| | Introduction | Summary and conclusions | Implications and recommendations | For more information
The full text of the 26 page study summary is available as a pdf file. It is broken down into three sections, reducing the download time, click to access - pages 1-9 (1,069 KB), pages 10-18 (1,533 KB), pages 19-26 (456 KB). You can download the latest version of the pdf reader software from the Adobe Acrobat web site.
Introduction
Cryptosporidium spp. (cryptosporidium) and Giardia spp. (giardia) are intestinal parasites that can infect humans, domestic livestock and wildlife, as well as other animals, including birds. They are single-celled organisms called protozoa. Human symptoms of infection include profuse, watery diarrhea, fever and nausea. Although giardia infections (popularly called "beaver fever") are treatable with drugs, cryptosporidium infections are not. As well, cryptosporidiosis can be life threatening for people with poorly functioning immune systems, such as those with AIDS or cancer, infants and the elderly. Consequently, these parasites represent a significant risk to public health.
Neither of these organisms can grow or reproduce outside of the digestive tracts of warm-blooded animals. These parasites form cysts or oocysts within the gut and are shed with feces. The cyst or oocyst allows the organism to survive outside of their host until ingested again, when they come out of their cyst and begin reproducing in the new host, and the cycle is repeated.
Cryptosporidium and giardia are transmitted by ingesting contaminated feces or drinking water. They are commonly found in aquatic environments. If they enter public water supplies, many people can become infected, and they have been responsible for outbreaks of waterborne disease worldwide.
In Canada, outbreaks have occurred in Collingwood, Ontario, Cranbrook and Kelowna, British Columbia, and more recently in North Battleford, Saskatchewan.
Domestic livestock, including beef and dairy cattle, are often perceived to be the leading environmental source of waterborne parasites. Several studies in North America have also found these organisms in treated sewage effluent and wildlife. Very few studies, however, have attempted to determine relationships between these sources and concentrations of protozoan parasites in streams throughout a large watershed.
In the spring of 1997, very high levels of cryptosporidium and giardia were present in the North Saskatchewan River, the raw water supply for the city of Edmonton. At the time, the river had high levels of turbidity, which made optimum treatment difficult (although the two City plants were able to meet regulatory standards at all times). As a result of the high number of parasites in the raw water, a few organisms reached the finished drinking water, and a precautionary boil-water advisory was issued for people with poorly functioning immune systems. Fortunately, no disease outbreak occurred.
Because much of the North Saskatchewan River basin upstream of Edmonton is used for livestock production, cattle were suggested as the main contributor to the high levels of these parasites in the river. In 1998, a study was launched to assess the relative contributions from the three potential sources in the watershed: agriculture, municipal sewage effluent and wildlife.
The research team was multi-disciplinary and included researchers from government, universities and private industry. It was funded through grants from the Canada-Alberta Beef Industry Development Fund, Alberta Agricultural Research Institute and Health Canada, as well as in-kind support from Alberta Agriculture, Food and Rural Development, Alberta Environment, Alberta Research Council, EPCOR, the University of Alberta and the University of Calgary.
The primary objectives of the study were to answer the following questions:
- Do cattle contribute significant amounts of cryptosporidium and giardia to surface water compared with wildlife and municipal sewage?
- Do watersheds with high densities of cattle and other livestock contribute greater quantities of parasites to the North Saskatchewan River than non-agricultural (forested) watersheds?
Because much of the watershed above Rocky Mountain House had little agricultural production, the study focused on the river basin between Rocky Mountain House and Edmonton. The three-year study included:
- Characterization of land use in the watershed;
- Prevalence of parasites in fecal material from livestock, wildlife and sewage;
- Water quality assessment of 20 streams draining to the river, wastewater effluent and raw/ treated drinking water; and
- Statistical comparisons of various land use activities with water quality.
The research program was designed to be comprehensive -- it covered all potential major sources of protozoan parasites. But because it is nearly impossible to locate or measure specific sources directly over such a large area, indirect methods were used. If concentrations of parasites in a stream were positively correlated with a certain land use factor, there is a good chance that the factor was responsible (at least in part) for the concentration.
The study did not attempt to deal with human health issues related to the rural population in the basin or whether the organisms found in samples were alive or infective. As well, different species in samples were not identified, because drinking water treatment plants have to assume that all species are potentially infective to human.
Summary and Conclusions
The North Saskatchewan River basin is large, with a multitude of land-use activities and sources of parasites. These parasites are transported from specific sources on the land to the river by runoff, which gathers in streams and finally enters the river. Because it is virtually impossible to pinpoint the movement of organisms from these non-point sources to the river over such a large land area, this study was designed to look at relationships between land-use factors, such as cattle density, and concentrations of parasites in streams that drain to the river.
