ASSESSMENT OF COBALT CONCENTRATIONS IN WASTEWATER AND VEGETABLE SAMPLES GROWN ALONG KUBANNI STREAM CHANNELS IN ZARIA,

KADUNA STATE, NIGERIA

M.D. SAEED AND S.O. OLADEJI

A PAPER PRESENTED AT 17TH INTERNATIONAL CONFERENCE ON FOOD QUALITY, SAFETY AND

ANALYSIS, DUBAI, UNITED ARAB EMIRATE

21ST – 22ND SEPTEMBER, 2015

INTRODUCTION

Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally in

chemically combined form. It is an essential trace dietary mineral for all animals. Cobalt is

naturally occurring element found in rocks, soil, water, plants and animals. Elemental cobalt is a

hard, silvery grey metal (ASTDR, 2004). However, it is usually found in the environment

combined with other elements such as oxygen, sulphur and arsenic. It is used in production of

alloys that are used in the manufacture of aircraft engines, magnets, grinding and cutting tools,

artificial hip and knee joints. . It enters the environment from natural sources and burning of coal

or oil or the production of cobalt alloys (Wong, 1996).

Wastewater

Wastewater is described as combination of the liquid or water-carried from residences,

institutions, commercial and industrial establishments together with groundwater and surface

water which results in the lowering the quality of water in the river because of anthropogenic

influences (Morrison et al., 2001). Wastewater is classified into; (a) Domestic Wastewater (from

homes, offices, hotels, institutions) comprises sewage (human waste like faeces) and grey water

from (bathrooms, kitchens, laundries) and (b) Industrial Wastewater which is the liquid

discharged from manufacturing processes such as brewery companies, sugar processing industry,

metal processing industry, tannery and photo finishing laboratory.

Vegetables

Leafy vegetables are essential components of the daily food intake (Faboya, 1983; Ladeji and

Okoye, 1993; Aletor and Adeogun, 1995). They provide the much needed minerals, vitamins and

supplementary protein as the populace depend largely on starchy staples (Taylor,

1996).Vegetables are annuals and biennials, whose succulent parts such as leaves, stems, flowers,

shoot, root and tubers are consumed as supplementary foods to diversify the diet. Population

growth and urbanization are creating increased demand for food, and concerns are rising about

malnutrition in peri-urban areas. There is also the growing concern that unenlightened methods of

vegetable production are having adverse effects on the environment (Olufolaji, 1989).

Aim of the Research

High rate of diseases in our society may be traced to the activities that people regard as

insignificant. This study is aimed at ascertaining the extent to which cobalt is accumulated in

wastewater and vegetables through man-made activities.

Objectives of the Research

1. Research intended to assess the quality of vegetables consumed in the study area with their

health implications using standard analytical methods.

2. It also intended to determine; cobalt concentrations in the wastewater and vegetables of the

study area with their seasonal variation (harmattan, dry and rainy seasons).

Literature Reviews

Monitoring of heavy metals content in fruits and vegetables collected from production and

market sites of Misurata, Libya were analyzed by Elbagermi et al (2012). The content of lead

(Pb), copper (Cu), zinc (Zn), cobalt (Co), nickel (Ni) and cadmium (Cd) in some selected fruits

and vegetables were measured using atomic absorption spectrophotometry. Their results showed

that the average concentrations detected ranged from [0.02-1.82, 0.75-6.21, 0.042-11.4, 0.141-

1.168, 0.19-5.143 and 0.01-0.362] mg/Kg for Pb, Cu, Zn, Co, Ni and Cd respectively. The level of

the metals found were compared with those reported for similar fruits and vegetables by the

FAO/WHO and they were below maximum contaminant levels.

Sampling

Wastewater samples from Kubanni stream were obtained on a four month basis at five different

points along the stream channels for the period of two years. Wastewater samples were collected

in plastic containers previously cleaned by washing in non-ionic detergent, rinsed with tap water

and soaked in 10% HNO3 for 24 hours and finally rinsed with deionized water prior to usage

(Ademoroti, 1996). Sample bottles used were rinsed with sampled water three times and then

filled to the brim at a depth of one meter below the wastewater from each of the five designated

sampling points. Sample bottles were labeled, stored in ice-blocked coolers and transported to the

laboratory while in the laboratory, they were stored in the refrigerator at 4 °C prior to analysis.

The full grown vegetable of [spinach (Amaranthus hybridus), lettuce (Lactuca sativa),

cabbage (Brassica oleracea), carrot (Daucus carota), okro (Hibiscus esculentus), onion (Allium

cepa) and tomato (Lycopersicon esculenetum)] were randomly handpicked from various garden

plots along Kubanni stream channels using hand-gloves, bulked together to form a composite

sample, wrapped in a big brown envelopes, labeled accordingly and transported to the laboratory.

