g. urine, sweat, or hair scales) and produce a number of byproducts. Some of these byproducts are harmful to health in high concentrations. In Denmark when controlling the quality of the pool water, the byproducts are divided into three groups, i.e. free chlorine, bound chlorine and trihalomethane. Free chlorine is gaseous chlorine and hypochlorite; bound chlorine comprises inorganic and organic chloramines; and trihalomethane is a collective term for the following four substances, chloroform, bromodichloromethane, dibromochloromethane and bromoform.

In this report it is evaluated if the concentrations of disinfection byproducts in pool water in Danish public swimming pools pose a health risk to the users. Monochloramin is used to represent chloramines, i.a. because too little data was available for other chloramines. Chloroform and to some extent bromodichloromethane is used to represent trihalomethane, mainly because it is present in the highest concentration.

For each of the three substances a toxicological profile is drawn up based on monographs elaborated by renowned institutions, e.g. US-EPA (IRIS), US-NLM (HSDB), IARC, WHO (guidelines for drinking water and recreational water, and Environmental Health Criteria), as well as scientific reports and research papers. The toxicological profiles have four sections, short-term effects, long-term effects, a summary of the toxicology, and an elucidation of the critical effects and their critical doses. The critical effect is the toxicological effect, which is the basis for the risk evaluation of using the swimming pool. The critical dose is the highest dose that does not cause the critical effect, also known as NOAEL (No observed adverse effect level).

Users of the swimming pools are exposed to the substances through three routes, skin contact with the pool water, inspiration of vapours, and ingestion of pool water. In the chapter on risk evaluation all three exposure routes are taken into account. Exposure scenarios has been set up for four model persons; 1-year old child, 10-year old child, adult recreational swimmer, and adult competition swimmer. The basis for calculating the average daily doses is the current guiding and maximum values in Denmark for concentrations of free chlorine, bound chlorine and trihalomethane in public swimming pool water, as well as literature data on measured concentrations. The average daily doses are compared to the critical doses for the critical short-term and long-term effects for the three representative substances.

In general the calculations show that in all the scenarios children and adult recreational swimmers are exposed to average daily doses of the three representative substances, which are substantially lower than limit values issued by international institutions (WHO and US-EPA) and the Danish EPA. Competition swimmers are exposed to higher average daily doses than the three other model persons. The higher doses are proportional to the longer exposure time; competition swimmers use the swimming pool much longer on a weekly basis than other users. For competition swimmers the calculated maximum average daily dose of chloroform is approximately twice the limit values issued by international institutions (WHO and US-EPA) and of the same order of magnitude as limit value calculated by the Danish EPA. For bromodichloromethane the calculated maximum average daily dose is approximately 10 times the dose that may be estimated from WHO's guideline value for drinking water.

In the scenarios, the calculations use the current Danish values for concentrations of disinfection byproducts in public swimming pool water. These values are maximum values. The average concentrations of disinfection byproducts will be lower because the swimming pools often is less polluted due to lower load of users. This is especially the case when competition swimmers use the swimming pools, whereby the average daily doses will be reduced and the calculated risks correspondingly lower.