Assessment of Noise and Heavy Metals (Cr, Cu, Cd, Pb) in the

Technol. , 2012, 46 (1), pp 494–499 ... The concentrations of Cu, Pb, Cr, and Cd in PM10 are 0.88, 0.56, 0.12, and 0.88 μg/m3, respectively. Among ...
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Assessment of Noise and Heavy Metals (Cr, Cu, Cd, Pb) in the Ambience of the Production Line for Recycling Waste Printed Circuit Boards Mianqiang Xue,† Yichen Yang,† Jujun Ruan,† and Zhenming Xu*,† †

School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China S Supporting Information *

ABSTRACT: The crush - pneumatic separation - corona electrostatic separation production line provides a feasible method for industrialization of waste printed circuit boards (PCBs) recycling. To determine the potential environmental contamination in the automatic line workshop, noise and heavy metals (Cr, Cu, Cd, Pb) in the ambience of the production line have been evaluated in this paper. The mean noise level in the workshop has been reduced from 96.4 to 79.3 dB since the engineering noise control measures were employed. Noise whose frequency ranged from 500 to 1000 Hz is controlled effectively. The mass concentrations of TSP and PM10 in the workshop are 282.6 and 202.0 μg/m3, respectively. Pb (1.40 μg/m3) and Cu (1.22 μg/m3) are the most enriched metals in TSP samples followed by Cr (0.17 μg/m3) and Cd (0.028 μg/m3). The concentrations of Cu, Pb, Cr, and Cd in PM10 are 0.88, 0.56, 0.12, and 0.88 μg/m3, respectively. Among the four metals, Cr and Pb are released into the ambience of the automatic line more easily in the crush and separation process. Health risk assessment shows that noncancerous effects might be possible for Pb (HI = 1.45), and noncancerous effects are unlikely for Cr, Cu, and Cd. The carcinogenic risks for Cr and Cd are 3.29 × 10−8 and 1.61 × 10−9, respectively. It indicates that carcinogenic risks on workers are relatively light in the workshop. These findings suggest that this technology is advanced from the perspective of environmental protection in the waste PCBs recycling industry. separation - corona electrostatic separation production line.7 This physical processing provides a feasible method for industrialization of waste PCBs recycling. It is of great importance for the improvement of human living environment and resources recycling. However, the data about the environmental impact of the recycling process are unavailable. This physical processing may generate high level noise and the powder of waste PCBs may be released into the workshop during the course of recycling. The injury resulting from exposure to high noise level has been recognized for many years.8−10 Noise monitoring including the following noise abatement action plans is imperative, and hence large quantities of antinoise laws and ordinances have been issued by many governments.11 In this context, noise assessment is introduced to estimate the noise exposure level to the workers in the automatic line workshop. The powder of waste PCBs contains high levels of toxic elements including Cu, Cr, Cd, and Pb, and exposure to these elements will probably result in significant health effects to the workers in the event of not being treated

1. INTRODUCTION With the development of information technology, large amounts of waste electric and electronic equipments (WEEE) are constantly generated worldwide.1 In 2006, the world’s production of WEEE was estimated at 20−50 million tonnes per year.2 China has become the biggest dumping ground of WEEE, accommodating more than 70% WEEE all over the world.3 Virtually every piece of electronic equipment has its electronic components fixed onto a PCB. And yet PCB recycling requires appropriate handling to avoid environmental contamination and to recycle valuable materials efficiently. Unfortunately, primitive technologies including acid-washing and incineration are still widely used in family run workshops in developed countries. The local environment is serious polluted.3−5 Thus, Regulations on Recovery Processing of Waste Electrical and Electronic Products was enacted in China to promote circular economic development and to protect the environment.6 Technologies adopted by corporations shall meet relevant requirements on comprehensive utilization of resources, environmental protection, labor safety, and human health made by the nation. Presently, physical processing has been proved to be technologically feasible for recycling valuable components from waste PCBs,4 and the independent technologies have been integrated into the crush - pneumatic © 2011 American Chemical Society

