Annals of Occupational Hygiene Advance Access originally published online on April 8, 2008
Annals of Occupational Hygiene 2008 52(4):213-225; doi:10.1093/annhyg/men011
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Exposure Assessment of Workers to Airborne PCDD/Fs, PCBs and PAHs at an Electric Arc Furnace Steelmaking Plant in the UK
Corus Research, Development and Technology, Swinden Technology Centre, Moorgate, Rotherham S60 3AR, UK
* Author to whom correspondence should be addressed. Tel: +44-170-982-5259; fax: +44-170-982-5400; e-mail: eric.aries{at}corusgroup.com
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Occupational exposure studies were undertaken at a UK electric arc furnace (EAF) steelmaking plant to investigate the exposure of workers via inhalation to dioxins, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) including benzo[a]pyrene (B[a]P). Surveys were undertaken in areas including the melting shop, the casting department and a furnace control cabin. The highest concentrations of dioxins and PCBs were found inside the melting shop nearby EAFs, whereas dioxin and PCB concentrations in the casting department and inside the control cabin were significantly lower. Risk characterization was carried out by comparing the daily intake of dioxins and PCBs through inhalation with the recommended tolerable daily intake (TDI). Health risk assessments were also carried out by combining exposure data with inhalation cancer potency factors to quantify the cancer risk. For the most exposed category of workers (melting shop workers), the estimated daily intake via inhalation was 0.35 pg WHO-TEQ kg–1 body weight (bw) in the worst case scenario. Considering that the average UK adult exposure to dioxins from the diet is 1.8 pg WHO-TEQ kg–1 bw day–1, the results indicated that the estimated daily intake of dioxins via inhalation at the EAF would not result in the recommended range of the TDI (1–4 pg WHO-TEQ kg–1 bw day–1) being exceeded. Cancer risks for a 40-year occupational exposure period were determined by multiplying the inhalation dose by the inhalation cancer potency factor for 2,3,7,8-tetrachlorodibenzo-p-dioxin. For melting shop workers, cancer risks from exposure to dioxins and PCBs ranged from 2.05 x 10–5 to 7.54 x 10–5. Under most regulatory programmes, excess cancer risks between 1.0 x 10–4 and 1.0 x 10–6 indicate an acceptable range of excess cancer risk, suggesting a limited risk from dioxin exposure for workers in the EAF plant. For the calculation of excess cancer risks, no account has been taken of the protection provided by protective respiratory equipment worn by EAF workers. If personal protective equipments were taken into consideration, it is likely that the excess cancer risks for EAF workers would have been lower and considered as negligible. The highest concentrations of PAHs were found in the melting shop and the casting areas of the plant. In the melting shop area, B[a]P concentrations ranged from 1.4 to 24.5 ng m–3, with a mean value of 7 ng m–3. No workplace exposure limits have been published by the Health and Safety Executive in the UK for PAHs; however, the B[a]P concentrations found were below the limit value of 150 ng m–3 (8-h time-weighted average) specified for workplace exposure in France. Exposure assessment of workers to PAHs via inhalation was carried out by calculating a potential cancer risk considering a 40-year occupational exposure period and B[a]Peq concentrations. Estimated cancer risks for the most exposed category of workers (i.e. melting shop workers) ranged from 3.66 x 10–6 to 1.64 x 10–5. The cancer risks determined in this study were well within an acceptable range of excess cancer risk of 1.0 x 10–4 to 1.0 x 10–6, specified by the US Environmental Protection Agency.
Keywords: benzo[a]pyrene • cancer risk • dioxins • occupational hygiene • polychlorinated biphenyls • polycyclic aromatic hydrocarbons • steel industry
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Melting of ferrous materials to produce steel is usually performed in electric arc furnaces (EAFs) and plays an important role in the recycling of steel scrap materials. A typical EAF consists of a refractory-lined steel vessel with the upper shell consisting of water-cooled panels and water-cooled roof. The electrodes for input of electrical power pass through the roof of the furnace. Most existing EAFs are powered by alternating current (AC furnaces) and have three electrodes. The roof also contains a fourth hole for direct extraction of waste gases. The Corus EAF plant investigated here operates two AC furnaces with capacities of 150 tonnes liquid steel. Scrap is charged from baskets into the EAF together with lime, which is used as a flux for slag formation. About 60% of the scrap is charged with the first basket, and then the roof is closed and the electrodes lowered to 20–30 mm above the scrap before striking an arc. After the initial charge has melted, the charging process is repeated by adding a second basket of scrap metal. At the end of the heat, slag is removed, prior to tapping the molten steel.
