Assessment of wetland/upland vegetation communities and evaluation of soil-plant contamination by polycyclic aromatic hydrocarbons and trace metals in regions near oil sands mining in Alberta

Abstract

Oil sands mining in Alberta, Canada, has been steadily increasing over the last 50years. The extent to which the surrounding vegetation has been altered/contaminated by pollutants released during bitumen extraction has not been a focus of oil sands environmental monitoring efforts. The objectives of this study were to assess plant species richness and composition in wetlands and uplands in the vicinity of oil sands mining areas and to measure levels of contamination of trace metals and polycyclic aromatic hydrocarbons (PAHs) in soils and plants. Twenty-two sites were selected in three locations: near to (OS, n=7), West (n=7), and East (n=8) of oil sands mining operations. Aboveground plant species were inventoried and soil was collected for a seedbank study. Soils and plants were collected for analyses of 28 metals and 40 parent and alkylated PAHs. Plant species richness and composition differed significantly among locations. More species were found in the OS sites, many of them being non-native, than in East and West sites, which contained almost exclusively native perennials. PAH levels were significantly higher in OS sites, and were mostly comprised of alkylated PAHs. Patterns of PAH distribution indicated contamination from bitumen/petroleum in four sites; other combustion types may have affected five additional sites at different levels. Metals were also elevated in OS sites. Metal levels were significantly correlated with distance to upgrader facilities. Ratios of some metals in soil vs. above- and belowground plant parts were significantly higher in West and East than in OS sites, likely due in part to pH as soil was acidic at the East and West locations but alkaline at OS sites. This study showed that sites located near oil sands mining operations were contaminated with PAHs and metals, and that the vegetation composition at these sites greatly differed from less disturbed areas.