1 Introduction

Atmospheric particulates, especially fine particles (PM2.5), can diffuse and absorb solar radiation and directly affect visibility and climate change (Booth et al. 2012; Cao et al. 2012b; Pöschl 2005; Ramanathan et al. 2001). Epidemiological studies have confirmed that cardiovascular morbidity and mortality are closely related to atmospheric particulate concentrations (Brook et al. 2010; Pope et al. 2002, 2009; Thurston et al. 2016). Atmospheric particulate matter (PM) is important carrier of toxic and harmful metal elements (such as Cr, As, Cd, Ni, Cu, Pb, Zn, etc.) and other organic pollutants (such as PAHs, VOCs). Studies show that smaller particle, due to its relative larger surface area, carries pollutants that are higher in quantity and complexity and obtains easier access to body’s respiratory system and blood circulation, thus impacting human health (Meng et al. 2013); consequently, PM2.5 has become a heated topic for current international atmospheric environment.

Many previous studies have analyzed the pollution characteristics, specific sources and toxicity of heavy metals in ambient PM, due to their adverse health effects (Chen et al. 2015; Satsangi et al. 2014; Schleicher et al. 2011; Tecer et al. 2012; Wild et al. 2009). Heavy metals, mostly from traffic and industrial emissions, are differed widely from the sites of ambient environment. Industrial activities such as metallurgical (steel, copper, stainless steel and other forms of nonferrous metals), concrete, ceramic and petrochemical industries have different characteristics of marker elements. For example, metallurgy production emissions are linked to high levels of Cr, Ni, Cu, Zn, Mn, Cd, As, Pb and Sn, while high levels of Ni and V are always regarded as the tracers of petrochemical industries or fuel–oil combustion (Querol et al. 2007). Marker elements may provide certain insights in the interpretation of PM emission sources in receptor-modeling studies.

With the rapid development of China’s economy and technology, the problem of urban air pollution has become more complicated and poses a great threat to human health. In 2013, The 2010 Global Disease Burden Assessment noted that in 2010, China’s outdoor PM2.5 pollution resulted in 1.234 million deaths and 25 million years of health life loss in China (Yang et al. 2013). At present, domestic research on atmospheric PM2.5 pollution is mainly focused on large cities such as Beijing, Shanghai, Guangzhou, Chengdu, Xi’an, Nanjing, Tianjin, etc., discussing the PM2.5 pollution characteristics, element composition, source apportionment and health risk (Cao et al. 2012a; Hu et al. 2012; Huang et al. 2014; Tao et al. 2013; Wang et al. 2006, 2013; Zhang and Cao 2015; Zheng et al. 2005). In recent years, haze events frequently occur over the Wuhan city cluster and its surrounding areas during autumn and winter, and have aroused widespread concern of the public. Unfortunately, study of urban atmospheric PM2.5 in central China is rarely reported at present (Guo et al. 2015; Lyu et al. 2016; Wei et al. 1999).

Huangshi City is located in the southeastern part of Hubei Province, at the south bank of the middle reaches of the Yangtze River. It is the suburban center of Wuhan city cluster and is also an important industrial base of raw materials in central China. Huangshi holds rich mineral resources, with more than 190 deposits of iron, copper and gold, providing favorable conditions for the metallurgical, chemical, building materials industries. However, long periods of mineral resource exploitation and smelting have seriously affected the ecological environment of Huangshi area, and heavy metal pollution is particularly serious (Cai et al. 2015; Du et al. 2015; Gao et al. 2003; Yan et al. 2007; Yu et al. 2005). Additionally in recent years, the number of motor vehicles in Huangshi increased yearly, motor vehicle emissions added serious burden to local air pollution. The study of atmospheric PM2.5 in Huangshi area is of great significance to understand the composition, content and source of heavy metals in urban atmosphere, so to protect public health and formulate practical control measures.

In this study, the PM2.5 samples were collected at a building rooftop of Hubei Polytechnic University, located in Huangshi, from March 2012 to February 2013. The mass concentrations of PM2.5 and 16 elements were analyzed. The element composition and sources were assessed, and the health risks of heavy metal elements were evaluated. We hope this study could provide basic data and reference for Huangshi atmospheric environmental management, pollution prevention and health protection.

2 Materials and Methods

2.1 Sampling and Analysis

The sampling site (30°12′35.47″N,115°01′30.38″E) of this study was located on the rooftop of the Environmental Science and Engineering Institute building (about 16 m above ground and 48 m above sea level) in Hubei Polytechnic University of Huangshi city, close to central China (Fig. 1). No single specific pollution sources were identified near the sampling site.

