Oil sands development contributes elements toxic at low concentrations to the Athabasca River and its tributaries

Airborne Contaminants.

Within 50 km of upgrading facilities (AR6), 11,400 metric tons of airborne particulates were deposited in 2008 during ∼4 mo of snowfall (figure 2 of ref. 13). The majority of the particulates consisted of oil sands bitumen, as indicated by the large proportion of oil per unit particulate mass and similar distributions of PAC and PPE in oil sands and particulates (figure S2 a and b in ref. 13). Differential fractionation of PPE during upgrading and low solubility of some elements in water may be responsible for any differences in the distribution of PPE in oil sands and in particulates (Fig. S2 A and B). Coke and fly ash from upgraders contain significant amounts of Ni and elements other than PPE, and relative concentrations of elements in ashed coke and fly ash (16, 17) are similar to those in snow particulates. Particulate elements decline more rapidly with distance from AR6 than do dissolved elements. Thus, partitioning between phases likely occurred before emission rather than after melting of snow (Datasets S1 and S2).

Type 2 and 3 deposition patterns implicate local sources, such as land clearing, mining, road dust, and other emissions related to oil sands development, as substantial additional sources of PPE contamination (Datasets S1 and S2). Oil sands industries have emitted airborne PPE for at least 30 y. Increased deposition attributed to fly ash was found 25 km north and south and 10 km east and west of upgrading facilities during snow surveys in 1978 and 1981 (21, 22). Deposition declined from 1978 to 1981 after installation of precipitators (22). By 2008, the area contaminated by particulates was nearly 2-fold larger than in 1978–1981. Deposition of particulates was about 34,000 metric tons in 2008, five times greater than emission inventories and close to annual deposition rates before precipitators (13).

Although no PPE were measured in earlier studies, deposition of other elements (e.g., total K, Na, and Ca and dissolved Al) was significantly greater in 2008 than in 1978, before installation of precipitators (paired t test; P < 0.006) and was greater than in 1981, after installation (P < 0.04). In contrast, deposition of particulate Al, V, and Ti and dissolved V was significantly lower in 2008 than in 1978/1981 (P < 0.03; SI Text). Hence, the success of technologies in controlling different elements appears uneven, although differences among studies also may relate to site, sampling, and analytical differences.

Nonetheless, excessive deposition of elements has occurred for more than 30 y, and emissions of As, Pb, and Hg to the air by Suncor and Syncrude increased ∼3-fold between 2001 and 2008 (23). Our estimates of the annual particulate deposition of Pb, Hg, and Ni, integrated within a 50-km radius of AR6, were 36%, 96%, and 59% lower, respectively, than reported annual emissions. This difference probably indicates that some emissions are deposited outside the 50-km radius. Hg concentrations in fishes respond rapidly to changes in atmospheric deposition of Hg (24); these changes are of concern because Hg concentrations in fishes from the AR and AD are already high (18).

Riverborne Contaminants.

Similarities between the relative concentrations of PPE in snow and river water link emissions of airborne elements to the AR and its tributaries (Fig. S2 C and D). PPE in the snow pack probably were released as a pulse during spring melt. In summer, PPE are deposited directly to waterbodies and the watershed. During snowmelt and rain events, elements are discharged to surface waters, but a proportion is retained in soil and vegetation. Particulate and dissolved Ni best represent the type 1 deposition pattern. In summer, when direct deposition of airborne contaminants to the river occurs, Ni concentrations are strongly correlated with concentrations of all other PPE in the AR and its tributaries (r² > 0.8, except Ag = 0.5; P < 0.001). In winter, when airborne elements are deposited to snow on river ice, particulate deposition of all PPE except Se declines exponentially from AR6, although some also are affected by local sources. In river water under ice, concentrations of Ni were not correlated with other PPE, suggesting that concentrations under ice reflect inputs from erosion or effluent discharge, not atmospheric sources. Concentrations of three PPE and four other elements known to be increased in oil sands process water are much greater in the AR only near tailings ponds or oil sands development in winter. This finding suggests tailings pond leakage or discharge as sources of elements to the AR.

The pattern of increased PPE concentrations in snow and the river system does not support the claim that contamination of the AR and its tributaries is only from natural erosion of oil sands. Concentrations of PPE did not increase significantly as water flowed through the McMF from midstream to stream mouth sites, in winter or summer (Dataset S3), and element concentrations in bottom and suspended sediments of tributaries did not reflect greater exposure to natural oil sands (25). Previous records of upstream-to-downstream trends in waterborne Ni and Zn concentrations during high flow (26) probably reflect runoff of snowmelt and rain from disturbed areas or areas contaminated by atmospheric deposition.

