IOSR Journal of Environmental Science, Toxicology and Food Technology (IOSR-JESTFT) e-ISSN: 2319-2402,p- ISSN: 2319-2399.Volume 12, Issue 1 Ver. II (January. 2018), PP 68-75 www.iosrjournals.org DOI: 10.9790/2402-1201026875 www.iosrjournals.org 68 | Page Estimating Health Risk Using a PBBK Model for the Trio Mixture of Mercury, Lead and Selenium Danjuma D. Maza, Joshua O. Ojo Department of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife, Nigeria Corresponding Author: Danjuma D. Maza Abstract: A physiologically-based biokinetic (pbbk) model for the trio mixture of lead, mercury and selenium, developed in our previous study was applied in a hypothetical environmental health risk assessment. The health risk index (HRI) to critical organs (liver, kidney, and the brain) resulting from the simultaneous exposure of individuals to the mixture of these elements were estimated. Three mining communities: Bagega, Dareta, and Abare villages of Anka L.G.A, Zamfara State, Nigeria, were used as case studies. In carrying out the hypothetical risk estimation, an exposed individual was assumed to have consumed contaminated cereals (maize, rice, and sorghum) cultivated locally in these three mining communities. Three co-exposure scenarios were simulated for each village based on selenium intake: low selenium intake (0.75μmol/kg/day), adequate selenium intake (2.5μmol/kg/day), and high selenium intake (7.5μmol/kg/day). The HRI to a given organ was calculated as the combined molar concentration of mercury and lead to the molar concentration of selenium (i.e. (Hg+Pb)-to-Se molar ratio). In general, the HRI to these critical organs were found to be highest when selenium intake was low, which were reduced greatly with adequate selenium intake and further reduced when selenium intake was high. At Bagega, when selenium intake was low, the simulated HRI was very high for all the three organs investigated (as high as1039, 32.7 and 5.9 for the liver, kidney, and brain, respectively). While at Dareta, with low selenium intake, only the HRI for the liver and kidney were very high (as high as 531.06 and 16.04, for liver and kidney, respectively). When selenium intake was high, only the liver had a high HRI at Bagega, while at Dareta and Abare the HRI for all three critical organs were low (< 1.0). The study showed that the health risk index to these organs were not only dependent on the concentrations of mercury and lead in these organs, but equally dependent on selenium intake. Keywords: health, lead, mercury, model, physiologically-based, risk. --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 16-01-2018 Date of acceptance: 03-02-2018 ------------------------------------------------------------------------------------------------------------------------------------- I. Introduction The elements Lead (Pb) and Mercury (Hg) are toxic to exposed individuals, while selenium is known to mitigate their toxic effect. Exposure to mercury is associated with a wide range of disorders and adverse health effects in humans and animals. These include, nervous system dysfunction, neurological, nephrological, immunological, cardiac, reproductive and renal disorders [1, 2, 3, 4]. Similarly, exposure to lead is implicated in a host of disease and health conditions, namely; brain damage, paralysis (lead palsy), impairment of liver structure and function, hypertension, cerebrovascular disease, cardiovascular disease, renal damage, anemia, gastrointestinal symptoms, kidney damage, damage to the reproductive and immune systems [5, 6, 7, 8]. Selenium, on the other hand, is an essential micronutrient required in trace amounts for normal growth and development in humans and animals [9]. Studies have shown that the toxicity of heavy metals such as mercury and lead results largely from the fact that they form insoluble complexes with selenium, thereby inducing selenium deficiency in target tissues [10, 11, 12, 13]. The concentration of free selenium required for its normal essential functions is therefore affected by the presence of lead or mercury in tissues. When selenium is bound to either lead or mercury, it becomes unavailable to carry out its essential functions, leading to adverse health effects and disorders. If an individual is simultaneously or sequentially exposed to these elements, lead, mercury and selenium, the interaction between these heavy metals and selenium is expected to modify their concentration in the various tissues and consequently their toxicity. A holistic estimation of the risk posed by lead and mercury to exposed individuals should therefore take into account the interaction between these toxic elements and selenium. However, in environmental health risk assessment of the toxic elements lead and mercury, their interaction with selenium is seldom taken into consideration. Furthermore, the use of Hg-to-Se molar ratio as the health risk index (HRI), in case of mercury toxicity, had been proposed by Ganther and cohorts as early as 1972 [14]. However, this proposal was given little or no attention because the specific underlying mechanisms of toxicity of mercury were not understood