Characteristics and aerosol size distributions of metal-containing paint particles at a spray-painting workplace

Abstract

The health effects of metal-containing paint-particles at various particle-size distributions on workers in a spray-painting workplace at an industrial ventilation equipment manufacturing plant. Samples were collected over 30 working days in 2014. Aerosol samples were collected for 8 h using the 10 impaction stages of a micro-orifice uniform deposit impactor. Metal-containing particles were analyzed using inductively coupled plasma with atomic emission spectroscopy (ICP-AES). Measurement results show that the particles with the highest mass concentrations were PM_>18 (1043.3 ± 412.5 μg m⁻³). The mass ratios of PM₁₀ to total PM ranged from 0.36 to 0.56. The submicron particles (PM₁) and ultrafine particles (PM_0.1) constituted 6.2% and 1.5% of the total PM mass, respectively. The most abundant metal elements in all particle sizes on all sampling days were Pb (55.1 ± 19.5 μg m⁻³) and Fe (42.1 ± 4.1 μg m⁻³). Significantly, the MMD of Cd, Ni, As and Cr of carcinogenic metals were in the range 0.4–2.1 μm (below respirable particle diameters), indicating that 50% carcinogenic metals could possibly be deposited in the non-ciliated gas-exchange regions of the lung. Most metal content contributed approximately 57.48–98.09% to the total PM content in submicron particles (PM₁), except Pb. Cancer risks of carcinogenic metals (Cd, Ni and Cr) in PM₁₀ for paint spraying process workers at the industrial ventilation equipment manufacturing plant nevertheless exceeded 10⁻⁶. In particular, the assessment of health risk of inhaled Cr in ultrafine particle (UFP) fractions was found to be higher than 10⁻⁶, indicating that a carcinogenic health effect existed in the spray-painting workplace.

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1. Introduction

Paint application by spraying is the most popular method in industry, for two main reasons: (1) it results in a uniform distribution of paint, and (2) it can deliver very small amounts of paint. Pigments can be incorporated in the paint to contribute color and decrease the cost of the paint. Fine powder pigments are mostly utilized in manufacturing and artwork.¹ Global demand for pigments amounts to roughly 9.7 million tonnes. The most important sales market in 2014 was the production of paints and varnishes which accounted for 45% of the total global demand.² World sales of pigments are projected to rise to US$ 24.5 billion in 2015, and reach US$ 27.5 billion in 2018.¹

Toxic metal-based pigments, such as heavy metals (Pb, Cd, Co, Cr, Ni, Mn, Cu and Zn) might be present in children's play paints due to their ubiquitous and persistent nature.³ Gondal and Hussain (2007) indicated that poisonous metals (Pb, Cu, Cr, Ca, Mg, Zn, Ti, Sr, Ni, Fe, Al, Ba, Na, K and Zr) exist in wastewater from paint manufacturing plants. The International Agency for Research on Cancer (IARC) has classified Cd, Ni and As, as carcinogenic to human (Group 1) and Pb as probably carcinogenic to humans (Group 2A).⁴ Fewer studies have investigated the health effects upon inhalation of metal-containing paint particles in workplaces, but Tsai et al. (1997) found that the total Pb, Mn, and Fe levels in hair of workers in paint factories were significantly different from those in health control subjects (p < 0.01).⁵

Many recent studies focus on the health effects of ultrafine and nano-particles in atmospheric environment.^6–8 The nano-/ultrafine particles of the atmospheric environment pose more serious adverse human health in different physicochemical properties than the large sized particles, because they have lower mass, ultrahigh reactivity, high surface area to mass ratio.^9–11 Blood transports ultrafine particles (UFPs) to lung and liver at 0.5 h and 24 h after the exposure.¹² Additionally, UFPs may be transported to the brain tissue via the olfactory nerve, blood circulation, olfactory nerve, perineural transport, and lymphatic system.^9,13 Moreover, metal-containing particles were similar to poorly soluble particulates (PSPs) in the body. Nikula et al. (2001) located about 57–91% of the retained PSPs in the interstitial compartments of the respiratory tract in three human study groups.¹⁴ Experimental results of inhalation toxicity studies of lung responses with PSPs indicate that rats had significantly more robust pulmonary activation responses, as evidenced by alveolar epithelial hyperplastic, inflammatory and septal fibrotic pulmonary responses to the retained particles.¹⁴ However, the size distributions of metal-containing paint particles on workers or users during spray-painting are not known. Therefore, analyzing the hazards and risks of exposure to different size metal-containing particles is an important and novel research topic.

Some toxic metals are regarded as significant contributors to human exposure through the respiratory tract. This study aims at the investigation of the potential carcinogenic effects of metallic ultrafine and submicron particles of solvent-based paints on workers at spray-painting workplaces in an industrial equipment manufacturing plant.