Digestion of Wastewater Samples for Cobalt Determination

1000 cm3 of each wastewater samples were transferred into a beaker and 50 cm3 concentrated

HNO3 were added. The beakers with the content were placed on a sand bath and evaporated down

to about 20 cm3. The beakers were cooled and another 5 cm3 concentrated HNO3 were added to

each beaker. The beakers were covered with watch glasses and returned to the sand bath. The

heating was continued and then small portion of HNO3 was added onto each beaker until the

solutions appeared light colour and clear. The beakers wall and watch glasses were washed with

deionized-water and the samples were filtered to remove any insoluble materials that could clog

the atomizer. Each volume was adjusted to 100 cm3 with deionized water. Determination of cobalt

in the wastewater samples were done at 241 nm wavelengths using Alpha-4 Model (AAS).

Digestion of Vegetable Samples for Cobalt Determination

3.0 g of the dry sample of each vegetable was ashed using Muffle furnace set at 450 °C on

cooling, the ash was transferred to a decomposition flasks and 1cm3 of concentrated HNO3 was

added. They were refluxed on a hot plate for 40 minutes and on cooling 20 cm3 of deionized water

was added, boiled for 3minutes and filtered. 10 cm3 of 2M HNO3 was added to the resulting

solutions in a 100 cm3 volumetric flask. They were made up to the mark with deionized water,

cobalt was determined at 241 nm wavelengths using Alpha-4 Model Atomic Absorption

Spectrophotometer (AAS) (AOAC, 1996).

Results and Discussion

The results of cobalt in wastewater and vegetables analyzed were expressed in form of bar-charts using Microsoft

Excel (Window 7 Professional), the results obtained were subjected to one way Analysis of Variances (ANOVA) and

Pearson Product Moment Correlations using Statistical Package for the Social Sciences (SPSS) 20.0 version

software. Null hypothesis was adopted and this was set at 95% Confidence Mean level to check if there is significant

difference in the concentrations of cobalt analyzed. Statistical decision for Pearson Correlation Coefficients (r) were

taken as follows;

(i) If 0.05 ≤ r ≤ 0.20 there is negligible relationship

(ii) If 0.21 ≤ r ≤ 0.40 there is low relationship

(iii)If 0.41 ≤ r ≤ 0.60 there is moderate relationship

(iv)If 0.61 ≤ r ≤ 0.80 there is substantial relationship

(v) If 0.81 ≤ r ≤ 1.00 there is very high relationship (Robert, 1992)

Cobalt in Wastewater

Harmattan 2013

Dry 2013 Rainy 2013 Harmattan 2014

Dry 2014 Rainy 20140

2

4

6

8

10

12

14

16

Fig. 1: Cobalt Concentrations in Wastewater from Kubanni Stream Channel, Zaria

Kwangila

Unguwa Fulani

Sabon gari

Tundun wada

Industrial Area Along Jos Road

Seasons

Cob

alt

in W

aste

wat

er in

mg/

L

Table 1:- Analysis of Variance for Cobalt in Wastewater (Locations and Seasons)

Analysis of Variance

Sum of Square

df Mean Square

F Signif.

Cobalt in Wastewater Between Groups(Locations) Within Groups Total Cobalt in Wastewater Between Groups(Seasons) Within Groups Total

110.970236.141347.111

46.090

301.021347.111

42529

52429

27.7429.446

9.21812.543

2.937

0.735

0.040

0.604

Table 2:- Summary of Pearson Product Moment Correlation for Cobalt in Wastewater

Variables SD r df Signif.

Cobalt 2013 15 9.107 3.624 0.726 13 0.002

Cobalt 2014 15 9.825 3.374      

Cobalt in Vegetables

Harmattan 2013

Dry 2013 Rainy 2013 Harmattan 2014

Dry 2014 Rainy 20140

2

4

6

8

10

12

14

Fig. 6: Cobalt Concentration in Vegetables from Kubanni Stream Channels, Zaria

CarrotLettuceOnionSpinachCabbageTomatoOkro

Seasons

Coba

lt C

once

ntra

tions

in V

eget

able

s (m

g/Kg

)

Table 3:- Analysis of Variance for Cobalt in Vegetable (Varieties and Seasons)

Analysis of Variance

Sum of Square

df Mean Square

F Signif.

Cobalt in Vegetable Between Groups(Among various vegetable) Within Groups Total Cobalt in Vegetable Between Groups(Seasons) Within Groups Total

84.445150.474234.919

15.901

219.018234.919

63541

53641

14.0744.299

3.1806.084

3.274

0.523

0.012

0.757

Table 4:- Summary of Pearson Product Moment Correlation for Cobalt in Vegetables

Variables SD r df Signif.

Cobalt 2013 21 4.357 2.030 0.720 19 0.001

Cobalt 2014 21 4.504 2.759      

Conclusion

There is need to find means of reducing the concentrations of this heavy metal (cobalt) which

might make the vegetables analyzed unsuitable for human consumption in nearby future by stop

using wastewater to irrigate the farmland in the studied area and stop indiscriminate discharge of

refuse on the body of Kubanni River by providing appropriate dumpsites within the vicinity for

this purpose