Évaluation de la vulnérabilité des ressources en eau vis-à-vis du risque viral

Assessment of virus contamination risk in water resources

Centre de Recherche sur l'Eau de Veolia Environnement, Chemin de la digue BP 76, 78603, Maisons-Laffitte, France

Auteur de correspondance : dorothee.lenes@veolia.com

Résumé

Une campagne métrologique d'un an a été initiée sur 13 ressources représentatives des eaux exploitées par Veolia Eau, en France métropolitaine. Cette étude a pour objectif d'établir une cartographie de la qualité microbiologique des ressources en fonction des saisons, mais aussi d'évaluer la vulnérabilité des ressources vis-à-vis du risque viral. En effet, les principaux virus (Norovirus I et II, Rotavirus, Adénovirus, Astrovirus) et parasites, responsables de gastro-entérites, sont recherchés dans le cadre de ces campagnes. En ce qui concerne l'occurrence, les Adénovirus sont nettement majoritaires dans les différents types d'eaux, suivis des Norovirus I et II et enfin des Rotavirus. De plus, la présence d'Adénovirus dans les eaux de surface, apparaît comme assez bien corrélée avec les autres virus, alors que l'analyse de la corrélation de présence des Adénovirus avec les autres virus en eau souterraine est quant à elle plus délicate et non probante. Enfin, les résultats des analyses virales et parasitaires ne sont pas toujours concordants avec le classement officiel en eau Influencée ou Non-Influencée des eaux souterraines.

Abstract

In order to assess the microbial safety of drinking water supplies, WHO has recently proposed the integration of risk assessment and risk management strategies into Water Safety Plans analogous to HACCP system used in the food industry. Under this framework, the evaluation of the vulnerability of sources water to enteric pathogens (i.e. parasites and viruses) is a major challenge. Once the alternative analytical method validated, a one-year microbial analytical monitoring has been implemented in 13 French resources which supply Veolia Water treatment plants. Those sampling campaigns aim to establish a map of the microbial water quality, observe the influence of seasons and aim to improve the knowledge of the viral water resources vulnerability and identify viral indicators and the correlation with enteric viruses. Indeed, a focus has been made on waterborne micro-organisms which can cause gastro-intestinal illness, as viruses (Norovirus I and II, Rotavirus, Adenovirus, Astrovirus), parasites (Giardia and Cryptosporidium) and bacteriophages (Somatic Coliphages, Male-Specific Coliphages). Viral samples are analyzed by a qualitative Polymerase Chain Reaction (PCR). The correlations between virus occurrence and the results of microbial indicators, bacteriophages, and physical parameters, are examined in the different types of resources (groundwater and surface water). First results show that Adenoviruses are the most frequently detected viruses in raw water (26%). Norovirus I is detected in 16% of the samples, Norovirus II in 7% and Rotavirus in 3%. No sample was positive for the enteroviruses, the HAV as well as the Astrovirus. The occurrence of enteric viruses in water resources was then compared with the occurrence of bacteriophages and then adenoviruses as viral indicators. Bacteriophages are often simultaneously detected with enteric viruses in surface water samples, but the detection of bacteriophages is not revealing of enteric viruses contamination (samples contaminated only with bacteriophages). For underground water, no obvious correlation is observed between bacteriophages and enteric viruses' occurrence. One explanation of the discrepancies could be the limited volume analysed for bacteriophages (1 mL) compared to viruses (1 L). As for the correlation with Adenoviruses, the presence of viral genome (Norovirus 1 and 2 and Rotavirus) is frequently associated with the occurrence of Adenoviruses. Moreover, the virus-positive samples found in some groundwater resources, considered as confined aquifers, indicate that those resources can be, in fact, vulnerable to contamination by viruses. This mapping of the resource water quality in France is a preliminary study that showed that surface and groundwater resources are both concerned with the presence of emerging microorganisms (i.e. non regulated microorganisms, in particular viruses). Nevertheless, further studies have to be carried out by using quantitative analytical methods in order to be able to include those data in a health risk assessment strategy.