industrial city in northern China

ORIGINAL PAPER

Risk assessment of atmospheric heavy metals exposure in Baotou, a typical industrial city in northern China

Kexin Li . Tao Liang . Lingqing Wang

Received: 11 March 2015 / Accepted: 1 September 2015 / Published online: 8 September 2015 ! Springer Science+Business Media Dordrecht 2015

Abstract Industrial activities have led to serious air pollution and the potentially toxic elements in atmo-

spheric particles can cause various health problems to

humans. In this study, inhalable particulate matter (PM10) and fine particles (PM2.5) were collected from

four typical sites in Baotou, an industrial city in

northern China. We investigated both the mass concentrations of particulate matter and the concen-

trations of heavy metals (Cr, Ni, Pb, Cd, Cu, Mn, Co,

and Zn) in the collected samples. We assessed the public health risks associated with atmospheric heavy

metal exposure. The results showed that the mass

concentrations of PM2.5 and PM10 as well as these heavy metal concentrations varied notably influenced

by the prevailing wind directions. Among the studied

metals, Zn, Mn, Pb, and Cr were the main metal pollutants in both PM10 and PM2.5. The results of the

health assessment showed that the eight heavy metals

studied pose significant non-carcinogenic risks and Cr, Cd, and Co pose lifetime lung cancer risks to local

residents, especially to children.

Keywords PM10 ! PM2.5 ! Heavy metals ! Health risk ! Baotou

Introduction

Mining activities are notorious for adverse environ-

mental impacts, including pollution, habitat loss, soil erosion, and geological disasters (Salomons 1995;

Klukanová and Rapant 1999; Aguilar et al. 2004; Luı́s

et al. 2011). Among these environmental problems caused by mining activities, the production and

dispersion of atmospheric particles has become a

great concern in recent years (Kaonga and Kgabi 2011; Chen et al. 2013; Serbula et al. 2014). Atmo-

spheric particulates are generated from numerous

sources, both natural and anthropogenic, but in areas near mining, mining operations are considered the

largest contributor. The processes of mining, such as

crushing, grinding, excavating, smelting, and refining, can produce large quantities of particulate matter

(PM), containing dangerously high levels of heavy

metals (Csavina et al. 2012). Inhalable particulate matter (PM10), particularly

fine particles (PM2.5), have been shown to cause adverse effects on human health, including asthma,

lung cancer, and cardiovascular diseases (Pope et al.

2002; Sanchez et al. 2009). Lung and other organ injuries from atmospheric heavy metal exposure have

also been well-documented (Espinosa et al. 2001;

Cancio et al. 2008; Leili et al. 2008).

K. Li ! T. Liang (&) ! L. Wang (&) Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China e-mail: [email protected]

L. Wang e-mail: [email protected]

123

Environ Geochem Health (2016) 38:843–853

DOI 10.1007/s10653-015-9765-1

Baotou city, one of the most industrialized cities of northwest China, has very poor air quality due to

large-scale mining activities in the area (Zhen 2012).

Toxic elements are mobilized and released into the air as particle matter from anthropogenic activities and

pose significant health risks to local residents. How-

ever, PM2.5 and PM10 of Baotou has only been monitored in very recent years. Moreover, little work

has addressed the association between the concentra-

tions of aerosol metallic elements and adverse health impacts on the local residents.

The objective of this study was to investigate both

the total mass and heavy metal concentrations of PM2.5 and PM10 as well as how these concentrations

varied spatially throughout the city. Sampling was

performed in four representative areas of Baotou, including a mining area (MA), an industrial area, a

residential area (RA), and the city center. This study

also aimed at estimating the non-carcinogenic health risks and lifetime cancer risks of heavy metals

exposure for local residents.

