Hebert, C. E., Campbell, D., Kindopp, R., MacMillan, S., Martin, P., Neugebauer, E., … Shatford, J. (2013). Mercury trends in colonial waterbird eggs downstream of the oil sands region of Alberta, Canada. Environmental science & technology, 47(20), 11785–92. doi:10.1021/es402542w
In Alberta, Canada, the Athabasca River flows northwards into the Peace-Athabasca Delta and western Lake Athabasca, providing an ecologically important and sensitive habitat for millions of birds to nest and stage. In addition, Alberta is home to the 3rd largest known reserve of oil in the world. Primarily found in the Fort McMurray region, the oil sands have been harvested since 1967 and are known to produce around 1.6 million barrels of oil per day, providing more crude oil to the United States than any other country.
Metal processing, coal incineration, waste dumping, and mining are all sources of mercury to the environment. Once it is released into the air, mercury gets deposited onto land or in rivers, and washed into waterbodies, where it can be converted by microorganisms into methylmercury, which is the toxic form of mercury that can bioaccumulate up the food chain and eventually make its way into humans via pathways such as fish and shellfish consumption (for more about this issue, see here!). The oil sands industry has previously been linked to the regional availability of mercury in Alberta. In fact, the petroleum industry was the primary source of mercury emissions to the air in Alberta’s industrial sector during 2011, accounting for around 40% of emissions. Aside from the local oil sands industry, forest fires and industry in Asia are two other potential sources of mercury to this region. Gaseous elemental mercury can actually undergo long-range atmospheric transport from Asia and be deposited over North America. The Richardson Backcountry Fire of 2011 was the biggest fire in Alberta in over 60 years and covered 700,000 hectares, which is the equivalent of almost 375,000 football fields, potentially increasing mercury levels locally.
The good news is that in Alberta, total overall annual emissions of mercury have generally decreased, however, there are still slight inter-annual variations and emissions from the oil sands operations remain slightly elevated. In order to gain a better grasp on specific sources of mercury to Alberta, a group of scientists from Canada sampled eggs from colonial waterbirds in order to assess any trends that may be occurring.
Eggs of California Gulls, Caspian Terns, Common Terns, and Ringed Billed Gulls were sampled from different sites located both downstream of the oil sands and upstream of the oil sands to determine if the oil sands are influencing mercury levels. These species of birds are useful because they are known to reflect local environmental conditions and they feed primarily on small prey fish, which are known to respond to changes of mercury levels in the environment within one to two years. If the eggs were all to show similar levels of mercury, it would indicate that atmospheric transport of mercury from Asia is occurring as the primary source of mercury, whereas if they were to show different trends based on place and time it would indicate that local sources may be more significant, such as the oil sands industry. The possibility of forest fires as a significant source of mercury can be investigated by looking at other contaminants that are associated with fire, such as polychlorinated dibenzodioxins/furans (PCDDs/PCDFs). In addition to looking for mercury levels and dioxins/furans, the group also looked at nitrogen stable isotopes from the eggs, which is a neat tool that can be used to assess trophic level, or essentially where birds (or any animal) are on the food chain.
Stable isotope of nitrogen from the eggs revealed that birds higher in the food-chain, such as Caspian terns and Common terns, appear to be accumulating mercury at a higher degree than they had in the past. This is not likely due to a change in diet, but due to a change in the actual loadings of mercury to the region. It was determined that the Richardson Backcountry Fire of 2011 did not appear to be a significant source of mercury to the sensitive ecosystem of the Peace-Athabasca Delta because they did not see an increase in the dioxin and furan (PCDD/PCDF) levels in eggs sampled in 2012. Additionally, the long-range transport of mercury from Asia was found to influence mercury only minimally in Alberta because different levels of mercury were observed at different sites, with higher levels observed downstream of the oil sands. In conclusion, it is likely that local mercury sources such as the oil sands are the most important factor governing mercury levels in this region of Canada. In general, most concentrations observed in the eggs were below the lower toxicity threshold; however some of the eggs did exceed this threshold, which is a cause for concern. The authors state that more research is needed in this area to make conclusive decisions on what the exact local sources may be, but indicate that they may be related to the oil sands industry.