Integration of Heavy Metal Pollution Indices and Health Risk Assessment of Groundwater in Semi-arid Coastal Aquifers, South Africa

doi:10.21203/rs.3.rs-1047297/v1

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Integration of Heavy Metal Pollution Indices and Health Risk Assessment of Groundwater in Semi-arid Coastal Aquifers, South Africa

https://doi.org/10.21203/rs.3.rs-1047297/v1

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The metal contaminated groundwater results in serious health issues and hence this study attempts to address metal contamination and its sources by using integrated techniques including indexed and statistical methods and its related health hazards. Groundwater pH varied from 5.3 to 8.3 indicating acidic to alkaline in nature. Heavy metal evaluation index and degree of contamination reveal that all the groundwater samples fall under low pollution and are appropriate for human consumption. According to the pollution index majority of the samples fall in the insignificant pollution zone. Water quality index reveal that 19% and 2% of the groundwater samples belong to the poor and very poor water quality category and are spatially situated on the central, northern and southern parts of the study region. Correlation matrix and principal component analysis reveal that weathering of aquifer matrix and anthropogenic activities are accountable for the release of heavy metals into groundwater. Furthermore, R-mode and Q-mode cluster analysis revealed two clusters which are linked to mixed sources including weathering and anthropogenic activities. Based on the hazard quotient the order of heavy metal impact is: Co>Pb>Cd>Zn>As>Mn>Cu>Cr>Fe>Ni for both children and adult. The hazard index values varied from 0.06 to 8.16 for children and from 0.02 to 2.14 for adult. In this study, it is discovered that 43% and 26% of groundwater samples pose non-carcinogenic health risk in children and adult, respectively. This study highly recommends treatment of contaminated groundwater before consumption in order to protect and maintain the public health.

Hydrology

heavy metal pollution

multivariate statistical analysis

pollution indices

water quality index

South Africa

Table 1: Parameters considered in PIG evaluation

Parameter	Relative weight (R_w)	Weight parameter	SANS (2015) and WHO (2011)
pH	3	0.06	6.5
As (µg/L)	5	0.11	10
Fe (µg/L)	4	0.06	300
Mn (µg/L)	4	0.06	100
Zn (µg/L)	4	0.06	5000
Pb (µg/L)	5	0.11	10
Ni (µg/L)	5	0.11	70
Cr (µg/L)	5	0.11	50
Cu (µg/L)	4	0.06	2000
Cd (µg/L)	5	0.11	3
Co (µg/L)	3	0.06	500
	∑Rw=47	∑Wp=1

Table 2: Relative weight of selected WQI parameters

Parameters	Assigned weight (wi)	Si (µg/L) (SANS 2015 and WHO 2011)	Relative weight (Wi)
pH	3	6.5	0.075
As	5	10	0.125
Cd	5	3	0.125
Cr	4	50	0.1
Cu	2	2000	0.05
Fe	2	300	0.05
Mn	5	100	0.125
Ni	4	70	0.1
Pb	5	10	0.125
Zn	2	5000	0.05
Co	3	500	0.075
	∑wi= 40		∑Wi= 1

Table 3: Statistical summary of physicochemical parameters of groundwater and water quality standard limits values in µg/L except for pH

	(N=53)				Standard limits
Parameter	Minimum	Maximum	Average	SD	SANS (2015)	WHO (2011)
Parameter	Minimum	Maximum	Average	SD	SANS (2015)	WHO (2011)
pH	5.30	8.3	7.1	0.9	5-9.7	6.5-8.5
As	BDL	3.6	0.5	0.8	≤10	10
Fe	2.70	1848.6	140.1	303.4	≤300	300
Mn	0.40	116.1	19.1	23.1	≤100	-
Zn	1.9	19964.5	499.9	2775.0	≤5000	5000
Pb	BDL	26.0	6.6	9.4	≤10	10
Ni	BDL	9.3	2.1	2.2	≤70	70
Cr	BDL	8.4	3.4	2.7	≤50	50
Cu	BDL	279.5	22.7	61.2	≤2000	2000
Cd	BDL	4.6	0.9	1.7	≤3	3
Co	BDL	8.4	1.8	3.0	≤500	-

Table 4: Results of the various quality indices

Index parameter	Minimum	Maximum	Average
HEI	0.08	10.25	1.83
C_d	-9.92	0.25	-8.17
PIG	0.07	1.03	0.25
WQI	7.27	89.44	25.91

