ICMGP - Conference Presentation

Abstract Information :

Despite a surge in mercury (Hg) pollution from artisanal and small-scale gold mining (ASGM) in Zimbabwe?s drainage basins, and the documented impacts of Hg on human and aquatic ecosystem health, little is known about Hg trophodynamics in the country?s major reservoirs. In the current study, we analyzed fish tissues for total Hg (THg) and stable isotopes of nitrogen and carbon (?15N and ?13C) to compare patterns of biomagnification between fish assemblages from a protected reservoir (Chivero) and a non-protected reservoir (Mazowe) and assessed consequences for human and aquatic ecosystem health. Dry weight THg concentrations for piscivorous fish were significantly higher (Welch?s t-test, p < 0.05) in ASGM impacted Mazowe reservoir while there were no significant differences between THg concentrations in herbivorous fish from the two reservoirs. Trophic magnification slopes (TMS), inferred from linear regressions between ?15N and log10[THg] revealed significant Hg biomagnification in Mazowe (TMS = 0.28; p < 0.05) and no evidence for Hg biomagnification in Chivero, (TMS = -0.005; p > 0.05). In Mazowe?s piscivorous fishes, 92% had wet weight THg concentrations that surpassed the USEPA threshold for Hg toxicity in aquatic wildlife (0.1 æg/g ww), while 17% surpassed the WHO THg toxicity threshold for human consumption (0.5 æg/g ww). Fish samples from Chivero were below the WHO and USEPA thresholds except for a single piscivorous specimen which marginally exceeded (0.102 æg/g ww) the USEPA threshold. To reduce the risk of exposure to Hg toxicity, the maximum fish consumption for piscivorous species from reservoirs directly impacted by ASGM operations, such as Mazowe, should not exceed 431 g/week for both male and female adult consumers. Overall, our findings demonstrate the importance of protected areas in preventing direct Hg contamination of freshwaters and the need for health agencies to provide fish consumption advisories to vulnerable communities.