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Threats to Sources of Drinking Water and Aquatic Ecosystem Health in Canada

2. Algal Toxins and Taste and Odour

Toxic blue-green algae bloom in Hamilton Harbour, Ontario, August 2001.Murray Charlton,1 Michele Giddings,2 Charles Holmes,3 Wayne Carmichael4 and Jeff Ridal5

1Environment Canada, National Water Research Institute, Burlington, ON
2Health Canada, Drinking Water Section, Ottawa, ON
3University of Alberta, Department of Biochemistry, Edmonton, AB
4Wright State University, Department of Biological Sciences, Dayton, OH
5St. Lawrence Institute for Environmental Research, Cornwall, ON

 


Current Status

Algal Toxins

Toxins are produced by blue-green algae (cyanobacteria) and other types of algae in quantities sufficient to cause death of animals and pose a risk to Canadians' health (Chorus and Bartram 1999). Cyanobacteria form heavy growths in ponds, lakes, reservoirs and slow-moving rivers throughout the world. Water blooms are composed of large numbers of cells or filaments, often in colonies. These cells can house toxins called cyanotoxins. When the waterbloom mass rises to the surface of the water, it is referred to as a surface scum or a surface water bloom. Although we do not know the extent to which cyanobacterial blooms occur across Canada, we do know they mostly appear in the hot summer months and are quite prevalent in the Prairie provinces as well as other water bodies across Canada. Cyanotoxins are the naturally produced poisons stored in the cells of certain species of cyanobacteria. These toxins fall into various categories. Some are known to attack the liver (hepatotoxins) or the nervous system (neurotoxins); others simply irritate the skin (dermotoxins). These toxins are usually released into water when the cells rupture or die. Most cyanotoxins have been isolated and characterized. Detection methods, including rapid screening, are being developed to help us learn more about them, especially to find out which toxins are a problem in Canada and what conditions encourage their production.

Hepatic Microcystins--the Cyclic Peptides

Sixty-five microcystin toxins have been identified. Toxin problems are associated with blooms of mainly cyanobacteria (bluegreen algae) during warm weather. Although high nutrient conditions (eutrophication) are not necessary for blue-greens, the resultant turbid water quality favour blue-greens that can control their buoyancy in order to receive adequate illumination. Monitoring of blue-greens and their toxins is difficult because the buoyant algae can be concentrated by wind by a factor of 1000 or more and even form scums at the downwind end of water bodies. Not all blooms of blue-green algae are toxic even for species known to be toxin producers (Chorus and Bartram 1999). Reliable prediction of blue-green algal blooms is rare but the severity of blooms is partially related to nutrient loads.

Predictability of toxin production is difficult or impossible but suspect species are known. Unfortunately, there are few biologists trained in phycology who would be able to identify the algae. Human threats from microcystin toxins have been identified in drinking water (Winnipeg, Regina, central Alberta), recreational water, and irrigation/stock watering sources. Particularly difficult problems exist in ponds and dugouts where no other sources exist. The occurrence of toxins is not restricted to highly eutrophic water or prairie systems; this is shown by the appearance of cyanotoxins in Lake Erie (Brittain et al. 2000). Blue-green algal toxins may be linked to bird deaths due to avian botulism.

Although humans are rarely killed by algal toxins, deaths have occurred in extreme exposures. In 1996, 101 patients were made ill and 50 died due to algal toxins in water used for hemodialysis at one treatment centre in Brazil (Jochimsen et al. 1998). The dose of toxin was delivered through exposure to about 150 litres of contaminated water used in the dialysis treatment. Kidney dialysis centres and home dialysis may be at risk from potentially contaminated water.

The blue-green algal toxin Microcystin-LR is currently used as an indicator for the presence of other toxins. No universal standards for microcystin toxins are available. There is potential for Canadian development of an industry to supply the standards. A field analytical kit is nearing completion at the University of Alberta. There is potential for commercialization of the field kit based on existing strengths, but support is required to complete validation of the procedure. Cost-effective laboratory analytical methods for routine monitoring of toxins are being established at Health Canada. The majority of microcystin toxins are irreversibly bound to tissues in affected animals. Thus, the overall exposure and the toxicity of bound forms is unknown.

Guidelines have been developed to help limit exposure. The proposed toxin guideline for consumption in Canada is 1.5 µg/L (WHO is 1.0, Australia 1.3, U.S.A. 1.0 µg/L). The proposed guideline does not cover potential for cancer risk from micro-cystin toxins which are likely to be tumour promoters. Human exposure threats from microcystins in the Prairie provinces is being studied by Health Canada in conjunction with the University of Alberta. Much of the Canadian foundation of expertise in algal toxins is centred or originated at the University of Alberta. Canadian expertise and experience is on par with the U.S.A., Australia, U.K. and Japan.

Taste and Odour

The presence of tastes and odours in potable water supplies has been increasing worldwide in both intensity and frequency in recent years. Taste and odour problems have been reported widely in Canadian waters including B.C.; Edmonton; Calgary; Lethbridge; Prairie lakes, ponds and dugouts; Regina; Winnipeg; Muskoka Lakes and Quebec City. In particular, taste and odour problems have increased in the lower Great Lakes and the St. Lawrence River (SLR). The occurrence in Great Lakes drinking water produces an aesthetic problem for millions of consumers, but in addition, invariably raises uncertainty about the safety of the drinking water frequently expressed by the public as "Is the water safe to drink and bathe in?"

