International Research Journal of Public and Environmental Health Vol.7 (3),pp. 74-80, June 2020 Available online at https://www.journalissues.org/IRJPEH/ https://doi.org/10.15739/irjpeh.20.011 Copyright © 2020 Author(s) retain the copyright of this article ISSN 2360-8803

Original Research Article

Assessment of heavy metals in water leaf (Talinum Triagulare) cultivated on Fadama soils through irrigation

in Nigeria

Received 15 January, 2020 Revised 25 March, 2020 Accepted 6 April, 2020 Published 6 June, 2020

1Bukar* P. H. and

2Onoja M. A.

1Niigerian Institute of Leather and Science

Technology Zaria, Nigeria. 2Ahmadu Bello

University Zaria, Nigeria.

*Corresponding Author Email: paul.hena@yahoo.com

In most developing countries, Nigeria inclusive, cultivation of vegetables through irrigation on farmlands near water channels or streams that passes through urban areas during dry season are common practice but in most cases the soils may be contaminated and the contaminants could be absorbed by the plants. In this work, assessment of heavy metal pollutants namely Aluminum, Cobalt, Iron, Lanthanum, Manganese, Chromium, Samarium, Scandium, Rubidium, Thorium, Vanadium and Zinc in water leaf (Talinum Triangulare) samples was done using instrumental neutron activation analysis (INAA) technique. The samples were obtained from fadama farm lands used for dry season farming through irrigation along the bank of river Ngadda and Alau dam in Maiduguri the Borno state capital in north east of Nigeria. The aim of the study was to determine the bioaccumulation of trace and heavy metal pollutants in water leaf vegetables, ascertain the health risk associated with the consumption of the vegetables and to compare the concentration values with the available Maximum Permissible Limit (MPL) recommended for consumable vegetables. The result obtained indicates that the concentrations of the elements varied from values below detection (BDL) to maximum as presented. Aluminum ranged from 880 ± 13 ppm to 1412 ± 25 ppm, Cobalt from 0.41 ± 0.04 ppm to 12 ± 0.82,Iron from 361 ± 38ppm to 2134 ± 60 ppm, Lanthanum from0.84 ± 0.04ppm to 2.15±0.06ppm, Manganese from 122.1 ± 0.04 ppm to 342 ± 1ppm, Chromium BDL to 82 ± 23ppm, Rubidium from 6.2 ± 0.6ppm to 48 ± 2.0 ppm, Samarium from 0.09 ± 0.01 ppm to 0.264 ± 0.01 ppm, Vanadium from BDL to 1.61 ± 0.35 ppm, Scandium from 0.07 ± 0.01ppm to 37.1 ± 1.40 ppm, Thorium from BDL to 28 ± 5 ppm, and Zinc from 25 ± 3 ppm to 42 ± 4 ppm. The result obtained showed that the maximum concentrations of Iron, Chromium, Cobalt and Manganese exceed the MPL values recommended by FAO/WHO of 425.5, 1.5, 0.3, and 25.95 respectively. Therefore, the continuous consumption of water leaf cultivated in the study area constitute health risk due to the fact that these heavy metals can accumulate in some sensitive body organs with time. Keywords: Assessment, bioaccumulation, metal pollutants, irrigation, Fadama soils, water leaf.

INTRODUCTION In recent years’ attention has been focused on the contamination of the environment with heavy metals because of the negative consequences on living organism. Heavy metals have high density and mostly toxic in nature for human, plants and animals regardless of their

concentrations (LWTAP 20004; Oves et al., 2012). Research has shown that human exposure to heavy metal and its intake were basically through food, inhalation and dermal contact (Khan et al., 2014; Ferre- Huguet et al., 2008; Kim et al., 2009; Martorell et al., 2011). The literature about heavy

Int. Res. J. Public Environ. Health 75 metals in food plants shows that both leafy and non-leafy vegetables are good accumulators of heavy metals (Khan et al., 2015). The contaminated soils on which plants were cultivated could be a primary route of human exposure to metal toxicants (Nabulo, 2010) hence heavy metals is viewed as an international problem because of the effects on ecosystem in most countries (Egila et al., 2014).