2. Methodology

2.1 Sampling site

This study involved the paint-spraying workplace of an industrial ventilation equipment manufacture plant in central Taiwan. The anti-rust paint and finishing coats of solvent-based paints were applied in the workplace by a pneumatic paint brush. The dilution proportion of solvent-based paint to diluting solvent (toluene) was 2 : 1. The distance between the sampling site and painting workshop was approximately 2 m. The samples were taken approximately 1.5 m above the ground.

2.2 Sampling methods

Samples was collected over 30 days in September (10 days), October (10 days) and December (10 days) during working days in 2014. Aerosol samples were collected for 8 h using a Micro-Orifice Uniform Deposit Impactor (MOUDI II, MSP, Model 110R) operating at 30 L min⁻¹. The nominal cut-off sizes of the 10 stages are: 18, 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, 0.18, 0.10 and 0.056 μm. The MOUDI instrument was applied to sample atmospheric aerosol particles, workplace aerosol analysis and industrial hygiene studies due to its smaller interstage pressure drop than low pressure impactors, minimizing potential evaporation of volatile aerosol species.^15–17 This investigation required uncoated substrates to avoid interference with chemical analysis of collected sample. Chen et al. (2011) found that particle bounce was insignificant, and PM_0.1 and PM_2.5 could be sampled accurately with less than 5% error at RH of 75–80% or 65–80% when using uncoated aluminum foils and Teflon filters, respectively.¹⁸ This study found that the mean RH was 75.2 ± 2.6% at the spray-painting workplace during the sampling periods. Another practical problem to be addressed is particle clogging in the nozzles owing to long-term or high particle concentration sampling.¹⁹ Consequently, the nozzle plates often became dirty and needed to be cleaned regularly.

Depending on the health-affecting particles, the American Conference of Governmental Industrial Hygienists (ACGIH) has reached agreement on definitions of the inhalable, thoracic and respirable fractions.²⁰ Respirable particles (50% cut-size of 4 μm) can penetrate beyond the terminal bronchioles into the gas-exchange region of the lungs. Additionally, the fractions of the airborne particles are defined as submicron particles (PM₁) (PM aerodynamic diameter less than 1.0 μm) and ultrafine particles (UFPs) (PM aerodynamic diameter less than 0.1 μm).

The impaction surface comprised 47 mm mixed cellulose esters (MCE) membrane filters (Advantec MFS Inc., 0.45 μm pore size). Filters were dried for 24 h in a desiccator at 25 °C under 50% relative humidity before and after each sampling. Each filter was weighed on an electrical balance with a sensitivity of 10 μg. The suspended PM concentration was determined by dividing the particle mass by the volume of the sampled air.

2.3 Metals analysis and quality control

Each sampling involved the collection of eleven (MOUDI stages) samples. All samples collected by the MOUDI were analyzed according to Method 7302 of the National Institute for Occupational Safety and Health, NIOSH. In this work, the following 12 metals elements were analyzed: aluminum (Al), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), zinc (Zn) and arsenic (As).

The using of trace metal grade of nitric acid was referred to method 7302 of NIOSH for preparing standards and diluted solution. Each filter was placed in a 75 mL Teflon microwave digestion vessel with a 10 mL mixture of concentrated nitric acid (65%, trace metal grade) and ultra-pure water with a volume ratio of 1 : 1, in preparation for microwave digestion. The microwave digestion Model CEM MARS 5 (CEM Corporation, Matthews, NC) consists of a 2450 MHz microwave power system with 0–1200 W output, a fluoropolymer-coated microwave cavity, a cavity exhaust fan and tubing to vent fumes, and a 12-position alternating turntable. The microwave digestion of samples involved two steps: (1) increase from room temperature to 200 °C over 6.5 min; (2) maintain temperature at 200 °C for a further 10 min. After the samples were cooled for 20 min, the digested solution was then diluted to 25 mL using 20% nitric acid. The resulting diluted solution was then used for the metal analysis. The metals were analyzed by inductively coupled plasma with atomic emission spectroscopy (ICP-AES) using an HORIBA Jobin Yvon Ultima 2000 device. Table 1 shows the operating conditions of the ICP-AES instrument. All samples and calibration strategy were prepared and analyzed according to Method 7302 of NIOSH. The calibration stock solutions (1000 μg mL⁻¹) is commercially available, and the method did not recommend a percentage concentration of nitric acid in the multi-element standard solution. The calibration was performed using multi-element (metal) standards (certified reference materials, CRMs) in a 3% (v/v) HNO₃ solution.

Table 1 ICP-AES operated parameters

Parameter	Value
Plasma setting
Reflected power (Watt)	1000
Normal speed of pump (rpm)	20
Plasma gas pressure (bar)	7.0
Sheath gas flow rate (L min^−1)	0.2
Auxiliary flow rate (L min^−1)	0
Sheath stabilisation time (s)	5.0
Nebulisation flow rate (L min^−1)	0.9
Nebulisation pressure (bar)	3
Sample options
Replicate times	3
Rinsing time (s)	10
Sample transfer time (s)	30

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The method detection limit (MDL) for each metal was determined according to US-EPA method for detection of MDL, 40 CFR Part 136. APPENDIX B, revision 1.11. Prepare 7 solutions with the same concentration of 5 times the estimated MDL. Analyze 7 the solutions by the whole method procedure, and calculate the MDL as in eqn (1):

MDL = s × t_{(n−1,1−α=0.99)} = 3.14s (1)

where s: standard deviation of measured concentrations of n solutions t: Student's t value (n = 7, t = 3.14).