Received: Revised: Accepted: Published: 494

July 21, 2011 October 26, 2011 November 29, 2011 November 29, 2011 dx.doi.org/10.1021/es202513b | Environ. Sci. Technol. 2012, 46, 494−499

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appropriately.12−14 Consequently, it is necessary to carry out research on the potential environmental problems in the automatic line workshop for recycling waste PCBs. The major objectives of this study are as follows: (1) to implement the engineering measures on noise reduction and to evaluate the effectiveness and feasibility and (2) to study the distribution characteristics of heavy metals in the workshop and to estimate the chronic risk of the recycling workers.

ADDing =

C × IngR × EF × ED BW × AT

(1)

ADDinh =

C × InhR × EF × ED PEF × BW × AT

(2)

C × SA × SL × ABS × EF × ED (3) BW × AT where C is the concentration of the contaminant in dust (mg/kg). For ingestion, the intake rate, IngR, of dust was 100 mg/day for adult. For inhalation, the intake rate, InhR, for a male was 15.2 m3/day; particle emission factor (PEF) was 1.36 × 109 m3/kg.17 For dermal contact, the exposed skin area, SA = 2253 cm2;18 the skin adherence factor, SL = 0.2 mg/cm2/day; the dermal absorption factor, ABS = 0.001.19 The average body weight (BW) of Chinese people was 60 kg for adults.20 In this study, exposure frequency, EF = 250 days per year; the exposure duration, ED = 10 years (the service life of the automatic line).7 The average time (AT) was 3650 days. Among the four metals studied, Cr and Cd were known to be carcinogenic.21 Because slow factors for carcinogenic risk through ingestion and dermal contact were not given by the US EPA, this study only considered carcinogenic risk resulting from inhalation. For carcinogens, the lifetime average daily dose (LADD) was calculated as shown in eq 417 ADDderm =

2. MATERIALS AND METHODS 2.1. The Automatic Line. The automatic line for recycling waste PCBs in industry-scale (Supporting Information Figure S1) was set up in a qualified recycling plant located in an economic development zone in Jiangsu, China. It is located in the subtropical humid climate zone, with obvious features of the monsoon (prevailing north winds in winter and southeasterly winds in summer). The technology consists of four parts: (1) the multiple scraping part, (2) the material screening part, (3) the multiple-roll corona electrostatic separation (CES) part, and (4) the dust precipitation part. The system is working under negative pressure and the workshop is closed. Dust produced during the recycling process was collected by a bagtype dust collector. The processing capacity can reach 600 kg/h. To avoid the pyrolysis of PCBs during scraping, the rotating speed of knives in grinders was controlled to 1800 rmp. Besides, the circulating water system was fixed on the grinders. Then the temperature of materials in the machines was controlled to 80 °C. So there was not toxic organic pollutant produced in this physical recycling process.7 2.2. Sample Collection. Noise in the workshop was monitored using an integrating sound level meter (AWA 5610B) and an octave filter (AWA 5722). The monitoring locations were described in Supporting Information Table S1. A middle volume air sampler was used to collect TSP and PM10 samples during the course of working days in March 2011. The flow rate was set as 0.120 m3/h. The sampler was placed near the automatic line about 2 m away and 1.7 m above the ground and sampling periods lasted for 8 h. During the sampling period, the range of average ambient temperature and relative humidity were 9−12 °C and 68−80%, respectively. For deposited surface dust, samples were collected by sweeping a plastic brush. 2.3. Digestion and Analysis of Heavy Metals. The samples (0.50 g crushed wasted PCBs, 0.50 g floor dust, filters) were digested according to the USA EPA method and a previous study,15,16 with modification. In this study, the samples were soaked by HNO3 (5 mL, 69%), HCL (15 mL, 36%), and H2O2 (2 mL, 30%) for 12 h. Then the mixtures were heated progressively to 190 °C to near 6 mL. After it was cooled, the solution was filtered into 100 mL volumetric flasks. Finally concentrations of Cr, Cu, Cd, and Pb were determined by an inductively coupled plasma atomic emission spectrometry (ICP-AES, IRIS-advantage 1000, THERMO, U.S.). For quality control, a blank test was also conducted with the same method. 2.4. Health Risk Assessment. The workers are exposed to heavy metals through three main pathways: ingestion, inhalation, and dermal contact. With the purpose of evaluating the health risk of workers in the automatic line workshop, health risk assessment was carried out in this study. The average daily dose contacted through ingestion (ADDing) and inhalation (ADDinh) and the average daily dose absorbed through skin (ADDderm) can be calculated as follows17

