A herring gull colony is no place for the faint of heart, says Robert Letcher, research scientist with Environment and Climate Change Canada (ECCC) and Head of the Environmental and Analytical Chemistry Research Group in the Wildlife and Landscape Science Directorate.
Letcher speaks from experience. To those unfamiliar with herring gulls, their colonies — such as those dotting the Great Lakes Basin — are populated by up to several thousand birds that, in spring, brood hundreds of nests holding two to four eggs. Letcher’s research into legacy and emerging organic contaminants in fish and wildlife has necessitated the collection of Great Lakes herring gull eggs for laboratory testing. Undertaking such fieldwork has meant clambering over the rocks of Lake Huron’s Chantry Island to collect eggs, infuriating the nesting gulls. “There is the ear-splitting noise of the birds and the continual threat of being seriously injured,” says Letcher, who is also an adjunct professor in the Department of Chemistry at Carleton University. “The parent birds continually attempt to attack you by raking your head with their feet and beak. They can also cover you with various bodily secretions.” In order to minimize such indignities — as well as potential injury — Letcher would hold a branch from a bush over his head while egg collecting, an expedient but somewhat dubious form of defence.
Robert Letcher is no stranger to challenging field studies, be it an excursion to Canada’s Arctic or gathering eggs from herring gull colonies. Photo credit: Robert Letcher
Though the work is difficult, it serves a key purpose: studies like Letcher’s provide a critical window on the environmental health of the Great Lakes. Formed by glaciers 14,000 years ago, the lakes — consisting of Superior, Michigan, Huron, Erie and Ontario — contain 21 percent of the world’s surface fresh water. They provide drinking water to more than one quarter of Canada’s population, not to mention millions more in the United States.
Once surrounded by vast, pristine forests, the lakes’ ecology has changed dramatically due to urbanization, agriculture, industrialization and logging. During the 1960s, Lake Erie was even declared “dead” due to an overload of phosphorous that caused algae blooms. Soon afterward, another issue emerged: that of dioxins. Formed as byproducts of various industrial processes such as the manufacture of herbicides and pesticides or chemical bleaching of paper pulp, dioxins are classified as persistent organic pollutants (POPs). This means that they have a high stability to chemical breakdown, bioaccumulate in the food chain and are toxic to humans and animals. In the early 1970s, dioxin-like POPs, such as polychlorinated biphenyls (PCBs), rose to serious levels in the Great Lakes, affecting a wide variety of fish-eating birds such as the double-crested cormorant, eagles, terns and herons. Either the eggs didn’t hatch or, if they did, the chicks had twisted beaks, crooked legs and deformed claws.
Eggs give a picture of what the herring gull mothers were exposed to prior to laying.
These tragic outcomes began to spur action. While the Canadian and US governments pursued treaties and agreements that would eventually result in the phasing out of certain POPs, it was clear that more research was needed on how such chemicals were affecting the ecosystem, including the birds. In the 1970s, the Canadian Wildlife Service (CWS) created the Great Lakes Herring Gull Monitoring Program (GLHGMP). Forty years later, the program still provides one of the most comprehensive sources of data on the environmental chemistry of the Great Lakes region.
Herring gulls are a sentinel species. As top predators in the aquatic food web, they have a much greater exposure to chemicals that bioaccumulate in animal tissues. Their eggs in turn provide a picture of what the mothers were exposed to before and during egg development. Since joining the CWS and ECCC in 2004, Letcher has been working with other ECCC researchers, including Chip Weseloh, Craig Hebert, Shane de Solla and Pam Martin, analyzing these archived egg samples to help understand the fate of legacy POPs, a category that includes flame retardant chemicals like polybrominated diphenyl ethers (PBDEs). More recently, Letcher and his coworkers have focused on what are called chemicals of emerging concern (CECs), including surfactant chemicals like perfluorinated sulfonic and carboxylic acids.
PBDEs are used to increase the fire safety of plastics and polymer-based materials in homes, cars and offices. In Canada, the vast majority of flame retardants come into the country as part of commercial or industrial products. Ironically, there is increasing criticism about the efficacy of flame retardants in helping protect against fire, something that the industry hotly disputes.