Fig. 1
figure 1

Location of Huangshi City. The green color in the map means protected areas (color figure online)

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Fifty-four PM2.5 samples were collected from March 31, 2012 to February 24, 2013 with battery-powered mini-volume samplers (Airmetrics, Oregon, USA) operating at a flow rate of 5 L/min. One 24-h PM2.5 sample was collected on 47-mm teflon filter (Whatman, England) every 6 day. The sampling was started at 9:00 am to next day at 9:00 am. Before and after sampling, the filters were conditioned at 20 ± 1 °C in relative humidity of 50 ± 2% for 24 h. The filters were then weighed by an electronic microbalance with a detection sensitivity of 1 μg (Mettle M3, Switzerland). The filter samples were stored at − 4 °C until pretreatment.

The mass concentration of PM2.5 was determined by gravimetric method. The element compositions were analyzed after being exposed to high-sensitivity X-ray fluorescence (Epsilon 5, Netherlands) under certain conditions (30 °C) for 22 min. Sixteen elements (Ca, Mg, Ti, Al, Cr, Mn, Cu, Zn, V, Fe, As, Pb, Cd, Co, Ni and W) were measured for each PM2.5 sample.

2.2 Enrichment Factors (EFs)

EFs are often used to assess the degree of element enrichment in atmospheric particulate matter and determine the geological or anthropogenic origin of a certain pollutant element. The equation for the EFs is:

$${\text{EF}} = \frac{{(C_{i} /C_{n} )_{\text{sample}} }}{{(C_{i} /C_{n} )_{\text{background}} }},$$
(1)

where i is the element of interest, C i is the concentration of i, and C n is the concentration of a reference element. (C i /C n )sample represents the concentration ratio of studied element collected in PM2.5 sample to the reference element, and (C i /C n )background is the concentration ratio of studied element to reference element of background soil. In this study, aluminum (Al) was chosen as the reference element, and the concentration of Al (7.19%) was taken from soil background values in China (China National Environmental Monitoring Center 1990). If the EFs value is between 0 and 1, it generally indicates that the element is not enriched in the atmosphere, but primarily originated from geological weathering. If the EFs value is between 1 and 10, it means that the element was influenced by both natural and anthropogenic sources. If the EFs is higher than 10, it indicates that the element was dominated by anthropogenic contributions. According to the study of Sutherland (2000), the pollution enrichment levels can be divided into a five-category system: when EFs is less than 2, it suggests nearly no enrichment or minimal pollution; when EFs is between 2 and 5, it suggests moderate enrichment; when EFs is between 5 and 20, it suggests significant enrichment; when EFs is between 20 and 40, it suggests highly enrichment; when EFs is greater than 40, it suggests extremely enrichment.

2.3 Source Apportionment

Positive matrix factorization (PMF) is a multivariate receptor model that estimates the source profiles and their contributions based on a weighted least square approach (Paatero and Tapper 1993). It is also a tool for analyzing atmospheric particulate source recommended by the US Environmental Protection Agency (US EPA) and the Ministry of Environmental Protection of China. In the present study, PMF 5.0 was employed with the inclusion of 16 elements in the model computation.

2.4 Health Risk Assessment

According to the human health risk assessment model based on those developed by the US EPA (2011a), exposure parameters suitable for Chinese were selected, exposure concentration (EC) was estimated to assess the health risks of ten inhalable heavy elements (Cr, Mn, Cu, Zn, V, As, Pb, Cd, Co and Ni) in PM2.5. The reference dose of W and Fe was not available, so the assessment of health risks in this study did not include W and Fe. The assessment subjects were divided into two groups: adults (> 15 years) and children (0–15 years), owning to the differences in their behavior and respiratory system (Li et al. 2016). In this study, Mn, Cu, Zn and V are non-carcinogenic, and Cr, As, Cd, Co, Pb and Ni are carcinogenic.

The average daily dose of heavy metals exposure through inhalation of particulate matter is calculated by following the Eq. (2):

$${\text{EC}}_{\text{inh}} = \frac{{C \times {\text{ET}} \times {\text{EF}} \times {\text{ED}}}}{\text{AT}},$$
(2)

where C represents heavy metal concentration in PM2.5 (μg/m3); ET is exposure time (h/day); EF is exposure frequency (day/year); ED is duration of exposure (a); and AT is the average exposure time through inhalation (h). For non-carcinogens, AT = ED × 365 days × 24 h/day; for carcinogens, AT = 70 × 365 days × 24 h/day. The parameters involved in the model are shown in Table 1.

