Assessment of nitrate and its health risk capability in groundwater used by residents around a dumpsite in Lagos, Nigeria Archives of Ecotoxicology

Anthropologic activities in our environment had been continuously associated with the release of nitrate a contaminant that has been linked with some dangerous health effects. This study assessed the concentration and health risk of nitrate in groundwater used by residents around a dumpsite. For this study groundwater samples were obtained randomly from 12 sampling sites near the Solos dumpsite at Igando, Alimosho local government area, Lagos, Nigeria. The water samples were analyzed for nitrate and some other physic-chemical parameters. The water quality index of the water samples was calculated to determine the suitability for consumption purposes. The non-carcinogenic hazard health risk associated with the nitrate level in the water samples was also assessed. The relationship between the nitrate in the water samples and the drinking water quality index (DWQI) was a positive one with r= 0.21 at p=0.517. The hazard index for ingestion (oral) route (HIoral) range were 0.024-0.962, 0.028-1.136 and 0.033-1.3 for male, female and children respectively. The dermal hazard index (HIdermal) shows range of 0.001-0.026 for male, 0.001-0.027 for female and 0.002-0,071 for children. Sample 6 had Total hazard index (HItotal) greater than 1for both female adult and children as 1.163 and 1.371 respectively. All water samples on this study had the presence of nitrate that were positive correlated with water quality index and only one of the samples nitrate concentration was associated with high health non-carcinogenic risk effect especially in children and women.


Introduction
With a lot of contaminants been released into our surrounding daily through anthropogenic activities, nitrate cannot be ignore as it is one of the most important contaminants released into the environment (Darvishmotevallia et al., 2019). Contamination of groundwater by Nitrate (NO3 -) has become prevalent and leading to reduction in the viability and quality of groundwater in the universe It has been reported that groundwater has the tendency of being contaminated by nitrate (Wongsanit et al., 2015). Some studies had reported high nitrate concentration in groundwater (Cheong et  In an effort to study the extent of the groundwater contamination 12 sampling sites were selected near the dumpsite from where the samples were taken. The samples were collected in 60 cl capacity polythene bottles. Prior to the collection, bottles were thoroughly washed and rinsed with sample to avoid any possible contamination in bottling and other precautionary measures were taken.

Sample Analysis
The samples were transferred to Biochemistry Drug laboratory and stored in cold room (4 • C). All the samples were analyzed for selected relevant physico-chemical parameters which include colour, pH, Electrical conductivity (EC), Total hardness (TH), nitrates and phosphates.

Drinking water quality index (DWQI)
In order to determine the suitability of the groundwater for consumption purposes, the water quality index was calculated. Hence, for calculating the DWQI, results of the physico-chemical parameters like pH, electrical conductivity, total hardness, nitrate and phosphate were used. The steps abduct for computing DWQI were i. Weight (wi) assignment ii.
Calculation of relative weight (Wi) iii.
Calculation of quality rating scale (qi), and iv.
Calculation of DWQI (a) Weight (wi) was assigned to each of the physico-chemical parameters with referenced to perceived relative influence in quality of groundwater for drinking generally. Nitrate was the highest weight of 5, pH, Electrical conductivity (EC) and phosphate were assigned the value of 3 and Total hardness (TH) was assigned the lowest value of 2 since it is believed to show less effect (Table 1).
(b) The following equation was used in calculating the relative weight (wi)

Equation 1
Wi connote the relative weight, the assigned weight of each parameter is wi and parameter numbers is n.
(c) To calculate the quality rating (qi) for the parameters; the concentration (Ci) (mg/dL) of each parameters in the groundwater sample was divided by the permissible standard (Si) (WHO 2011), and multiplied by 100. The following equation was used in calculating qi: (d) The sub-index (SI) was computed by using SIi= Wi x qi Equation 3 . (e) DWQI was computed by using

Equation 4
Sub-index of the ith parameter is SIi, relative weight is Wi, quality rating is qi, and n is the parameters number

Human health risk assessment
To evaluate the health risk associated with water contaminated four methods such as identification of hazard, evaluation of dose response, assessment of exposure and risk (Adimallaet al., 2018a; Li et al., 2016; Narsimha and Rajitha 2018) were computed. Humans can be exposed to NO3 -contaminated water via consumption of the water and skin popularly known dermal contact. Therefore, the chronic daily intake (CDI: mg/kg/day), and dermal absorbed dose (DAD: mg/kg day) were calculated to evaluate the doses gotten via the individual route. Equation 8 HQoral and HQskin-Is the non-carcinogenic for oral and skin hazard quotient, respectively. DAD and CDI show the dermal absorbed dose (mg/kg/day) and chronic daily intake (mg/kg/day), respectively RfD-Is the reference dose of a particular contaminant (US EPA 2001).

Ingestion route
The oral reference doses of nitrate-nitrogen is 1.6 mg/kg/day (Integrated Risk Information System, US Environmental Protection Agency 1989) and the reference dose of skin nitrate nitrogen intake was 0.18 mg/kg.d (Yang et al., 2012)

Total hazard index (HItotal)
The total hazard index (HItotal) which represents the cumulative non-carcinogenic risk is estimated by summing up hazard quotients (HQoral and HQdermal) and are calculated by Equations (9) and (10):

Statistical Analysis
The data obtain for the nitrate and other physic-chemical parameters were analyzed using SPSS version 22 and Graphad prism 8  Houatmiaet al., (2016) to assess the quality of water for the sole aim of drinking. The relationship between the nitrate in the water samples and the DWQI was a positive one with r= 0.21 at p=0.517 as indicated in Fig. 2.   It has been reported that nitrate at higher concentration in the body create risk to health by hindering the bond between oxygen and hemoglohin as a result of the nitrite produced from its breakdown and this lead to methemoglobinemia and this could kill infants and children (Huang et al., 2011). This study focus on non-carcinogenic health risk that can be associated from contamination of groundwater used by residents around a dumpsite.  46.4% parts of the area where the study was conducted in northern China were higher than 1 and children have a higher susceptibility of exposure to nitrate contaminants. Children having a higher level of susceptibility in terms of the health risk from the HItotal value were also observed in this study. Sadler et al., (2016) reported that the ingestion of nitrate contaminated water with the first trimester of pregnancy was associated with high risk of birth defects in susceptible populace in Indonesia. In rural part of China, Zhaiet al., (2017) discovered that groundwater nitrate concentration is higher than permissible limit and that in terms of exposure to risk, children> female> male are at higher risk of health hazards from oral route. This was also reported in this study as shown in Table  2.

Conclusion
It has been proven that a dumpsite is one of the sources of leachate which do increase nitrate level in groundwater when it percolates into groundwater around the environment which a landfill is located. This study therefore made the following:  All water samples on this study had the presence of nitrate that were positive correlated with water quality index  Of all the water samples, 41.67% of them were classified as very poor water, while 58.33% of them fall in the category of unsuitable for oral consumption  Only one of the water samples nitrate concentration is associated with high health non-carcinogenic risk effect especially in children and women.

Declaration of interest
There is no conflict of interest in this work.