COMMENTARY || What are natural levels of Athabasca River contaminants?
Careful research on "background" contaminant levels needed to understand industrial impact, argues UAlberta geochemist.
By WILLIAM SHOTYK
We are grateful to Dr. David Schindler and his colleagues for bringing attention to our recently published studies on the levels of trace elements in the Athabasca River, but must correct some inaccuracies they stated.
One goal of our metal-free, ultra-clean SWAMP (Soils, Waters, Air, Manures and Plants) lab at the University of Alberta is to better understand the effect that human activities have on potentially toxic trace elements that show up in soil, water, air, manure and plants. Since all trace elements occur naturally in our environment, we first need to distinguish between natural inputs and those caused by human activity. The main disagreement we seem to have is the apportionment between natural inputs to the river versus industrial sources.
In the lower reaches of the Athabasca River, we collected sphagnum moss from rain-fed peat bogs surrounding open-pit mines and upgraders because this plant serves as a natural monitor of air quality. As well, it had been suggested that heavy-metal emissions to air were affecting river-water quality.
We found that concentrations of silver, cadmium, lead, antimony and thallium—all potentially toxic trace elements—are no more abundant in the moss from northern Alberta than moss from remote areas far removed from industry.
Using precisely dated peat cores from bogs in the same area covering the last 200 years, we show that concentrations of lead in the air have been in decline since the late 1970s, likely the result of the introduction of air-pollution control technologies. Peat cores from these bogs also show that atmospheric contamination by the other heavy metals has been declining.
We have also been testing water directly, including groundwaters. We do not “filter out” particles before testing—we measure the total amount present in the water, the amount dissolved, but also the amount found in and on the particles themselves, and their mineral composition.
In our paper published recently about arsenic in the Athabasca River, we showed that both the dissolved and the total concentrations are no more abundant downstream of industry than they are upstream.
In our paper on lead, we found that it is no more abundant downstream of industry than upstream, in either size fraction. As for trace metals such as silver, cadmium, antimony and thallium, the concentrations in the dissolved fraction are extremely low, and their total concentrations are also no more abundant downstream of industry than upstream. This does not mean that industrial contributions do not exist, but rather that they cannot be distinguished from natural background levels.
The simplest explanation for all of our results to date lies in the bituminous sands themselves. Extraction and digestion of the organic and mineral fractions of bituminous sands in the metal-free, ultra-clean SWAMP lab shows that only four metals are more abundant in bitumen relative to the mineral (sand and silt) fraction: vanadium, nickel, molybdenum and rhenium.
Virtually every other element is found almost exclusively in mineral form. With most of the potentially toxic trace elements found primarily in mineral form, and given the low solubility of these minerals in water, availability of these elements to aquatic life is expected to be low.
What is urgently needed now is a systematic study of trace elements in the entire suite of traditional foods of First Nations peoples, including their chemical forms.
High-quality data for trace elements in plant and animal life is scarce, because this requires careful sampling and handling, sensitive analytical methods and rigorous quality control with proper precautions to minimize sample contamination at each step. Again, the challenge is to first establish natural “background” values for all of the relevant contaminants, to be able to understand the impacts of human activities.
William Shotyk is the Bocock Chair for Agriculture and the Environment at the University of Alberta.