Table 1 Exposure parameters via respiration
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The risk of exposure to heavy metals through inhalation is calculated by Eqs. (3) and (4) (Li et al. 2016; You et al. 2017):

$${\text{HQ}} = \frac{{{\text{EC}}_{\text{inh}} }}{{{\text{Rf}}C_{i} \times 1000}},$$
(3)
$${\text{ELCR}} = {\text{IUR}} \times {\text{EC}}_{\text{inh}} ,$$
(4)

where HQ is non-carcinogenic quotient; ELCR is excess lifetime carcinogenic risk; RfC i is the inhalation reference concentration, mg/m3; IUR is the inhalation unit risk, per μg/m3.

3 Results and Discussion

3.1 Mass Concentrations and Characteristics of PM2.5 and Elements

Table 2 shows the mass concentrations of atmospheric PM2.5 and 16 elements in Huangshi. The results indicate that during the sampling period, the average annual PM2.5 concentration in Huangshi is 104.4 μg/m3, and the mean values of PM2.5 in spring, summer, autumn and winter are (96.9 ± 27.0) μg/m3, (60.7 ± 24.7) μg/m3, (111.1 ± 45.8) μg/m3 and (114.0 ± 43.8) μg/m3, respectively. Compared with the average 24-h (75 μg/m3) PM2.5 mass concentration standard set from China’s “Environmental Quality Standards” (GB 3095-2012 2012), except for summer, Huangshi PM2.5 concentration in spring, autumn and winter is 1.29 times, 1.48 times and 1.52 times higher than national average, respectively. The concentration of PM2.5 in autumn and winter is evidently higher than that in summer, which is similar to many other studies. The main reason is that solar radiation is relatively weak during autumn and winter in Huangshi when the atmospheric boundary layer is low, the pollutants are difficult to disperse, and less rainfall also contributes to the accumulation of pollutants. While during summer, solar radiation is stronger and boundary layer is higher, assisted by frequent rainfall removing pollutants, PM2.5 concentration could remain at a lower level. Comparing with other cities, annual average of PM2.5 mass concentration in Huangshi is similar to that of Beijing (101 μg/m3, Zheng et al. 2005), Shanghai (103.07 μg/m3, Wang et al. 2013) and Shijiazhuang (101.4 μg/m3, Wang et al. 2013), however, significantly higher than that of Xiamen (34.1 μg/m3, Zhang and Cao 2015), Shenzhen (32.0 μg/m3, Zhang and Cao 2015), Chongqing (59.1 μg/m3, Zhang and Cao 2015), and other cities in Europe or North America (Cheng et al. 2016; Salameh et al. 2015).

Table 2 PM2.5 (μg/m3) and 16 metal elements (ng/m3) mass concentrations in Huangshi city
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Element W has the highest concentration in PM2.5 of Huangshi (2348.1 ng/m3). W is a rare metal element, commonly used for special alloy steel, which are massively produced for cutting tools and mining tools. Tungsten ore reserves are abundant in Huangshi, together with enterprises of special steel production and processing, resulted in the high enrichment of W in PM2.5 of this region. While no similar report is found in studies of other cities. The order of mass concentration of studied element is W > Fe > Zn > Ca > Al > Pb > As > Cu > Mn > Cr > Ti > Cd > Ni > Co > V. Among them, the average concentration of Pb, Cd and As is 293.3, 21.4 and 196.9 ng/m3, respectively, which is 0.6 times, 4.3 times and 32.8 times of the reference concentration limit in the Ambient Air Quality Standard of China (GB 3095-2012 2012). Element As exceeds the limit drastically. V has the lowest annual average concentration (2.1 ng/m3), well below the reference concentration of WHO (1000 ng/m3). The average annual concentrations of Zn, Cu, Mn, Cr, Ni and Co are 582.1, 51.9, 51.8, 31.1, 6.1 and 2.9 ng/m3, respectively; however, the current Ambient Air Quality Standard of China (GB 3095-2012 2012) has no concentration limits requirement for these elements.

