Comprehensive Evaluation of Some Toxic Metals in the Surface Water of Louhajang River, Bangladesh

doi:10.21203/rs.3.rs-177235/v1

Louhajang River, Bangladesh, crosses Tangail, which is a densely industrialized and urbanized city. Louhajang River is an essential water source for domestic, irrigation, and urbanization purposes. This study reports the levels of pH, electrical conductivity (EC), and some toxic heavy metals in 40 water samples collected during summer and winter seasons from Louhajang River. The levels were found to be in the ranges of pH 6.22-7.43 and EC 345-798 mS/cm, Cr 0.18-13.2, Ni 0.02-19.04, Cu 0.96-15.92, As 2.18-12.51, Cd 0.02-2.42, and Pb 0.49-15.74 µg/L. The winter season reported higher levels of the examined parameters than the summer season with significant variation (p < 0.05) for all parameters, with the exception of Cd. The metal contents were assessed against local and international standards for drinking, irrigation and aquatic life purposes where different trends were observed. The heavy metal evaluation index (HEI) and the ecological risk index (ERI) reported low to moderate risks. The spatial distribution of metal contents assigned hot spots in some sites along the riverbed, which were attributed to specific manmade sources. The health risk assessment for three population categories, i.e., adult male, adult female, and children, were examined in terms of hazard index (HI) and total cancer risk (TCR) for oral and dermal pathways during both seasons. Cr and Cd recorded HI more than unit in all cases, indicating possible non-cancer risk. TCR values of As for the three examined population categories during both seasons were > 1.0×10^-6, indicating possible cancer risk, while that of Pb were < 1.0×10^-6. For Ni, about 10-25% of the sampled sites recorded TCR > 1.0×10^-6.

Environmental Policy

Toxic metals

water quality

river contamination

heavy metal evaluation index

ecological risk assessment

health risk assessment

Table 1 Parameters used for health risk assessment calculations

Symbol	Definition	Values	References
C	Metal concentration (µg/L)	Specific	-
IR	Ingestion rate (L/day)	2, 1.6, and 1.0 for adult male, adult female, and children, respectively	(USEPA 2011)
EF	Exposure frequency (day/year)	350 for regular activities	(USEPA 2011)
ED	Exposure duration (year)	70 for adult and 12 years for children	(USEPA 2011)
BW	Body weight (kg)	65, 55, and 16 for adult male, adult female, and children, respectively	(USEPA 2015)
AT	Averaging time for non-carcinogens	365 × ED	(USDOE 2011)
SA	Exposure skin area (cm²)	19000, 16000 and 6800 m² for adult male, adult female, and children, respectively	(USEPA 2011)
K_p	Permeability coefficient (cm/h)	2×10^-3, 2×10^-4, 1×10^-3, 1×10^-3, 1×10^-3 and 1×10^-4 for Cr, Ni, Cu, As, Cd and Pb, respectively	(USEPA 2011)
ET	Exposure time (h/day)	0.75, 1.00, and 0.50 for adult male, adult female, and children, respectively	(USDOE 2011)
EV	Event frequency (event/day)	1	(USEPA 2011)
RfD_oral	Reference dose (mg/kg/day)	Cr 0.003, Ni 0.02, Cu 0.04, As 0.0003, Cd 0.005, and Pb 0.0035	(USEPA 2008; USDOE 2011)
ABS_dermal	Dermal absorption fraction (unitless)	Cr 0.001, Ni 0.001, Cu 0.01, As 0.03, Cd 0.001, and Pb 0.001	(USEPA 2011)
CSF	Cancer slop factor	Ni 0.0017, As 1.50, Pb 0.000009	(USEPA 2011; USDOE 2011)
PLa	Permissible concentration in water (mg/L)	Cr 0.05, Ni 0.07, Cu 1.3, As 0.01, Cd 0.003, Pb 0.015	(ATSDR 2012)

Table 2 Descriptive statistics of pH, electrical conductivity (EC, mS/cm), and toxic metal concentrations (µg/L) in surface water samples collected during summer (S) and winter (W) seasons from Louhajang River, Bangladesh

Statistical parameter	pH		EC		Cr		Ni		Cu		As		Cd		Pb
Statistical parameter	S	W	S	W	S	W	S	W	S	W	S	W	S	W	S	W
Minimum	6.22	6.55	345	647	0.18	0.25	0.02	0.03	0.96	1.54	2.18	3.06	0.02	0.02	0.49	0.78
Maximum	7.31	7.43	654	798	9.43	13.2	11.9	19.04	9.95	15.92	8.94	12.51	1.73	2.42	9.84	15.74
Mean	6.95	7.12	535.48	724.00	4.36	6.10	3.17	5.07	4.80	7.67	4.88	6.84	0.37	0.51	3.94	6.30
Medium	6.98	7.22	558.50	734.00	4.41	6.17	2.60	4.15	5.06	8.10	4.82	6.76	0.30	0.41	3.26	5.22
SD^a	0.25	0.22	78.66	37.78	1.94	2.72	3.08	4.93	2.23	3.57	1.34	1.87	0.39	0.55	2.74	4.38
RSD^b	3.55	3.08	14.69	5.22	44.58	44.55	97.17	97.17	46.53	46.53	27.38	27.35	107.15	107.39	69.54	69.55
Kurtosis	2.16	-0.36	-0.46	-0.72	0.70	0.71	2.30	2.30	-0.10	-0.10	1.14	1.14	3.19	3.14	-0.98	-0.98
Skewness	-1.38	-0.82	-0.52	-0.37	0.40	0.40	1.63	1.63	0.15	0.15	0.55	0.55	1.71	1.69	0.53	0.53
P^c	0.002		0.000		0.001		0.042		0.000		0.000		0.175		0.005
BDWS^d	NR^e		NR		50		100		1000		50		5		50
WHO^f	NR		< 1500		5		70		2000		10		3		10
TRV^g	NR		NR		11		52		9		150		2		3
ALWPL^h	NR		NR		2000		150000		4000		50000		1800		7000
ILWPLⁱ	NR		NR		100000		200000		200000		100000		10000		200000

