Assessment of the level of selected heavy metals (Hg and Pb) in water, sediment, and fish muscle from gold mining sites: A case study in Dima district, Gambela, Southwest Ethiopia

Abstract

Background Artisanal small scales gold mining is a common economic activity in many developing regions, providing livelihoods for local communities. However, this practice often comes at a significant environmental cost. Gold mining in the stud y areas potentially contaminates the aquatic environment since the mining tailings from the amalgamation process are directly discharged into the water body. Due to these practices, mining and agricultural activity in the catchment area of the Akobo River are suspected of adding to the streams connected to the river’s heavy metal load. However, no previous study has been done on the levels of selected heavy metals in the Akobo River. Objectives. The study aimed to assess the level of selected heavy metals Hg and Pb in water, sediment, and the muscles of six fish species collected from the gold mining site. Methods. This study was conducted in the Dima district of Gambela, Ethiopia, specifically at the Akobo River and gold mining sites. It utilized a cross-sectional research design. A total of thirty samples were collected from July 18 to 19, 2022, which included twelve water samples, twelve sediment samples, and six distinct fish samples. The levels of lead (Pb) and mercury (Hg) were determined using Inductively Coupled Plasma Mass Spectrometry (ICP MS). The results were analyzed and compared across sites using a one-way analysis of variance (ANOVA) Results. The finding indicated that Hg was below the detected limit in the water, while Pb ranges 0.52±0.006 to 0.58±0.010 mg/L. In sediments ranges between 0.177±0.002 to 0.272±0.002 mg/kg, and Hg ranges between 0.034±0.001 to 0.084±0.001 mg/kg dry weight, respectively. In the fish samples range between 2.313±0.002 to 3.306±0.002 mg/kg, And Pb ranges 0.195±0.002 to 0.247±0.015 mg/kg dry weight, respectively. Therefore, in the water sample was above the WHO (2011) permissible limits. While Pb and Hg in sediment were below TEL and (ERL) set by CCME and NOAA. Hg and Pb in the fish sample were above the threshold limit by FAO/WHO. The highest Hg and Pb levels were reported in B. docmak, 3.306±0.002 mg/kg and 0.247±0.015 mg/kg, followed by S. filamentosus, 2.313±0.002 mg/kg and 0.206±0.002 mg/kg dry weight, respectively, where both fish were collected at the same station, ST-3 (downstream). Conclusion: Therefore, Akobo River fish and water are not suitable for food, Drinking and other domestic purposes, such as cooking and washing, since the level of heavy metals Hg and Pb level, which are known to be carcinogens, were exceeded the safe limit set by the Ethiopian standard (ESA, 2013) and (FAO/WHO, 2011). Recommendation: Regional and local authorities should aware communities on the health and environmental risks of heavy metal exposure. Stakeholder must regularly monitor fish, water, and sediment quality to track pollution levels. Regulatory bodies should enforce strict waste control measures for mining facilities. Sustainable mining and agricultural practices must be promoted to protect the Akobo River and public health.