Toxins in Great Blue Heron Eggs an indicator of contaminants in the Georgia Basin

What is Happening?

Environment Canada's Canadian Wildlife Service monitors toxin levels in Great Blue Herons (Ardea herodias) from the Georgia Basin. Herons are a good long-term indicator of toxic contaminants in the Georgia Basin ecosystem because they feed on a wide variety of fish, invertebrates and small mammals and because coastal populations do not migrate. By measuring contaminant levels in heron eggs, trends in toxic contaminant levels can be evaluated. Since herons feed mainly on young fish, changes in the amount of contaminant entering the food chain are rapidly reflected in their prey and subsequently in their eggs.

Since 1977, Environment Canada has monitored the level of two persistent organic pollutant groups in Great Blue Heron eggs: organochlorine pesticides and industrial organochlorines (PCBs, dioxins and furans). In addition to monitoring changes in levels over time, Environment Canada also examined how these levels vary geographically. Over 20 colonies were sampled in the 1980s and 1990s. Three of these colonies, located in the Georgia Basin, were chosen for in-depth monitoring (see Map). One reflected general non-point source urban pollution (UBC), the second a rural (Nicomekl) habitat and the third a point-source pollution from a pulp-and-paper mill (Crofton).

Organochlorine pesticides

Organochlorine pesticides are chemicals that were used to control agricultural pests. The levels of three of these chemicals are monitored by Environment Canada: DDE (dichlorodiphenyldichloroethylene), chlordane and dieldrin. Despite a ban on all three chemicals in Canada, they are still routinely detected in Great Blue Heron eggs since they do not easily breakdown in the environment, persisting for many years after the original application. These pesticides bioaccumulate in wildlife, and concentrations are biomagnified as they rise through the food chain, so that organisms at the top of the food chain are impacted the most.

As shown in the graphs below, levels of these three organochlorine pesticides in the Georgia basin colonies declined in the 1980s, and have since fluctuated at lower levels. Although some levels rose again in the mid-1990s they again declined to lower levels. The highest levels were consistently measured at the urban colony. This likely reflects the colonies’ location at the mouth of the Fraser River, where runoff accumulates from the high intensity agriculture in the Lower Fraser Valley. Moderate levels at the rural site likely reflect its low-intensity agriculture on the Nicomekl River. The industrial site is not near any agriculture.

Source: Laurie Wilson. Environment Canada, Canadian Wildlife Service, Delta, BC. 2003. Data are presented as arithmetic means.

GRAPH DATA

Industrial Organochlorines

Polychlorinated biphenyls (PCBs), dioxins (polychlorinated dibenzo-p-dioxins, PCDDs) and furans (polychlorinated dibenzofurans, PCDFs) are another set of contaminants also routinely detected in heron eggs. They originate from a wide variety of industrialized activities such as coolants in electrical products (PCBs), chlorine bleaching in kraft pulp and paper mills (dioxins and furans) and incineration of municipal and industrial wastes (dioxins and furans).

Because dioxins, furans and PCBs exhibit similar toxic effects, a system has been developed to estimate the combined toxic effect of exposure to these types of chemicals. Each type of dioxin, furan and PCB has been assigned a 'toxic equivalent factor' (TEF). The value of the TEF is based on the toxicity of the particular formulation relative to the toxicity of 2378-TCDD (one of the most toxic types of dioxins). For example, the TEF of 2378-TCDD is 1, whereas the TEF of PCB 126 is 0.1, as research has determined that PCB 126 is 1/10th as toxic to birds as 2378-TCDD. The actual toxicity is then calculated by multiplying the concentration of the contaminant by its TEF. This produces a toxic equivalent quotient (TEQ) and the total toxicity of a mixture of chemicals can be estimated by summing the TEQs for all contaminants present.
Source: Laurie Wilson, Environment Canada, Canadian Wildlife Service. 2003. Note that * = years where TEQ values for dioxins and furans were not measured.

GRAPH DATA

As can be seen in the above graphs, the long-term monitoring of the heron colonies in the Georgia Basin found that the combined toxicity (TEQs) of industrial organochlorines in heron eggs was fairly constant until about 1989, after which time it decreased to its present low level. Since 1990, TEQs from dioxins and furans in particular have decreased substantially. This trend is particularly noticeable at Crofton, near a pulp and paper mill, where TEQs were highest during the 1980s, before plummeting after 1991. TEQ values are now dominanted by PCBs.

PCB levels declined in the 1980s before fluctuating at lower levels in the 1990s. The urban non-point source colony (UBC), which forages in the Fraser River estuary, had the highest PCB TEQ's in relation to the point source (Crofton) and rural (Nicomekl) colonies.

Why is it Happening?