Water leaf are edible vegetables that form an essential part of the human diet and as food crops they are generally consumed because of their nutrition value ( Rumteke et al., 2016; Zhou et al., 2016; Deribachew et al., 2015) and they may contain a number of essential and toxic metals (Yang et al., 2011; Waqas et al., 2015). The cultivation of water leaf vegetables through irrigation suggest that the water from the river might have mixed up with the storm from the town either the point source(PS) and non-point source (NPS) storm of the municipality as anthropogenic activities such as solid waste deposal, waste water irrigation, sludge application, automobile exhaust, mining and smelting processes, urbanization, agricultural activities and industrialization contribute heavy metals into the soil environment(Facchineli, 2001; Chen et al., 1999; Tsai et al., 2001; Shi et al., 2005) and also use of excessive agrochemicals (Muchuweti et al., 2006; Tongesayi et al., 2013), this is so as sediments near urban areas commonly contain high levels of contaminants (Cook and Wells, 1996, Lamberson et al., 1992)among which are heavy metals.

River Ngadda around which the study is centered transcends the Borno state capital. Maiduguri and since the capital is a major city some activities that generate solid waste from domestic, public institutions, and small scale industries, occurred on a daily basis. This waste might not be properly disposed, and release heavy metals into the environment. For example, car accumulator battery services and metal works in form of car body maintenance, metal welding which are sources of disposing heavy metals into the environment could be eroded to the soil along the bank of the river or washed into the river during rainy season or transported by wind in particulate form into the river as windstorm is a characteristic of such a desert environment and these heavy metals could accumulate in the sediment of the river overtime and mixed with the water during irrigation processes. These contaminate the soil and the water leaf absorbs it during growth which could be a primary route of human exposure to metal toxicants (Nabulo et al., 2011) hence heavy metals are viewed as an international problem because of the effects on ecosystem in most countries (Egila et al., 2014). Therefore, the aim of these study is to assessed the bioaccumulation of heavy metals in water leaf cultivated through irrigation along the bank of river Ngadda and Alau dam. MATERIALS AND METHODS This study covers an area that lies on latitude 11o48’N to11o 52’N and longitude 13o06’E to 13o14’E Figure 1, mostly

within Maiduguri township and at the outskirt of the town. Sample Collection Water leaf vegetable samples were collected on three sites of fadama farmlands along river Ngadda and Aluu dam. The samples were labeled with the identification codes (F1, F2, F3). On each sites, five samples were collected on each plot of study area and homogenized to constitute a sample site. The area of study has a light annual rainfall and the rainy season run between the month of June and September thus dry season farming thrives in the area. The locations points for the collection of samples were obtained using Global Positioning System (GPS) to enable repeatability in subsequent future study. Sample Preparation The fresh vegetable samples were properly identified at The Herbarium in Biology Department of Ahmadu Bello University, Zaria, after which they were taken to laboratory, thoroughly washed with running tap water and properly rinsed with double distilled water to remove possible particulate pollutants. The moisture and water droplets were carefully removed with the help of blotting papers. The samples were air dried and oven dried at low temperature and there after ground and sieved to required particle sizes using a sieve that were pre-cleaned. They were then put in sample bottles, labeled and capped, then taken to Centre for Energy Research and Training (CERT) Ahmadu Bello University, Zaria for further preparation and analysis.

Sample Preparation for Neutron Activation Analysis

Instrumental Neutron Activation Analysis (INAA) is a technique which is use for multi-elemental determination in a matrix. It is a sensitive method for accurate determination of elemental concentration in materials and was used in this study employing Nigeria Research Reactor-1 (NIRR-1) facility located at Ahmadu Bello University Zaria, Kaduna state of Nigeria. The detail and function of NIRR-1 is seen in the work of Jonah et al., 2006; Jonah 2008).