Taste and odour compounds can be man-made (industrial, municipal, etc.) or biogenic. This section will focus on biological compounds. Taste and odour compounds are produced by microscopic organisms such as algae, bacteria, fungi and protozoa. They represent a wide variety of odourous compounds that can be detected by our olfactory senses in very low concentrations at the parts per trillion level (ng/L). The most common compounds produce earthy, musty tastes and odours. Two compounds, geosmin and 2-methylisoborneol (MIB), have been widely reported. In some cases, production of these compounds occurs in situations where high nutrient conditions favour blooms of known algae producers. However, the recent occurrences in the Great Lakes come at a time where nutrient levels have reached their lowest levels in decades. In these cases, the sources of these compounds are unknown (algae or bacteria). Nutrient-poor lakes and reservoirs can have different compounds (fishy odour) produced by chrysophyte algae (Watson et al. 1999).

The taste and odour problems mainly occur in late summer--some are in winter under ice, but the intensity can vary from severe to innocuous year to year. Predictability of the problems is low. Little is known about the environmental conditions that trigger their production. Taste and odour compounds may come from species living in the water, on surfaces, in the bottom sediments or may be produced onshore and washed into the waters during runoff events. Other factors may include temperature, light levels, water clarity, changing nutrient ratios, changing water levels, the presence of zebra mussels and shifts in the phytoplankton makeup in the lower Great Lakes.

Studies of the toxicological properties of taste and odour compounds are scarce. The presumption has been that, while they can produce serious aesthetic problems, they do not present a risk to aquatic organisms or human consumers of drinking water or fish tainted by them. Toxicological studies are needed. Both geosmin and MIB have been non-mutagenic in bacterial tests. Some activity was found in tests with sea urchin eggs (Nakajima et al. 1996) and geosmin and MIB have shown to be genotoxic and estrogenic to rainbow trout hepatocytes (Gagné et al. 1999) but at very high concentrations relative to environmental levels, i.e., at concentrations several orders of magnitude higher than those which produce an off-flavour in water or tainting of fish. The picture is a mixed one across different levels of test organisms, but there is the suggestion that higher aquatic organisms may be more likely to show effects, albeit at very high concentrations.

Control measures by municipal water purification plants to remove taste and odour are usually expensive. Municipalities are reluctant to implement expensive control measures when the ecological and environmental details of these compounds remain unknown. Without further identification of the sources it is difficult to undertake actions to avoid or minimize taste and odour events.

There have been recent advances in the analytical methods for MIB, geosmin and other taste and odour compounds, and presently there is a wide variety of sensitive analytical methods available. Currently, funding is needed for development of stable isotope analyses to determine biosynthesis site (terrestrial, aquatic), movement/stability of these compounds through the watershed (soil, surface/ground water) and surface waters (e.g., Niagara River, Great Lakes). Contracting out is needed for the synthesis of a particular isotopically labelled standard, geosmin-d3, since the supply from CSIRO in Australia has been exhausted. A sensitive and rapid protocol has been eveloped to identify and measure the aldehydes; however, these compounds are unstable and difficult to work with. Currently, there is a need to develop a method of stabilizing these compounds in field samples and during analyses.

Taste and odour problems occur in B.C. (interior); Edmonton; Calgary; Lethbridge; Prairie lakes, ponds, and dugouts; Regina; Winnipeg; lower Great Lakes; Muskoka Lakes and Quebec City.

Trends

Toxins

Algal blooms seem to be increasing but the problems are sporadic. Temperature, insolation, rainfall and water level variations and increasing eutrophication are positive factors. It is likely that the frequency of algal blooms and taste and odour problems will increase. There is a risk to health when using home dialysis treatment in areas prone to blooms. Exotic species causing increasing ecological shifts and disturbed ecosystems seem to favour blue-green algae. Shifting N/P ratios due to atmospheric deposition of N and little N retention at sewage plants will likely stimulate blue-greens and/or toxin production.

Taste and Odour

The frequency of taste and odour events is increasing particularly in the Great Lakes region. At the same time, consumers' demands for high quality water will remain or increase. Taste and odour events erode consumer confidence in municipal drinking water supplies leading to a rise in the use of bottled water. Expectations of the public are increasing due to recent publicity about the need for source protection. Water suppliers are forced to install treatment facilities at great expense that are not needed in some years. Future water sources will likely be of lower quality and this will increase demand for monitoring and treatment.