The Fraser River, the largest watershed in British Columbia, flows into the Strait of Georgia. The Fraser River Watershed occupies one quarter of British Columbia's land mass and is home to a diverse range of flora and fauna, as well as two thirds of BC's human population. Extensive development of forestry-related and agricultural industries have resulted in the release of large quantities of chlorinated hydrocarbons into the Fraser River Watershed and the Georgia Basin (see map). They can persist in the environment for decades before breaking down, and during that time accumulate in wildlife. As shown in the above figure, concentrations increase up the food chain, so that top predators such as eagles and fish eating herons have the highest levels of contaminants.

The decline in chlorinated contaminants in heron eggs began after the passing of legislation either banning or severely restricting the production and use of chlorinated chemical products in Canada.

DDT was banned in Canada in 1970. Ongoing low levels of DDE in heron eggs may likely reflect atmospheric deposits from regions where DDT is still used, as well as persistent historic residues in soils of past intensive agricultural use in BC. The granting of permits for the use of chlordane, with the exception of its use to control subterranean termites by licensed pesticide applicators, were suspended in 1985. Even its use against termites was voluntarily discontinued, with the understanding that the existing stock would be sold, used or disposed-of by the end of 1995. The sale of dieldrin was heavily restricted in the mid-1970s, with the last registered use of the compound in Canada occurring in 1984.

The manufacture of PCBs has been banned in North America since 1977 and since then its use, import and sale in Canada has been strictly controlled. The concentrations of PCBs observed in heron eggs, since 1977, have dropped considerably. However, the continued presence of this toxic contaminant in heron eggs in the Georgia Basin reflects on its persistence as well as the ongoing low-level inputs and atmospheric deposition of the PCBs currently circulating in local and world-wide ecosystems (Wilson et al. 1996). In BC, the amount of PCBs still in use continues to decline, with only 2264.6 tonnes used in 2003 compared to 4942 tonnes in 1992 (see PCBs in Cormorant Eggs indicator).

Forestry-related industries were an important source of dioxins and furans in BC. In 1989, most industrial processes which resulted in the production of dioxins and furans were banned. For instance, pulp mills changed from molecular chlorine bleaching to alternative bleaching technologies and the use of chlorophenolic wood preservatives and anti-sapstains were severly restricted. Consequently, between 1989 and 1996, the total daily loading at all coastal BC mills for the dioxin 2378-TCDD, fell from over 50 mg per day to under 3 mg per day, a 95% decline, and the furan 2378-TCDF, declined by 99%. The daily loading for these chemicals continue to decline (see the Dioxin and Furan indicator).

Heron colonies near pulp mills show much higher levels of dioxins and furans while colonies near Vancouver show higher levels of PCBs. This demonstrates the impacts on the environment that industrial activity and large residential populations can have.

In addition to local contamination sources, some of the toxin contamination may have been transported into the Georgia Basin from distant sources. Many chlorinated compounds are volatile, and move through the atmosphere, condensing in cooler regions. Alpine areas in BC and Yukon have recorded some of the highest toxin levels in the region. When alpine glaciers melt, these toxins move into the aquatic ecosystem. Climate change may exacerbate this as snow pack which has been accumulating toxins for many years melts (Elliott et al. 2002).

Why is it Significant?

Organochlorine pesticides

Even historically high DDE levels measured in heron eggs were likely too low to have seriously affected the reproductive success of herons. However, wildlife higher in the food chain, such as Bald Eagles, may have experienced reproductive failure due to these DDE levels (Elliott et al. 1996).

Organochlorine pesticides are known to affect eggshell thickness. Eggs with thin, brittle shells are easily damaged and can reduce avian reproductive success. Heron eggshells measured between 1977 - 1986 were consistently thinner than those measured before 1947 (Harris et al. 2002). On-going analysis of eggshell thickness at the three Georgia Basin colonies (UBC, Crofton and Nicomekl) since 1987 showed a consistent increase in eggshell thickness up to 1999 (Harris et al. 2002).

Industrial Organochlorines (PCBs, dioxins and furans)

Elevated levels of dioxins and furans have been shown to affect heron chick development. As can be seen in the graph below, the Crofton heron colony located near a large pulp and paper mill on Vancouver Island, failed to produce chicks and had very high dioxin/furan toxicity in their eggs in 1987 (Elliott et al. 1989). The following year toxicological studies were conducted on some heron eggs from the Crofton colony and some from several less contaminated sites. The artifically incubated embryos and chicks from the Crofton colony were found to have significantly higher levels of specific detoxifying enzymes in their livers, higher rates of fluid retention in newly hatched chicks (evidence of dioxin exposure) and overall reduced growth rates compared to those from cleaner sites (Bellward et al. 1990; Hart et al. 1991). Adult heron incubating behaviour and nest attentiveness may also have been a factor during 1988 as herons at Crofton showed a greater range of incubation times compared to herons at less contaminated sites (Moul 1990). The poor nesting success at the UBC colony in 1988 may have been in part attributable to elevated dioxin/furan exposure. Further evidence of potential impacts is that reductions in dioxin/furan levels in heron eggs, at UBC as well as at Crofton, over the next several years coincided with reproductive success (Sanderson et al. 1994).