Production of steel by the EAF process may produce traces of organic micro-pollutants such as dioxins, namely polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). From an occupational hygiene point of view, there is a lack of information on the concentrations of these species in the workplace atmosphere of EAF plants, particularly for PCBs and PAHs. Sweetman et al. (2004) carried out a survey for the UK Health and Safety Executive (HSE) of workplace PCDD/F concentrations in an EAF plant in the UK and reported PCDD/F concentrations of 2.4–4.7 pg WHO-TEQ m–3 for fixed-position measurements. However, Sweetman et al. (2004) indicated that aluminium recycling industry exhibited higher potential dioxin exposures in the workplace and reported PCDD/F concentrations between 5.3 and 72.7 pg WHO-TEQ m–3 nearby rotary furnaces at five different aluminium recycling plants. Davy (2004) presented a review of the legislation with respect to dioxins in the workplace and confirmed that the main area of concern in the metal recycling industry was for workers in secondary aluminium smelters.
In view of the toxicological importance of the cited groups of organic pollutants, it was considered important to investigate the potential exposures of Corus EAF workers. Accordingly, surveys were carried out to determine workplace concentrations of the selected pollutants in various areas, including the melting shop, a furnace control room and the casting area of the plant. This paper summarizes the concentrations of PCDD/Fs, PCBs and PAHs found in the workplace air of the EAF plant, provides estimation of intakes for workers and assesses the health risks for personnel exposed to these substances.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Terminology
PCDDs and PCDFs are two families of chemicals that are formed inadvertently in industrial processes as a result of incomplete combustion of organic material. There are 75 PCDD and 135 PCDF congeners, of which only 17 are considered to be biologically active, namely those chlorinated at the 2,3,7,8 positions. Each congener is assigned a toxicity rating (referred to as toxic equivalent factor or TEF). Of the 17 2,3,7,8-chloro-congeners, the most toxic is 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2,3,7,8-TCDD) and is assigned a TEF of 1; other congeners are assigned toxicity ratings relative to this compound. The overall toxicity of a sample may be obtained by multiplying the concentrations of the individual target compounds by their respective TEFs to obtain as the corresponding toxic equivalent concentrations (TEQs) and the total TEQ of a sample is obtained by summation of the individual TEQs. This system, which was introduced in 1988 by the North Atlantic Treaty Organization, Committee on Challenges to Modern Society (NATO, 1988), was revised in 1998 by the World Health Organization (WHO) to provide TEF values for humans and wildlife and to include a set of PCBs exhibiting dioxin-like activity (Van den Berg et al., 1998).
PAHs comprise a large group of compounds consisting of two or more aromatic rings fused together. Several PAHs are carcinogenic or mutagenic. Among these, a group of 16 PAHs has been identified as priority pollutants by the US Environmental Protection Agency (US EPA). In this study, PAH compounds are indicated as follows: naphthalene (Naph), acenaphthylene (Acy), acenaphthene (Ace), fluorene (Fluor), phenanthrene (Phen), anthracene (Ant), fluoranthene (Flant), pyrene (Pyr), benz[a]anthracene (B[a]Ant), chrysene (Chry), benzo[b]fluoranthene (B[b]Flant), benzo[k]fluoranthene (B[k]Flant), benzo[a]pyrene (B[a]P), dibenz[a,h]anthracene (D[a,h]Ant), benzo[g,h,i]perylene (B[g,h,i]Per) and indeno[1,2,3-cd]pyrene (Ind[1,2,3-cd]Pyr). To characterize the carcinogenic potency of PAH mixtures, potency equivalency factors (PEFs) have been proposed. In particular, Nisbet and Lagoy (1992) and subsequently Collins et al. (1998) have proposed a list of PEFs for the 16 US EPA PAHs, in which B[a]P is used as a reference compound and assigned a PEF value of 1. In this study, the PEFs proposed by Nisbet and Lagoy (1992) have been used.
