Health Risk Assessment of Heavy Metals in the Water of the Loutété River, Mfouati District, Southeast Congo ()
1. Introduction
Water is an indispensable element in everyday life and its use in different areas of life depends on its physical and chemical properties. Water can be contaminated by heavy metals, these metals in drinking water can come from various sources such as natural sources, urbanization, industrialization, agricultural runoff, mining activity and traffic emissions (Li & Wu, 2019; Zhang et al., 2019; Nkpaa et al., 2018; Cobbina et al., 2015). Mining activity is the major source of heavy metal pollution in waters. These are delivered to rivers, streams, lakes, estuaries, and lagoons through runoff (Wang et al., 2008; Audry et al., 2010; Korça & Demaku, 2020; Negahban et al., 2020). The phenomenon of water runoff results in increased concentrations of heavy metals in water, which in turn will pose a risk to human health (Wang et al., 2008). The health risk has been assessed by the US Environmental Protection Agency (USEPA, 1989) which shows that humans can be exposed to heavy metals by ingestion (mouth) and skin contact (Wang et al., 2008; Audry et al., 2010; Fu et al., 2009; Li et al., 2009; USEPA, 1989). The Loutété River, located in the Bouenza department (southern Congo Brazzaville), is a tributary of the Niari River. For several years it has been influenced by the activities of a plant processing a polymetallic ore rich in metallic sulfides. Currently this plant is in full abundance. The local population uses this water for agriculture, fishing, washing dishes, cooking tubers, etc. In view of all these activities, the physical-chemical properties and heavy metal contents are not known. It is in this perspective that we propose to know the quality of this water and to evaluate the sanitary risk for health.
2. Materials and Methods
2.1. Study Area
The Loutété River, located between the southern latitude of 367178.59 to 370507.20 UTM and eastern longitude of 9512957.94 to 9515800.06 UTM. This area is characterized by an equatorial climate, a vegetation of savannah type and a soil of ferralitic type. The temperature varies between 25˚C and 36˚C during the rainy season against 18˚C and 24˚C during the dry season. Annual rainfall varies between 1050 and 1650 millimeters (Matini et al., 2011).
Figure 1 below represents selected study area of Mfouati in this study.
2.2. Sampling and Analysis
A sampling campaign was conducted in October 2014 (dry season) during which six stations were selected. In each station, 1L of surface water was taken, stored in a Teflon bottle and acidified with nitric acid. The physico-chemical parameters
(pH, electrical conductivity, total dissolved salts) were measured on site using a HANNA multi-parameter measuring device. The acidified water was kept in a refrigerator at 4˚C in the laboratory and sent to the black tip analytical laboratory (SGS) to determine the heavy metal content by ICP-OES.
2.3. Exposure Assessment
The Environmental Protection Agency has shown that heavy metals can enter the human body through the mouth, nose and skin. Equations (1) and (2) have been used to estimate exposure doses from mouth and skin contact (Grzetic & Ghariani, 2008; Khan et al., 2008; USEPA, 2011).
(1)
(2)
Cw: average concentration of metals in water; IR: ingestion rate; EF: ingestion rate; ED: exposure duration; BW: average body weight; AT: average time; SA: exposed skin area; Kp: skin coefficient of permeability in water; ET: exposure time; CF: unit conversion factor.
Table 1 below represents values of the parameters to calculate the exposure doses by mouth and skin contact
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Table 1. Parameters recommended by US. EPA for non-carcinogenic risk assessment of metals (USEPA, 1989).
2.3.1. Non-Carcinogenic Risk Index (HQ)
The potential non-carcinogenic risk of exposure to contaminants (HQ) was calculated by the ratio of the exposure doses to contaminants calculated according to the exposure routes (Exp) (ingestion, dermal) to the reference dose (RfD). HQ was calculated by the following equation: to estimate the non-carcinogenic risk, HQ was calculated by the following equation (Khan et al., 2008):
HQ ing/Derm = (Exp ing/Derm)/(rfd ing/Derm) (3)
when HQ less than 1 the risk is considered non-carcinogenic, HQ greater than 1 may be a major potential health concern.
To calculate the hazard quotient for the potential non-cancer risk (HQ), the toxicity reference dose value was used. Table 2 below gives the values toxicological reference parameters for selected metals (RfD).
2.3.2. Total Risk Index (HI)
Total Risk Index (HI) has been used to assess the risk to human health from exposure to multiple metals. The risk index is the sum of the quotient risk calculated for the entire metal (USEPA, 1989; USEPA, 2011).
THI = ΣHQ = HQPb + HQMn + HQFe + HQCu + HQZn + HQCr (4)
when HI > 1, exposure to water can have an adverse effect on human health (Naveedullah et al., 2014).
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Table 2. Toxicological reference parameters for selected metals.
3. Results and Discussion
3.1. Physico-Chemical Parameters of the Water of the Loutété River
The results of the physico-chemical parameters are presented in Table 3 below to interpret the physico-chemical properties of the water.
Temperatures vary between 22.4˚C and 25˚C with an average of 23.61. The highest temperature is observed in station six. In all six stations, these temperatures are below the standard established by the WHO (30 - 40). The pH values range from 4.77 to 8.49 with a pH maximum in S4. The values are close to the WHO standard. The TDS values are between 175 and 255. These values are well below the WHO standard (1400).
3.2. Heavy Metals in Water
Table 4 below gives concentrations of heavy metals obtained in the six stations of the river Loutété.
