Heavy Metals Contamination and Human Health Risk Assessment in Shallow Groundwater Wells in Qara- Hanjeer Sub-basin, NE Kirkuk -Iraq

Groundwater is one of the main sources for human consumption, and irrigation in arid and semi-arid rejoins in the world. Local peoples in the agricultural areas of Iraq generally consume shallow groundwater from farm wells. This study aims to evaluate health risk due to heavy metals contamination such as (Fe, Co, Zn, Ni, Mn, As, Cu, Cr, Mo and Pb) in groundwater from Qara-hanjeer sub-basin (NE Kirkuk-Iraq). The quantification of contamination index based on heavy metals; Cd, HPI and MI showed that anthropogenic activities have not modified the groundwater chemistry at least in a large scale. Health risk assessment model revealed that Hazard Quotient (HQ) values for both (HQing), (HQdrm) and HI for the heavy elements within water samples for dry and wet seasons were all significantly lower than (1) for the child and adults, suggesting no potential non-carcinogenic health risks via dermal exposure. However accessible concentrations of (Zn), (Mo) and (Pb) in some wells in the southern area of the study indicates that it is possible that over time and with increasing in concentrations of these elements in groundwater as a result of seepage of wastewater or sewage to the well, we have the environmental problems in the mentioned area.


Introduction:
Groundwater all over the world is becoming a natural resource of strategic importance due to its limited availability, quality deterioration, increasing demand and limited replenishment.
Hence, increased usage of such water for personal and agricultural needs makes protection of groundwater resources to be seen as possible solutions to mitigating water scarcity in arid and semi-arid regions. A vast literature gathered over many years from all over the world, especially for arid areas of the Middle East, cite the inorganic, organic and biological content and contaminants in freshwaters focused primarily on urban and agricultural areas [1]. To highlight some of the geomedical issues related to heavy metals effects in groundwater on human health, investigation of their accumulation and concentrations in various environmental sampling media which can directly threaten wellbeing of exposed inhabitants via ingestion and dermal absorption routes. In agricultural areas, increased heavy metal accumulation induced by application of inorganic fertilizers (commercial fertilizers) contributes to excessive leaching of these metals such as cadmium (Cd), Lead (Pb) and zinc (Zn) into soil and ground-water bodies [2]. There is undoubtedly a lack of knowledge regarding potential soil and groundwater contamination in less populated areas and small rural cities in Iraq, especially in areas of agriculture where the inhabitants who lives in usually consumes water from wells. Investigations have outlined the environmental contamination of the intensively agricultural soils and groundwater in Qara-Hanjeer town in NE of Kirkuk Municipality -Iraq and typical rural villages around where mostly farmers have their homes are located in their farms, they almost consume groundwater is unaware of the risk of contamination of this water by some heavy metals. Specific object of this study is to characterize the potential health risks of heavy metals in groundwater on both adults and children and evaluate the most significant contaminant and exposure pathway with regard to human health, in this regard different indices were used to assess heavy metal pollution of water resources including; Cd (Contamination Degree), HPI (Heavy Metal Pollution Index) and MI (Metal index), to evaluate CDI(Chronic Daily Intake Indices), HQ (Hazard Quotient) and HI (Hazard Index) and the non-carcinogenic and carcinogenic potential health risks of human exposure to multiple environmental contaminants via soil and drinking water pathways. semi-arid with annual rainfall of (302) mm year -1 and evapotranspiration of (2974) mm year -1 , with a mean maximum temperature of 43.9 °C during July and by a mean minimum temperature of 4.9 °C during January [3]. The main observed structure in the area is Qarahanjeer syncline (asymmetrical, double plunging, long and broad syncline extends for 65 Km in NW-SE direction), it is bounded by Chamchamal anticline and by Kirkuk anticline to the northeast and southwest respectively [4].