Table 2 shows that the detection limit by ICP-AES for the 12 metals was 0.005–0.079 μg m⁻³. The field and laboratory blank samples subjected to the same analytical procedure as samples were regularly analyzed. Sample data were corrected by subtraction of the filter blanks. This study measured recoveries with one media blank and two spiked media blanks per 20 samples. The recovery efficiencies were determined by performing the same experimental procedure on a solution that contained known metals concentrations as on the samples. The recovery values of metals were 95.1–101.5%.

Table 2 Method detection limit and recommended values based on the health risk assessment of metals^a

Metals	Wave length (nm)	MDL		Recommended values
		μg L^−1	μg m^−3(*^)	RfD (mg d^−1 kg^−1)	SF ((mg kg^−1 day^−1)^−1)
a *Air volume = 14.4 m^3 (sampling flow rate: 30 L min^−1; collecting time: 8 h), RfD: reference dose via inhalation, SF: slope factors for carcinogenic risk via inhalation, —: no data.
Al	308.27	44.5	0.077	—	—
Cd	226.80	37.9	0.066	—	6.3
Co	228.61	12.1	0.021	—	—
Cr	267.56	12.5	0.022	—	4.20 × 10^1
Cu	324.75	11.9	0.021	1.0 × 10^−3	—
Fe	259.94	32.7	0.057	—	—
Mn	257.61	3.2	0.005	1.43 × 10^−5	—
Mo	202.03	8.5	0.015	—	—
Ni	231.64	15.5	0.027	—	8.40 × 10^−1
Pb	220.35	42	0.073	3.6 × 10^−3	—
Zn	213.85	45.3	0.079	3.0 × 10^−1	—
As	193.76	45	0.078	—	1.51 × 10^1

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2.4 Health risk assessment

The health risks to workers from inhaling metals during work in the spray-painting workplace were evaluated by quantifying the risk of developing cancer using a probabilistic approach. This study adopted the inhalation exposure model of the EPA baseline risk assessment approach.²¹ The EPA Integrated Risk Information Database (IRIS) and International Agency for Research on Cancer (IARC) classify pollutants as carcinogens or non-carcinogens.²² This investigation found that Cr, Ni, Cd, and As are carcinogenic, while Cu, Zn, Pb, Hg, and Mn are non-carcinogenic, affecting the human immune system through the respiratory system.

The average daily exposure dose of metallic particles through inhalation (ADD_inh) was calculated using the following equation:^23,24

The hazard quotient (HQ) is used to estimate the non-carcinogenic effect of metallic particles. A hazard index (HI) equals the sum of multiple-chemical or multiple-route HQ. An HI > 1 indicates that non-carcinogenic effects may occur. Thus, a greater HI value indicates a higher probability of non-carcinogenic effects.²⁵ ADD_inh is used for non-carcinogenic materials, and Lifetime-Averaged Daily Dose (LADD) is used for carcinogenic materials. The cancer risk (CR) estimates are compared to carcinogenic regulatory levels of concern, 10⁻⁶ (one in one million people) to 10⁻⁴ (one in ten thousand people). Health risk can be quantified using the following equations:

CR = LADD·SF (5)

where ADD_inh denotes the life-averaged daily dose from inhalation (unit: mg d⁻¹ kg⁻¹); RfD is the reference dose (mg d⁻¹ kg⁻¹), and SF is the cancer slope factor (mg kg⁻¹ day⁻¹)⁻¹. The detailed symbol description of the calculate equations can be found elsewhere.²⁴ Table 2 also shows the values of RfD and SF employed in this study.^26–29

3. Results and discussion

3.1 Concentrations of spray-painting particulate matter

The mean concentrations of atmospheric particulate matter (PM) in different particle sizes at a spray-painting workplace are shown in Table 2. The differences of particulate masses among various sampling days were tested with the non-parametric Kolmogorov–Smirnov test. Results indicate that the particulate masses for different size distributions did not differ statistically among the 30 samples because the pray-painting processes were stable during the sampling periods.

The concentration of total PM in the spray-painting workplace was 2741.4 ± 505.9 μg m⁻³. The particles with the highest mass by size were PM_>18 (1043.3 ± 412.5 μg m⁻³); these were followed by PM_5.6–10 and PM_3.2–5.6 with particulate masses of 420.9 ± 80.1 and 414.8 ± 51.2 μg m⁻³, respectively. The mass ratios of submicron particles to total PM and UFPs to total PM were 6.2 ± 2.5% and 1.5 ± 0.7%, respectively. The mass ratios of thoracic particles to total particles ranged from 36.4% to 58.6 with an average of 49.5 ± 9.0%. Thus, toxic metal-containing paint may be transported to the head airways and enter the airways of the lung via thoracic PM inhalation during the spray-painting process.