Conventional preparation method of vegetable samples for irradiation which was provided by Jonah et al. (2006) was adopted after which the samples were then sealed in an irradiation vial. Standard Reference Material (SRM) NIST 1573a which is a direct representative of the vegetable sample was also put in the same type of vial with that of the sample.

Sample Analysis The interaction of the sample and the neutron flux is based on the activation equation (Equation 1)

R = (1)

Bukar and Onoja 76

Figure 1: Maiduguri township map

Source: Land and Survey 2012

Where R = reaction rate, N = number of interacting isotope,

(E) =cross-section (in cm) at neutron energy E (in eV), ⱷ =

neutron flux per unit of energy E (eV). In terms of neutron velocity. It is expressed in equation (2)

R = ∫𝜎(𝑣)ϕ′(𝑣)𝑑𝑣∞0 = ∫𝑛(𝑣)𝑣𝜎(𝑣)𝑑𝑣∞0 (2) Where v the neutron velocity (m s−1), σ(v) the neutron

cross section (in m2) for neutrons with velocity v; n(v)dv the neutron density (m−3) of neutrons with velocities between v and v+dv, considered to be constant in time.

The relative method of neutron activation analysis for element determination in sample analysis was employed, therefore the sample and standards were irradiated simultaneously and the induced intensities measured. For data processing the gamma-ray spectrum analysis software WINSPAN, 2004 used by (Liyu, 2004) based on the practice of using the activity induced at time after irradiation for time t was employed according to Equation (3)

(3)

Where At is activity of element Q at the end of radiation

(ds-1), is neutron capture cross section of element (m2),

ρ is fractional abundance of particular isotope of element Q,

is atomic weight of element Q to be measured , is

Avogadro’s number (mol-1) , is decay constant of induced

radionuclide (s-1), ti is irradiation time (s), is is the flux of

neutron used in irradiation (nm-2s-1) and is weight of

element Q irradiated. The sample and standard parameters were then related

by Equation (4)

= (4)

Where Asam is activity of the unknown sample, Astd is

activity of the standard.The standard is irradiated and counted under similar conditions as the sample, therefore common parameters in Equation (4) cancelled out then the mass of the element in the sample relative to the standard comparator is calculated using Equation (5)

= (5)

Where msam = mass of element in the sample, mstd = mass

of element in standard, λ = decay constant for the isotope.

Int. Res. J. Public Environ. Health 77

Table 1. Concentration of elements determined in water leaf in different sites by INAA

Sample Al Mn Rb Sc Th V Cr Co Sm Zn Fe La F1 880±13 122.1±0.4 6.2±0.6 10±1.00 28±5 1.61±0.35 82±23 12±3 0.09±0.01 14±2 361±38 0.84±0.04 F2 1441±43 342±1 48±2.0 29±1.00 1.6±0.1 BDL 31±01 1.04±0.02 0.264±0.01 80±4 3104±84 2.15±0.06 F3 1412±25 330±1 14±1.0 0.15±0.01 BDL 1.6±0.5 BDL 0.41±0.04 0.19±0.01 70±3 2134±60 1.2±0.10

BDL: Below Detection Limit All concentrations are in part per million (ppm) or μgg-1

Figure 2a: Concentration of elements determined in water leaf

RESULTS Table 1 present the concentration values of the various elements determined in water leaf vegetables using INAA technique and then graphically plotted using bar chart Figures 2a-2c. The graph was plotted in three figures to enable the grouping of values according to their magnitude.