Materials and methods

Description of sampling sites

Baotou is located in the central Inner Mongolia Autonomous Region of China. The city is situated

on the Tumochuan and Hetao Plateau, and the Yin

Mountains cross the urban area in the central part. The area borders Mongolia to the north, and in the south,

the Yellow River runs through the city west to the east

for 22 km. Baotou has a cold, semi-arid, continental monsoon climate. The mean annual temperature is

7.2 “C. The annual average rainfall is approximately 310 mm, with the majority mostly occurring in July and August when the southeast monsoon carries

rainwater into the province. The prevailing wind

direction is northwest, with an average wind speed of 1.2 m s-1. Due to the arid climate and large temper-

ature differences between day and night, dust storms

frequently occur in this area, especially in spring. As shown in Fig. 1, four sampling sites of different

types of areas were selected in Baotou. The first

sampling site was within the Bayan Obo as a representative MA. Bayan Obo is a typical mining

region in north Baotou where a large-scale open-cut

(rare earth elements)–Fe–Nb pit is located, and large quantities of raw ore are mined. The second sampling

site was a typical smelting area (SA) in west Baotou,

which was surrounded by numerous chemical and metallurgical factories, refineries, and power plants.

This area is the site to which raw ores from Bayan Obo

are transported by railroad for further processing. The third sampling site was a city center area (CA),

characterized by a highly dense population, heavy

traffic, and commercial activities. Finally, the forth sampling site was a representative RA of Baotou,

located northeast of the CA.

Fig. 1 Map of the study area and sampling sites

844 Environ Geochem Health (2016) 38:843–853

123

Sample collection and analysis

PM10 and PM2.5 samples were collected on quartz microfiber filters (MK360, Munktell, Sweden) using a

mid-volume aerosol sampler (LaoYing 2030, Qingdao

Laoshan Institute of Applied Technology, Qingdao, China) at a flow rate of 100 L min-1. The sampling

height was about 1.5 m. At each sampling site, twelve

12-h samples of both PM10 and PM2.5 were collected within different timeperiods between July 25, 2013, and

August 30, 2013. Meteorological parameters such as

wind speed, wind direction, temperature, and humidity were also recorded at the time of sample collection.

All quartz microfiber filters were dried in a

desiccator for 48 h. The filters were weighed before and after aerosol sampling to determine the mass of

PM10 and PM2.5. The filters were subsequently sealed

in a filter holder and stored at -20 “C until analysis. To prepare samples for measurement of heavy

metals concentrations, each filter was cut into frag-

ments. The fragments were placed in a PTFE crucible and then digested in amixture ofHNO3,HClO4 andHF

which was heated until about 0.5 mL of colorless

solution was obtained. After cooling, the solution was filtered and diluted to a total of 25 mL with Milli-Q#

water. The concentrations of Cr, Cu, Zn, Pb, and Mn

were analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES, Optima 5300 DV,

Perkin Elmer), and the concentrations of Cd, Co, and

Ni were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS, ELAN DRC-e, Perkin Elmer

SCIEX). Each measurement was performed in dupli-

cate, and each group had three replicates. National reference samples, replicates, and blanks were also

measured to ensure accuracy of the results. The relative

error of the results was on average better than 5 %.

Risk assessment

Exposure dose

In this study, the risk assessment model developed by the Environmental Protection Agency (EPA) of the

United States was used to evaluate the health risks

posed by heavy metals in PM2.5. Considering the variety of physiological characteristics and living

styles of Baotou city residents, we divided them into

three groups: male ([16 years), female ([16 years) and children (\16 years). Since metal exposure can

occur through direct inhalation, ingestion, and dermal contact, the exposure concentration (EC, lg m-3), chemical daily intake (CDI, mg kg-1), and dermal

absorbed dose (DAD, mg kg-1) were calculated to assess total exposure dose. EC, CDI, and DAD were

calculated according to the Human Health Evaluation

Manual (Part A), Supplemental Guidance for Dermal Risk Assessment (Part E), and Supplemental Guid-

ance for Inhalation Risk Assessment (Part F) (EPA

1989, 2004, 2009). The equations are as follows:

CDI = C ” IngR” EF” ED” CF

BW” AT ð1Þ

DAD ¼ C ” SA” AF” ABS” EF” ED” CF BW” AT

ð2Þ

EC ¼ C ” ET” EF” ED AT

ð3Þ

where C stands for the metal concentration in PM2.5 (mg kg-1 for CDI and DAD, lg m-3 for EC). All of the exposure factors for these models are shown in

Table 1.

