Asbestos mining waste impacts on the sedimentological evolution of the Bécancour chain of lakes, southern Quebec (Canada)

More than a century (1877–2011 CE) of asbestos mining activities in the Thetford Mines region have resulted in the accumulation of gigantic mineral waste piles on the banks of the Becancour River (southern Quebec, Canada). This river widens downstream from the mining sites to form a chain of lakes, successively: Stater Pond, Trout Lake, Lake William and Lake Joseph. A previous paleolimnological investigation revealed that waste erosion and transport strongly modified and polluted Trout Lake. However, questions remain about the extent of the mining contamination within the Becancour River Basin and its impacts at other spatial scales. Here, we aimed to address this lack of knowledge by analyzing the sedimentological evolution of Stater Pond, Lake William, Lake Joseph and Lake Becancour (upstream reference site). Radiometric dating (210Pb, 137Cs, 14C) and analyses of geochemical composition (ICP-AES/ICP-MS), computed tomography, magnetic susceptibility, loss-on-ignition and grain size were performed on sediment cores retrieved at these sites. In contrast to Lake Becancour, yet similar to Trout Lake, we found that Stater Pond and Lake William have received high mineral matter loads since the creation of the Lake Asbestos Mine during the 1950s. Recent lake sediments at these downstream sites were highly enriched in magnesium, chromium and nickel. Comparison of their geochemical signature with that of sedimentary source materials from within the drainage basin demonstrated that they predominantly originate from mining waste erosion. Consequently, Stater Pond and lakes Trout and William are nowadays exposed to very high sediment accumulation rates (up to 1.4 cm yr−1; 0.6 g cm−2 yr−1) and heavy metal enrichment. Evidence for contamination was also found in Lake Joseph, thereby indicating that wastes are transported and deposited over ≥25 km downstream from the former mining sites. Our study highlights the high risks and dangers associated with asbestos pollutants in aquatic ecosystems.