Sampling
Air samples were collected using high-volume samplers (Graseby Andersen), equipped with polyurethane foam plugs (Supelco: 6 x 7.6 cm) and glass fibre filters (Whatman GF/A 110 mm). The samplers were operated during 12 h at a constant flow rate of 0.2 m3 min–1, and checks were made every 2 h to replace filters and to record the magnehelic gauge readings. A schematic of the EAF melting shop and the casting bay area at Corus Engineering Steel Works is given in Fig. 1. The EAF plant investigated comprised two furnaces, designated as ‘N’ and ‘T’ furnaces. In the melting shop area, high-volume samplers were situated
- (i) nearby control cabins of N and T furnaces (N and T furnace locations),
- (ii) behind N and T furnaces in the tapping area (N and T furnace tapping pit locations),
- (iii) above N furnace (i.e. 15–20 m) near a stationary crane (basket crane level location) and
- (iv) inside N furnace control cabin (N furnace control cabin location).
- (ii) behind N and T furnaces in the tapping area (N and T furnace tapping pit locations),
In the casting area, situated in a separate building directly adjacent to the melting shop, sampling was carried out at two locations:
- (i) near the flushing station and
- (ii) at a location designated as positions 8 and 9 by plant personnel.
- (ii) at a location designated as positions 8 and 9 by plant personnel.
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Finally, measurements were also performed outdoors near the main entrance of the site. A total of two sampling campaigns were carried out in September 2005 and 2006.
Analytical procedure
The operation of the laboratory for PCDD/Fs and PCBs analysis has been described in detail elsewhere (Anderson and Fisher, 1996; Aries et al., 2004). Briefly, samples were spiked with 13C12-labelled internal standard solutions and extracted with toluene by accelerated solvent extraction (150°C for 12 min, 2000 psi) using a Dionex ASE 200. A 10% fraction of the total extract was retained for PAH determinations and was subjected to clean-up on basic alumina columns to remove saturated hydrocarbons. After clean-up, PAHs were determined by gas chromatography–mass spectrometry (GC/MS) in selected-ion monitoring mode using an Agilent 6890 GC coupled to an HP 5973 inert mass-selective detector. Injections were performed in splitless mode, with a helium flow rate of 1.0 ml min–1, a front inlet temperature of 270°C and a DB5-MS capillary column (60 m x 0.25 mm x 0.25 µm).
The remainder of the total extract (i.e. 90%) was subjected to a three-stage clean-up procedure using liquid chromatography for PCDD/F and PCB determinations. Multi-layered silica chromatography columns were used for the clean-up of total extracts, Florisil chromatography was used to separate PCDD/Fs from PCBs and basic alumina chromatography was used to remove large amounts of saturated hydrocarbons from the PCB fractions. Prior to analysis, recovery standards were added, and cleaned-up extracts for PCDD/Fs and PCBs were analysed by high-resolution gas chromatography–high-resolution mass spectrometry using a Hewlett-Packard 6890 gas chromatograph coupled to a Micromass Autospec Ultima high-resolution mass spectrometer. A 60 m x 0.25 mm x 0.25 µm DB5-MS capillary column was used. The MS was operated at 10 000 resolution in the positive-ion mode at 34 eV energy.
