Abstract
River water that receives treated wastewater can be contaminated by pathogens including enteric viruses due to fecal pollution, which may represent an important public health hazard. There is a great diversity of enteric viruses and fecal bacteriophages, especially F-specific RNA bacteriophages (FRNAPHs), are commonly proposed as indicators of viral pollution due to a variety of characteristics such as their structural similarities to the main enteric viruses, their high concentrations in raw wastewater and their environmental survival rate, which is better than other cultivable enteric viruses. However, evaluating the viral contamination of water on the basis of FRNAPH concentration levels continues to present a challenge. This is because the quality of detection is strongly dependent on the quantity of viral particles, high spatio-temporal variabilities and the physico-chemical conditions of the water during sampling. To overcome these limitations, the present study aims to evaluate whether the bivalve mollusk Dreissena polymorpha (zebra mussel) could be considered a suitable experimental model for assessing the viral contamination of rivers. In order to determine this, the capacity of D. polymorpha to accumulate FRNAPHs and assimilate them into their soft tissue was studied. This provided a proof of concept for the use of D. polymorpha to evaluate the viral contamination of surface water. Two experiments were conducted: (1) an in situ experiment to confirm that zebra mussels naturally accumulated FRNAPHs and (2) a laboratory experiment to determine the accumulation and depuration kinetics of FRNAPHs in D. polymorpha tissue. The study highlights the capacity of the mussels to accumulate infectious FRNAPHs both on a laboratory scale under controlled conditions as well as in situ at different sites that are representative of different bodies of water. An analysis of the mussels’ soft tissue showed that they were capable of reflecting the water’s contamination level very quickly (within less than 24 h). Moreover, the soft tissue retained the viral load much longer than the water due to a low depuration rate. The analysis of FRNAPH concentrations in mussels exposed in situ suggested that there were differences in contamination levels between sites. These preliminary results underline the potential utility of zebra mussels in assessing viral contamination by measuring the accumulation of FRNAPHs in their tissue. This may ultimately enable stakeholders to use zebra mussels as a means of monitoring viral pollution in surface water.
Highlights
River water is often used as a source of drinking water, to irrigate crops or for recreational purposes
The first part of this study focused on the accumulation of F-specific RNA bacteriophages (FRNAPHs) in D. polymorpha mussels under natural conditions at representative surface water body sites within the WFD
The highest concentration was measured at Colmar, on the Ill river, suggesting that the Colmar site, located just downstream of the city, was impacted by anthropic activities. These results were consistent with previous studies showing the accumulation of enteric viruses in D. polymorpha [31,32] as well as the accumulation of infectious FRNAPHs in edible mollusk species [8,25]
Summary
River water is often used as a source of drinking water, to irrigate crops or for recreational purposes. It can be contaminated by many pathogens, especially enteric viruses, due to fecal pollution. The small size of these viral particles (ranging between 25–100 nm), together with the low infectious dose of enteric viruses (~10–1000 infectious units) and their high viral load in stools (~106 –109 particles/g) and high environmental survival rates make them significant pollutants of river water [3,4,5,6]. Assessing the viral contamination of water is challenging because of the rich diversity of enteric viruses, their low concentrations in water and the lack of routine cell culture systems that can be used to evaluate their infectivity. Concerning surface water, high volumes of water (1–1000 L) from a single sampling point generally need to be concentrated into small volumes (0.1–1 mL) for analysis
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