Distribution and aquatic ecotoxicological risks of metal(loid)s in surface sediments of headwater streams on the Central African Copperbelt

Globally, stream ecosystems draining mining landscapes experience alarming metal(loid) pollution, threatening the attainment of “2030 UN-SDGs 6 and 14”. This study was conducted monthly in the north-western Zambian Copperbelt between May 2022 and April 2023 to investigate the spatiotemporal distribution and ecotoxicological risks of As, Cr, Cu, Ni, Pb, and Zn in stream sediments. Pb (12.7), Cu (2073), and Zn (126.6) mg/kg were highest in the dry season. Generally, metal concentrations (mg/kg) followed the order Pb (5.98) <As (6.98) <Zn (49.6) <Ni (99.7) <Cr (109.2) <Cu (418.3). Streams with anthropogenic inputs were most impacted by Cu (1691-2073 mg/kg), up to 28% above the local background value. Cu, Ni, and Cr exhibited “moderately–severe” enrichment and “moderate” and “low-to-medium” contamination. The contamination factor (CF) ranged from “low-to-moderate” to “very high” [Pb (0.63) >As (0.81) >Zn (1.33) >Ni (2.39) >Cr (6.16)>Cu (46.01)]. KSC sediments were enriched from “none-to-minor” to “very severe”, with increasing enrichment (EF) [Pb (0.64) >Zn (0.89) >As (1.48) >Ni (1.82) >Cr (2.59) >Cu (30.45)]. Ecological risk assessment indicated a “low risk” (mPERI 41.7-47.4), while the toxicity risk index (TRI, 13.1-19.3) depicted “moderate-to-considerable” ecotoxicological risk to benthic biota. Based on the sediment quality guidelines, As and Cr concentrations were “potentially hazardous”; Cu and Ni were “hazardous”, while Pb and Zn were “non-toxic”. While the overall ecotoxicological risk was considerably low, proactive interventions must be instituted to mitigate anthropogenic metal pollution for the effective and sustainable management of CACB aquatic ecosystems.