Accumulation and distribution of mercury in agricultural soils, food crops and associated health risks: A case study of Shenda gold mine-Geita Tanzania

Abstract

Contamination of the environment and foodstuff by potentially harmful elements (PHEs) has become a serious concern due to the associated health risks to the population. In the present study total mercury (Hg) levels in soil and food crops from farms around Shenda gold mine in Geita Tanzania was determined by Cold Vapor Atomic Fluorescence Spectrometry (CVAFS). Generally, it was found that there was significant different of Hg content in soil and food crops (P < 0.05) among studied sites. The total Hg concentrations determined were in the ranges of; soils (0.003-0.1220 mg/kg), rice (0.0752-0.1587 mg/kg) and vegetables (0.0556-0.3439 mg/kg) all measurement were based on dry weight basis (dw). Total Hg levels in soil were compared with the maximum allowable concentration (MAC) set by Tanzania Bureau of Standards (TBS) and United Kingdom (UK). All studied soil samples were within acceptable range (2 mg/kg) set by TBS and UK (1 mg/kg). Total Hg contents in food crop samples were compared with Chinese MAC of Hg (0. 01 and 0.02 mg/kg for leafy vegetables and grains respectively in a fresh weight basis). It was observed that Hg contents in potato leaves, pumpkin leaves and Chinese cabbage were within the MAC while Hg levels in cassava leaves and rice grains exceeded the MAC. In addition, Hg associated health risks to consumers of contaminated foods for residents around Shenda gold mine were estimated. The estimated weekly intake (EWI) of Hg due to consumption of rice grain was above the provisional tolerable weekly intake (PTWI) set by FAO/WHO (1.6 mg/kg bw/week) while the EWI due to consumption of leafy vegetables were below the PTWI. Target hazard quotient (THQ) was < 1 due to consumption of vegetables while THQ value for rice was >1, indicating a potential non-carcinogenic risk to adult population from the consumption of rice grain from the study area. Therefore, people living near Shenda goldmine might be potential victim of Hg accumulation in soil and food crops, thus necessary management options have to be in place.