Risk assessment and source analysis of trace elements in soils around county landfills in Tibet

The ecology of the Qinghai‒Tibet Plateau is fragile, and the ecosystems in the region are difficult to remediate once damaged. Currently, landfilling is the mainstay of domestic waste disposal in China, and numerous, widely distributed county landfills exist. trace elements (TEs) in waste are gradually released with waste degradation and cannot be degraded in nature, affecting environmental quality and human health. To reduce the chance bias that exists in studies of individual landfills, we selected 11 representative county landfills in Tibet, total of 76 soil samples were collected, eight TEs (arsenic (As), mercury (Hg), chromium (Cr), copper (Cu), lead (Pb), cadmium (Cd), nickel (Ni), and zinc (Zn)) were determined, and analysed for the current status of pollution, risk to human health, and sources of TEs to explore the impact of the landfills. The results showed that only a few landfills had individual TEs exceeding the risk screening value of the Soil Environmental Quality Risk Control Standard for Soil Contamination (GB 15618-2018) (pH > 7.5). Most of the soils around the landfills had moderate levels of pollution, but some individual landfills had higher levels, mainly due to Cd and Hg concentrations. Source analysis showed that Hg originated mainly from atmospheric transport; the other TEs came mainly from the weathering of soil parent material and bedrock. The potential risk from TEs to human health was low, and the risk to children was greater than the risk to adults. Among the three exposure routes, oral ingestion resulted in the highest carcinogenic risk and noncarcinogenic risk, with a contribution rate of more than 95%. Among the TEs, Ni had the highest carcinogenic risk, followed by Cr and As, and As had the highest noncarcinogenic risk.