Estimating Health Risk Using a PBBK Model for the Trio Mixture of Mercury, Lead and Selenium

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.