3.2 Size distribution of metallic elements concentrations

Table 4 shows the concentrations of metallic elements that were collected in the workplace atmosphere with the spray-painting process. The mean concentrations of total metals in the all fractions were 109.1 ± 12.0 μg m⁻³. The most abundant elements of all fractions were Pb (55.1 ± 19.5 μg m⁻³) and Fe (42.1 ± 4.1 μg m⁻³). The next most abundant elements were Al, Cr and Zn, ranging from 2.6 μg m⁻³ to 4.2 μg m⁻³. The anti-corrosive paints in this study consisted of a yellow pigment (ZnCrO₄) and anti-corrosive pigment (mixed of Pb₃O₄ and Fe₂O₃), according to the material safety data sheet of the globally harmonized system of anti-corrosive paint products. Powders of white pigments such as Al(OH)₃, SiO₂ and TiO₂ were also used in the product of finishing coats in this study. Moreover, Zn is generally applied as a metallic pigment for paint coating and anti-corrosive primer.³⁰ Past studies of paint factories in Taiwan have utilized mixtures of red lead pigment (Pb₃O₄) and drier (lead naphthalate and manganese naphthalate) in anticorrosion primers.⁵

Table 3 Concentrations (mean ± SD) of particulate masses in the ambient air of spray-painting workplace for various particle sizes (unit: μg m⁻³)^a

PM diameter (μm)	Mean ± SD (n = 30)	Accumulative percentage (%)	Kolmogorov–Smirnov test (p value)
a Total PM: sum of all stages of MOUDI, thoracic particles (aerodynamic diameter < 10 μm), submicron particles (aerodynamic diameter < 1.0 μm), UFPs (aerodynamic diameter < 0.1 μm).
>18	1043.3 ± 412.5	38.1	0.837
10–18	358.8 ± 104.5	52.1	0.655
5.6–10	420.9 ± 80.1	67.5	0.847
3.2–5.6	414.8 ± 51.2	82.6	0.991
1.8–3.2	207.7 ± 48.4	90.2	0.983
1.0–1.8	108.3 ± 39.9	94.2	0.491
0.56–1.0	49.2 ± 9.6	95.9	0.944
0.32–0.56	27.0 ± 10.5	96.9	0.963
0.18–0.32	30.4 ± 10.6	98.0	0.806
0.10–0.18	20.3 ± 8.2	98.8	0.999
0.056–0.10	17.5 ± 12.2	99.4	0.500
<0.056	16.1 ± 7.6	100.00	0.698
Total PM	2741.4 ± 505.9
Thoracic particles/total PM	49.5 ± 9.1
Submicron particles/total PM	6.2 ± 2.5
UFPs/total PM	1.5 ± 0.7

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Table 4 Mean media diameter (MMD) and mean concentrations of metals with respect to particle size in the spray-painting workplace (unit: ng m⁻³)

Aerodynamic diameter (μm)	Al	Cd	Co	Cr	Cu	Metals (n = 30)		Mo	Ni	Pb	Zn	As
						Fe	Mn
a Unit: ng m^−3.b Concentrations (mean ± SD) of 12 metals for the sum of all size ranges.
>18	1763.6	4.9	153.9	769.6	9.0	8458.9	89.2	204.3	17.0	21 964.9	1103.9	1.2
10–18	401.1	0.3	65.7	331.2	2.8	5439.5	38.6	74.5	9.7	8865.2	137.3	1.0
5.6–10	333.2	0.5	59.9	255.9	6.2	4864.3	33.9	67.9	9.3	7760.0	128.4	1.0
3.2–5.6	541.5	0.3	106.5	419.3	4.0	5593.7	38.1	89.9	24.1	8364.0	154.8	1.1
1.8–3.2	257.6	0.9	174.7	309.6	4.0	4125.7	26.7	75.3	41.7	3561.1	139.0	0.6
1.0–1.8	101.1	1.5	35.1	250.2	4.0	3963.8	22.0	65.1	7.6	2399.1	130.0	0.5
0.56–1.0	82.3	2.1	16.1	126.7	10.1	1972.0	34.5	34.1	45.9	954.2	145.6	0.6
0.32–0.56	131.7	1.8	21.2	64.8	2.1	2015.8	26.6	19.3	11.8	831.8	108.4	0.4
0.18–0.32	115.9	1.4	5.7	13.3	1.4	1113.6	91.1	8.3	7.2	84.2	210.1	1.2
0.1–0.18	28.0	0.5	5.5	15.1	3.8	1056.8	96.6	2.7	20.4	225.3	149.7	0.7
0.056–0.1	375.6	0.3	8.1	12.0	4.6	1124.3	56.9	2.6	6.5	28.3	122.0	0.4
<0.056	33.3	1.3	10.6	12.1	42.3	2370.1	142.2	2.7	32.6	58.6	306.0	3.1
Total PM (μg m^−3)	4.2 ± 2.6		0.7 ± 0.3	2.6 ± 0.7		42.1 ± 4.1	0.70 ± 0.2	0.7 ± 0.1	0.2 ± 0.1	55.1 ± 19.5	2.8 ± 2.5
Mean total metals^b (μg m^−3)	109.3 ± 12.0
MMD (μm)	2.2 ± 1.1	0.4 ± 0.2	2.0 ± 0.4	2.1 ± 0.5	0.8 ± 0.4	1.9 ± 0.6	0.2 ± 0.1	2.0 ± 0.4	0.9 ± 0.6	3.2 ± 0.7	0.9 ± 0.5	1.3 ± 1.1