Risk characterization

The hazard quotient (HQ) was calculated based on

exposure dose to assess non-carcinogenic risks posed

by airborne metals. The equations are as follows:

HQing ¼ CDI=RfDo ð4Þ

HQinh ¼ EC=ðRfCi” 1000 lg mg&1Þ ð5Þ

HQderm ¼ DAD= RfDo” GIABSð Þ ð6Þ

where RfDo is oral reference dose (mg kg-1 day-1), RfCi is inhalation reference concentrations (lg m-3), and GIABS is the gastrointestinal absorption factor.

The RfDo, RfCi, and GIABS values for Cr(VI), Ni (refinery dust), Cu, Cd (diet), Pb, Zn (metallic), Co,

and Mn (diet) were used from the screening level

tables provided by the US EPA (2014). The hazard index (HI) is equal to the sum of the HQ

values for ingestion, inhalation, and dermal contact

and represents the total potential non-carcinogenic risks of different pollutants. An HI\1 indicates that there is no significant risk of non-carcinogenic effects,

and when HI is[1, a non-carcinogenic effect is likely to exist (EPA 1989).

Environ Geochem Health (2016) 38:843–853 845

123

Cadmium, Cr and Ni (carcinogens) and Pb and Co

(probable carcinogens) were chosen for further eval-

uations as they were classified as problem chemicals by the International Agency for Research on Cancer

(IARC 2014). Based on others’ previous studies

(Greene and Morris 2006; Fang et al. 2013), the individual lifetime lung cancer risk (Ric) was calcu-

lated as follows:

Ric ¼ C ” ED” IURð Þ=70 years ð7Þ

where C is the contaminant concentration (lg m-3) and IUR is the inhalation unit risk as defined by the US

EPA Integrated Risk Information System (IRIS). The exposure duration (ED) was 92 days year-1 for

70 years in this study. The IUR values for each metal

were used from the screening level tables provided by the US EPA (2014).

Due to the fact that heavy metals exposure during

childhood may result in a higher lifetime cancer risk than a similar duration exposure during adulthood (EPA

2009), evaluating only Ric may underestimate cancer

risks. Thus, it is necessary to take into account age at the time of the exposure. Therefore, age-dependent adjust-

ment factors (ADAFs), as recommended by the US

EPA, were used in this study (EPA 2009). Exposure at an age\2 years old requires a tenfold adjustment and at ages 2–16 years old requires a threefold adjustment. No

adjustment is needed for exposure at 16 years and older. The equations for lifetime cancer risk were

altered to including ADAFs, as follows:

For a baby 0&2 yearsð Þ:Rb

¼ Ric ” 10 ADAFð Þ ” 2 years

70 years

! ” ð8Þ

For a child 2&16 yearsð Þ:Rc

¼ Ric ” 3 ADAFð Þ ” 14 years

70 years

! ” ð9Þ

For an adult [ 16 yearsð Þ:Ra

¼ Ric ” 1 ADAFð Þ ” 55 years

70 years

! ” ð10Þ

The actual lifetime lung cancer risk (R) is the sum

of the risk values at each stage in life:

R ¼ Rb þ Rc þ Ra ð11Þ

Cancer risks less than 1 9 10-6 are considered negligible by the US EPA.

Results and discussion

The mass concentrations of PM10 and PM2.5

The mass concentrations of PM10 and PM2.5 deter- mined for the four sampling sites in Baotou city are

shown in Fig. 2. The average mass concentrations for

PM2.5 and PM10 ranged from 26.4 to 129.2 and 71.2 to 318.3 lg m-3, respectively, with the highest concen- trations found in SA followed by CA, RA, and MA in

Table 1 Exposure factors used in assessing health risks

Factor Definition Value Unit References

Male Female Children

BW Average body weight 62.7 54.4 15 kg Duan (2012)

IngR Ingestion rate 100 100 200 mg day-1 EPA (1989)

SA Surface areas of the skin that contacts the airborne particulates

4220 3820 2160 cm-2 Wang et al. (2008)

AF Skin adherence factor for the airborne particulates 0.07 0.07 0.2 mg cm-2 EPA (2004)

EF Exposure frequency 180 180 180 days year-1 Hu et al. (2012)

ED Exposure duration 24 24 6 years EPA (2009)

ET Exposure time 24 h day-1

AT Averaging time ED 9 365 days

ABS Dermal absorption factor 0.001 for Cd, 0.01 for other metals

– Hu et al. (2012)

