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Depuis la mise en évidence de trihalométhanes dans les eaux potables en 1974, demultiples travaux ont démontré la présence de nombreux composés génotoxiques dans l'eau deboisson. L'eau potable obtenue à partir d'eau de surface subit un traitement incluantgénéralement une étape de chloration. Il est aujourd'hui largement admis que l'activitégénotoxique des eaux de boisson provient principalement de la chloration des substanceshumiques, composés organiques naturels contenus dans l'eau brute et issus de la dégradationdes déchets animaux et végétaux. Les très faibles concentrations en composés génotoxiquesdans les eaux potables nécessitent la concentration des échantillons, procédé qui risquetoutefois de modifier la génotoxicité. Plusieurs tests mettant en oeuvre des cellulesprocaryotes ou eucaryotes, des plantes ou des mammifères, ont permis de mettre en évidenceles effets génotoxiques dans des eaux potables chlorées. L'identification des composésgénotoxiques est réalisée au moyen des données de la spectrométrie de masse et de laspectroscopie UV ou RMN (proton ou carbone). Ces agents sont généralement non volatils,acides et polaires. Bien que certains composés inorganiques interviennent parfois, lamajeure partie de la génotoxicité est attribuée aux agents organohalogénés (bromés ou/etchlorés), les principaux étant les trihalométhanes, acides acétiques, acétonitriles,cétones, et hydroxyfuranones. La fixation de normes contribue à limiter l'exposition despopulations aux agents potentiellement dangereux. La qualité des eaux de boisson peut êtreaccrue en utilisant une eau brute moins chargée en matière organique, et en améliorant letraitement chimique tout en veillant à conserver la qualité microbiologique de l'eauproduite.In 1974, two independent studies - one in the Netherlands and the other in the UnitedStates - demonstrated the occurrence of trihalomethanes in drinking water. Following studiesshowed that these chemicals were common contaminants of drinking water and that chloroform,i.e. one of these trihalomethanes, was carcinogenic in rodents. Further investigationsdemonstrated that extracts of chlorinated drinking water induced significant mutagenicity inthe Ames/Salmonella assay. In the present paper we will fist discuss the methods used todetect the genotoxic activity of drinking water and, then, the methods developed to identifythe compounds responsible for this activity. After this, we will present the main genotoxicchemicals identified in drinking water, before finally considering several propositions tolimit the exposure of populations to these genotoxic compounds.Drinking water is usually produced through a multistage process which includes one orseveral chlorination steps. It is now widely accepted that the genotoxic activity ofdrinking water mainly originates from the reaction of chlorine with humic substances presentin raw water. Humic substances are natural organic matters (resulting from the degradationof plants and animal tissues) of very complex structure with most chemical functionsarranged in aromatic rings or aliphatic chains. The identification of a genotoxic activityin drinking water usually requires concentration of the water samples. Even though such aprocess implies a probable qualitative/quantitative alteration of the constituents of watersamples, the extremely low amounts of genotoxic compounds in drinking water requireconcentration steps. Among the many genotoxicity tests carried out, the Ames test (whichdetects reverse mutations in bacteria Salmonella typhimurium) is the assay which was themost frequently used in the field of drinking water mutagenicity. Other tests were performedon eucaryotic cells. Assays detecting micronuclei or chromosomal aberrations in plants, ormutations in mold, yeast, or maize enabled the detection of genotoxic effects of drinkingwater extracts. Tests on mammal cells also showed that drinking water extracts induced pointmutations, sister chromatid exchanges, chromosomal aberrations and micronuclei. In vivotests on aquatic organims such as newt or mussels demonstrated the micronuclei inducingeffect of unconcentrated drinking water samples.Regarding the identification of thecompounds responsible for the genotoxicity, it is obviously not possible to identify all ofthe thousands of chemicals that may be involved. But such a process is important in order toevaluate the specific genotoxicity and the risk associated with (at least) the mainchemicals occurring in drinking water. The identification process usually follows threesteps: 1. concentration of the sample can be performed using reverse osmosis, freeze drying,liquid-liquid extraction, and/or adsorption on non ionic resin followed by extraction withorganic solvent; 2. the purification step uses one or a combination of chromatographic techniques (TLC,packed column liquid chromatography, HPLC or GC); 3. structural identification of the chemical is performed using data from massspectrometry, and proton and carbon NMR, or UV spectroscopy. The analysis of the genotoxic compounds of drinking water showed that they are rathernon-volatile, quite acid and not stable at high pH, rather polar, and with a mean molecularweigh around 200.Turning now to the identity of these compounds, it is considered that the genotoxicityof drinking water is mainly due to organohalogenated chemicals. Some inorganic chemicals(this class of chemicals is usually not recovered in drinking water extracts) which inducegenotoxic or carcinogenic effects must, however, be recalled. Arsenic, nitrates, bromatesand radon are natural or human-activity-related drinking water contaminants which areresponsible for cancers in rodents or in humans. Among the many genotoxic or carcinogenicorganohalogenated compounds identified in drinking water, the most abundant chemicals arechlorinated and/or brominated trihalomethanes. Other important groups of compounds arechlorinated and/or brominated derivatives of acetic acids, acetonitriles, ketones, phenoliccompounds. The chlorinated hydroxyfuranones, although present at concentrations lower than0.1 µg/l in drinking water, can be responsible for more than half of the Ames mutagenicity.MX, the most potent of these chlorohydroxyfuranones, has been submitted to intensivetoxicological studies worldwide and was very recently identified as a potent carcinogen inrats.Now that the presence of genotoxic compounds in drinking waters is a well documentedand accepted fact, the perspectives lies in the better identification of the impact of thesedrinking water contaminants. The development of more sensitive tests such as the Comet assay(detection of DNA strand breaks) or the 32P postlabelling assay (detection of DNA adducts)should be pursued. Moreover, the interaction between genotoxic compounds and DNA must beinvestigated more thoroughly, including the identification of adduct structures. Moreglobally, it is of interest to better assess the impact of these agents on public health andon the occurrence of specific human cancers. At present, even though a few individual watercontaminants are classified as human probable carcinogens, the chlorinated drinking water(in itself) is not considered as carcinogenic to humans. Exposure to these potentiallyharmful agents can be limited with 1. improving drinking water quality - i.e. decreasing the formation of genotoxins - byusing raw water containing lower amounts of organic matter; and 2. modifying the water chemical treatment by using lower amounts of chlorine and/orcombining chlorine with other disinfectants. The public health can also be protected by the setting of guidelines for drinkingwater: each compound identified as dangerous would be given a concentration threshold whichshould never be exceeded. The Environmental Protection Agency in the U.S.A. and the WorldHealth Organisation are authorities setting such guidelines. Finally, we believe it isimportant to limit the concentration of genotoxic compounds in drinking water as much aspossible, and one way to do so is to use chlorine in smaller amounts and in a more efficientway. But it is of paramount importance to keep in mind that the disinfection process (inwhich chlorine still plays a major role) and the providing of a microbiologically safedrinking water should never be jeopardized

Identification de composés génotoxiques dans les eaux de boisson