Many jurisdictions — including Canada — have imposed restrictive regulations on the production and use of PBDEs, Letcher says. This has resulted in, for example, the total discontinuation of the commercial fire retardant formulations Penta- and Octa-BDEs, which contain PBDEs. (In 2009, Penta- and Octa-BDEs were added to the Stockholm Convention on Persistent Organic Pollutants, the international environmental treaty to eliminate or restrict the production and use of POPs.) An exception is the highly brominated PBDE decabromodiphenyl ether, or BDE-209. Thus, although PBDE in the environment has been decreasing, BDE-209 levels have been increasing since the mid- to late-1990s. Letcher is also seeing increasing trends in some of the chemicals that replaced PBDEs over the same time period.
Most recently, Letcher and fellow GLHGMP researchers have discovered a set of previously unknown contaminants that they believe are the breakdown products of flame retardants. In some cases, these substances are even more persistent and bioaccumulative than the compounds from which they were derived.
Amila De Silva, research scientist with the Canada Centre for Inland Waters, has discovered that three top predators, including the Great Lakes’ double-crested cormorant, have perfluoroalkyl phosphinic acids (PFPIAs) in their bloodstream. The long-term effects are unknown. Photo credit: Glenn Barrett and Shane de Solla (cormorant). Photo credit: Glenn Barrett and Shane de Solla (cormorant)
According to Letcher, the new contaminants “look a lot like PBDE flame retardant chemicals.” For example, his group has identified them as methoxylated-polybrominated diphenoxybenzenes (MeO-PB-DiPhOBzs) and suggested that they are produced when a precursor flame retardant photodegrades in sunlight and then is further changed by enzymes in the birds. Data from the monitoring program shows they may have been contaminating Great Lakes herring gulls for the past 30 years. “There is clearly a growing number of different chemicals that are being used as new replacement flame retardants. This is a change from 10 or 15 years ago, when the manufacture for this purpose was based on a fewer number of chemicals, for example, PBDEs,” Letcher says.
The effects of increasing complexity in flame retardant formulations affect more than just herring gulls. A growing body of evidence indicates that exposure to flame retardants leads to the disruption of endocrine, or hormone, and immune systems in both animals and humans. On top of that, many flame retardants are carcinogenic. “From a complex mixture standpoint, one could argue that things are getting worse as there are an ever-increasing number of CECs — new replacement flame retardants — being reported in the environment and wildlife. The chemical complexity is further magnified since many of these CECs are not environmentally stable and break down into other forms,” Letcher says.
Research into the new brominated contaminants MeO-PB-DiPhOBzs indicates that the source may be tetradecabromo-1,4-diphenoxybenzene (TeDB-DiPhOBz), a flame retardant in current use. Letcher’s research group, including postdoctoral fellow Guanyong Su, in collaboration with Doug Crump, a molecular toxicologist with the ECCC, has shown that TeDB-DiPhOBz, when exposed to sunlight, breaks down into new molecular forms with lesser numbers of bromine atoms, in addition to generating a more complex breakdown mixture overall. The sunlight breakdown mixture includes polybrominated-dibenzofurans, which are dioxin-like compounds. Letcher’s team and collaborators have established that it is “highly likely that as TeDB-DiPhOBz loses an increasing number of its 14 bromine atoms, the new breakdown molecules become more able to persist and bioaccummulate in organisms exposed to them, such as herring gulls and what they eat,” he says.
In addition to chemically identifying these sunlight breakdown products, the team is investigating their physiological effects on birds. For example, they are undertaking toxicogenomic (gene expression) studies using DNA microchips, specially designed to identify possible effects. Crump has established that the sunlight breakdown mixtures alter the expression of genes associated with several important toxicological pathways. These studies, involving the injection of commercial chicken eggs as well as the use of embryonic liver cells, are showing toxicogenomic changes that may include developmental, reproductive and hormonal effects. Such effects are not dissimilar to those of the dioxin-like compounds that spurred the creation of the GLHGMP all those years ago.