CF Conversion factor 10-6 kg mg-1

846 Environ Geochem Health (2016) 38:843–853

123

that order. Compared to the Air Quality Standard of

China (PM2.5\ 75 lg m-3 and PM10\ 150 lg m-3), only SA had concentrations of PM10 and PM2.5 that were much higher than the limit values. In MA, low

levels of both PM10 and PM2.5 were found, which may

be attributed to the dry climate and strong wind. The mass concentration ratio of PM2.5 to PM10 for

MA, SA, CA, and RA were 0.37, 0.41, 0.51, and 0.42,

respectively. The average mass concentration ratio was 0.43, meaning that particles between 2.5 and

10 lm contribute to weight more than particles below 2.5 lm. Table 2 summarizes several previously reported PM2.5/PM10 values. Compared to other cities,

Baotou had a lower PM2.5/PM10, indicating a higher

coarse particle fraction. Among the different sampling sites, the mass concentration ratios of PM2.5 to PM10 were ranked in the following order: MA\ SA\R- A\CA. The highest coarse fraction found in MA may be due to the large quantities of dust produced by

excavating associated with mining. CA had a rela-

tively high fraction of fine particles compared to the other sites in Baotou. This may be a result of either

heavy traffic in the city center or the wind direction

since CA is in the downwind direction of SA, which

had the highest level of PM2.5.

Heavy metals concentrations in PM10 and PM2.5

The heavy metal concentrations in PM2.5 and PM10 of the ambient air are shown in Fig. 3. The highest heavy

metal concentration in PM10 and PM2.5 were found in

SA, followed by CA, RA, and MA. It is worth noting that, contrary to expectations, the metal concentrations

in particles from MA, a typically active MA, were the

lowest. In order to focus on the composition of the PM, the unit of the metal concentration was changed from

‘‘lg m-3’’ to ‘‘mg g-1.’’ This change showed that MA now had the highest concentration of metals in PM10 and PM2.5 (Fig. 4). The low value when expressed as

volume was a result of the low PM concentrations in the air. Although low PM2.5 concentrations (weight

per volume of air) were measured at MA, compara-

tively high metal content (mg g-1) of the collected PM2.5 was observed, suggests that it is an important

source of heavy metals.

Table 3 shows the metal concentration ratios of PM2.5 to those in PM10 in the four sites of Baotou.

According to previous studies (Lee and Hieu 2011;

Fang et al. 2013), trace metals are mainly distributed in the fine particles.

Risk assessment

Non-carcinogenic risk assessment

HQ and HI for Cr, Ni, Pb, Cd, Cu, Mn, Co, and Zn in

PM2.5 samples of each site were calculated using the

health risk assessment model of the U.S. EPA. In general, the integrated HI for Baotou residents living

in any of the four sampling sites were all higher than

the safe level (safe level = 1), indicating a rather high

Fig. 2 Concentrations of PM10 and PM2.5 in Baotou (lg m-3) (MA mining area, SA smelting area, CA city center area, RA residential area)

Table 2 The average ratio of PM2.5/PM10 in different areas

Sites PM2.5/ PM10

References

Baotou, China

SA (smelting area) 0.41 This study

MA (mining area) 0.37

CA (city center area) 0.51

RA (residential area) 0.42

Shenzhen, China 0.73 Lai et al. (2007)

Zhuhai, China 0.71

Hong Kong, China 0.68 Cheng et al. (2006)

Seoul, Korea 0.73 Kim et al. (2006)

Birmingham, UK 0.66 Yin and Harrison (2008)

Environ Geochem Health (2016) 38:843–853 847

123

health risk level from metal exposure in PM2.5 (Fig. 5). Residents living in MA and SA faced a

higher health risk than residents living in the city

center or RA. Among the different groups of residents at the four sites, the integrated HI values increased in

the order of male\ female\ children. The HI values for children were 2–4 times higher than those for adult males and females, indicating that children not only

experienced a higher non-carcinogenic risk, but were

also more vulnerable to it. In this study, the HQ values for the three exposure

pathways of ingestion, inhalation, and dermal contact

varied among the different sites (Fig. 6). There were

notable differences between children and adults. For adults in all sampling sites, the HQ values of the three

exposure pathways had the same trends: inhala-

tion[ ingestion[ dermal contact. The average con- tribution of HQinh to HI was 62.6 and 60.2 % for adult

males and adult females, respectively. However, for

children, the HQing was the highest, indicating that ingestion was the most health threatening exposure.