Regard to seasonal variation, the mass concentrations of Ca, Mg, Ti, Al, Cr, Mn, As and Ni all show the highest concentration in winter and the lowest concentration in summer, which is consistent with the variation of PM2.5 mass concentration. The seasonal variations of Fe, Cu, Zn and Pb are similar, which is high in spring, autumn and winter, while lower in summer. Mass concentration of V is highest in summer and lowest in winter, while Cd concentration is highest in autumn and lowest in spring. W mass concentration shows a trend of spring > summer > autumn > winter. The possible reasons for most of the metal element concentrations being lowest in summer are: (1) high frequent precipitation in summer enhances wet deposition effect; (2) the surface runoff formed by the summer rainfall to certain extent suppress fugitive dust caused by city traffic, and reduce their contribution to atmospheric particulate; (3) flourishing vegetation in summer absorbs and removes some heavy metals from the atmosphere. The seasonal variation of particular elements may be related to specific pollution sources in the region, which remains to be further studied.

As shown in Table 3, PM2.5 metal element concentrations in China’s large- and medium-sized cities are significantly higher than those of overseas, indicating that domestic urban air pollution of metal elements is more severe and lead to greater damage to human health. Because of the differences in sampling time, sampling season, type of sampling site, analysis method and emission source in different cities, there are big differences in the concentration of metal elements in PM2.5 in different cities at home and abroad.

Table 3 Element concentration (ng/m3) in PM2.5 in Huangshi comparison with other cities
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3.2 EF Characteristics and Source of Elements

3.2.1 EF

The annual EF for 16 elements is shown in Fig. 2. It is clear that the EF value of W is the highest, nearly reaching 277853.2; followed by Fe and Cd, which exceed 10,000; Zn, As, Pb and Cu also show high EF (> 100); Ca, Cr, Co, Mn and Ni appear to be greater than 10. It suggests that these extremely enriched elements were probably largely affected by anthropogenic emissions, in consistent with the highly industrialized environment studied. W is possibly related to the prosperous special steel industry, while Fe and Cd are more likely impacted by the industrial processes of iron and steel smelting. The enrichment of Ca may be related to cement production and construction fugitive dust. The EF values of Mg and V are 7.4 and 4.3, respectively, which suggests that they were influenced both by natural and anthropogenic sources. Ti has an EF of 0.9, mainly originating from natural sources such as crust or rock weathering.

Fig. 2
figure 2

Enrichment factor (EF) of 16 elements in Huangshi PM2.5

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The order of the mean annual EF value of element in Huangshi city is: W > Fe > Cd > As > Pb > Zn > Cu > Cr > Co > Ni > Ca > Mn > Mg > V > Ti, which also shows their accumulation degree. According to the Sutherland classification of enrichment factor (Sutherland 2000), the mean value EF of W, Fe, Cd, As, Pb, Zn, Cu, Cr, Co and Ni is greater than 40, indicating that these elements are super-enriched and critically harmful. The EF of Ca, Mg and Mn is between 5 and 20, indicating significant enrichment, and the EF value of V is between 2 and 5, which is moderate enrichment. The EF value of Ti is less than 2, generally no enrichment.

3.2.2 PMF Fingerprints

The source apportionment of 16 elements in PM2.5 is determined by PMF source analysis method. After several times of operation, analysis and comparison, four factors were extracted by the PMF model, and the result of factor profiles is shown in Fig. 3. The extracted factors are interpreted as follows.

Fig. 3
figure 3

PMF fingerprints of 16 elements in Huangshi PM2.5

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Factor 1 has high loadings of Ca, Ti and Al, and explains 66.3, 63.2 and 47.4% of variance, respectively. Ca is a representative indicator of cement dust, mainly from cement and gypsum plants or construction sites (Kim et al. 2004). Ti and Al are important markers of crustal source or soil dust (Lough et al. 2005; Viana et al. 2008). Thus, factor 1 is related to crust dust or soil dust.

Factor 2 explains approximately 89.6% of the variance in As, which has the highest loading. Many previous studies have shown that emissions from coal combustion contains higher concentration of As (Duan and Tan 2013; Kang et al. 2011; Tian et al. 2010). This factor is attributed to emissions from coal combustion.

Factor 3 explains 81.7% of the variance for W. Furthermore, the factor profile is dominated by Ni, V, Cr and Cd, which explains 72.5, 64.2, 54.5 and 53.4% of the variance, respectively. W is mainly used in alloy manufacturing and metal processing (Yih and Wang 1979). In addition to fuel combustion (Vallius et al. 2005), Ni and V could also derive from the mineral extraction process (Brown et al. 2007). Cr and Cd are the symbolic elements (Alleman et al. 2010) in particulate matter which emitted from the petrochemical industry; they also come from the high temperature combustion of coal, oil and garbage (Uberoi and Shadman 1991). Huangshi is an important base for iron ore and nonferrous mineral production in China, many metal manufacturing and processing, metal smelting enterprises. All these industrial activities may have an important contribution to the heavy metal elements, such as W, Ni, V, Cr and Cd in PM2.5. Therefore, factor 3 is possibly from anthropogenic source, which is related to the activities of the chemical and metallurgical industries.