Daily Intake of Metals (DIM) The level of exposure from consumption of the vegetable investigated could be quantified using an index referred to as daily intake of metals (DIM) which was calculated using Equation (6)

(6)

Where M is the metal concentration in the vegetable (mg/kg), C is the conversion factor, I was the estimated quantity of vegetable taken on daily basis, and W is the average weight of a human being. The conversion factor (from fresh to dry weight of vegetable) of 0.085 was adopted from average weights of an adult and a child were approximated to be 55.9 and 32.7 kg respectively, while the average quantities

Bukar and Onoja 78

Figure 2b: Concentration of elements determined in water leaf

Figure 2c: Concentration of elements determined in water leaf

of vegetable taken on daily basis by adults and children were 0.345 and 0.232 kg/person/day respectively based on reports of (Wang 2005) and (FAO/WHO.

Therefore, to estimate the health risk of any pollutant is to determine the level of exposure to that pollutant and the route(s) of exposure to a particular tissue or organ and since in this study, the daily intake of metals (DIM) was used as the exposure index, evaluation of DIM based on the stated assumptions revealed a minimum of 1.11 x 10-1 mg and a maximum of 7.66 x 10-1 mg for adults, while the

children had a minimum of 3.03 x 10-1 mg and a maximum of 8.69 x 10-1 mg. It can be observed from the results that all the daily intakes of metal in water leaf for all the elements for children were higher than the corresponding values for adults which imply that children tend to take in more metals than adults, and this could be due to tenderness of children’s body tissues. Again, the metals with relatively high DIM values (eg: Al = 0.837 mg, Fe = 0.464 mg for adults and Al = 0.962 mg, Fe = 0.533 mg for children) are mainly major elements with high natural abundances.

Int. Res. J. Public Environ. Health 79 DISCUSSION Figure 2a showed the graph of the concentrations of elements with natural abundant values namely Aluminum, iron and Manganese determined in the water leaf samples. It is obvious from the graph that at all the four site the values of Al> Fe>Mn. This variation trend in concentration could be attributed to the fact firstly, Al and Fe are naturally abundant and secondly since the study area is predominantly in or around the municipal council, anthropogenic activities might have contributed significantly to their deposit in the soils used for the cultivation of the vegetable and absorbed by the plants during growth. In the study carried out by Ukpabi et al. (2016) with regard to heavy metals in water leaf at Aba, south east of Nigeria, Fe concentrations in water leaf samples ranged from 86.0 ± 1.92 to 110 ± 0.67 ppm while Zn concentrations in water leaf samples ranged from 3.16 ± 0.87 to 76.1 ± 0.02 ppm This values were less than the one obtained in this study but fairly correlate this could be explained by the fact that the environment in this study were predominantly within metropolis and using irrigation with water that might have mixed up with storm from municipality.

It can be observed from Figure 2b at sample site B1 concentration of Co > Sc > Eu while at B4 Th was much higher in concentration than Cr > Co >Eu >Sc >Sb. At sites B2 and B3 all the elements determined were almost of the same concentration.

Figure 2c present the graph of the concentrations of the elements Zn, Sm, Rb and La. It is obvious from the graph that at all the four sites Zn>Rb> La while Sm is having the least concentration value. Conclusion From the result obtained and presented it showed that there were variation in the degree of absorption of the various heavy metals by water leaf The bioaccumulation of the naturally abundant heavy metals Al and Fe by water leaf were more than the other elements. The high concentrations of Al and Fe as indicated in figure 2a and that of Zn in Figure 2b absorbed by water leaf could be attributed to the fact that apart from the fact that these elements were naturally abundant, most of the small and medium scale industries within the metropolis utilized materials that contain these heavy metals in addition to them being utilized by almost every household on a daily basis, thus, this might have generated a lot of waste containing these heavy metals and disposed along the bank of river Ngadda and Alau dam or be transported directly to the farmlands along the bank of the river through rain storm, wind and erosion. The heavy metals which might have been deposited at the bottom of the river could be carried with irrigation water and be deposited on the soils of the farmlands during irrigation processes and hence be absorbed by the water leaf.

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