Chromium concentrations range from 0.08 to 5.8 µg/l, with an average of 1.96 µg/l. These concentrations are lower than the WHO standard. The copper concentration varies between 0.6 and 14.5 µg/l, with an average of 5.58 µg/l. The copper concentration is lower than the WHO standard. The Iron concentration varies between 0.2 and 386.05 µg/l, with an average of 122.37 µg/l. Its concentration is lower than the WHO standard. Lead whose concentration varies between 1.02 and 370 µg/l with an average of 103.1 µg/l. The concentration of lead exceeds the admissible limit for lead recommended by the WHO which is 10 µg/l. Zinc whose concentration varies between 8.02 and 248.7 µg/l, with an average of 76.06 µg/l. The concentration is lower in zinc than the WHO standard. Manganese concentration varies between 37.1 and 328.08 µg/l with an average of 162.31 µg/l. The concentration of Manganese is lower than the WHO standard. The low concentrations observed in the surface water are due to the exchange between polluted ores and the surface water. On the other hand low concentrations can be explained by co-precipitation by oxides or absorption on mineral surfaces (Wu et al., 2009). The concentration of arsenic varies between 0.7 and 30 µg/l. The arsenic concentrations exceed the respective guideline value for drinking water (10 µg/L) respectively in the station (S1).
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Table 3. Physico-chemical parameters.
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Table 4. Heavy metal concentration in water (µg/l).
S.D: Standard deviation.
3.3. Correlation between Heavy Metals in the Waters of the Loutété River
Correlation analysis establishes the relationship between heavy metals in the samples. A high correlation (r = 1, or close to 1) shows a positive association between two metals (Saeedi et al., 2012; Lu et al., 2010). The table below gives us the correlations between the different metals. Correlations exist between: [Zn-Pb] r = 0.89; [Mn-Pb] r = 0.69; [Fe-Pb] r = 0.97; [Zn-Mn] r = 0.71; [Fe-Mn] r = 0.81; [Fe-Zn] r = 0.90. In view of these values we note that these metals taken two by two have the same sources and similar geochemical behavior.
Table 5 below shows correlation between two elements.
3.4. Health Risk Assessment
3.4.1. Non-Carcinogenic Risk Assessment for Dermal Contact with Water
Table 6 below shows the hazard quotient (HQ) results for a potential non-cancer hazard and the cumulative hazard indices (for adults).
The dermal hazard quotient (HQ derm) values calculated for the waters of the Loutété River show that HQ derm is less than 1 for all heavy metals at all stations. This indicates that there is no health risk to the population exposed by dermal contact. The calculated ingestion risk quotient values (ing HQ) for the following heavy metals: Cr, Cu, Fe, Mn, Zn are less than 1 at all stations. Except in the case of Arsenic and lead where we observe (HQ ing) is higher than 1 in the stations S1 for arsenic and S4, S6 for lead. This shows that the metal arsenic
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Table 5. Correlation between heavy metals in the water of the river Loutété.
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Table 6. Hazard Quotient (HQ) for a potential non-carcinogenic risk and cumulative hazard indices (for adults).
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Table 7. Hazard Quotient (HQ) for potential non-carcinogenic risk and cumulative hazard indices for children.
and lead can cause adverse effects by ingestion of water for the population. Considering the mean value, HI ing > 1. This indicates that there is an adverse effect on the health of the population. The average of HI derm < 1. This indicates that there is no adverse effect on the health of the population.
3.4.2. Non-Carcinogenic Risk Assessment for Children
Table 7 shows the hazard quotient (HQ) results for a potential non-cancer hazard and the cumulative hazard indices (for children).
The dermal HQ values calculated by dermal contact for all heavy metals As, Fe, Cu, Zn, Mn, Cr and Pb for children are lower than 1 in all six stations. The risk is observed when HQ is greater than or equal to 1. In our case, in station S4 we observe that HQ > 1 for lead. This shows that lead is dangerous for populations exposed by dermal contact. In the case of ingestion, the heavy metals Cr, Cu, Zn, Mn do not pose any risk to the population because the value of the risk quotient HQ lower than 1 in all stations. The following metals Arsenic, Lead and Iron pose a risk problem in the following stations: S1, S2 for arsenic; S4, S6 for Lead; and S1, S2, S4, S6 for Iron. The average HI ing > 1 and the average HI derm < 1 as observed previously in the adult case. This brings us to the same conclusion.
4. Conclusion
The general objective of this study was to evaluate the health risk of populations exposed to heavy metals by ingestion and skin contact. The concentrations of heavy metals (Pb, As, Cu, Zn, Cr, Fe, Mn) were determined by ICP-OES. The health risk was estimated by dermal contact and ingestion. The physico-chemical parameters were measured using a HANNA multi-parameter. Regarding the results of heavy metals in water, the concentrations of heavy metals in water are lower than the standard of the O.M.S. The risk on health in the case of the adult the average of HI ing > 1. This leads to adverse health effects. The average HI derm < 1. This means that there are no significant adverse health effects. In the case of children, the average HI ing > 1 and the average HI derm < 1 as observed previously in the case of adults. This brings us to the same conclusion as in the case of the adult. The chemical composition of the river water is characterized by an alkaline pH with the exception of station S4. The pH values range from 4.77 (S4) to 8.49 (S5). These measured values respect the WHO standards for water (6.5 < pH < 9.5). The electrical conductivity measured in these waters is between 278 µS/cm (S1) and 455 μS/cm (S6), these values are lower than the WHO standard (1000 µS/cm). The values of total dissolved salts (TDS) in the water are between 175 and 255. These values are lower than the WHO standard (1400).