C × InhR × EF × ED (4) PEF × BW × AT where acronyms signified the same variables as in eq 2, but AT = 70 × 365 d. A hazard quotient (HQ) for noncancer risk was calculated to make the comparison with the health guideline, whereas for carcinogens LADD is multiplied by the slope factor (SF) to produce the cancer risk level. The formulas for determining the HQ, HI, and cancer risk are as follows17,21 ADD HQ = (5) RfD LADDinh =

HI =

∑ HQ i

(6)

(7) Risk = LADD × SF The Reference Dose (RfD) is estimates of daily exposure below which adverse noncancer health effects are unlikely. If the HQ < 1, then noncancerous effects are unlikely. If the HQ ≥ 1, then adverse health effects might be possible. If the HQ > 10, then it suggests high chronic risk.20 The hazard index (HI) is the sum of HQ.

3. RESULTS AND DISCUSSION 3.1. Assessment of Noise in the Workshop. 3.1.1. Noise Monitoring. The automatic line for recycling waste PCBs has a number of noise sources such as shredder, hammer grinder, vibrating screen, and bag-type dust collector. Table 1 shows the monitoring result of noise generated by each facility in the workshop. It is clear that the major noise sources in the automatic line workshop are crushing machines. The noise level exceeded the Occupational Safety and Health Standards. The maximum permissible limit for the equivalent continuous sound level (Leq) is 90 dB (A) for workers who work for 8 h per day in the workshop.22 Supporting Information Figure S2 and Figure S3 illustrate the relationship between the hearing impairments, 495

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Table 1. Date of Noise Generated by Each Facility in the Workshop noise sources

shredder

hammer grinder-1

hammer grinder-2

CES

vibrating screen

cyclone

dust collector

noise level dB (A)

92.2

91.5

91.1

70.7

63.7

60.7

80.6

were isolated within a cabin made of plywood (3 mm), which was packed with fine glass wool (100 mm) and damping materials. Table 2 shows the design calculation of the noise insulator. According to mass law of sound insulation, sound transmission loss can be calculated by the following equation25

incidence of disease, and noise. It can be derived that the rate of hearing impairments and incidence of disease to operators who work in the workshop for ten years were 20% and 17%, respectively. The emitted noise of the crushing machines has aerodynamic, electromagnetic, and mechanical origins. Aerodynamic noise is a result of pressure fluctuations due to fluctuation of fluid forces. These excited forces are caused by flow fields, turbulent flow, the interaction of the blades with air, and turbulent flow with inner wall of the machines. Noise of electromagnetic origin is generated by vibration of parts which is caused by fluctuations of the magnetic flux. The vibrating force is the result of integrating of Laplace, Maxwell, and Coulomb forces. For mechanical noise, it is provoked by vibration of bearings, pedestal, and body of the crushing machines involving frictional force and impact force. 23 The changing load leads to the changing noise generating mechanisms. All noise generating mechanisms combine to produce a noise spectrum characterized by broadband noise (Figure 1).