Letcher says that it is challenging quantifying not only the amount in the environment but the degree of risk such contaminants pose to the biota that are exposed to them. Based on the latest available data, the team has identified tens of parts-per-billion as a “threshold of concern,” Letcher says. In some gull colonies, including one on an island on the American side of Saginaw Bay in Lake Huron, the new brominated contaminants MeO-PB-DiPhOBzs are being found in eggs in concentrations as high as several hundred parts-per-billion. Although worrisome, more research on this front is required, as there is simply nothing currently known as yet on the biological or toxicological effects of MeO-PB-DiPhOBzs.
In addition to a lack of research into these CECs, Letcher believes that the ones that have been found are just “the tip of the iceberg when considering potentially unknown CECs in gull eggs.” Not all are flame retardants: another class of CECs includes such chemicals as perfluorinated sulfonate and carboxylate compounds. To date, Letcher’s team has chemically screened and in some cases found more than 210 different new CECs as a result of screening herring gull eggs and maternal gull tissues. These include a large suite of per-/polyfluoroalkyl substances (PFASs), which are used as surfactants and water repellents in everything from fire-fighting foams to textiles. However, what the future effects on herring gulls — as well as other birds and wildlife in the Great Lakes area will be — is anyone’s guess.
Another chemist undertaking studies into biotransformation and bioaccumulation of POPs in aquatic organisms is environmental chemist Amila De Silva, a research scientist with the federal Canada Centre for Inland Waters, based in Burlington, Ont. De Silva is the lead author in a recently published Environmental Science & Technology article describing the presence of perfluoroalkyl phosphinic acids (PFPIAs), which are perfluoroalkyl acids (PFAAs), in the blood of three major fish-eating species in North America. These top predators include the double-crested cormorant of the Great Lakes, St. Lawrence River northern pike and bottlenose dolphins in Sarasota Bay, Fla. and Charleston Harbor, SC.
PFAAs are used in a range of commercial and industrial applications while PFPIAs, specifically, are used as a surfactant in pesticides to prevent foaming, which helps with application. De Silva’s study is the first ever to measure PFPIA contamination in a diversity of wildlife; other research focused solely on levels in human blood while another focused on levels in a singular species of fish. Her results were surprising. Based upon blood samples taken from the birds, fish and dolphins from five cormorant colonies, two separate areas along the fast-moving St. Lawrence as well as the two southeastern United States marine locations, PFPIAs were found “with 100 percent detection frequency, indicating that these compounds are not a regional issue,” De Silva says. The urban-impacted sites had the highest PFPIA levels, she adds, with Ontario’s Hamilton Harbour cormorant population having the highest blood concentration of all the studied wildlife. Hamilton Harbour is well known for having multiple inputs: industrial, commercial and residential.
Interestingly, says De Silva, who investigated PFAAs as part her PhD studies in environmental chemistry at the University of Toronto, PFPIAs also appear to be ubiquitous in residential homes. In 2011, De Silva tested indoor dust samples from 102 homes in Vancouver and found PFPIAs in 85 percent of them. “We should be concerned because so little is known about the effects of PFPIAs or their degradation products on organisms,” says De Silva. She adds that there are currently no regulatory controls on PFPIAs under the Canadian Environmental Protection Act.
De Silva points to one study by Magali Houde of the ECCC, who published a paper on perfluorophosphonates (PFPA) toxicity on green algae. (PFPAs are degradation products of PFPIAs). Houde reported that PFPAs can impact the algae antioxidant defense system. Studies are also underway at the U of T on the effects of PFPAs and PFPIAs in rats.
In 2012, De Silva, together with Scott Mabury and Holly Lee of U of T, published findings showing that PFPIAs are metabolized to PFPAs in fish. This was a “groundbreaking result,” as it was previously thought that PFPIAs are not altered by natural environmental processes or degraded by sunlight. Such results, says De Silva, highlight how little is known about PFPIAs, their fate in the environment and their effect on organisms.
It is estimated by Canada’s Chemicals Management Plan that there are about 4,300 chemicals of commerce in the environment whose environmental and health risks are largely unknown. If progress is to be made in understanding these risks and taking action to prevent harm to both humans and wildlife, it will be because of the work of researchers like De Silva and Letcher and the powerful insight provided by decades worth of hard-won herring eggs.