Additionally, we found that children faced higher

health risks through dermal contact than adults. The HQderm for adult females and males among all sites

were all lower than the safe level (=1), meaning there

was not a non-carcinogenic risk posed by heavymetals

Fig. 3 Concentrations of eight metals in a PM2.5 and b PM10 in Baotou (lg m

-3) (MA mining area, SA smelting area,CA city center area, RA residential area)

848 Environ Geochem Health (2016) 38:843–853

123

Fig. 4 Concentrations of eight metals in a PM2.5 and b PM10 in Baotou (mg g

-1) (MA mining area, SA smelting area,CA city center area, RA residential area)

Table 3 The ratios of metal concentrations in PM2.5 to that in PM10

MA (mining area) SA (smelting area) CA (city center area) RA (residential area)

Cr 1.30 1.58 1.23 1.54

Ni 1.72 0.81 0.76 1.17

Cu 1.25 4.51 1.64 2.58

Cd 1.26 3.37 1.73 4.47

Pb 1.38 1.38 2.37 1.10

Zn 1.42 2.66 1.34 2.70

Co 0.85 0.60 0.37 0.88

Mn 0.81 1.57 1.23 2.12

Environ Geochem Health (2016) 38:843–853 849

123

in PM2.5. On the contrary, for children, the values of

HQderm were all higher than the safe level and

accounted for a larger proportion (20.0 % in average for children, 12.1 % in average for adults) in the

integrated HI values.

HIs for Cr, Mn, Cd, and Pb were notably higher than those for other elements (Table 4). In most

places, the HI values for Cr and Mn were close to or higher than the safe level, indicating that in Baotou,

they might pose non-carcinogenic health risks to both

adults and children. Additionally, we found that the Cr HI for children was 2–3 times higher than that for

adults at each site, and therefore, Cr might pose higher

potential health risks to children. Except for Cr and Mn, the HIs for each selected metal for both adults and

children were mostly within the safety range and

ranked in the following order: Pb[Cd[Co[ Ni[Cu[Zn for CA site, Cd[ Pb[Co[Ni[ Cu[Zn for all other sites. The higher HIs for Pb in CA site may be attributed to the heavier traffic burden in the city center. Furthermore, the Pb and Cd HIs for

children slightly exceeded the safe level, indicating

that Pb and Cd pose potential health risks to children and should be studied more extensively.

Lifetime cancer risk assessment

Particulate matter in air, especially in heavily indus-

trialized urban environments, contains a variety of known human carcinogens. In this study, five

Fig. 5 Non-carcinogenic risks (HI) of residents in Baotou (MA mining area, SA smelting area, CA city center area, RA residential area)

850 Environ Geochem Health (2016) 38:843–853

123

carcinogens were investigated. We evaluated the

lifetime cancer risks for residents at each site using

the mean concentration of each carcinogenic metal in PM2.5 and Eq. (11) (Table 5). In all four selected

sampling sites in Baotou, the lifetime lung cancer risk

was in excess ([1 9 10-6) as posed by the total of five carcinogenic metals (Pb, Cr, Co, Ni and Cd), indicat-

ing that carcinogenic risk is not negligible. Among the

sites, SA had the highest risks, followed by MA, RA and CA. This indicates that SA residents might face a

higher level of cancer risks posed by heavy metals in

PM2.5. Among the five selected carcinogenic metals, the

cancer risks of Cr, Cd, and Co at all sampling sites

were higher than the threshold value 1 9 10-6. The leading heavy metal was persistently Cr which posed

cancer risks 2–3 orders of magnitude higher than the threshold value as well as those posed by other metals.

The lifetime cancer risks of Pb and Ni (all sites except

for SA) were lower than 1 9 10-6, implying negligi- ble carcinogenic risk estimates.

