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 mercuric content, pollution and contamination characteristics of water, sediments, edible muscles of a non-piscivorous fish (Oreochromis nilotica Linnaeus 1758 [Cichlidae]) and yams (Dioscorea alata) in mercury-based artisanal and small-scale gold mining (ASGM) impacted Namukombe stream and its propinquity, Busia gold district, Uganda were evaluated. Human health risk assessment from consumption of the fishes and yams as well as dermal contact with sediments from the stream were performed. Forty-eight (48) samples of water (12), sediments (12), fish (12), and yams (12) were taken at intervals of 0, 10, 20 and 30m from up, middle and down sluices of the stream and analyzed for total mercury (THg) using US EPA method 1631. Results showed that water in the stream is polluted with mercury (Hg) in the range of 0.00 to 1.21±0.070mg/L while sediments contain Hg up to 0.14±0.04ugg-1. THg content of the edible muscles of Oreochromis nilotica ranges from 0.00 to 0.11±0.010ugg-1 while yams contain 0.00 to 0.30±0.001ugg-1 of Hg. The estimated daily intakes (EDIs) ranged from 0.0049 to 0.0183ugg-1day-1 and 0.020 to 0.073ugg-1day-1 for fish consumed by adults and children respectively. The corresponding health risk indices (HRIs) ranged from 0.0123 to 0.04576 and 0.05 to 0.183. EDIs were from 0.0042 to 0.1279ugg-1day-1 and 0.013 to 0.394ugg-1day-1 for yams consumed by adults and children respectively. The HRIs recorded were from 0.011 to 0.320 and to 0.033 to 0.985. All the mean THg contents of the investigated matrices were within acceptable WHO/US EPA limits except for water samples. Consumption of yams grown at 0m up sluice of Namukombe stream may pose deleterious health risks as reflected by the HRI of 0.985 being very close to 1.0. From pollution and risk assessments, Hg usage should be delimited in Syanyonja ASGM areas; solutions to abolish mercury based ASGM in the area ought to be sought at its soonest to avert the accentuating health, economic and ecological disaster arising from the continual discharge of Hg into the surrounding areas. Other safe gold recovery methods such as use of borax should be encouraged. Waste management system for contaminated wastewater, used Hg bottles and tailings should be centralized to enable Hg waste management in ASGM areas in Syanyonja.

Physicochemical quality of water and health risks associated with consumption of African lung fish (Protopterus annectens) from Nyabarongo and Nyabugogo rivers, Rwanda

“…The current study was done in Nyabarongo and Nyabugogo rivers of Rwanda. The apparatus were those previously used [5,6]. Study approval was granted by Department of Chemistry, College of Science and Technology, University of Rwanda (Approval No.…”

“…On Nyabugogo river, samples were taken from Giticyinyoni (10° 55′ 22″ S and 300° 2′ 52″ E). Water samples (n =1 for each site) were obtained in triplicate between April 2019 and May 2019 (10:00 to 11: 00 am, Central African Time) as described by Omara et al [5]. Fish (6.2 to 8.1 cm; 700-903 g) were caught in triplicate from Nyabarongo river (n =3 for each site), identified and prepared for analysis as described before [7].…”

“…Estimated daily intake (EDI, mg/kg/day) for fish was calculated as described elsewhere (Eq. 3) [5,7,9].…”

“…where C hm = metal concentration in water or fish, S A is exposed area = 4350 and 2800 cm 2 for adults and children [9], W ir is water ingestion rate = 21.0 and 1.8 L/day for adults and children [10], E d is the exposure duration = 67 years [11], E f is the exposure frequency = 365 days/year, AF is skin adherence factor = 0.7 and 0.2 mg/cm 2 /day for adults and children, F ir is fresh fish ingestion = 48 g/person/day, C f is conversion factor for fresh to dry weight for fish = 0.208, W ab is average body weight = 15 kg and 60 kg for children and adults, T aet is the average exposure time = E d × E f [5,12]. Health risk index, the total risk of a non-carcinogenic element was evaluated using target hazard quotient (THQ) (Eq.…”

“…Health risk index, the total risk of a non-carcinogenic element was evaluated using target hazard quotient (THQ) (Eq. 4) [5,7,13].…”