a standard deviation; b relative standard deviation; c p value of independent sample t-test; d Bangladesh Drinking water standard (DoE, 1997); e not reported; f Word Health Organization standard (WHO, 2004); g Toxicity reference value (USEPA, 1999); h Aquatic life water permissible limits (CCME, 2007); i Irrigation life water permissible limits (CCME, 2007; NRMMCA, 2011)

Table 3 Comparison of the mean toxic metal concentrations (μg/L) in surface water samples collected during summer and winter seasons from Louhajang River, Bangladesh, with other water samples from some rivers in Bangladesh and others across the globe

River name	Region	Cr	Ni	Cu	As	Cd	Pb	References
Louhajang (S^a)	Bangladesh	4.35	3.16	4.79	4.88	0.36	3.93	Present study
Louhajang (W^b)	Bangladesh	9.04	5.07	7.67	6.83	0.51	6.30	Present study
Buriganga	Bangladesh	114.00	150.00	NR^a	134	59	119	Bhuiyan et al. 2015
Meghna	Bangladesh	14.54	5.00	NR	11.32	3.04	4.40	Islam et al., 2020
Shitolokkha	Bangladesh	56.80	24.60	NR	8.38	1.84	15.60	Islam et al., 2020
Pasur	Bangladesh	40.00	21.40	NR	12.34	9.80	26.60	Islam et al., 2020
Rupsha	Bangladesh	45.20	18.70	NR	3.52	6.50	18.40	Islam et al., 2020
Korotoa	Bangladesh	77.70	35.5	67.00	41.5	9.5	31	Islam et al., 2015
Zohreh	Iran	2.50	12.5	NR	NR	0.5	9.9	Ahmadee et al., 2016
Yellow	China	6.54	1.97	NR	2.4	0.03	0.21	Gao et al., 2019
To Lich	Vietnam	2.90	7.60	NR	39.10	8.10	NR	Thuong et al., 2013
Huai	China	23.08	46.19	NR	NR	61.74	155.0	Wang et al., 2017
Tarim	China	0.43	1.79	NR	3.07	0.02	0.45	Xiao et al., 2014

^a summer season; ^b winter season; ^c not reported

Table 4 Pearson's correlation coefficient matrices of pH, electrical conductivity (EC), and toxic metal concentrations in surface water samples collected during summer and winter seasons from Louhajang River, Bangladesh

Summer season
	pH	EC	Cr	Ni	Cu	As	Cd	Pb
pH	1.000
EC	0.346^*	1.000
Cr	0.200	0.029	1.000
Ni	0.039	-0.231	0.450^**	1.000
Cu	0.079	0.177	0.100	0.253	1000
As	-0.274	0.061	-0.299	-0.340^*	0.233	1000
Cd	0.093	-0.057	0.382^*	0.389^*	-0.012	-0.504^**	1.000
Pb	0.176	-0.107	0.269	0.045	0.269	-0.229	0.246	1.000
Winter season
pH	1.000
EC	0.162	1.000
Cr	0.032	0.154	1.000
Ni	0.121	-0.150	0.450^**	1.000
Cu	-0.150	0.099	.0100	0.253	1.000
As	0.174	0.386^*	-0.299	-0.340^*	0.233	1.000
Cd	0.005	-0.364^*	0.382^*	0.389^*	-0.012	-0.504^**	1.000
Pb	0.147	0.048	0.269	0.045	0.269	-0.229	0.246	1.000

*Correlation is significant at the 0.05 level (2-tailed)

**Correlation is significant at the 0.01 level (2-tailed)

Table 5 Rotated component matrix obtained from principal component analysis of pH, electrical conductivity (EC), and toxic metal concentrations in surface water samples collected during summer and winter seasons from Louhajang River, Bangladesh

Parameter	Summer season			Winter season
Parameter	PC1	PC2	PC3	PC1	PC2	PC3
pH	0.281	0.784	0.039	0.242	0.291	0.773
EC	-0.192	0.816	0.101	0.160	0.766	0.176
Cr	0.663	0.095	0.291	0.765	-0.105	0.093
Ni	0.640	-0.302	0.348	0.657	-0.283	-0.053
Cu	-0.074	0.085	0.925	0.446	0.376	-0.714
As	-0.793	-0.151	0.325	-0.300	0.790	-0.069
Cd	0.773	-0.019	-0.015	0.507	-0.638	0.060
Pb	0.386	0.099	0.432	0.609	0.065	-0.014

Table 6 Hazard index and total cancer risk through oral and dermal pathways for adult male, adult female and children of some toxic metals in water samples (n= 40) in the summer and the winter seasons from Louhajang River, Bangladesh

Index

Comprehensive Evaluation of Some Toxic Metals in the Surface Water of Louhajang River, Bangladesh

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