Irritant Effect of Disinfection Byproducts in Swimming Pool Water
Zent.bl. Hyg. Umweltmed. 200, 491-503
© Gustav Fischer Verlag 1997/98
Zentralblatt für Hygiene und Umweltmedizin
Hygiene Institute of Heidelberg University Medical Center, Department of Hygiene and Medical Microbiology
Lothar Erdinger, Frank Kirsch, and Hans-Günther Sonntag
Abstract [original English]
Compounds which can occur as disinfection by-products (DBP’s) in swimming pool water were examined for their mucous membrane irritating potential. Previous studies using the rabbit eye test (Draizé  test) have shown that the irritating potential of typical concentrations of free and combined chlorine are insufficient to explain the degree of eye irritation that can result from exposure to swimming pool water. Other DBP’s which may be responsible for eye irritation include halogenated carboxyl compounds (HCC’s) which act as precursors during the formation of chloroform. In this study, a modified HET-CAM Test (Hens Egg Test at the Chorion Allantois Membrane) has been used to investigate the mucous membrane irritating effects of HCC’s. Some of the compounds tested were found to have a significantly increased irritating effect when compared to a chlorine/chloramine mixture of the same concentration, several mixtures of HCC’s where [sic] even more active at lower concentrations than single compounds. However, the irritating effects of individual compounds as well as of mixtures of HCC’S were not sufficiently intense to allow the identification of those compounds specifically responsible for the overall observed increase in irritation. HCC’s were therefore tested in the presence of aqueous chlorine solution. When combined with aqueous chlorine, a number of compounds exhibited significantly enhanced effects. Our results show that the eye irritating effects of low concentrations of DBP’s can be investigated using a modified HET-CAM assay. Moreover, results obtained using this assay suggest that the mucous membrane irritating potential of swimming pool water is a consequence of the effects and synergistic action of a number of DBP’s in the presence of chlorine. Further work should be carried out in order to establish an indicator for eye irritating effects of swimming pool water.
In one study conducted on the effect of swimming pool water on the cornea, 68% of the test subjects reported that after swimming they saw rainbows and/or halos around light sources, and 94% exhibited epithelial erosion . These events were at least partially attributed to the hypotonic effect of swimming pool water. In other studies, it could also be shown that in pools with 0.5% NaCl content, less damage to the cornea occurred  than in pools operated without
salt added. In addition, chloramines have been suspected for a long time to be responsible for the irritant effects . In one study back in 1951, it was found that different water treatment methods had different impacts on the irritant effect . But for the most part, chlorine (the most commonly used disinfectant) was held responsible for the effects.
But chlorine is currently the only water disinfectant that meets the requirements necessary from a hygiene standpoint for safe use in swimming pools.
The mechanism by which chlorine inactivates microorganisms is to a large extent unknown . It stands to reason that we should look for a fundamental cause in the chemical reactivity of chlorine. This high reactivity, however, also leads to byproducts, where organic matter contained in the water is chemically altered by the disinfectant. In addition to chloroform, many other byproducts are formed which have been only partially identified. For drinking water applications, in the USA detailed studies were conducted back in the beginning of the 1980s, where various compounds were quantitated.
Chloroform and other byproducts are inevitably also formed in swimming pool water. But since chloroform represents the end product of a multistep chain of reactions, more byproducts must be contained in the water.
As has already been mentioned, the most important disinfection byproduct for swimming pool water is chloroform, which can affect the swimmer through the water and through the air [11, 3]. The best known reaction mechanism by which chloroform can be formed using chlorine from organic compounds is the haloform reaction. This reaction occurs via several steps, where carbonyl compounds with methyl groups in the α position are converted first to α-chlorinated ketones and ultimately to chloroform and an organic acid.
While the toxicological properties of chloroform have been relatively well studied  and sufficient data are also available concerning its uptake in swimming pools , not much information is available concerning the type and concentration of its immediate precursors. However, in principle, compounds with a halogen atom in an α position relative to a double bond are regarded as having irritant effects on mucous membranes.
Chloroacetone was used as a chemical warfare agent for this reason, because of its severe irritant effect in the gaseous state.
Within this study, tests were conducted on the irritant activity relative to mucous membranes for substances that sometimes already had been detected in swimming pool water. Other compounds were taken as model compounds in the study, in order to be able to take into account their effects. The goal was to determine the threshold concentration for the effect of these substances, so we could demonstrate their fundamental significance in the origin of eye irritation in swimming pools while taking into account realistic exposure times.
We were able to show that under the indicated test conditions, the reaction in the HET-CAM test is somewhat more sensitive than in the Draize test. From this we conclude that this model is suitable in principle for detecting the effect of low material concentrations of compounds with an irritant effect.
In the test, the studied individual halogenated organic compounds proved to be irritants only in concentrations that are not usually found in swimming pools. The concentrations found so far in swimming pools are considerably lower. However, higher concentrations could be measured in outdoor swimming pools than in indoor pools, where concentrations of up to 100 μg/L could be detected.
Based on our results, it is therefore likely that the irritant effect occurring in swimming pools is not due to one individual compound, but rather many compounds present in the water contribute to this effect. At the same time, the concentrations of these compounds are dependent
on pool load and can fluctuate considerably over the day . From personal experience, eye irritation is also dependent on pool load. Since the chlorine concentration in modern pools is automatically regulated and generally is not subject to large fluctuations, this can also be considered as evidence that the irritant effect is primarily due to other compounds.
Concerning the question of the extent to which other classes of compounds (besides halogenated organic keto compounds) also contribute to the irritant effect, at the moment we can only speculate. Since the oxidizing agents used in water treatment (chlorine and if necessary ozone) are very reactive, byproducts possibly having activity can also be formed by an oxidative route .
In continuing investigations, the model for studying irritant effects should be developed further so that it can be used for directly testing swimming pool water.
In order to develop simple prevention strategies, the mechanism for chloroform formation in swimming pools and especially the resulting intermediates should be studied. Ultimately, effective countermeasures can be further developed only if we know these interrelationships.