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Fig. 1 shows the mean normalized size distributions of total metal concentrations in the workplace atmosphere, which had a two-modal distribution located at 1.8–3.2 μm and 5.6–10 μm. The mass median diameter (MMD) for the total metals concentrations in the workplace was 2.4 ± 1.1 μm, suggesting that airborne of total metals was incorporated in fine particle in this study. Table 3 also shows the MMD of individual metals in the spray-painting workplace. The highest MMD was 3.2 ± 0.7 μm, found in Pb. Inorganic Pb can be deposited in the respiratory tract when aerosols are inhaled. Abadin (2007) indicated that smaller inhaled particles (PM diameter < 4.5 μm), can reach the alveolar region and be absorbed after extracellular dissolution or ingestion by macrophages.³¹ Studies have suggested that 95% of inorganic Pb inhaled as submicron particles (PM₁) is absorbed by the human body.³²

Fig. 1 Size distributions of total metal concentrations in ambient air at the spray-painting workplace.

The MMD of Cd, Cu, Mn, Ni and Zn were in the range 0.2–0.9 μm, indicating that airborne particles of these metals were incorporated in submicron particles. Notably, the Cd, Ni, As and Cr of carcinogenic metals of MMD were below the level of respirable particles (PM diameter < 4 μm), implying that 50% carcinogenic metals could possibly be deposited in the non-ciliated gas-exchange regions of the lung. Thus, chronic exposure by workers' inhalation in the spray-painting area may lead to long-term adverse health effects. The health-assessment of cancer risk for carcinogenic metals is discussed later in this study.

3.3 Metals content in particles

Fig. 2 illustrates the relative total metals content contribution of particles sampled at the spray-painting workplace. Fig. 2(a) shows that mean percentage contributions of total metals content in UFPs and PM_0.1–1 within PM₁₀ were 44.5% and 39.3%, respectively, indicating that the total metal contents in submicron particles (PM₁) contributed about 83.8% within total metal contents of PM₁₀. Fig. 2(b) shows that total metals content in UFPs (41.5%) contributed most to the total PM content, followed by PM_0.1–1 (36.7%) and PM_1–3.2 (9.6%). Notably, the mean percentage contributions of total metal contents were found to increase with decreasing particle size, demonstrating that UFPs pose greater adverse health effects than larger particles per unit mass.

Fig. 2 The relative total metal content contribution in various particle sizes within (a) PM₁₀ and (b) total PM.

Fig. 3 depicts the mean percentage contributions of individual metal content in particles of various particle sizes. The highest contributions in UFPs of all sizes was Cu (83.96%) and As (68.45%). The part metal (Al, Cu, Fe, Mn, Ni, Zn and As) contributions in UFPs of all sizes exceeded 43%, with percentage contributions in the range of 43.13–83.96%. In this study, metal-based pigment (i.e. Pb and Cr) of anti-corrosive paints contributed most in PM_0.1–1 was 38.96% and 43.91%, respectively. However, submicron particles (PM₁) contributed approximately 57.48–98.09% to the total PM content in almost metals, except Pb, for which 67.22% came from particles with diameter <10 μm. The low contribution of Pb in PM₁ might be caused by the specific gravity of individual metals. The specific gravity of Pb is 11.36 g cm⁻³ (at 20 °C), which is much than that of other metals (2.7–8.9 g cm⁻³). The Pb would be contained in a larger mass than other metals at the same aerosol volume. The Pb-containing particles were difficulty suspended during spray-painting process. Thus, the Pb content was contributed in large size particles.

Fig. 3 Distribution of individual metal content in particles according to various particle sizes.