Risk characterization
Workplace exposure limits (WELs) for hazardous substances are published in the UK by the HSE in the EH40 document (EH40, 2005). However, WELs are not available for many persistent organic pollutants, such as PCDD/Fs. For total PCBs, a long-term WEL of 0.1 mg m–3 (8-h time-weighted average) is specified, but it was originally defined to address exposures to PCBs of workers exposed to transformer oils. However, it does not take into consideration the carcinogenic activity of the 12 dioxin-like PCBs, since transformer oils were constituted predominantly of other less toxic PCB isomers. The absence of an exposure limit for PCDD/Fs and the fact that the PCB WEL was not relevant to the carcinogenic activity of the 12 dioxin-like PCBs meant that alternative methods had to be used to assess the exposure of EAF workers. No WELs are assigned for PAHs in the UK, but in France, a threshold limit value (8-h time-weighted average) of 150 ng m–3 has been defined for B[a]P in the workplace (Maitre et al., 2003).
Two methods were used to estimate the risk for EAF workers through inhalation. First, estimated daily intakes of PCDD/Fs and WHO-12 PCBs were calculated taking into account the amount of time EAF workers spent in each area of the plant and assuming daily inhalation rates of 1.3 and 1.5 m3 h–1 for light and moderate activities, respectively, and an 8-h working shift (US EPA, 1997). The estimated daily intakes were compared with the recommended tolerable daily intake (TDI). In 1998, the WHO European Centre for Environment and Health recommended a TDI of 1–4 pg WHO-TEQ kg–1 body weight (bw) (including the WHO-12 PCBs), while in November 2001, the UK Committee on the Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) recommended that a TDI of 2 pg WHO-TEQ kg–1 bw day–1 be established based upon effects on the developing male reproductive system mediated via the maternal body burden, and it is considered adequate to protect against possible effects such as cancer and cardiovascular effects (COT, 2001).
Health risk assessments were also carried out by combining exposure data with inhalation cancer potency factors in order to quantify cancer risks. Essentially, two pieces of information are needed to assess inhalation cancer risks. These are the inhalation cancer potency for the substance expressed in units of inverse dose as a potency slope [i.e. (mg kg-day–1)–1] and an estimate of the average daily inhalation dose in units of milligram per kilogram-day (mg kg-day–1). Cancer risk is calculated by multiplying the inhalation dose by the inhalation cancer potency factor to result in a potential inhalation cancer risk. The following equation illustrates the general formula for calculating potential cancer risk.
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By multiplying the potential cancer risk by 106, it is possible to determine the theoretical number of cancer cases per million of people.
The equation for computing the dose from exposure to air pollutants via inhalation is:
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- Ci = concentration of the compound in ambient air (µg m–3),
- DIR = daily inhalation rate (l kg–1 bw-day–1),
- A = inhalation absorption factor,
- EF = exposure frequency (day per year),
- ED = exposure duration (years) and
- AT = averaging time period over which exposure is averaged (day).
- DIR = daily inhalation rate (l kg–1 bw-day–1),
For PCDD/Fs and PCBs, WHO-TEQ concentrations were used for potential cancer risk calculations by multiplying them with the inhalation potency factor for 2,3,7,8-TCDD of 1.3 x 105 (mg kg-day–1)–1 (OEHHA, 2005). Using the PEF approach, potential cancer risk calculations were performed by multiplying the workplace air B[a]Peq concentrations by the inhalation potency factor for B[a]P of 3.9 (mg kg-day–1)–1 (OEHHA, 2005). Daily inhalation rates of 1.3 and 1.5 m3 h–1, corresponding to 149 and 172 l kg–1 bw for an adult of 70 kg, were used for light and moderate activities, respectively (US EPA, 1997). An averaging time of 365 day year–1 (i.e. AT = 25 550 day) was used. An inhalation absorption factor of 1 was used assuming 100% absorption. Finally, an EF of 250 day year–1 and 40-year occupational ED was used.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Concentrations of PCDD/Fs and WHO-12 PCBs in the workplace air and in the ambient environment of the EAF steelmaking plant
Concentrations of PCDD/Fs and WHO-12 PCBs are summarized in Table 1, where it may be seen that the highest concentrations of PCDD/Fs and PCBs were found in the melting shop, followed by the casting area and the control cabin. In EAF steelmaking, PCDD/Fs and PCBs are likely to be formed in the furnace owing to the presence of chlorine and carbon residuals in the scrap metal. When scrap metal is charged in the furnace, chemical reactions may occur between residual molten metal at the bottom of the furnace and the new charge of scrap. During charging, the roof is removed and significant release of fumes and particulate matter takes place inside the melting shop before it is replaced. Fumes and particulates cannot be completely removed by the secondary extraction system, and as a result, it is normal to find significantly higher concentrations of PCDD/Fs and PCBs in the melting shop area than in the casting area. With regard to N furnace control cabin, lower PCDD/F and PCB concentrations were observed since the control cabin is equipped with an air filtration device.