In factor 4, the loadings of Pb, Zn, Cu and Mg are higher, which explains 74.2, 69.6, 39.9 and 35.9% of the variance, respectively. Pb and Zn are often used to indicate motor vehicle exhaust (Grieshop et al. 2006; Tecer et al. 2012). The high loading of Cu is a clear marker of vehicles exhaust, tires and brakes abrasion (Kuang et al. 2004), while the presence of Mg could be derived from traffic fugitive dust. Therefore, the origin of this factor is mainly related to traffic exhaust emissions.

3.3 Health Risk Analysis

Carcinogenic risk and non-carcinogenic analysis of 10 toxic heavy metal elements contained in Huangshi PM2.5 are shown in Table 4. Element As has the highest non-carcinogenic risk (4.32), significantly higher than the limit of US EPA, indicating that As may lead to non-carcinogenic health risks for both adults and children. The non-carcinogenic risk order is As > Mn > Cd > Co > Ni > Cr > V. Li et al. (2016) found that the HQ values of As, Mn and Cd in PM2.5 were 3.07, 3.06 and 1.20, respectively, in Chengdu, China, implying a non-carcinogenic risk for both adults and children, which is similar to the order of non-cardiogenic risk value in this study.

Table 4 Cardiogenic risk of inhalable toxic heavy metals in Huangshi PM2.5
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As seen from Table 4, the risks of carcinogenic heavy metals for adults and children are similar, both following the descending order of Cr > As > Cd > Co > Pb > Ni. For adults, the carcinogenic risk values for Cr and As were 8.60 × 10−4 and 2.78 × 10−4, respectively, which exceeded the carcinogenic risk threshold (10−6–10−4); the carcinogenic risk of Cd exceeded 1 × 10−4, but within the range of cancer risk thresholds. For children, the carcinogenic risk value of Cr is 2.15 × 10−4, which exceeds the threshold of carcinogenic risk. The carcinogenic risk of As is 6.96 × 10−5, slightly lower than 1 × 10−4, which means potential carcinogenic risk for children. The carcinogenic risk of adults with six carcinogenic elements was higher than that of children. The carcinogenic risk found in this study was significantly higher than that in Nanjing (Hu et al. 2012), Chengdu (Li et al. 2016) and Tianjin (Chen et al. 2015), implying greater impact on the public health, the local environmental protection departments should take appropriate measures to reduce its harm.

4 Conclusion

During the period from March 2012 to February 2013, PM2.5 samples were collected in Huangshi city, and the concentrations of 16 metal elements were analyzed. The main conclusions were as follows:

  1. 1.

    The annual PM2.5 average concentration in Huangshi city is 104.4 μg/m3, which is significantly higher than that of the national environmental air quality standard, indicating a critical pollution condition. Element W content is highest in PM2.5, V concentration the lowest; As and Cd content exceeded the standard by 32.8 times and 4.3 times. Most elements showing seasonal trend of high in winter and low in summer, similar with seasonal variation of PM2.5 mass.

  2. 2.

    EF analysis shows that, except Ti, the other 15 elements were all enriched in different degrees. W, Fe, Cd, As, Pb, Zn, Cu, Cr, Co and Ni are extremely enriched, Ca, Mg and Mn are significantly enriched, and V is moderately enriched.

  3. 3.

    PMF source analysis results show that there are four main sources of metal elements in PM2.5 of Huangshi area: soil dust or fugitive dust (Ca, Ti, Al), coal combustion (As), chemical industry and metallurgical industry (W, Ti, Ni, V, Cr, Cd), motor vehicle emissions (Pb, Cu, Zn, Mg).

  4. 4.

    The results of health risk assessment showed that the non-carcinogenic risk of element As is higher than 1, indicating a high risk of non-carcinogenesis for adults and children. The carcinogenic risk of Cr and As is higher than the tolerate limit (1 × 10−4) and may therefore poses a greater risk of cancer in adults. For children, the carcinogenic risk of Cr is higher than the threshold range (10−6–10−4), indicating that there may be a greater risk of cancer.