In addition to dioxin and furan toxicity, other factors may have had an effect on reproductive success in the Crofton colony. The presence of people or eagles can cause incubating or chick-rearing adult herons to flush from a colony, leaving their young exposed. Eagles will attack adult herons and take chicks from nests, but probably of greater significance is opportunistic predation by ravens and crows once the colony is temporarily abandoned. In 1995, despite lower levels of dioxin and furan toxicity, herons at the Crofton colony once again abandoned their nests after laying eggs. Disturbance from nearby construction was identified as a possible factor. This heron colony has now moved to a nearby island, where local residents have secured habitat. For more information on habitat conservation, visit the Great Blue Heron population indicator.

There is still a concern that combined with habitat loss contaminant levels may endanger heron populations. Monitoring shows that Great Blue Heron populations in the region are decreasing. There are only an estimated 2000 pairs in coastal British Columbia, and these birds belong to their own subspecies which has been given a status of "special concern " by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Similarly the BC Ministries of Sustainable Resource Management and Water, Lands and Air Protection have placed this sub-species on their blue-list as it is considered to be both vulnerable and at risk.

Although the toxic threat to herons has decreased, the cumulative effect of exposure to low concentrations of multiple contaminants is still a concern in the Georgia Basin. This is particularly so when combined with the additional stresses of risks from predators and habitat loss and destruction.

What is Being Done?

The Canadian Wildlife Service (CWS) continues to monitor and assess the significance of chlorinated contaminants (such as DDE, PCBs, and dioxins and furans) on key indicator species, such as the Great Blue Heron, throughout BC. Research to understand the impact of exposure to low concentrations of multiple contaminants is also being conducted. CWS continues to monitor reproductive success and other parameters at selected heron colonies. These projects have been funded in part by the Georgia Basin Ecosystem Initiative and are part of the federal government's commitment to ensure that toxic chemicals do not adversely affect the health of the region's ecosystems.

CWS maintains a specimen bank, so that present and past specimens can be analyzed in the future for new chemicals. For example, in 1977, dioxins were not recognized as a significant toxin. When dioxin levels became an environmental issue in the 1980s, scientists were able to analyze archived specimens for dioxin levels, and assess the toxicological impacts on local heron populations. Currently, polybrominated diphenyls ethers (used widely as flame retardants in furniture and plastic) and mercury have been identified as chemicals of concern, and researchers are now reanalyzing past specimens to see if this chemical is impacting local wildlife.

Apart from contaminants, habitat loss can have a major effect on heron populations. Herons can habituate to some degree of disturbance as evidenced by the heron colony that existed in Beacon Hill Park, Victoria. However, new or unpredictable disturbances introduced while the birds are nesting are not well tolerated. Loss of critical habitat for herons in the Georgia Basin remains a concern. It is challenging for wildlife managers to protect habitat and reduce disturbance for herons in the Georgia Basin since nearly three quarters of the heron population nest on private land. Tidal variation during the winter also forces herons to feed in more inland grasslands and marshes. In an effort to preserve heron habitat, the Canadian Wildlife Service has formed a partnership with the BC Ministry of Water, Land and Air Protection, and the Wild Bird Trust of BC to establish the Heron Stewardship Program. For more information about this initiative, visit the Great Blue Heron indicator.

For more information contact:   John.Elliott@ec.gc.ca or Laurie.Wilson@ec.gc.ca

Check the following sites for additional information on this indicator:

• Hinterland's Who's Who - Great Blue Heron
• Canadian Bird Trends Database
• Canadian Wildlife Service
• What you can do for wildlife
• Environment Canada's Millennium Eco-Communities
• Pacific and Yukon Region Canadian Wildlife Service Ecotoxicology
• Environment Canada's S&E Bulletin - High-Altitude POPs and Alpine Predators
• Persistent Organic Pollutants - POPs
• PCB - Polychlorinated Biphenyls
• Endocrine Disrupting Substances (EDS)
• Chlorinated Substances Action Plan
• ARET: Accelerated Reduction/Elimination of Toxics
• Pollution Prevention Fact Sheets
• National Office of Pollution Prevention
• Flame Retardants: A Threat to the Environment?

The following Web sites are not under the control of Environment Canada (EC) and they are provided solely for the convenience of users. Environment Canada is not responsible for the accuracy, currency or the reliability of the content. Environment Canada does not offer any guarantee in that regard and is not responsible for the information found through these links, nor does it endorse the sites and their content. Users should be aware that information offered by non Government of Canada sites that are not subject to the Official Languages Act, and to which Environment Canada links, may be available only in the language(s) used by the sites in question.

• The Great Blue Heron Book
• Important Bird Areas of Canada
• North American Commission for Environmental Cooperation
  • North America eliminates use of chlordane

For references used in this indicator click here.