Table 5 compares the individual metal content in particle-size distributions obtained in this and other studies. In this study, the most abundant metal content in UFPs was Fe (384.18 ± 210.46 μg mg⁻¹). The next highest metal content was of Zn and Al in UFPs, at 45.49 ± 24.46 μg mg⁻¹ and 42.41 ± 25.35 μg mg⁻¹, respectively. The metal content of UFPs in the spray-painting workplace was higher than in the solvent-based and water-based paint manufacturing plant and foundry workshop for all metals except Pb. In fine cleaning and mold preparation procedure of foundry, Cr and Pb are most abundant in fine particles (PM diameter < 5 μm).³³ In terms of metals concentrations, the solvent-based paint dust particles contain extremely high concentrations of lead and zinc compared to water-based paint dust.³⁴ Although the solvent-based paint has the most abundant metal content of both Pb and Zn in this study and solvent-based manufacturing paint, the Pb content of PM_0.1–1 in solvent-based spray-painting workplace of this study was 5.3 times higher than that of PM_{0.921–0.970} in solvent-based manufacturing paint, while the Zn content of both is similar. Recently, a few studies have been compared the size distribution of individual metal content in particles among different spray-painting workshops elsewhere in the world. The metal content particles of various sizes is difficult to compare, due to with the many factors affecting metal content, such as raw material, metal-based pigment types, industrial process, working environment and sampling equipment. However, since metal content values may vary, further studies on health effects of solvent-based paint emissions in different paint types, dilution proportion of diluting solvent and paints, types of pneumatic paint brush and are required in different industrial applications.

Table 5 Comparison of metal contents of varying particle sizes in different workplaces

Dust particles type	Particle size range (μm)	Metal contents (μg mg^−1)
		Al	Cd	Co	Cr	Cu	Fe	Mn	Mo	Ni	Pb	Zn	As
a —: no data.b ND: not detected.c Reference: this study.d Ref. 34.e Ref. 33.
Solvent-based spray-painting workplace^c	0.1–1	14.1 ± 9.3	0.3 ± 0.2	2.4 ± 1.4	7.8 ± 5.8	0.7 ± 0.2	268.6 ± 86.9	13.0 ± 2.1	2.3 ± 1.4	3.4 ± 0.9	83.2 ± 70.1	26.7 ± 11.1	0.1 ± 0.01
	<0.1	42.4 ± 25.4	0.2 ± 0.1	1.8 ± 1.1	2.4 ± 1.8	4.2 ± 1.5	348.2 ± 210.5	19.9 ± 17.3	0.6 ± 0.7	3.7 ± 3.1	8.6 ± 7.3	45.5 ± 24.5	0.3 ± 0.01
Solvent-based manufacturing paint^d	0.921–0.970	—^a	—	—	ND^b	1.55 ± 0.55	—	—	—	ND	15.68 ± 11.78	30.46 ± 10.58	0.10 ± 0.02
Water-based manufacturing paint^d	7.901–8.465	—	—	—	ND	0.0091 ± 0.015	—	—	—	ND	0.057 ± 0.022	1.66 ± 1.26	0.02 ± 0.01
Foundry (fine cleaning)^e	<5	—	0.008 ± 0.001	0.220 ± 0.005	1.723 ± 0.011	—	—	—	—	—	0.491 ± 0.004	—
Foundry (mold preparation)^e	<5	—	0.079 ± 0.002	0.032 ± 0.006	0.384 ± 0.003	—	—	—	—	—	2.382 ± 0.026	—

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3.4 Health risk assessment of metallic particles

Assessments of the risks to workers were estimated based on the atmospheric concentrations of toxic metals in the spray-painting workplace. Table 6 presents the assessments of non-cancer hazards, according to a hazard quotient (HQ) for four metals (Cu, Mn, Pb and Zn). The hazard index (HI) is the sum of four metals and meant the total non-carcinogenic effects with respect to size of particles. In total PM, the HQ value was highest in Pb (3.4 × 10⁻¹), second highest in Mn (8.3 × 10⁻³) and third highest in Zn (2.1 × 10⁻⁴). The HI values in PM_0.1, PM₁ and PM₁₀ were below 1, and ranged from 3.0 × 10⁻³ to 1.6 × 10⁻¹. Clearly, the HQ values of Cu, Mn and Zn in total PM were all below 8.3 × 10⁻³. Thus, the major contribution for the HI value in the total PM was Pb, with a mean of 97% of HI.

Table 6 Health-risk assessment of non-carcinogenic metals in the spray-painting workplace

PM diameter	HQ				HI
	Cu	Mn	Pb	Zn
PM0.1	8.5 × 10^−5	2.4 × 10^−3	5.4 × 10^−4	3.1 × 10^−5	3.0 × 10^−3
PM1	1.2 × 10^−4	5.3 × 10^−3	1.4 × 10^−2	7.5 × 10^−5	1.9 × 10^−2
PM10	1.5 × 10^−4	6.7 × 10^−3	1.5 × 10^−1	1.2 × 10^−4	1.6 × 10^−1
Total PM	1.7 × 10^−4	8.3 × 10^−3	3.4 × 10^−1	2.1 × 10^−4	3.5 × 10^−1
UFPs/PM10	0.57	0.35	0.004	0.27
PM1/PM10	0.78	0.79	0.09	0.65
UFPs/PM1	0.80	0.66	0.04	0.48
PM10/total PM	0.88	0.82	0.44	0.56

