There is an urgent need to step-up monitoring of lakes for microbes known as cyano-bacteria, which can pose a severe pollution risk to water including public drinking supplies, an Environmental Protection Agency study has found.
Toxins from cyano-bacteria are among the most lethal substances known, and the study highlights increasing evidence they are responsible for many animal deaths and acute effects in humans. The bacteria sometimes produce toxins and are most menacing in the form of "algal blooms" - concentrations or proliferations of the bacteria which form a scum on the surface of a water body.
The study was conducted by some of Europe's leading experts on cyano-bacteria and water, led by Dr Andrew Petersen of Cork Institute of Technology. It found a fifth of 55 lakes surveyed contained blooms caused by cyano-bacteria. The blooms are, despite their toxin-producing ability, relatively simple cells containing chlorophyll, which they use for photosynthesis.
At least nine types of toxic cyano-bacteria were present and causing "actual or potential nuisance in 23 lakes", including some of the larger and more important water-bodies in the Republic such as Caragh Lake in Co Kerry, Iniscarra reservoir in Co Cork, and Lough Derg on the Shannon. The study warns that with small sampling levels during the time of carrying out a national survey, "it was considered that the level of toxicity encountered substantially underestimated the true position".
Rapid, reliable tests need to be developed to detect the bacteria and their toxins, which may be present in the event of a bloom.
The EU funded the three-year study in an effort to improve knowledge about the bacteria known in the past as blue-green algae. Determining safe levels of the toxin and conditions where it might occur was part of the brief.
The report says concerns about lakes are justified. This is in the context of a worsening problem of eutrophication (where pollutants enrich water, upset its chemical balance and deplete oxygen).
Eutrophication was believed to promote the growth of cyano-bacteria. This study strongly underlines that link.
Enrichment of water by phosphates and nitrates has been the single biggest environmental problem contributing to a slow decline of lakes and rivers in recent years. If eutrophication and phosphate loadings are not controlled, there will be an ever-present risk of blooms.
The researchers claim that shallow limestone-based lakes, such as many of those in the west, are especially vulnerable.
"Substantial blooms of the organisms were associated with most highly enriched lakes," the study notes. Local authorities should be routinely testing supplies for their presence, the scientists recommend, while a programme for the national monitoring of lakes is necessary.
There is, it says, an absence of statutory limits in place in Ireland or the EU for maximum permitted levels of toxins or the bacteria themselves in either drinking water or recreational water bodies. Such limits would be critical to the effective protection of water.
In a separate review of scientific evidence of the health effects of cyano-bacterial toxins, a high number of animal deaths, including livestock, is noted.
The most commonly reported human illnesses associated with cyano-bacteria are skin conditions and gastrointestinal effects such as vomiting and diarrhoea.
Where cyano-bacteria are well dispersed, there is no immediate risk to animals or humans. No reports of illness are linked to recreational contact with the microbe or even water consumption in the absence of blooms of the organism.
In recent years, however, investigations in China strongly link cyano-bacterial toxins with liver cancer. Because of this link, the authors warn those with hepatitis B or C to avoid water which may contain particular cyano-bacterial toxins known as hepta-toxins.
The EPA study notes: "Toxin production may be determined genetically but it is unclear whether `toxic' strains of cyano-bacteria produce toxins or if `non-toxic' varieties have a potential to become toxic under specific environmental conditions." Blooms interfere with filtration at water treatment works and create taste, odour and colour problems, besides occasionally producing toxins with more harmful effects. Prudent management could alleviate the problem at source.
Increases in cyano-bacterial numbers may be prevented by depriving the organisms of nutrients, whereas the addition of chemicals will destroy a bloom but may well release toxins into water. Relatively simple filtration techniques remove the bacterial cells from water but advanced and costly treatments (rarely evident in Irish water treatment systems) are needed to eliminate the toxins, the study warns.