R = 18lg m + 12lg f − 25

(8) 2

where m is density of plywood, 2.4 kg/m ; f is the octave center frequency. Then the A-weighted sound level after introduction of noise insulator is calculated as shown in eq 9 n ⎧ ⎫ ⎪ (Lpi + Ci)/10⎪ ⎬ LA = 10lg⎨ 10 ∑ ⎪ ⎪ ⎩ i=1 ⎭

(9)

where Lpi is sound pressure level after introduction of noise insulator; Ci is the corrected value of sound pressure level. It can be seen that the designed value of sound transmission loss for crushing machines is 22.4 dB. 3.1.3. Performance Evaluation. The noise spectrum of crushing machines before and after introduction of noise insulator is shown in Figure 1. The noise level was reduced from 96.2 to 78.2 dB. Practice has proved that the sound transmission loss of noise insulator is related to the spectrum characteristics of noise sources.25 In this study, the effect of noise reduction of the noise insulator was remarkable in the mid and high frequency area according to the frequency spectrogram. It can be seen that noise in the frequency ranged from 500 to 1000 Hz, which caused greater harm to human beings, was controlled effectively. Noise of 1000 Hz decreased 29 dB, while noise of 500 Hz decreased 17.8 dB. Another interesting phenomenon was observed in this study. Noise of low frequency was amplified to some extent. The possible reason for this result was the vibration of the insulator as a result of the bad solid isolation. After introduction of noise insulator, noise monitoring at different locations (Supporting Information Figure 1) was carried out in the workshop. Figure 2 represents the noise generating model. This type of visual representation throws light on the noise dose received by the workers. Very high noise hotspots were marked inside the noise insulator. However, there were no workers working in that location. No areas were observed to have noise levels higher than 90 dB (the safe limit prescribed by the OSHA)22 in the working place. The noise level varied within 3 dB. The mean value was 79.3, and a 17.1 dB reduction was achieved by employing the engineering noise control measures. In addition, personal hearing protective devices such as ear plugs are

Figure 1. The noise spectrum of crushing machines before and after employing the engineering noise control measures.

3.1.2. Management Strategy. In view of this situation, engineering control methods were carried out in this factory with the purpose of noise reduction. The type, geometry, and rotor’s radius and revolving speed are determined in the design phase according to the properties (e.g., hardness, intensity, and cohesiveness) of waste PCBs.24 So techniques of sound insulating were adopted in this workshop (control of noise in the transmission path). The shredder and hammer grinders Table 2. Design of Noise Insulator

octave frequency band (Hz) items

125

250

500

1000

2000

4000

A-weighted sound level, LA dB(A)

measured value of sound pressure level (dB) sound transmission loss of 3 mm plywood, R (dB) sound absorption coefficient of fine glass wool, α sound transmission loss of noise insulator (dB) corrected value, Ci (dB) calculated value of sound pressure level (dB)

62.8 11 0.25 10.8 −16.2 35.8

76.1 14 0.6 11.8 −8.6 55.7

87.3 19 0.85 18.3 −3.2 65.8

95 23 0.87 22.4 0 72.6

84.7 26 0.87 25.4 1.2 60.5

80.9 27 0.85 26.3 1.0 55.6

96.2

496

73.8

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Figure 2. Noise generation model in the workshop.

the automatic line more easily in the crush and separation process. 3.2.2. Heavy Metals Distribution in TSP and PM10. Table 4 shows the mean concentrations of heavy metals (Cu, Cr, Cd,

