Mercuric pollution of surface water, superficial sediments, Nile tilapia (Oreochromis nilotica Linnaeus 1758 [Cichlidae]) and yams (Dioscorea alata) in auriferous areas of Namukombe stream, Syanyonja, Busia, Uganda

Abstract

The mercury content and the contamination characteristics of water, sediments, ediblemuscles of a non-piscivorous fish (Oreochromis niloticaLinnaeus 1758 [Cichlidae])and yams (Dioscorea alata) from Namukombe stream in Busia gold district of Ugandawere evaluated. Human health risk assessment from consumption of contaminatedfish and yams as well as contact with contaminated sediments from the stream wereperformed. Forty-eight (48) samples of water (n=12), sediments (n=12), fish (n=12)and yams (n=12) were taken at intervals of 10 m from three gold recovery sites locatedat up, middle and down sluices of the stream and analyzed for total mercury (THg)using US EPA method 1631. Results (presented as means±standard deviations)showed that water in the stream is polluted with mercury in the range of<detectionlimit to 1.21±0.040 mg/L while sediments contain mean THg from<detectionlimit to 0.14±0.040ugg−1. Mean THg content of the edible muscles ofO. niloticaranged from<detection limit to 0.11±0.014ugg−1whileD. alatacontained from<detection limit to 0.30±0.173ugg−1mean THg. The estimated daily intake rangedfrom 0.0049ugg−1day−1to 0.0183ugg−1day−1and 0.0200ugg−1day−1to 0.0730ugg−1day−1for fish consumed by adults and children respectively. The correspondinghealth risk indices ranged from 0.0123 to 0.0458 and 0.0500 to 0.1830. Estimated dailyintake was from 0.0042ugg−1day−1to 0.1279ugg−1day−1and 0.0130ugg−1day−1to0.3940ugg−1day−1forD. alataconsumed by adults and children respectively. TheHow to cite this articleOmara T, Karungi S, Kalukusu R, Nakabuye BV, Kagoya S, Musau B. 2019. Mercuric pollution of surface wa-ter, superficial sediments, Nile tilapia (Oreochromis niloticaLinnaeus 1758 [Cichlidae]) and yams (Dioscorea alata) in auriferous areas of Na-mukombe stream, Syanyonja, Busia, Uganda.PeerJ7:e7919 http://doi.org/10.7717/peerj.7919 health risk indices recorded were from 0.011 to 0.320 and 0.033 to 0.985 for adultsand children respectively. The mean THg content of the sediments, edible musclesofO. niloticaandD. alatawere within acceptable WHO/US EPA limits. About 91.7%of the water samples had mean THg above US EPA maximum permissible limit formercury in drinking water. Consumption ofD. alatagrown within 5 m radius up sluiceof Namukombe stream may pose deleterious health risks as reflected by the health riskindex of 0.985 being very close to one. From the pollution and risk assessments, mercuryuse should be delimited in Syanyonja artisanal gold mining areas. A solution to abolishmercury-based gold mining in the area needs to be sought as soon as possible to avertthe accentuating health, economic and ecological disaster arising from the continuousdischarge of mercury into the surrounding areas. Other mercury-free gold recoveringmethods such as use of borax, sluice boxes and direct panning should be encouraged.Waste management system for contaminated wastewater, used mercury bottles andtailings should be centralized.