As well, numbers of parasites entering the river in streams draining agricultural watersheds (those with livestock) were compared with those draining non-agricultural or forested watersheds (those influenced primarily by wildlife). Municipal sewage effluent is also a potential source and therefore loads from municipal sewage treatment facilities were compared with those from streams.
Two questions were addressed during the study:
- Do cattle in cow-calf operations contribute significant amounts of cryptosporidium and giardia to surface water compared with wildlife and municipal sewage effluent?
- Do watersheds with high densities of cattle and other livestock contribute greater quantities of cryptosporidium and giardia to the North Saskatchewan River than non-agricultural (forested) watersheds?
Key findings that address these questions are as follows:
Parasite prevalence
- Concentration and prevalence of giardia in beef cattle feces were higher than in feces from any other type of livestock or wildlife, except for muskrat. Concentration of cryptosporidium was moderately high in beef cattle feces, although prevalence was low. Concentration and prevalence of cryptosporidium were also moderately high in dairy cattle, although not as high as in ranched elk.
- Prevalence and concentration of cryptosporidium in wildlife fecal samples were zero or low, although prevalence and concentration may have been affected by freshness of the sample. Prevalence and concentration of giardia were high in muskrat samples, whereas those from beaver and coyote were moderate.
Water quality
- Streams draining agricultural lands contributed the highest loads of parasites to the North Saskatchewan River, compared with loads from sewage effluent, non-agricultural streams and from the watershed above Rocky Mountain House. However, streams draining non- agricultural (forested) areas occasionally contribute relatively high loads during summer storm events. On average, agricultural watersheds contributed 56% of the cryptosporidium load and 79% of the giardia load in the river at Edmonton in spring and summer.
- Giardia concentrations were high in municipal sewage effluent; however, the total giardia load from municipal sewage facilities was small (less than 2% of the total load entering the North Saskatchewan River during runoff periods) when compared with the total parasite load from the watersheds. Cryptosporidium loads were even smaller. Municipal sewage effluents from the facilities that discharge continuously contribute a year-round base load of giardia to the river. These effluents tend to be a primary source during the winter and likely at other times of the year when river flows are low.
Relationship between land use and water quality
- Concentrations of cryptosporidium and giardia were significantly higher in streams draining watersheds with more intensive agricultural (livestock) production, compared with non-agricultural watersheds.
- In spring, levels of cryptosporidium and giardia in streams were correlated with total livestock density and percentage of cattle yards along watershed streams. As well, giardia levels were correlated with density of beef cattle in spring. In summer, levels of both organisms were correlated with total livestock density. Giardia was also correlated with beef cattle density and grazing factors, whereas cryptosporidium was also correlated with density of dairy cattle and hogs. In fall, giardia concentrations were correlated with dairy cattle and hogs.
- There was no correlation between municipal wastewater discharges and stream parasite levels.
Cryptosporidium and giardia are common in the North Saskatchewan River basin. These parasites were found in feces from livestock and wildlife as well as in raw municipal sewage. Parasites were also present in streams draining non-agricultural and agricultural watersheds, in treated municipal sewage effluents and in the raw source for drinking water. As well, they were present in the North Saskatchewan River at Rocky Mountain House, which represents the watershed above the study area. In treated drinking water, they were undetectable or at such low levels that there would be no cause for concern, although there is some risk from peak parasite levels during major runoff events.
The primary source of parasites, bacteria, nutrients, organic matter and other water quality variables in the North Saskatchewan River is the nonpoint source runoff from the agricultural watersheds as opposed to point sources like wastewater effluents. In general, areas of the North Saskatchewan River basin with high runoff potential contributed more parasites than areas where the runoff potential was low. This emphasizes the importance of runoff processes in surface water contamination.
It is likely that beaver and muskrat contribute to stream giardia levels, as concentrations in feces from both species were relatively high. However, there was no correlation between beaver activity along the streams and stream parasite levels. Beaver dams may retain parasites from the watershed above them. The prevalence of cryptosporidium in wildlife feces was so low that they are an unlikely source of this organism.
The results of the sampling program upstream and downstream of individual cattle operations are inconclusive, although concentrations of giardia were significantly higher downstream of one cattle operation, compared with upstream.