Instead, our results indicate that the source of PPE was from oil sands development. In tributaries, overall land disturbance caused a major flux of PPE to water (Fig. 2 and Dataset S4). In summer, increased concentrations of many PPE were significantly related to development at midstream and tributary mouth sites (Fig. S1 and Dataset S4). At less disturbed tributary sites, concentrations of most PPE were greatest under winter ice (Dataset S4). However, at more disturbed tributary sites, concentrations of several PPE were greater in summer than winter (Dataset S4), indicating the impact of land disturbance. If the source were natural erosion of oil sands, concentrations at all sites would have been greater in summer than winter.

In the AR, PPE concentrations were greater downstream of oil sands development, particularly in summer, and many remained increased over upstream concentrations at downstream and AD sites (Fig. 3 and Dataset S6). This increase may be the result of natural increases in BG concentrations downstream, based on the river continuum concept (27). However, among all PPE, the pattern of increases over upstream concentrations in the AD and LA was similar to increases ND (Fig. S1), indicative of a persistent anthropogenic signal with oil sands development as the most likely source. Long-term trends (1989–2006) at an AR site downstream of oil sands development show that metal concentrations generally decreased, but with no significant trends after flow adjustment except for a decline in Pb (28). In contrast, from 1960–2007, stream flow and concentrations of three elements decreased, but turbidity, nutrients, As, and Al increased at Old Fort, just within the AD, probably because of anthropogenic disturbance (29). In sediments, metal concentrations increased downstream to the AD and LA (30), indicating deposition of suspended particulates in the meandering channels of the AD.

Increased airborne deposition of elements for ∼40 y probably has increased PPE and PAC (13) concentrations in surface soils, vegetation, snow, and runoff over a broad area of boreal forest. Although RAMP has sampled snow for hydrologic monitoring (31), pollutant concentrations were not reported, despite past recommendations for regional monitoring of contaminants in snow (21, 22). Given the lack of detailed long-term monitoring, it is difficult to tell how much upstream concentrations have increased over true BG as the result of long-term airborne deposition (13). Previously, concentrations of several elements in tributaries to the AR have exceeded guidelines for the protection of aquatic life during spring (26). These concentrations were thought to be natural and useful as baseline data to assess future emissions (26). However, reaches of these tributaries are within 50 km of AR6, where we show that deposition of many elements to snow is increased. Emissions from new and expanded upgrading facilities will further increase regional BG concentrations.

Concentrations of Cd, Cu, Pb, Hg, Ni, Ag, and Zn in melted snow and in tributary and AR water exceeded guidelines for the protection of aquatic life (SI Text) to the greatest extent at sites near development (Fig. S3). For example, seven PPE exceeded guidelines in snow at ND sites, whereas only Cd exceeded guidelines at some BG sites (Fig. S3). Cd in snow was 200- and 30-fold greater than the hardness-dependent and interim guidelines, respectively, of the Canadian Council of Ministers of the Environment (CCME) Water Quality Guidelines for the Protection of Aquatic Life, and Ag was 13-fold greater than CCME guidelines at one AR site in February (Fig. S3) (32). Other highly toxic metals (Cd, Cu, Pb, Hg, Ni, and Zn) exceeded guidelines by up to 5-fold (Fig. S3). Guidelines were exceeded more often in summer than in winter at AR sites.

Similarly, guidelines were exceeded during the spring freshet (26), when metals should be most toxic because water hardness decreases from >100 mg/L to <5 mg/L. For example, under these conditions, the CCME guideline of 2–4 μg Cu/L would be acutely lethal to minnow embryos (33), creating an annual risk of recruitment failure for 19 fish species that spawn in the AR and its tributaries in spring or early summer (34). Metal mixtures also can act synergistically (35), and some PPE potentiate PAC toxicity to aquatic organisms (19).

PPE concentrations in melted snow and in tributary and AR water did not exceed drinking water quality guidelines (Fig. S3). Nevertheless, increased deposition of elements considered priority pollutants under the US EPA Clean Water Act are of concern to human health. As indicated, a fish consumption advisory exists for Hg in walleye from the AR (18), and the AD wetlands provide an increased potential for Hg methylation (36). Links have been proposed between diseases prevalent in Fort Chipewyan and the carcinogenicity of PAC (6, 12). Effects of PAC can be potentiated by coexposure to As (20), which is above BG concentrations downstream of development as far as the AD. Also, high loadings of Cd to snow may present health risks because moose bioaccumulate Cd in liver and kidneys, reflecting regional distributions of Cd in vegetation (37). Monitoring PPE in vegetation and country foods where oil sands emissions fall on aboriginal treaty lands is essential.

Conclusions.

Contrary to claims made by industry and government in the popular press, the oil sands industry substantially increases loadings of toxic PPE to the AR and its tributaries via air and water pathways. This increase confirms the serious defects of RAMP (11–13), which has not detected such patterns in the AR watershed. Detailed long-term monitoring is essential to distinguish the sources of these contaminants and control their potential impacts on environmental and human health (13). A robust monitoring program to measure exposure and health of fish, wildlife, and humans should be implemented in the region affected by oil sands development (38, 39).