Bio-Accessibility and Health Risk Assessment of Heavy Metals in Indoor Dust From Higher Institutions in Ondo State, Nigeria

32 Quality of indoor air has been a major concern over time particularly in urban areas. Amidst the 33 indoor air parameters, particulate matter/dust is of core interest owing to the fact that it acts as 34 sediment for metals and other pollutants. Considering the ample amount of time spent indoor by 35 students, this study has been mapped out to investigate the quality of air in tertiary institutions in 36 Ondo State, Nigeria based on their proximity to more anthropogenic activities. Herein, pH, 37 conductivity, and anion concentrations in the indoor dust samples were estimated employing 38 standard analytical methods. Our findings revealed a sequence of anion concentration level as 39 follows, Cl - >SO 42- >NO 3- . Also, the concentrations of some selected metals were analyzed using 40 flame atomic absorption spectrophotometer (FAAS). The variation in metal concentration 41 observed in most study sites was in the order Cu>Zn>Cr>Pb>Cd. The mean heavy metal 42 variation followed the trend based on the sample collection sites considered in the present study 43 with FE>OA>FU>HT and Cu (0.480mg/kg), Zn (0.409mg/kg), Cr (0.407mg/kg), Pb 44 (0.149mg/kg) and Cd (0.029mg/kg) being the highest concentration of each of the metals. 45 However, all the metal concentrations were below the permissible level. The result from non- 46 carcinogenic study indicates that the average daily dose (by ingestion) was found to be the core 47 exposure pathway such that ADDing> ADDderm> ADDinh. Nevertheless, the hazard quotient 48 (HQ) and hazard index (HI) were less than 1. This implies that no potential health risk. More 49 generally, a relative degree of safety and strict regulations is suggested to be put in place to 50 maintain the status. 51


Introduction
Air quality is a major concern with respect to the fast growing population and unprecedented rise    of (each) sample was weighed into a beaker and 50 mL of distilled water was added. The mixture 114 was left for 30 min and stirred at regular intervals. Then, the conductivity was read with a 115 conductivity meter (Jenway4520, UK), which was pre-calibrated using 1M KCl at 25°C.

Analysis of anionic concentration of dust sample
117 2 g of (each) sample was dissolved in 100 mL of distilled water in a 250 mL Erlenmeyer flask 118 and placed in a mechanical shaker for 24h for equilibration to prepare a stock sample. Thereafter, 119 the solution was filtered and subsequently used for the determination of chloride, sulfate, and 120 nitrate.

121
Chloride content determination 122 The chloride content of (each) sample was determined by Mohr's method (Meija et al. 2016).

123
Typically, 2 mL of stock sample was taken and 0.02g of NaHCO3 was added until effervescence 124 ceased. Upon completion, 2 mL of K2Cr2O4 was introduced and stirred to enhance equilibration.

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The solution was titrated to the first permanent appearance of red Ag2Cr2O4. The percentage of 126 chloride is calculated using the formula below.  Nitrate content determination 139 The nitrate content of (each) sample was determined by the Phenoldisulphonic method adopting  Typically, 3 mL of (each) sample was measured from the stock solution into the centrifuge tube The tube was centrifuged for 10 min until the solution was clear. 5 mL of the clear solution was 144 put in a glass evaporating dish, placed on a water bath at 50⁰C to evaporate to dryness, and 145 cooled. Upon completion, 1mL of phenoldisulphonic acid was added. After 10min, 10 mL of 146 water was added, transferred to 100 mL volumetric flask, and was made alkaline by the addition 147 of 2 mL conc. NH4OH followed by thorough mixing. The absorbance at 410 nm was measured 148 by using a UV/ Visible Spectrophotometer; (Spectrum lab 752, England). 179 Where, The data obtained in this study were subjected to statistical analysis using MS Excel. The   235 The selected heavy metal concentrations determined in the samples are shown in Table 2. higher than that obtained for cadmium and lead. Dust from the sample sites is, therefore, more  The non-carcinogenic risk of the studied metalss was assessed via the three exposure pathways 309 considered in the present work using the hazard quotients (HQ) and hazard indices (HI) of metal 310 intake from the samples. HQ and HI were determined as presented in Table 3. The calculated 311 HQ ranged from 3.93 x 10 -10 to 5.920x 10 -5 . The trend in the HQ obtained from the study sites 312 was in the order FE>OA>HT>FE. However, the magnitudes of the HQ were below 1×10 −4 .

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Consequently, remediation of the study sites is not needed (Zheng et al. 2010a).It was observed 314 that for most of the study sites that the HI reported for the metals was Cr >Pb> Cd > Cu > Zn.

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The results were at variance with previous report Pb> Cd> Zn> Cu> Cr for street dust (Hu et al. The study do not involved experimentation on animals or man.