Based on the relatively high prevalence and concentration of cryptosporidium and giardia in livestock feces; the higher concentrations and loads of parasites in agricultural streams compared with non-agricultural streams; and the correlations between numbers of parasites in streams and livestock land-use factors, it appears that livestock (including beef and dairy cattle, ranched elk and bison) are a major source of parasites to the river. However, further research into polymerase chair reaction (PCR) and other DNA-identifying technology is required to pinpoint specific sources of these parasites in environmental water samples.
Implications and Recommendations
Before this study began, little was known about protozoan parasites in a large northern river basin. As with many studies that are essentially "breaking new ground", more questions were raised than were answered. Findings from this study do suggest that livestock in the watershed are a major contributor to levels of parasites in the river. However, other sources also contribute, and statistical relationships need to be confirmed with further detailed study. Because potential sources of these organisms are present throughout the watershed, additional sampling would be needed to measure direct linkages between livestock and parasite levels in streams.
Alberta’s Agriculture industry
Alberta has the largest beef industry in Canada. The Alberta beef industry should be a leader in applying measures to reduce their impact on the environment. We recommend that runoff from livestock operations be managed so that impacts on surface water can be minimized.
Beneficial Management Practices should be evaluated for Alberta to assess how well they reduce sources of parasites and other contaminants that may affect surface waters. Research into ways to reduce parasite infections in cattle is needed. This could benefit Alberta producers by reducing scours and mortality. As well, the beef industry should continue their efforts in educating producers on environmentally sustainable practices through extension materials, seminars and workshops. These measures should reduce concentrations in drinking water and therefore the risk to public health.
Additional sampling should be done on creeks above and below cattle operations, including beef and dairy. These sites should be tied in to management practices used on the farm. More intensive sampling should be done along streams draining agricultural watersheds to identify areas that contribute disproportionately to parasite loads in tributary streams.
Municipal wastewater
Sewage treatment plant operators need to understand their contribution to parasite concentrations in the river. A study should be done to evaluate how different treatment technologies remove parasites from wastewater. Treatment facilities that allow a large percentage of organisms to pass through may need to upgrade their operation. The presence of both parasites in all effluents monitored suggests that some people in the basin are infected. Public health authorities may wish to determine the extent of infections. A data gap that should be addressed is the contribution of parasites and other contaminants from private sewage disposal systems, especially those that discharge to the surface.
Drinking water treatment
Cryptosporidium and giardia in surface water are a risk to human health when the water is used as a raw water source for drinking. The risk is low if treatment plants are operating effectively. However, the water treatment process can be compromised during peak runoff periods such as spring runoff and following heavy rainfall when contaminant loads, including parasites, in the river are high. It is at these times that the risk of parasites getting through to the treated water supply is greatest.
Each plant in the basin should be assessed to determine how well parasites are removed. Drinking water treatment plants should be designed or upgraded to cope with actual levels of parasites in the source water. Because small treatment facilities are not required to monitor parasites in raw or treated drinking water, they typically do not include monitoring costs in their budgets. Therefore, the Alberta government should set standards for these parasites similar to those of the United States Environmental Protection Agency, as well as collect and analyze samples during runoff periods.
At present, drinking water treatment operators must assume that all protozoan parasites in their raw water supply are potentially infective. Further research is needed to develop methods for assessing whether organisms are alive and which species are infective to humans.
Wildlife management
Although the prevalence of giardia in beaver and muskrat was fairly high, control of these animals on streams is not practical. However, to reduce the transmission among aquatic mammals, livestock and humans, removal of these aquatic rodents from dugouts that are used as drinking and watering supplies may be warranted.
High concentrations of parasites were present in samples from the non-agricultural streams during summer runoff periods. Although the breaching of beaver dams likely contributed to these concentrations, additional study should be done of other sources in non-agricultural watersheds. As well, sediments on the bottom of beaver ponds and creeks should be sampled to determine whether they retain parasites until washed out during high flows.
In summary, this research program has illustrated the complexities associated with identifying watershed sources of waterborne parasites. Watershed streams and wastewater effluents contribute to levels of parasites in the North Saskatchewan River. We recommend that all watershed stakeholders, including wastewater operators, drinking water treatment plant operators, livestock producers, rural residents and other landowners and industries work together to reduce the impact that all land uses have on the water quality of the North Saskatchewan River. Support is required from provincial and municipal governments as well as private landowners and the agricultural industry to assist watershed and community groups in implementing water quality protection programs.
For more information, contact:
Lisa Tymensen
Analytical Water Research Scientist
Irrigation and Farm Water Division
Alberta Agriculture and Rural Development
403-381-5165
lisa.tymensen@gov.ab.ca |
|