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Fig. 4 displays the means and standard deviations of the cancer risk (CR) for Cd, Ni, As and Cr in the spray-painting workplace of interest herein. The CR of the total PM was highest in Cr (2.4 × 10⁻³ ± 6.1 × 10⁻⁴), second highest in Ni (4.3 × 10⁻⁴ ± 1.0 × 10⁻⁴) and third highest in Cd (2.2 × 10⁻⁶ ± 7.2 × 10⁻⁸). The cancer risk of total PM in Cr was 2.4 × 10⁻³, which was 552 and 1100 times higher than those in Ni and Cd, respectively. With respect to Cr (2.2 × 10⁻⁵), the cancer risk of toxic metals (Cd, Ni, and As) in UFPs did not exceed the 10⁻⁶ benchmark level. In submicron particles (PM₁), cancer risk of Cr and Ni were exceeded the 10⁻⁶ benchmark level, with values in the range of 2.3 × 10⁻⁶ to 2.2 × 10⁻⁴. With respect to As, the cancer risk of toxic metals (Cd, Ni, and Cr) in thoracic particles also exceeded the 10⁻⁶ benchmark level. However, the cancer risks of Cr associated with UFPs, submicron particles, and thoracic particles significantly exceeded the 10⁻⁶ benchmark level.

Fig. 4 Health-risk assessment of atmospheric carcinogenic metals in the spray-painting workplace.

Although the Cu, Mn, Pb, and Zn of non-carcinogenic effects in the spray-painting workplace may be negligible, the estimated cancer risks (Cd, Ni, and Cr) in thoracic particles for spray-painting workers still exceeded the 10⁻⁶ cancer risk level. Therefore, the carcinogenic risks for workers are relatively possible during long-term occupational exposure.

4. Conclusions

This study was conducted to investigate the concentrations and size distributions of metallic paint-particles at a spray painting workplace. The total PM mass during spray-painting processes was 2741.4 ± 505.9 μg m⁻³. The top three masses of the particulate size were PM_>18 (1043.3 ± 412.5 μg m⁻³), PM_5.6–10 (420.9 ± 80.1 μg m⁻³) and PM_3.2–5.6 (414.8 ± 51.2 μg m⁻³), respectively. The mass of PM₁₀ contributed approximately 49% to the ambient total PM at a workplace where solvent-based paint spraying was conducted. The mass of PM₁₀ contributed approximately 49% to the ambient total PM at a workplace where solvent-based paint spraying was conducted. The most abundant elements among all particle sizes were Pb (55.1 ± 19.5 μg m⁻³) and Fe (42.1 ± 4.1 μg m⁻³). The highest MMD of Pb was 3.2 ± 0.7 μm, Cd, Cu, Mn, Ni and Zn was incorporated in submicron particles. The total metal content in UFPs of total PM content was 1.1 and 4.3 times higher than those in PM_0.1–1.0 and PM_1.0–3.2, respectively. Nevertheless, the most abundant levels of Pb in non-carcinogenic effects that arise in the spray-painting process may not be particularly severe. Cancer risks (Cd, Ni and Cr) in thoracic particles for paint spraying process workers at an industrial ventilation equipment manufacturing factory dramatically exceeded 10⁻⁶ in the cause study. Significantly, the cancer risk of Cr were also greater than the benchmark value of 10⁻⁶ in UFPs, suggesting that correct personal protective equipment should be used by workers in a solvent-based anti-corrosive paint spraying workplace.

Acknowledgements

The author would like to thank the Institute of Labor, Occupational Safety and Health, Ministry Labor of Republic of China (ILOSH) and the Ministry of Science and Technology (MOST) in Taiwan for their financial support under the Grant No. ILOSH-1033044 and MOST 105-2221-E-166-002.

