Assessments of Heavy Metals in Local Fertilizers in Nigeria

Sani A and Sani U

Published on: 2024-06-01

Abstract

The rapid increase of heavy metal contamination is related to the industries, agricultural, domestic and medical purposes. There is much concern over the hazardous effects of heavy metals on plants, animals and human life. Their effects mainly depend on the level of exposure, dose and chemical toxicity risk index. The town of Kankara in Katsina state is a farming and agricultural settlement with a high number of local fertilizers industries. The evaluation of toxic metals in the local fertilizers is not underestimated due to the practical implications of heavy metals to health and environment. This research is aimed to assess the level of heavy metals such as lead, arsenic, cadmium and mercury in local fertilizers. The samples were collected from four major soils that are used in making the local fertilizer. The samples were analysed using Energy Disperse X-ray Fluorescence (EDXRF) in order to determine the elemental concentration in the samples. The Atomic Absorption Spectroscopic (AAS) analysis was performed in order to determine the targeted toxic metals. The results showed that in all the four soil samples, there is presence of heavy metals. The following metal oxides and heavy metals were recorded in all the four soil samples; PbO, CuO, ZnO, MgO, Fe2O3, NiO, Fe, K, Ca, Cu, Zn, Rb, Sr, Zr and Si were found in all the 4 collected samples. The results for the Dark brown soil showed that 0.20, 0.10, 0.29, 0.10 and 0.80 mg/kg for Cu, Zn, Fe, Zr and Ga respectively. For White soil, 0.42, 0.05, 0.30, 0.20, 0.25 and 0.23 mg/kg of Fe, K, Ca, Cu, Zr and Sr were recorded. Black soil, 0.30, 0.40, 0.10, 0.05, 0.02, 0.05 and 0.08 mg/kg of Si, K, Fe, Cu, Zn, Rb and Sr were recorded. For red soil, 0.34, 0.50, 0.01, 0.10, 0.20 and 0.40 mg/kg of Si, K, Fe, Cu, Zn and Mn were recorded. The results obtained from AAS analysis showed the presence of Cu, Cd, As and Pb in all the four soil samples. The concentration is within the recommended dose limit as recommended by WHO and FAO. However, heavy metals have hazardous effects even at low concentration as revealed in the literature. The research recommends that the workers should adhere to the safety precautions during the working hours by using facemasks and google glasses. The workers should also avoid long staying and inhaling the dust from the local fertilizer.

Keywords

Cadmium; Arsenic; Local fertilizer; AAS

Introduction

Soil contamination by heavy metals is among the major global concern [1]. Heavy metals are any metallic element with a high density of about 5 g/cm³ and is harmful even at low quantity [2]. The concentration of heavy metals in soils, water and plants are linked with the influence of human activities. Heavy metals are deposited in to soils through waste disposal, agricultural, industrial and social activities [3]. Excessive use of fertilizers and insecticides for farming activities pollutes the soil and water on a large proportion [4]. The use of agricultural manures contributes immensely in the increase of heavy metals in soils [5,6]. Human body is exposed to heavy metals through ingestion. Inhalation and absorption through skin and cells membrane [7]. Heavy metals like Cadmium, Copper, Nickel, Arsenic, Mercury, Manganese Iron, Cobalt and Zinc are essential for plants growth and normal functions. However, excessive amount of any one of them can cause serious effects [8,9]. The toxic metals have a tremendous effect on plants which causes damage to the roots system and affects the proper growth of the plants [10]. Toxic metals such as Cd, Cr, Hg and Pb are known to cause effects on kidney, liver and reproductive capacity in both men and women [11]. The toxicity of some metals is alarming. Despite that they are naturally occurring elements. Indigestion of Pb in human body causes serious health effects which includes weight loss, anemia, neurological impairments, kidney and liver damage. Similarly, Ni by ingesting it even at low level causes cancer, kidney and lungs damage. Ingestion of Cd causes reactions in the form of free ions that causes metabolic reactions that occur in the human body. Allergic reactions are noticed at short term exposure to some heavy metals [12-14]. These toxic metals are present in all components of the environment- land, atmosphere and aquatic systems and they have most severely affected the environment. The toxic trace metals have no identified biological function and show toxicological cases even at trace concentrations. The presence of Cadmium in food is poisonous to human health and adsorption of a few milligrams can lead to several serious diseases or neoplasia. Likewise, lead has toxic effect in adults as well as young children [15].