Groundwater Quality:
All groundwater samples were analyzed for major ions and heavy metals, the results are tabulated in Tables 1, 2     Heavy metals analysis in the studied well shows that their concentrations, however they did not exceed the permissible limit of drinking water according to WHO. 2017, therefore one should avoid the use of polluted groundwater and must ensure that the water used is not polluted and subject to repeated testing and analyses [7] .

3.1: Contamination Degree (Cd):
This index is used to determine the degree of contamination of groundwater samples with heavy metals [8]. This index shows the suitability of drinking water samples for domestic consumption. The degree of contamination is calculated by the following equation (1) [9].
Where: cf i can be obtained by the equation below: Where: cf i : Contamination factor for the i th parameter CA: Measured value for the i th parameter,

3.2: Heavy Metal Pollution Index (HPI):
The coefficient of (HPI) measures the distribution of heavy elements in water, evaluates the content and the degree of groundwater contamination by these elements, and explains the difference in concentrations of elements and their impact on water quality and the critical value is 100 [10] . This parameter is calculated according to the following equations [11]: W i : The relative weight of element i coefficients, ranged between (0-1), Table 6.   Table 7 present that all samples in the study area for dry and wet seasons did not exceeds the critical values of (HPI) values, and the samples (according to a classification by [13]      This index gives the state of water pollution based on its content of heavy metals [14].  MI water quality classification according to [15] as presented in table (10) shows that the samples are slightly to moderately affected by pollution based on their content of heavy metals indicating anthropogenic activities to be source of pollution within the area table (11), and they are on the threshold of danger of drinking (MI = 1), except the sample (W3) which shows a serious pollution by heavy metal and it is non-potable for drinking purposes (MI> 1).

Health Risk Assessment Model:
Humans exposed to heavy metals through different pathways, such as by inhalation by mouth and nose or by most common methods through direct ingestion and skin absorption by skin exposure to heavy metals. The risk assessment method is used to assess the actual or potential adverse effects of pollutants on humans, animals and plants living in an area and focus on causes of these pollutants [1]. To evaluate the health hazard of the heavy elements in the groundwater of the study area, the following indices has been calculated:

4.1: Chronic Daily Intake Indices (CDI):
The chronic daily dose of heavy elements in water is estimated by the two tracks, namely, ingestion [16] and skin contact [17]. The health risks of non-carcinogenic and carcinogenic effects were evaluated using mathematical expressions achieved from the USEPA Risk Assessment Guidance for Superfund methodology. The dose received through the individual pathway considered was determined using Equations (7) and (8)
CDI drm = (8) Where: (CDI ing ) and (CDI drm ) are the average daily dose (mg kg -1 day -1 ) by ingestion, and dermal absorption respectively. CW is concentration of the estimated metal in water (mg l -1 ) ; IR is the intake rate (L day -1 ); EF is exposure frequency (days year -1 ); ED is exposure duration (year); BW = body weight (kg); AT is averaging time (days), and CF 1 is mass conversion factor from μg to mg (0.001); CF 2 is unit conversion factor (L/1,000 cm 3 ) (0.001); SA is drinking water exposed skin area(cm2), Kp is dermal permeability coefficient (cm hr -1 ), ET is exposure time during bathing and shower (min day -1 ), EF is exposure frequency (days year -1 ).

4.2: Hazard Quotient (HQ) and Hazard Index (HI) Indices:
Health Risk Index (HI) is used to assess the probability of non-carcinogenic effects of heavy metals. HI represents the total risk of the two cycles (HQ) [19]. If both (HQ) and (HI) are exceeded, they indicate that there are carcinogenic effects of the elements from the two main pathways (ingestion and skin contact), which may have adverse effects on human health [20]. The HQ (ingestion and dermal contact) and HI for non-carcinogenic risk of some trace metals in drinking water can be calculated using Equations. (9), (10), and (11).

Conclusion:
In order to assess the impact of heavy metals on groundwater resources of Qara-hanjeer sub basin. The chemical quality and the sources of the heavy metals (As, Co, Cr, Cu, Fe, Mn, Ni, Zn, Mo and Pb) in (6)