Genetic and chemical markers to determine who contaminated the river. Was it a human, a pig or a cow?

Following the new directives on water in bathing zones and for shellfish production, regulations on water quality have been reinforced. The new Bathing-water directive, applicable in 2015, provides that local governments must establish, by 2011, bathing-water profiles that identify local sources of pollution and the measures required to improve water quality. The goal is to improve management of the risks caused by pathogenic micro-organisms of faecal origin in sensitive zones, e.g. bathing waters and zones for shellfish production.

There are a number of sources of the faecal pollution found in surface waters all the way to the sea, including household wastewater and non-collective water treatment, runoff water, spreading of liquid manure or simply pasture zones along rivers. To detect them, monitoring labs generally cultivate intestinal bacteria, e.g. Escherichia coli or Enterococcus, present in humans and other animals. However, they have no means to distinguish the origin of the contamination.

Enhancing the diagnosis to meet regulatory goals

Two projects, Traceur and Marquopoleau, were launched by a dozen scientific organisations to provide the water sector with analytical tools capable of determining, in less than 48 hours, the human or animal origin of faecal contamination and also of distinguishing between porcine and bovine pollution. The work combined two approaches. The first was microbiological and based on identifying micro-organisms specific to humans, pigs and cows, using techniques to amplify viral or bacterial DNA sequences. The second was chemical, to detect synthetic and natural molecules that are specifically human or animal.

A set of markers was thus developed and tested in different environments. They are capable of indicating whether the origin is human (bacteriophages, Bacteroidales, Bifidobacterium, steroids, perfumes, flame retardants, caffeine, etc.), porcine (Lactobacillus, Bacteroidales, steroids) or bovine (Bacteroidales, steroids). These innovative, analytical tools are in the process of being transferred and developed in water-analysis labs participating in the Marquopoleau project.

Marquopoleau, an original transfer from research to applied analysis

This project, launched in 2009, is an opportunity for the analysis labs, under real conditions and using their own equipment, to test the traceability methods developed by the research teams for certain bacterial markers, e.g. Bacteroidales, the most common anaerobic bacteria in the intestinal flora, that are specific to humans or pigs or cows. Marker concentrations in faecal matter are sufficient for detection in aquatic environments, in spite of the dilution. The relevance of these tools has thus already been confirmed for surface water to which wastewater-treatment or farm effluents are discharged. They will be tested on the scale of an entire river basin for fresh water and in a coastal zone for bathing water. The persistence of these markers in environments is another important parameter for the traceability of faecal pollution that is also being studied in the lab to produce a true "toolbox" intended for the people involved in improving water quality. The simple, fast and reliable tools will put them in a position to meet the requirements of the new regulations addressing water monitoring and health risks.