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Microbial Source Tracking: New forensic approaches to identify sources of fecal pollution |
| By: Scott Unger (S&T Liaison) |
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The Problem
Outbreaks of waterborne disease pose threats to human health, while beach closures, boil water advisories, and shellfish closures cost Canadian taxpayers millions of dollars every year. Municipalities and other watershed managers need new science-based tools to help them target cleanup strategies more effectively to deal with fecal pollution and damage to ecosystems.
A recent study found 1766 boil water advisories in communities across Canada on a single day in 2008. Fecal bacteria at levels exceeding health and safety standards caused 2701 days of advisories and closings of U.S. Great Lakes beaches in 2006. Pathogens from fecal pollution sources have caused most of the 288 outbreaks of waterborne disease across Canada from 1974 to 2001, including outbreaks in Kelowna, BC; North Battleford, SK; and Walkerton, ON. Statistics like these have prompted many agencies to invest in programs to reduce fecal pollution of our lakes and rivers.
Programs to build combined sewer overflow and stormwater holding tanks are costly undertakings for municipalities. While they have been valuable in reducing overall water pollution, they have often proved unable to address the full range of fecal pollution problems – beach closures, for example. Similarly, while beneficial management practices can reduce agricultural run-off into streams and rivers, there is uncertainty about the effectiveness of some practices for reducing fecal contamination from cattle, hog or poultry farms.
A scientific approach that can identify the specific source of fecal pollution in water is needed so that cleanup actions can be better targeted at the cause of the problem.
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- Canadian livestock (like cows, pigs and poultry) produced 177 million tonnes of manure in 2001, roughly equivalent to the fecal waste of 2.4 billion people.
- 20 Canadian and U.S. cities are estimated to release more than 90 billion litres of untreated sewage into the Great Lakes each year.
- Canada geese gathering on public beaches can produce as much as 1 kg of fecal droppings in a day.
- Seagulls can produce as many as 64 fecal droppings in a day.
Seeking Solutions through S&T
Fecal pollution comes from diverse sources such as municipal wastewater effluents, failing on-site sewage systems, livestock manure, and pet and wildlife droppings. Tracing pollution back to its precise source has always been a problem for agencies responsible for water management and protection.
Microbial source tracking (MST) is an emerging field that aims to identify specific sources of fecal pollution. Work by Environment Canada scientists and other national and international researchers has been instrumental in developing this innovative toolbox of methods. In general, the MST approach is based on comparing the similarity of microorganisms collected from aquatic ecosystems to microorganisms collected from nearby fecal pollution sources, then making inferences about the likely source of fecal contamination. Among the methods are forensic techniques such as DNA fingerprinting of E. coli from water samples and fecal pollution sources, as well as looking for human or animal-specific microorganisms in water samples.
Methods in the MST toolbox:
- Genetic fingerprinting to compare the DNA of E. coli from water and fecal pollution sources
- Antibiotic resistance profiling to compare patterns of resistance between E. coli from water and fecal pollution sources
- Identification of human or animal-specific strains of Bacteroides spp. bacteria in water
- Identification of human or animal-specific pathogens (e.g., Cryptosporidium spp., viruses) in water
Recent collaborations with the cities of Toronto, Hamilton and Ottawa have helped test various MST approaches at urban beaches. Unexpectedly, MST methods have sometimes concluded that bird droppings, rather than municipal sewage, can be the predominant source of fecal pollution at beaches. Interestingly, these MST studies have also found that beach sand can act as a reservoir for accumulating E. coli, and contaminating adjacent beach waters.
A Canadian workshop was held in March 2005 to discuss the state of science of microbial source tracking techniques. It featured a variety of experts in the field and succeeded in identifying the benefits and limitations of MST. It was also helpful in bringing advances in MST to the attention of water policy and program managers who need science-based tools to investigate water pollution and to help mediate conflicts between stakeholders.
Transforming Knowledge into Action
Who can use these results?
In many ways the application of MST is leading to a new understanding of the importance of different sources of water pollution. This has enormous implications for more effective and targeted approaches to resolving issues of fecal contamination of source waters used for drinking, recreation and food production. For example, Canadian water infrastructure is suffering from a deficit of over $50 billion in investment, and the cost of renewing, upgrading and investing in water infrastructure in Canadian municipalities is estimated in the billions of dollars every year. With MST tools to more clearly identify the source of pollution, water quality decision makers can make more strategic investments to better target reduction in contamination in a cost-effective manner.
Other organizations playing a source-water protection role in watershed management can also benefit from the MST approach. Conservation Authorities in Ontario, for example, will have more accurate tools to identify the prominence of specific fecal pollution sources like human sewage or dairy cattle, rather than spreading scarce pollution cleanup dollars across an entire region or farming community.
Greater accuracy in pinpointing precise sources of fecal pollution, including farm animal waste, illegal sewer hook-ups and damaged or faulty septic beds, also provides a science base for mediating discussion between stakeholders in a community. It can be useful to municipalities, watershed managers, conservation authorities and farmers alike, in identifying trends and cost-effective solutions to water pollution problems.
- MST approaches have been applied in Canada and many other countries and have been instrumental in leading to effective remediation of polluted waters.
- MST methods have been able to identify unexpected sources of fecal pollution, and contribute multiple lines of evidence in support of pollution cleanup decisions.
- Environment Canada is continuing research to test MST methods and to ensure the MST toolbox is supported by the best available science.
Benefits to Canadians
Impacts of fecal pollution on human health, aquatic ecosystems and local economies can be significant. Already, Canadian municipalities have seen positive results from the microbial source tracking approach. In some instances, bird control measures are leading to reduced numbers of beach closures. In other cases, repairs to urban wastewater infrastructure are reducing the quantity of sewage released to the aquatic ecosystems.
The capacity to better target cleanup to specific pollution sources will result in more cost-effective solutions, saving taxpayer dollars and contributing to greater overall reduction of contaminants entering the environment. A preventative approach to identify and reduce sources of fecal pollution has many advantages over the reactive approaches of closing beaches and shellfish areas, issuing boil water advisories, and dealing with waterborne disease outbreaks.
The outcome of continued MST research will be improved science-based tools to help water managers meet federal, provincial, territorial or municipal microbial water quality guidelines, objectives and regulations. The new knowledge gained from MST research will also contribute to the development of better source water and aquatic ecosystem protection plans, now required by many jurisdictions in Canada.
For more information:
Edge, T.A. and K.A. Schaefer (ed.). 2006. Microbial Source Tracking in Aquatic Ecosystems: The State of the Science and an Assessment of Needs. National Water Research Institute, Burlington, Ontario. NWRI Scientific Assessment Report Series No. 7 and Linking Water Science to Policy Workshop Series. 23 p.
Microbial Source Tracking Guide. U.S. Environmental Protection Agency. 2005.
Microbial Source Tracking (MST): Towards Effective Identification of Fecal Pollution Sources. MST Applications workshop report. 2004.
Water Environment Research Foundation. 2006. Workshop on Microbial Source Tracking in Water, San Antonio, Texas, 2005. Workshop report. 114 p.
S&T Liaison | Tel 905 315 5228 | Fax 905 336 4420
© Her Majesty the Queen in Right of Canada, represented by the Minister of Environment, 2008.
Catalogue No. En164-15/12-2008E; ISBN 978-1-100-11301-2
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