Distribution and aquatic ecotoxicological risks of potentially toxic elements in surface sediments of headwater streams on the Central African Copperbelt

Globally, mining activities contribute to the contamination of stream ecosystems with potentially toxic elements (PTEs), posing risks to aquatic and human health, and threatening the attainment of the 2030 UN-SDGs 6 and 14. This study assessed the distribution and ecological risks of arsenic (As), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in stream sediments of the north-western Zambian Copperbelt, within the Central African Copperbelt (CACB). Monthly samples were collected from May 2022 to April 2023 from six headwater streams to determine the PTE sediment pollution dynamics and potential impacts on aquatic life. Results showed that Cu (2073 mg/kg), Pb (12.7 mg/kg), and Zn (126.6 mg/kg) concentrations in sediments were highest in the dry season. PTEs accumulation followed the order: Pb < As < Zn < Ni < Cr < Cu, with Cu exceeding local background levels by up to 28%. Contamination was highest for Cu, Ni, and Cr, categorized as "moderately severe" to "low-to-medium." The contamination factor (CF) ranked from "low-to-moderate" for Pb and As to "very high" for Cu. Similarly, the enrichment factor (EF) varied from "none-to-minor" to "very severe," with Cu showing the greatest enrichment. Risk assessments indicated a "low" overall ecological risk (mPERI: 41.7 - 47.4) but a "moderate-to-considerable" toxicity risk (TRI: 13.1 - 19.3) for aquatic biota. Based on sediment quality guidelines, As and Cr were "potentially hazardous", Cu and Ni were "hazardous", while Pb and Zn were "non-toxic". Despite the relatively "low" overall risk, continuous monitoring and mitigation efforts are cardinal to mitigate anthropogenic PTE pollution and ensure adaptive sustainable management of CACB aquatic ecosystems.