Spatial distribution and potential ecological and health risks associated with heavy metals in the Ijero-Ekiti mining site, Nigeria

doi:10.1016/j.regsus.2024.03.004

Abstract

Abstract:

Artisanal gold mining, a labor-intensive and antiquated technique, is a growing industry and the source of income for rural communities all over the world. However, artisanal gold mining has potential negative and long-term effects on economy, environment, and society. This study collected soil samples from 16 sample points including a control point to examine the pollution degrees and spatial distribution of heavy metals, as well as ecological and health risks associated with heavy metal pollution in the Ijero-Ekiti mining site, Nigeria. Geographical Information System (GIS) and remote sensing technologies were used to identify regions with high concentrations of heavy metals and assess the environmental impact of gold mining activities. The results show that the mean heavy metal concentrations of 16 soil pointa are 8.94 (±5.97) mg/kg for As, 0.18 (±0.54) mg/kg for Cd, 0.11 (±1.06) mg/kg for Co, 14.32 (±3.43) mg/kg for Cr, 6.89 (±0.64) mg/kg for Cu, 48.92 (±11.77) mg/kg for Fe, 135.81 (±30.75) mg/kg for Mn, 5.92 (±0.96) mg/kg for Ni, 5.72 (±1.66) mg/kg for Pb, and 13.94 (±1.38) mg/kg for Zn. The study reveals that heavy metal concentration in soils follows the order of Mn>Fe>Cr>Zn>As>Cu>Ni>Pb>Co>Cd. An analysis of soil samples indicates that 3 principal components (PCs) account for 70.008% of the total variance and there are strong positive correlations between various pairs of heavy metals. The total potential ecological risk index (309.599) in the study area is high. Non-carcinogenic risk suggests that there may be long-term health impacts on people who work in the mining areas due to chronic exposure to the environment. Based on the study, the hazard index of carcinogenic health risks associated with heavy metals through ingestion is 520.00×10^-4. Dermal contact from As and Cr also increases the risk of cancer, with the highest hazard index value of 18.40×10^-4. The lowest exposure pathway, with the hazard index value of 0.68×10^-4, indicates that the inhalation of heavy metals has a comparatively low risk of cancer. This study recommends the formulation of policies to monitor the Ijero-Ekiti mining site and other regions in Nigeria where indiscriminate artisanal gold mining activities exist.

Key words: Artisanal gold mining, Heavy metals, Exposure pathway, Potential ecological risk, Geo-accumulation index, Ijero-Ekiti mining site

Johnson Adedeji OLUSOLA, Adeyinka Oluyemi ATURAMU, Olufunke ASAOLU, Olusesan Sola OGUNLEYE. Spatial distribution and potential ecological and health risks associated with heavy metals in the Ijero-Ekiti mining site, Nigeria[J]. Regional Sustainability, 2024, 5(1): 100110.

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Sample point	Latitude (N)	Longitude (E)	Elevation (m)
A	07°49′08′′	05°05′11′′	370
B	07°49′14′′	05°05′22′′	350
C	07°49′29′′	05°06′37′′	378
D	07°49′32′′	05°06′50′′	370
E	07°50’35′′	05°06′60′′	380
F	07°51′46′′	05°06′36′′	400
G	07°52′60′′	05°07′55′′	385
H	07°53′60′′	05°07′30′′	390
I	07°53′70′′	05°08′40′′	350
J	07°54′23′′	05°08′60′′	390
K	07°54′60′′	05°09′30′′	400
L	07°55′50′′	05°10′50′′	389
M	07°56′30′′	05°11′33′′	367
N	07°57′30′′	05°11′50′′	400
O	07°58′50′′	05°11′60′′	358
Control point	07°58′60′′	05°14′09′′	900

Heavy metal	Wavelength (nm)	Detection limit (mg/L)	Heavy metal	Wavelength (nm)	Detection limit (mg/L)
Arsenic (As)	193.7	0.0050	Iron (Fe)	248.3	0.0046
cadmium (Cd)	228.8	0.0028	Manganese (Mn)	279.5	0.0010
Cobalt (Co)	283.3	0.0020	Nickel (Ni)	232.0	0.0040
Chromium (Cr)	213.9	0.0010	Lead (Pb)	217.0	0.0120
Cadmium (Cu)	324.8	0.0040	Zinc (Zn)	285.2	0.0030

