Contamination and health risk assessment of heavy metals in road dust in Bayan Obo Mining Region in Inner Mongolia, North China

doi:10.1007/s11442-015-1244-1

Abstract

Abstract:

The objective of this study was to investigate the concentration and spatial distribution patterns of 9 potentially toxic heavy metal elements (As, Cd, Co, Cr, Pb, Cu, Zn, Mn, and Ni) in road dust in the Bayan Obo Mining Region in Inner Mongolia, China. Contamination levels were evaluated using the geoaccumulation index and the enrichment factor. Human health risks for each heavy metal element were assessed using a human exposure model. Results showed that the dust contained significantly elevated heavy metal elements concentrations compared with the background soil. The spatial distribution pattern of all tested metals except for As coincided with the locations of industrial areas while the spatial distribution of As was associated with domestic sources. The contamination evaluation indicated that Cd, Pb, and Mn in road dust mainly originated from anthropogenic sources with a rating of “heavily polluted” to “extremely polluted,” whereas the remaining metals originated from both natural and anthropogenic sources with a level of “moderately polluted”. The non-cancer health risk assessment showed that ingestion was the primary exposure route for all metals in the road dust and that Mn, Cr, Pb, and As were the main contributors to non-cancer risks in both children and adults. Higher HI values were calculated for children (HI=1.89), indicating that children will likely experience higher health risks compared with adults (HI=0.23). The cancer risk assessment showed that Cr was the main contributor, with cancer risks which were 2-3 orders of magnitude higher than those for other metals. Taken in concert, the non-cancer risks posed by all studied heavy metal elements and the cancer risks posed by As, Co, Cr, Cd, and Ni to both children and adults in Bayan Obo Mining Region fell within the acceptable range.

Key words: road dust, heavy metal elements, contamination assessment, health risk assessment, Bayan Obo Mining Region

Kexin LI, Tao LIANG, Zhiping YANG, Zhiping YANG. Contamination and health risk assessment of heavy metals in road dust in Bayan Obo Mining Region in Inner Mongolia, North China[J].Journal of Geographical Sciences, 2015, 25(12): 1439-1451.

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I_geo value	Class
I_geo≤0	Unpolluted
0 < I_geo≤1	Unpolluted/Moderately polluted
1 < I_geo≤2	Moderately polluted
2 < I_geo≤3	Moderately polluted/Strongly polluted
3 < I_geo≤4	Strongly polluted
4 < I_geo≤5	Strongly polluted/Extremely polluted
I_geo > 5	Extremely polluted

Factor	Definition	Value		Unit	Reference
Factor	Definition	Adults	Children	Unit	Reference
BW	Average body weight	70	15	kg	EPA, 1989
IngR	Ingestion rate	100	200	mg·day^-1	EPA, 1989
InhR	Inhalation rate	20	7.6	m³·day^-1	Zheng et al., 2010a
PEF	Particle emission factor	1.36×10⁹		m³·kg^-1	EPA, 2001
SA	Surface areas of the skin that contacts the airborne particulates	5700	2800	cm^-2	EPA, 2004
SL	Skin adherence factor	0.07	0.2	mg·m^-3	EPA, 2004
EF	Exposure frequency	180	180	days·year^-1	Zheng et al., 2010a
ED	Exposure duration	24	6	years	EPA,2001
ET	Exposure time	24		hours·day^-1
AT (non-cancer risk)	Averaging time	ED×365		days
AT (cancer risk)	Averaging time	70×365		days
ABS	Dermal absorption factor	0.03 for As, 0.001 for other metals		-	EPA,2004
CF	Conversion factor	1×10^-6		kg·mg^-1	EPA,2004

Concentration	Maximum	Minimum	Mean	Geometric mean	Median	S.D.	Inner Mongolia B.
Cd	4.63	1.21	2.20	2.05	1.83	0.90	0.037
Co	41.27	20.65	26.94	26.62	25.74	4.49	9.0
Cr	260.80	85.09	141.24	136.76	139.60	38.46	35.7
Cu	51.09	20.49	36.39	35.75	36.36	6.79	12.7
Pb	526.70	88.04	183.93	167.51	160.50	95.41	13.5
Zn	729.00	192.00	299.37	283.92	261.80	117.51	47.5
As	19.46	8.01	12.02	11.78	11.49	2.57	6.1
Ni	49.82	24.96	31.25	30.85	29.41	5.52	16.6
Mn	7956.00	1575.00	3407.30	3206.43	3172.00	1349.94	434.3

Concentration	Cd	Co	Cr	Cu	Pb	Zn	As	Ni	Mn	Reference
Bayan Obo	2.20	26.94	141.24	36.39	183.93	299.37	12.02	31.25	3407.30	This study
Hangzhou	1.59	19.96	51.29	116.04	202.16	321.40		25.88	509.56	Zhang and Wang, 2009
Urumqi	1.17	10.97	54.28	94.54	53.53	294.47		43.28	926.60	Wei et al., 2009
Shanghai	1.23		159.30	196.80	294.90	733.80		83.98		Shi et al., 2008
Baoji		15.90	126.70	123.17	433.20	715.30	19.80	48.80	804.20	Lu et al., 2009
Nanjing			139.0	238.0	113.0	307.0		47.0	786.0	Liu et al., 2014
Inner Mongolia B.	0.037	9.0	35.7	12.7	13.5	47.5	6.1	16.6	434.3	Xu et al., 2004 Gao et al., 2007
China B.	0.07	11.2	53.9	20.0	23.6	67.7	11.2	23.4	482.0	Xu et al., 2004

I_geo	Cd	Co	Cr	Cu	Pb	Zn	As	Ni	Mn	Reference
Bayan Obo	5.21	0.98	1.35	0.90	3.05	1.99	0.36	0.31	2.30	This study
Hangzhou	3.14	0.10	-1.10	1.70	2.42	1.51		-0.88	-0.98	Zhang and Wang, 2009
Urumqi	0.80	-0.30	-0.10	0.40	0.30	0.50		0.00	0.00	Wei et al., 2009
Shanghai	2.65		0.50	2.19	2.94	2.54		0.84		Shi et al., 2008
Baoji				1.79	3.19	2.58	3.04	0.17	-0.21	Lu et al., 2009