Conclusion

The concentration of PM10 and PM2.5 at all sampling sites except for the SA industrial site was all below the

Air Quality Standard of China. SA had the highest

metal concentrations per volume of air, while MA had the highest metal concentrations per mass of particles

collected. Zn, Mn, Pb, and Cr were the main metal

pollutants in both PM10 and PM2.5. Most selected heavy metals were enriched in the PM2.5 fraction at

different sampling sites. For the health assessment, all

eight selected heavy metals in PM2.5 posed non- carcinogenic risks to all groups of residents. Cr, Cd

and Co were the most significant contributors to

cancer risks in this assessment. Cr had the highest lifetime cancer risk on residents. We hope these results

will help raise focus on enforcing more stringent

limitations on industrial emissions. Among different groups of people, children experienced the highest

health risk in Baotou, followed by adult females and

Fig. 6 Non-carcinogenic risk distribution of different exposure way for a children, b adults (female), c adults (male) in Baotou (MA mining area, SA smelting area, CA city center area, RA residential area)

T ab

le 4

H I v al u es

fo r ea ch

n o n -c ar ci n o g en ic

m et al

in P M

2 .5 co ll ec te d in

B ao to u

A d u lt s (m

al e)

A d u lt s (f em

al e)

C h il d re n

C A

R A

S A

M A

C A

R A

S A

M A

C A

R A

S A

M A

C r

0 .5 9

0 .6 2

0 .6 9

1 .7 7

0 .6 3

0 .6 6

0 .7 2

1 .9 1

3 .4 9

3 .4 7

2 .9 6

1 1 .2 8

N i

0 .0 3

0 .0 3

0 .0 6

0 .0 4

0 .0 3

0 .0 3

0 .0 6

0 .0 4

0 .0 4

0 .0 5

0 .0 6

0 .0 7

C u

0 .0 2

0 .0 3

0 .0 3

0 .0 3

0 .0 2

0 .0 4

0 .0 3

0 .0 4

0 .1 4

0 .2 9

0 .2 3

0 .2 7

C d

0 .2 9

0 .4 9

0 .6 0

0 .5 2

0 .3 0

0 .5 2

0 .6 1

0 .5 6

0 .7 8

1 .8 8

1 .2 9

2 .2 6

P b

0 .3 0

0 .2 1

0 .2 6

0 .3 1

0 .3 4

0 .2 5

0 .3 0

0 .3 5

2 .4 7

1 .7 8

2 .1 8

2 .5 3

Z n

0 .0 2

0 .0 1

0 .0 2

0 .0 2

0 .0 2

0 .0 2

0 .0 2

0 .0 2

0 .1 3

0 .1 1

0 .1 3

0 .1 4

C o

0 .0 5

0 .1 0

0 .1 6

0 .1 6

0 .0 5

0 .1 1

0 .1 7

0 .1 7

0 .1 8

0 .4 8

0 .4 2

0 .8 6

M n

0 .9 0

1 .3 7

3 .2 6

1 .1 4

0 .9 0

1 .3 8

3 .2 6

1 .1 4

0 .9 6

1 .5 5

3 .3 7

1 .3 5

T o ta l

2 .1 8

2 .8 8

5 .0 6

3 .9 8

2 .2 9

3 .0 0

5 .1 7

4 .2 3

8 .2 0

9 .6 2

1 0 .6 4

1 8 .7 7

M A m in in g ar ea , S A sm

el ti n g ar ea , C A ci ty

ce n te r ar ea , R A re si d en ti al

ar ea

b

Environ Geochem Health (2016) 38:843–853 851

123

then adult males. Thus, more attention should be paid on protecting children from pollution hazards.

Acknowledgments This work was sponsored by the National Science Foundation of China (41401591 and 41571473).

Compliance with ethical standards

Conflict of interest The authors declare that they have no conflict of interest.

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Table 5 Lifetime lung cancer risk (R values) of residents in Baotou

MA SA CA RA

Cr 2.24E-04 3.25E-04 1.17E-04 1.56E-04

Ni 7.54E-07 1.13E-06 6.12E-07 6.34E-07

Cd 4.25E-06 7.66E-06 3.35E-06 4.55E-06

Pb 1.25E-07 5.71E-07 3.85E-07 2.61E-07

Co 2.77E-06 5.89E-06 1.46E-06 2.40E-06

Total 2.32E-04 3.40E-04 1.22E-04 1.64E-04

R values higher than safe value (1 9 10-6) are highlighted in bold

MA mining area, SA smelting area, CA city center area, RA residential area

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