Class	Description	Class	Description
I_geo<0	Unpolluted	3≤I_geo<4	Heavily polluted
0≤I_geo<1	Unpolluted to moderately polluted	4≤I_geo<5	Heavily to extremely polluted
1≤I_geo<2	Moderately polluted	I_geo≥5	Extremely polluted
2≤I_geo<3	Moderately to heavily polluted

Heavy metal	RfD			CSF			Reference
Heavy metal	Ingestion (mg/(kg•d))	Dermal contact (mg/(kg•d))	Inhalation (mg/(kg•d))	Ingestion	Dermal contact	Inhalation	Reference
As	0.0003000	0.0003000	0.0004000	1.5	1.5	150.0	Department of Environmental Affairs (DEA, 2010)
Cd	0.0000500	0.0000500	0.0000570	-	-	6.3
Co	0.0200000	0.0000057	-	-	-	9.8
Cr	0.0030000	-	-	-	-	-
Cu	0.0370000	-	-	-	-	-
Fe	-	-	-	-	-	-
Mn	-	-	-	-	-	-
Ni	0.0200000	0.0056000	-	-	-	-
Pb	0.0036000	-	-	8500.0	-	420.0
Zn	0.3000000	0.0750000	-	-	-	-

Sample point	As (mg/kg)	Cd (mg/kg)	Co (mg/kg)	Cr (mg/kg)	Cu (mg/kg)	Fe (mg/kg)	Mn (mg/kg)	Ni (mg/kg)	Pb (mg/kg)	Zn (mg/kg)
A	3.45	0.60	BDL	17.22	10.22	8.45	220.20	6.34	0.60	16.10
B	92.30	0.40	0.00	1.30	4.50	10.22	90.90	0.56	0.76	12.78
C	4.50	0.02	BDL	14.22	8.60	90.89	300.20	7.77	3.43	15.82
D	0.90	0.04	0.16	35.24	9.20	30.30	70.25	5.34	0.23	13.27
E	1.20	0.50	0.13	3.23	6.12	7.44	60.34	0.60	2.56	8.89
F	3.45	0.06	BDL	9.20	4.90	35.60	66.20	4.44	1.22	7.24
G	4.45	0.12	0.17	10.66	4.66	29.90	45.60	3.36	2.45	17.34
H	5.34	0.06	0.19	35.20	10.44	120.44	432.20	13.45	1.76	24.16
I	6.26	0.04	0.01	30.20	7.24	160.23	46.76	9.89	1.90	20.13
J	6.26	0.02	BDL	36.22	9.12	90.99	145.23	8.87	8.82	18.55
K	0.90	0.04	BDL	4.22	9.10	39.34	70.74	7.20	3.73	21.57
L	3.22	0.05	BDL	11.20	6.00	50.60	44.40	4.56	17.01	12.06
M	0.88	0.30	BDL	1.20	3.50	4.40	300.30	0.34	8.26	5.68
N	0.76	0.40	BDL	2.67	4.45	24.60	65.50	7.90	20.45	9.78
O	0.27	0.06	BDL	2.80	5.30	30.42	78.30	8.20	12.60	5.70
Control point	0.90	0.45	BDL	26.50	10.22	30.44	70.89	7.78	13.20	12.60
WHO permissible limit (soil)	10.00	0.80	100.00	100.00	36.00	36.00	500.00	35.00	85.00	50.00
Mean	8.94	0.18	0.11	14.32	6.89	48.92	135.81	5.92	5.72	13.94
Standard error of mean	5.97	0.54	1.06	3.43	0.64	11.77	30.75	0.96	1.66	1.38
Standard deviation	23.13	0.21	4.12	13.30	2.46	45.58	119.09	3.71	6.42	5.37
Variance^#	535.36	0.04	17.00	176.89	6.06	2077.78	14,181.32	13.77	41.27	28.71
Skewness^#	3.82	0.71	3.87	0.50	-0.74	1.08	1.45	0.84	1.34	0.15
Standard error of Skewness^#	0.58	0.58	0.58	0.58	0.58	0.58	0.58	0.58	0.58	0.58
Kurtosis^#	14.72	-1.23	14.99	-1.40	-1.69	0.50	1.04	-0.16	0.70	-0.70