Non-lethal method for the assessment of bioavailable metals in aquatic ecosystems surrounding ASGM activity

Abstract

The need for refined non-lethal techniques for the monitoring of the bioavailability and accumulation of toxic metals in aquatic ecosystems in Artisanal small-scale gold mining sites has motivated the current study. The respective fin clips and white muscle of 13 fish species from selected ASGM hotspots in the Upper uMzingwane catchment area were collected and analysed using an Inductively Coupled Plasma Mass Spectrophotometer for xenobiotics (As, Cd, Hg, Pb) and trace metals (Cr, Cu, Li, Ni) often associated with this highly unregulated, illicit trade. The oxidation of sulphide ore bodies ingrained in greenstone-hosted quartz-carbonate veins endemic in gold panning hotspots in the study area has been known to result in the leaching of xenobiotics into water bodies with their subsequent accumulation in aquatic biota. A comparison of the levels of the xenobiotics in the respective fin clips and white muscle of the fish species under study, together with an assessment of the levels in their respective aquatic environments may give a clue as to the bioavailability and mobility of the metals. Notably, As, Cd and Cr concentration in sediment samples ranged from 533.88 to 16185.03 ppb; 35.5–36.4 ppb; and 37173.36–273651.69 ppb respectively. Rock cutlets; Chiloglanis paratus and Chiloglanis pretoriae were the greatest metal accumulators. Of note was the mercury concentrations in Chiloglanis pretoriae and Chiloglanis paratus fin clips ranged from, 0.17–0.35 mg/kg and 0.23–13.35 mg/kg respectively. Chromium concentration in Chiloglanis pretoriae and Chiloglanis paratus in fin clips ranged from 43.15 to 57.87 mg/kg and 44.87–244.86 mg/kg respectively. The study concludes that fin clips can, indeed, be used as a non-lethal means to assess the bioavailability of metal species in an aquatic ecosystem.