Materials And Methods

Description of the Study Area

The study area is Kankara (11’45⁰00N-12’00⁰00N, 7’15⁰00E-7’30⁰00E), which is the local government in Katsina state, Nigeria. The area spans over 1,260 km² and has a population of about 434,700 from 2023 population projection. The area is flat topography. The people of the area are mainly farmers.

Figure 1: Map of Katsina state showing Kankara (UMYU, Cartography, 2014).

Samples Collection

In the present study, the samples collected from four major soils that are used in preparing the local fertilizers. The samples include:

Dark brown soil
White soil
Black soil
Red soil

Materials

The following materials were used in the study;

Energy Disperse X-ray Fluorescence (EDXRF)
Atomic Absorption Spectrometry Machine (AAS VGP 120 Model)
Electronic weighing balance
Sample container
Mantle and peddle

Methods

The assessment of elemental analysis of the samples was performed using EDXRF in order to determine the elemental concentration in the samples. The AAS analysis was performed for the determination of toxic metals in the samples.

Results and Discussion

Table 1: Elemental analysis results of Dark brown soil sample.

Sn	Element Symbol	Concentration in mg/kg
1	Cu	0.2
2	Zn	0.1
3	Fe	0.29
4	Zr	0.1
5	Ga	0.8
6	TiO₂	0.9
7	MnO	0.3
8	CaO	0.06
9	K₂O	2.23
10	CuO	0.03
11	ZnO	0.02
12	Cr₂O₃	0.04
13	V₂O₅	0.03
14	PbO	0.01
15	Rb₂O	0.01
16	NiO	0.01
17	Cl	0.05
18	ZrO₂	0.03
19	Ta₂O₅	0.03
20	SrO	0.5
21	Nb₂O₅	0.12
22	Bi₂O₃	0.04
23	Sb₂O₂	0.3
24	Y₂O₃	0.002

Table 1 showed the result of elemental analysis of the dark brown soil. The soil contained heavy metals like Cu, Zn, Fe, MnO, CuO, ZnO, PbO at a proportion of 0.20, 0.10, 0.29, 0.03, 0.02, 0.01 mg/kg, respectively. The result also showed the presence of other non-toxic elements which includes NiO, Cl, Ta₂O₅, Sb₂O₂ and Y₂O₃.

Table 2: Elemental Analysis results of white soil sample.

Sn	Element Symbol	Concentration in mg/kg
1	Cu	0.42
2	Zn	0.05
3	Fe	0.3
4	Zr	0.2
5	Ga	0.25
6	TiO₂	0.81
7	MnO	0.23
8	CaO	0.33
9	K₂O	1.32
10	CuO	0.04
11	ZnO	0.01
12	Cr₂O₃	0.001
13	V₂O₅	0.02
14	PbO	0.01
15	Rb₂O	0.01
16	NiO	0.01
17	Cl	0.01
18	ZrO₂	0.09
19	Ta₂O₅	0.04
20	SrO	0.5
21	Nb₂O₅	0.12
22	Bi₂O₃	0.04
23	Sb₂O₂	0.54
24	Y₂O₃	0.002

Table 2 showed the result of elemental analysis of the white soil. The soil contained heavy metals like Cu, Zn, Fe, MnO, CuO, ZnO, PbO at a proportion of 0.42, 0.05, 0.30, 0.23, 0.04 and 0.01 mg/kg, respectively. The results also showed the presence of other non-toxic elements which includes NiO, Cl, Ta₂O₅, Sb₂O₂ and Y₂O₃.

Table 3: Elemental Analysis results of Black soil sample.

Sn	Element Symbol	Concentration in mg/kg
1	Cu	0.3
2	Zn	0.4
3	Fe	0.1
4	Zr	0.01
5	Ga	0.25
6	TiO₂	0.09
7	MnO	0.03
8	CaO	0.16
9	K₂O	2.85
10	CuO	0.24
11	ZnO	0.02
12	Cr₂O₃	0.002
13	V₂O₅	0.002
14	PbO	0.01
15	Rb₂O	0.01
16	NiO	0.01
17	Cl	0.01
18	ZrO₂	0.002
19	Ta₂O₅	0.002
20	SrO	0.5
21	Nb₂O₅	0.12
22	Bi₂O₃	0.04
23	Sb₂O₂	0.54
24	Y₂O₃	0.002

Table 3 showed the result of elemental analysis of the black soil sample. The soil contained heavy metals like Cu, Zn, Fe, MnO, CuO, ZnO and PbO at a proportion of 0.30, 0.40, 0.10, 0.03, 0.24 and 0.01 mg/kg, respectively. The results also showed the presence of other non-toxic elements which includes NiO, Cl, Ta₂O₅, Sb₂O₂ and Y₂O₃.