used to reduce the amount of sound energy transmitted to workers’ ears. According to Supporting Information Figure S2 and Figure S3, noise will not cause harm to human health in this automatic line workshop. The experiment proves that the noise insulator is effective. Therefore, the noise reduction measure for the crushing machines is feasible. It is of a certain reference value for the noise control in a similar workshop. 3.2. Assessment of Heavy Metals in the Workshop. 3.2.1. Mass Concentrations of Particles and Heavy Metals. The mass concentrations of TSP (particles below 100 μm diameter) and PM10 (particles below 10 μm diameter) in the workshop for recycling waste PCBs were 282.6 and 202.0 μg/m3, respectively. The average concentrations of TSP and PM10 in this study were below the Chinese grade III guideline (applied to specific industrial zone), the limit of which was 500 μg/m3 for TSP and 250 μg/m3 for PM10. The concentrations of TSP collected in the typical workshop in southeast China for recycling waste PCBs by low-tech recycling methods14 ranged from 1129 to 1688 with an average of 1430 μg/m3, which was considerably high (5 times higher) than that in the workshop adopting the physical technology. The ratio of PM10 to TSP mass concentration in the workshop in this study was 0.71. This means particles below 10 μm diameter contribute to 71% of the particles below 100 μm diameter. This value was equal to that in Tianjin, China.26 It is suggested that the air in the workshop is dominated by fine particles and might pose health risks to the workers. The concentrations of Cr, Cu, Cd, and Pb in crushed waste PCBs, airborne particles (particles below 10 μm), and floor dust are presented in Table 3. Four metals were detected in all

Table 4. Cr, Cu, Cd, and Pb Concentrations in TSP and PM10 Cr Cu Cd Pb

waste PCBs (mg/g)

airborne particles (mg/g)

floor dust (mg/g)

0.54 120.10 0.13 5.84

0.59 4.35 0.079 2.77

0.043 18.28 0.014 4.32

PM10 (μg/m3)

PM10/TSP

0.17 1.22 0.028 1.40

0.12 0.88 0.016 0.56

0.71 0.72 0.57 0.4

and Pb) in TSP and PM10. It can be seen that Pb (1.40 μg/m3) and Cu (1.22 μg/m3) were the most enriched metals in TSP samples collected in the workshop followed by Cr (0.17 μg/m3) and Cd (0.028 μg/m3), and the same trend was found for PM10. The content of Cd was the least among the four metals in the present study in both TSP and PM10. This was consistent with the study in a typical workshop located in Guiyu involved in e-waste recycling for more than ten years.15 However, the concentration of Cr was extremely higher than Cu, Pb, and other metals in Guiyu which was different from this study. In addition, the ratios of metal concentrations in PM10 to that in TSP were calculated, as shown in Table 4. A predominant occurrence of Cr, Cu, and Cd in fine particles was observed. But Pb had higher composition in coarse fraction than in fine particle mode. Deng et al.15 also reported the same distribution characteristics for Cr, Cd, and Pb other than Cu. This indicates that variable particle size classification applied in different studies and different particle sources (e.g., employing different technologies) give rise to various distribution characteristics.27 3.2.3. Heavy Metal Risk Assessment. The results of the average daily doses and hazard quotients for each noncancer metal are shown in Table 5. For ingestion, the trend of HQ for the heavy metals was Pb > Cu > Cr > Cd. The HI via dust ingestion exposure was 1.964. The contributions of Cr, Cu, Cd, and Pb to HI were 0.82, 26.58, 0.81, and 71.79%, respectively. For inhalation, the HQs were ranked in the order Cr > Cu > Pb > Cd, and the HI was 2.88 × 10−4. When considering the contribution, Cr contributed to 66.6% followed by Cu (20.14%). For dermal contact, the sequence of HQ was

Table 3. Cr, Cu, Cd, and Pb Concentrations in Waste PCBs, Airborne Particles, and Floor Dust Cr Cu Cd Pb

TSP (μg/m3)

the samples. It demonstrated that toxic metals were released into the air and floor dust in the workshop. Compared with Cu and Cd, Cr and Pb were released into the ambience of 497

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Table 5. Average Daily Doses and Hazard Quotients for Each Noncancer Metal and Exposure Pathwaya ADDing Cr Cu Cd Pb a