References

1. Acmite Market Intelligence, Market Report: World Pigment Market, Acmite Market Intelligence: Ratingen, Germany, 2nd edn, 2010.
2. Ceresana, Market Study: Pigments, Ceresana Market Intelligence: Constance, Germany, 4th edn, 2016.
3. A. Rebelo, E. Pinto, M. V. Silva and A. A. Almeida, Microchem. J., 2015, 118, 203–210.
4. M. A. Gondal and T. Hussain, Talanta, 2007, 71, 73–80.
5. Y. Y. Tsai, C. T. Wang, W. T. Chang and C. W. Huang, Anal. Sci., 1997, 13, 447–450.
6. B. Kim, J. S. Lee, B. S. Choi, S. Y. Park, J. H. Yoon and H. Kim, Ann. Occup. Hyg., 2013, 57, 728–739.
7. A. Aranda, Y. Díaz-de-Mera, A. Notario, D. Rodríguez and A. Rodríguez, Environ. Sci. Pollut. Res., 2015, 22, 18477–18486.
8. C. S. Zhu, J. J. Cao, C. J. Tsai, Z. X. Shen, S. X. Liu, R. J. Huang, N. N. Zhang and P. Wang, Environ. Sci. Pollut. Res., 2016, 23, 4569–4575.
9. G. Oberdörster, Z. Sharp, V. Atudorei, A. Elder, R. Gelein, W. Kreyling and C. Cox, Inhalation Toxicol., 2004, 6, 437–445.
10. E. Diapouli, A. Chaloulakou and N. Spyrellis, Sci. Total Environ., 2007, 388, 128–136.
11. C. H. Lai, K. Y. Chuang and J. W. Chang, Environ. Sci. Pollut. Res., 2013, 20, 1772–1780.
12. G. Oberdörster, Z. Sharp, V. Atudorei, A. Elder, R. Gelein, A. Lunts, W. Kreyling and C. Cox, J. Toxicol. Environ. Health, Part A, 2002, 65, 1531–1543.
13. C. Loane, C. Pilinis, T. D. Lekkas and M. Politis, Rev. Neurosci., 2013, 24, 323–335.
14. K. J. Nikula, V. Vallyathan, F. H. Green and F. F. Hahn, Environ. Health Perspect., 2001, 109, 311–318.
15. S. C. Chen, C. J. Tsai, H. D. Chen, C. Y. Huang and G. D. Roam, Aerosol Sci. Technol., 2011, 45, 596–603.
16. S. Kudo, K. Sekiguchi, K. H. Kim, M. Kinoshita, D. Möller, Q. Wang, H. Yoshikado and K. Sakamoto, Atmos. Environ., 2012, 62, 172–179.
17. C. S. Zhu, C. C. Chen, J. J. Cao, C. J. Tsai, C. C. K. Chou, S. C. Liu and G. D. Roam, Atmos. Environ., 2010, 44, 2668–2673.
18. S. C. Chen, C. J. Tsai, C. C. K. Chou, G. D. Roam, S. S. Cheng and Y. N. Wang, Atmos. Environ., 2010, 44, 533–540.
19. N. Liu, A. Awasthi, Y. H. Hung and C. J. Tsai, Atmos. Environ., 2013, 69, 325–333.
20. ACGIH – American Conference of Governmental Industrial Hygienists, Particle Size-Selective Sampling for Health-Related Aerosols. Report of the ACGIH Technical Committee on Air Sampling Procedures, ed. J. H. Vincent, ACGIH, Cincinnati, OH, 1999, ISBN 1-1882417-30-5.
21. US EPA, Integrated risk information system, Available at: http://www.epa.gov/iris, U.S. Environmental Protection Agency, 2012, accessed 23 March 2015.
22. H. Z. Tian, Y. Wang, Z. G. Xue, K. Cheng, Y. P. Qu, F. H. Chai and J. M. Hao, Atmos. Chem. Phys., 2010, 10, 20729–20768.
23. T. S. Shih, W. J. Lee, M. Shih, Y. C. Chen, S. L. Huang, L. C. Wang, G. P. Chang-Chien and P. J. Tsai, Environ. Int., 2008, 34, 102–107.
24. K. Y. Chuang, C. H. Lai, Y. P. Peng and T. H. Yen, Environ. Sci. Pollut. Res., 2015, 22, 19451–19460.
25. US EPA, Risk Assessment Guidance for Superfund: Volume III—Part A, Process for Conducting Probabilistic Risk Assessment Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, D.C., 2001, p. 20460.
26. A. J. Baars, R. M. C. Theelen, P. J. C. M. Janssen, J. M. Hesse, M. E. van Apeldoorn, M. C. M. Meijerink, L. Verdam and M. J. Zeilmaker, Re-evaluation of human-toxicological maximum permissible risk levels, National Institute of Public Health and the Environment (RIVM Report: 71170125), 2001.
27. L. Ferreira-Baptista and E. D. Miguel, Atmos. Environ., 2005, 39, 4501–4512.
28. X. Lu, X. Wu, Y. Wang, H. Chen, P. Gao and Y. Fu, Ecotoxicol. Environ. Saf., 2014, 106, 154–163.
29. X. Liu, Y. Zhai, Y. Zhu, Y. Liu, H. Chen, P. Li, C. Peng, B. Xu, C. Li and G. Zeng, Sci. Total Environ., 2015, 517, 215–221.
30. B. Muller, Pigm. Resin Technol., 2001, 30, 357–362.
31. H. Abadin, Toxicological profile for lead, Atlanta: Agency for Toxic Substances and Disease Registry, 2007.
32. A. C. Wells, Deposition in the lung and uptake to blood of motor exhaust labelled with ²⁰³Pb, Inhaled Particles IV, Pergamon Press, 1975, pp. 175–189.
33. J. Hlavay, K. Polyák’ and G. Wesemann, Fresenius' J. Anal. Chem., 1992, 344, 319–321.
34. S. L. Huang, C. Y. Yin and S. Y. Yap, J. Hazard. Mater., 2010, 174, 839–842.

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