A pollutant tracking model for the mitigation of mercury-induced contamination on surface and groundwater resources:

Abstract

Artisanal and small-scale gold mining is one of the many economic activities in the world commonly practiced in Asia followed by Africa and then Latin America. In Africa, Uganda is one of the few countries that carryout artisanal mining with this activity carriedout in the central, western, eastern and north-eastern regions of the country. This activity involves use of rudimentary tools to extract the ore and use of mercury to separate the gold from the ore. In eastern Uganda, this activity is more dominant in Tiira, Busia. The continuous use of mercury in the gold-ore separation has led to its continuous accumulation in the water bodies over a long period of time leading to many health complications such as neurobehavioral effects, motor coordination disorders, and cardiovascular diseases. Wanyana et al. (2020) conducted a cross-sectional study from June to July 2018 among 183 miners from Ibanda, Mubende, Amudat and Busia in Uganda. Results from laboratory checkup from miners’ urine and blood showed blood and urine to have concentrations of 60 μg/l and 70.6 μg/l of mercury respectively which are above the WHO standards. Alternatives to use mercury for gold-ore separation such as use of Borax has been introduced but has not been adopted because it takes a long time to recover the gold nuggets from the ore which is time wasting. This study focuses on using existing physical models to ascertain the extent the movement of the contaminant in surface and groundwater resources and propose possible mitigation measures to curb the contamination on-site and off-site. This study involved characterization of the mercury concentration, developing pollutant tracking models for mercury transportation and determining optimal mitigation strategies to curb the contamination. A sampling size of 106 peopleconsisting of focused group discussions, miners, household survey and key important persons was analyzed using questionnaire and interviews. Laboratory water quality assessment was done to determine mercury concentration in the existing 13 water points. Surface and ground water quality was modelled in a coupled system of WEAP and MODFlow packages. Optimal mitigation measures were obtained by performing optimal runs in design of experiments analysis. The questionnaires were used to get the community, miners and leaders’ perception about mercury usage and its related effects. The mercury sample used at site was analyzed and found to contain other heavy metals such as Lead (0.22mg/l), Nickel (0.093mg/l). Water quality assessment of the river water sampling points yielded high concentrations of mercury and lead of 55.1mg/l and 49.7mg/l respectively. WEAP model calibration yielded an R2 value of 0.96, NSE value of 0.73 and MODFlow model calibration yielded an R2 value of 0.76. An optimal value of 0.4567 from the Minitab model that was used to get an optimal measure. Further studies are recommended to be carried out on the River Okame cleansing capacity, sediment transport modelling and model coupling to get a better image of the whole problem in surface and ground water resources.