Table 5: Classification of pollution indices

Index method	Class	Extent of pollution	% of groundwater samples
Index method	Class	Extent of pollution	% of groundwater samples
HEI	< 400	Low	100
	400 - 800	Medium	-
	> 800	High	-
C_d	< 1	Low	100
	1 - 3	Medium	-
	> 3	High	-

Table 6: Average values of Ow & PIG

pH	As	Fe	Mn	Zn	Pb	Ni	Cr	Cu	Cd	Co	PIG	Pollution zone
O_w	O_w	O_w	O_w	O_w	O_w	O_w	O_w	O_w	O_w	O_w	PIG	Pollution zone
0.07	0.01	0.03	0.02	0.01	0.07	0.00	0.00	0.00	0.03	0.00	0.23	Insignificant pollution
0.08	0.00	0.52	0.02	0.00	0.23	0.00	0.01	0.00	0.16	0.00	1.03	Low pollution

Table 7: Pearson correlation matrix of analysed parameters

	pH	As	Fe	Mn	Zn	Pb	Ni	Cr	Cu	Cd	Co	HPI	HEI	C_d
pH	1
As	0.00	1
Fe	0.14	-0.07	1
Mn	0.15	-0.22	0.06	1
Zn	-0.15	-0.09	-0.06	-0.04	1
Pb	0.46	-0.18	0.33	0.21	-0.09	1
Ni	-0.02	-0.07	0.08	0.24	-0.09	-0.28	1
Cr	0.00	-0.25	0.19	-0.11	0.29	0.90	-0.23	1
Cu	0.00	-0.12	-0.10	0.25	-0.05	0.35	-0.34	0.18	1
Cd	0.57	-0.13	0.41	0.10	-0.09	0.92	-0.25	0.89	0.09	1
Co	0.55	-0.14	0.28	0.09	-0.09	0.94	-0.28	0.94	0.17	0.97	1
HEI	0.41	-0.16	0.71	0.24	0.16	0.84	-0.10	0.71	0.15	0.86	0.79	1
C_d	0.41	-0.16	0.71	0.24	0.16	0.84	-0.10	0.71	0.15	0.86	0.79	0.87	1
												0.87	1	1

Significant correlation (p 0.05) are in bold

Table 8: Varimax rotated principal component analysis

	Principal components (initial eigenvalue= 1)
Quality parameter	PC 1	PC 2	PC 3
pH	-0.002	0.911	0.089
As	-0.397	0.014	-0.587
Fe	0.345	-0.492	0.186
Mn	-0.069	0.072	0.777
Zn	0.232	0.607	0.042
Pb	0.965	0.191	0.042
Ni	-0.278	-0.175	0.628
Cr	0.941	0.031	-0.075
Cu	0.229	0.785	-0.14
Cd	0.972	0.035	-0.042
Co	0.953	0.17	-0.091
Total	4.134	2.161	1.424
% variance	37.586	19.648	12.941
Cumulative %	37.586	57.235	70.176

Significant component loadings are in bold

Table 9: Statistical summary of the heavy metals’ hazard quotients (HQ) and hazard index (HI) for both children and adult

Heavy metal	Min	Max	Average
As (Children)	0.013	1.426	0.190
As (Adult)	0.003	0.373	0.050
Cd (Children)	0.000	1.102	0.224
Cd (Adult)	0.000	0.289	0.059
Co (Children)	0.000	3.345	0.735
Co (Adult)	0.000	0.876	0.192
Cu (Children)	0.000	0.839	0.068
Cu (Adult)	0.000	0.220	0.018
Fe (Children)	0.000	0.317	0.024
Fe (Adult)	0.000	0.083	0.006
Mn (Children)	0.002	0.580	0.095
Mn (Adult)	0.000	0.152	0.025
Pb (Children)	0.000	2.225	0.568
Pb (Adult)	0.000	0.583	0.149
Zn (Children)	0.001	7.986	0.200
Zn (Adult)	0.000	2.092	0.052
Cr (Children)	0.000	0.335	0.046
Cr (Adult)	0.000	0.088	0.012
Ni (Children)	0.000	0.056	0.004
Ni (Adult)	0.000	0.015	0.001

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First submitted to journal
04 Oct, 2021

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Integration of Heavy Metal Pollution Indices and Health Risk Assessment of Groundwater in Semi-arid Coastal Aquifers, South Africa

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