Knowledge and Program Needs

Toxins

Toxins in raw and finished water are poorly studied. Although there are some traditional problem areas, new problems in the Great Lakes are occurring despite 30 years of nutrient reductions. There is a need to discover ways to optimize treatment methods in advance of new occurrences. Methods for analysis of the algal toxins are still under development. There is a need for real-time field determination methods. Analyses are hampered because standards are unavailable for most of the 65 known microcystins as well as the other cyanotoxins. There is a need to study seasonal trends in toxin production and concentration. More baseline monitoring is needed even in non-bloom conditions to help understand factors responsible for the blooms. More work on environmental triggers and ecological shifts causing blooms of toxin-producing algae are needed. Understanding of food chain transfer, for example, mussels-gobies-bass, is needed. Training of biologists in algal taxonomy has virtually disappeared and this will hamper efforts to understand the problems. Monitoring is needed to determine whether the presence of toxin spikes may increase overall exposure relative to sporadic grab sampling information. There is a need for methods validation and development. The significance of toxin binding to tissue needs to be found. Studies on the connection between toxin production and taste and odour problems are needed.

Algal toxins may be stressful especially for species not adapted in disturbed or artificial areas. At the moment it is not known whether the effects are due mainly to toxins dissolved in water or in the algae. Some of the toxins are contact irritants and their role and relevance in recreational waters is unknown.

The best way to monitor using either cell counts or toxin analyses is not known. The effects of basin hydrology and surface water movements on the generation of algal species that contain toxins needs further study. Potential effects of climate change are likely to increase the problems but this needs further knowledge. Not all blooms are toxic and the reasons for initiation of toxin production need to be discovered. Treatment methods to eliminate threats to drinking water need to be developed so the algal cells are not lysed or stimulated to release contained toxins.

Taste and Odour

There is a fundamental lack of knowledge on biological sources and triggers to production of taste and odour compounds. Little is known of the chemistry and biological fate, place of production, volatility, degradation, bio-accumulation, fish tainting, and effects on food processing. Problems in the Great Lakes have occurred despite lowered nutrient levels. The increased presence of the compounds in certain water bodies may signal synoptic changes to the ecosystem. Hypotheses about the potential for further nutrient controls to decrease the frequency and extent of events need to be tested. The potential links to UV radiation, climate change, zebra mussel populations and water level variations need to be investigated. Potential health effects due to exposure via consumption, dermal, and inhalation contact should be checked. Structure activity relationships should be investigated to determine whether toxicity effects are expected. Treatment of taste and odour problems is effective at some water plants and less effective at others. Treatment technologies are expensive and need to be optimized. Predictive models in the short and long term are needed to predict taste and odour events. The potential for Chrysophyte and Haptophyte species to cause problems in the Great Lakes need to be investigated. Some work has been published on toxicology to organisms from bacteria to rainbow trout hepatocytes. Is the existing work sufficient in the light of exposure analysis or is further testing warranted with mammalian systems and/or human cell lines? What is the biological function of these compounds: are they produced for a purpose or metabolic waste?

  • Re-establish basic ecological knowledge capacity, for example, algal taxonomy to identify sources.
  • Increase capacity for real-time toxin determination: assist in methods development/standards production (capitalize on existing Canadian strengths).
  • Increase knowledge of environmental triggers and management possibilities for algal biomass, toxin and taste/odour production towards protection/remediation.
  • Develop predictive models of toxin/taste/odour production.
  • Increase knowledge on chemistry, chemical and biological fates, e.g., volatility, degradation, bioaccumulation.
  • Increase knowledge of health effects of taste and odour compounds and novel biotoxins (consumption, dermal exposure, inhalation).
  • Provide an appropriate level of public awareness that will reduce exposure to toxic waterblooms and prevent undue public concern when it is not warranted.

References

  • Brittain, S.M., J. Wang, L. Babcock-Jackson, W.W. Carmichael, K.L. Rinehart and D.A. Culver. 2000. Isolation and characterization of Microcystins, cyclic hepatapeptide hepatotoxins from a Lake Erie strain of Microcystis aeurginosa. J. Great Lakes Res. 26(3): 241-249.
  • Chorus, I. and J. Bartram (ed.). 1999. Toxic cyanoabacteria in water--a guide to their public health consequences, monitoring and management. E & N Spon, London. 416 p.
  • Gagné, F., J. Ridal, C. Blaise and B. Brownlee. 1999. Toxicological effects of geosmin and 2-methylisoborneol on rainbow trout hepatocytes. Bull. Environ. Contam. Toxicol. 63: 174-180.
  • Jochimsen, E.M., W.W. Carmichael, J. An, D.M. Cardo, S.T. Cookson, C.E.M. Holmes, M.B. Antunes, D.A. de Melo Filho, T.M. Lyra, V.S.T. Barreto, S.M.F.O. Azevedo and W.R. Jarvis. 1998. Liver failure and death after exposure to microcystins at a hemodialysis center in Brazil. New England J. Med. 339(13): 873-878.
  • Nakajima, M., T. Ogura, Y. Kusama, N. Iwabuchi, T. Imawaka, A. Araki, T. Sasaki and E. Hirose. 1996. Inhibitory effects of odor substances, geosmin and 2-methylisoborneol, on early development of sea urchins. Water Res. 30: 2508-2516.
  • Watson, S., B. Brownlee, T. Satchwill and E. McCauley. 1999. The use of solid phase microextraction (SPME) to monitor for major organoleptic compounds produced by chrysophytes in surface waters. Water Sci. Technol. 40: 251-256.