Table 4: Elemental Analysis results of red soil sample.

Sn	Element Symbol	Concentration in mg/kg
1	Cu	0.34
2	Zn	0.5
3	Fe	0.01
4	Zr	0.6
5	Ga	0.15
6	TiO₂	0.81
7	MnO	0.1
8	CaO	0.33
9	K₂O	1.32
10	CuO	0.4
11	ZnO	0.2
12	Cr₂O₃	0.02
13	V₂O₅	0.003
14	PbO	0.01
15	Rb₂O	0.2
16	NiO	0.01
17	Cl	0.01
18	ZrO₂	0.09
19	Ta₂O₅	0.04
20	SrO	0.5
21	Nb₂O₅	0.12
22	Bi₂O₃	0.06
23	Sb₂O₂	0.7
24	Y₂O₃	0.004

Table 4 showed the result of elemental analysis of the red soil sample. The soil contained heavy metals like Cu, Zn, Fe, MnO, CuO, ZnO and PbO at a proportion of 0.34, 0.50, 0.01, 0.60, 0.40 and 0.20 mg/kg, respectively. The results also showed the presence of other non-toxic elements which includes NiO, Cl, Ta₂O₅, Sb₂O₂ and Y₂O₃.

Table 5: AAS analysis results of the soil samples.

Sample	Cu in mg/kg	Cd in mg/kg	As in mg/kg	Pb in mg/kg	Permissible limits by WHO in mg/kg	Elements
Dark brown soil	0.34 ± 0.01	0.11 ± 0.01	0.57 ± 0.02	8.70 ± 0.05	10	Cu
Black	0.30 ± 0.02	0.13 ± 0.01	2.74 ± 0.02	3.04 ± 0.02	7	Cd
White	0.42 ± 0.02	0.15 ± 0.01	1.05 ± 0.02	2.50 ± 0.01	10	As
Red	0.20 ± 0.02	0.14 ± 0.01	1.25 ± 0.02	2.92 ± 0.05	10	Pb

Table 5 showed the results obtained from AAS analysis which shows that Dark brown soil contained 0.34, 0.11, 0.57 and 8.70 mg/kg of Cu, Cd, As and Pb respectively. The black soil sample contained 0.30, 0.13, 2.74 and 3.04 mg/kg of Cu, Cd, As and Pb respectively. The white soil sample contained 0.42, 0.15, 1.05 and 2.50 mg/kg of Cu, Cd, As and Pb respectively. The red soil sample contained 0.20, 0.14, 1.25 and 2.92 mg/kg concentration of Cu, Cd, As and Pb respectively.

Discussion

There is no data in the previous studies on the potential health risks of Cu, Cd, As and Pb in the study area. However, the previous studies highlighted the hazardous of heavy metals in food, drinking water and air.

In this study we aimed to assess the level of heavy metals in local fertilizer produced in Kankara using EDXRF and AAS. The results obtained showed that there is presence of heavy metals most especially Cu, Cd, As and Pb. The results indicated that the heavy metals are within the recommended limit as provided by WHO and FAO. The excessive inhalation of the heavy metals by the workers will gradually exceed the recommended limits as it is at the threshold.

Conclusion

Constant monitoring of the workers at the local fertilizers industry is paramount in order to ensure that the exposure to the heavy metals does not exceed the recommended limit. The workers are recommended to adhere to all the necessary precautions such as the use of face masks, Google glasses and reduce the exposure time in order to reduce the harmful effects of exposure to heavy metals.

Acknowledgment

The authors would like to acknowledge the technologies of the central laboratory of Umaru Musa Yar’adua University, Katsina for running the analyses of our samples.

Conflict of Interest

The authors have no any conflict of interest.

Global Journal of Materials Science and Engineering