4.91 2.09 1.60 4.93

× × × ×

10−5 10−2 10−5 10−3

ADDinh 5.49 2.33 1.79 1.28

× × × ×

ADDderm

10−9 10−6 10−9 10−7

2.21 9.40 7.20 2.22

× × × ×

10−7 10−5 10−8 10−5

RfDing 3.00 4.00 1.00 3.50

× × × ×

10−3 10−2 10−3 10−3

RfDinh 2.86 4.02 1.00 3.52

× × × ×

RfDderm

10−5 10−2 10−3 10−3

6.00 1.20 1.00 5.25

× × × ×

10−5 10−2 10−5 10−4

HQing 1.64 × 10−2 5.22 × 10−1 1.60 × 10−2 1.41E-0

HQinh 1.92 5.80 1.79 3.64

× × × ×

10−4 10−5 10−6 10−5

HQderm 3.68 7.83 7.20 4.23

× × × ×

10−3 10−3 10−3 10−2

ADD (mg/kg/day): average daily dose; RfD (mg/kg/day): reference dose; HQ (unitless): hazard quotient.

■

Pb > Cu > Cd > Cr. The HI was 6.10 × 10−2 and Pb (contributed to 69.34%) posed the highest risk. The HQ for Cu, Cr, and Cd was less than one which suggested that noncancerous effects were unlikely. Among the four heavy metals, the HQ for Pb contacted through ingestion was the highest (exceeded the RfD by 1.41 times). The possible reason for this result was that Pb had a high concentration in waste PCBs and could be released more easily during the crush and separation process. The results were consistent with the study on the dust collected in the waste PCBs recycling workshop.20 In that study the HQing for Pb exceeded the RfD by 50.2 times. In the three main exposure routes, ingestion of dust resulted in the greatest health risk to the workers. For Cr, Pb, Cu, and Cd, the trend of HQ contacted through different exposure pathways was ingestion > dermal contact > inhalation. It is concluded that different exposure pathways presents different levels of risk for each metal. Table 6 shows the LADD and risk for Cr and Cd through inhalation. The LADD for Cr and Cd were 7.84 × 10−10 and

AUTHOR INFORMATION Corresponding Author *Phone: +86 21 54747495. Fax: +86 21 54747495. E-mail: [email protected].

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ACKNOWLEDGMENTS This work was supported by the National High Technology Research and Development Program of China (863 program 2009AA06Z318) and the National Natural Science Foundation of China (Grant No. 21077071).

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Table 6. Lifetime Average Daily Doses and Risk for Each Carcinogenic Metal via Inhalation LADDinh (mg/kg/d) Cr Cd

−1

7.84 × 10 0 2.56 × 10−10

SFinh (mg/kg/d)‑1

risk

42.0 6.30

3.29 × 10−8 1.61 × 10−9

REFERENCES

2.56 × 10−10, respectively. Though Cr exhibited higher risk than Cd, the carcinogenic risk of Cr was lower than its threshold value (the range of threshold value was 10−6− 10−4).17 This indicates that carcinogenic risks on workers are relatively light in the workshop. In short, the working environment for recycling waste PCBs is greatly improved. Noise in the automatic line workshop is controlled effectively. What is more, the hazard indexes of Cr, Cu, and Cd are lower than their threshold values. However, the HQ contacted through ingestion for Pb is 1.41 in the present study. It indicates that adverse health effects might be possible. Consequently, it is suggested that personal protective devices such as masks are used to reduce the exposure level to heavy metals. This is the first report on noise and heavy metals analysis with regard to the physical process for waste PCBs recycling. It is hoped that the latest data could assist in the goal of industrialization of the technology by providing relevant environmental information.

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ASSOCIATED CONTENT S Supporting Information * Figures showing the engineering schematic of the automatic line for recycling waste PCBs; figures showing the relationship between exposure years and rate of hearing impairments, and incidence disease; table showing the noise monitoring location. This material is available free of charge via the Internet at http://pubs.acs.org. 498

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