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PCBs were systematically found at higher concentrations than PCDD/Fs. For example, in the melting shop area, total WHO-12 PCB concentrations ranged from 144 to 1313 pg m–3 with a mean concentration of 586 pg m–3, whereas total 2,3,7,8-PCDD/F concentrations were 2.6–69.5 pg m–3 with a mean value of 24.5 pg m–3. The lowest concentrations of PCDD/Fs and PCBs in the workplace were found inside the control room of N furnace where the total WHO-12 PCB concentrations were 57–129 pg m–3 with a mean concentration of 99 pg m–3, while the total 2,3,7,8-PCDD/F concentrations were 3.1–5.4 pg m–3 with a mean value of 4.1 pg m–3. All PCDD/F and PCB concentrations determined in the workplace were significantly higher than those found in outdoor ambient air where the total TEQ concentrations ranged from 0.022 to 0.03 pg WHO-TEQ m–3. It should be noted that the values reported for outdoor air were estimated using limits of detection of PCDD/Fs, since most congeners were not detected in the samples. The outdoor concentrations determined during this study (0.02–0.05 pg WHO-TEQ m–3) compared favourably with typical urban ambient air concentrations in the UK (0.02–0.103 pg WHO-TEQ m–3) reported by AEAT (1999).
Total TEQ concentrations were determined using the WHO-TEF scheme by taking into account both PCDD/Fs and PCBs. Total TEQ concentrations ranged from 0.29 to 8.62 pg WHO-TEQ m–3, from 0.48 to 2.45 pg WHO-TEQ m–3 and from 0.25 to 0.39 pg WHO-TEQ m–3, in the melting shop area, the casting area and inside the control cabin of N furnace, respectively. For these areas of the works, the average total TEQ concentrations were 2.71, 0.75 and 0.31 pg WHO-TEQ m–3, respectively. As may be seen from Table 2, the concentrations found at the Corus EAF plant were in good agreement with those reported by Sweetman et al. (2004) elsewhere in the UK, where PCDD/F concentrations were in the range 2.4–4.7 pg I-TEQ m–3. Compared with other industrial processes, PCDD/F exposures at EAF plants appeared to be higher than in municipal waste incinerators (Hu et al., 2004) and iron ore sintering (Shih et al., 2006), but significantly lower than in the aluminium recycling industry.
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PCDD/F and WHO-12 PCB congener profiles in the workplace air of the EAF steelmaking plant
Information on congener profiles may be presented either as concentration profiles of the 12 PCB- and the 17 PCDD/F-targeted compounds or in terms of the relative contribution of each congener to the total TEQ [WHO-TEQ + I-TEQ]. Fig. 2 illustrates typical PCDD/F and PCB congener profiles determined in air samples collected near N furnace cabin, in the casting area and inside the control cabin of N furnace. Although the concentrations of individual congeners varied from location-to-location, congener profiles were almost identical at each sampling site. Typically, PCDFs were found in higher concentrations than PCDDs (except OCDD), and the most abundant congeners were OCDF, 1,2,3,4,6,7,8-HpCDF and 2,3,4,6,7,8-HxCDF (Figs 2A, B and C). Generally, PCDD/F congener concentrations did not exceed 15 pg m–3. PCBs 118, 105 and 77 were particularly abundant, with concentrations in the range 100–500, 10–80 and 5–35 pg m–3, in the melting shop, casting area and inside the control cabin (Fig 2A1, B1 and C1), respectively. Figure 2A2, B2 and C2 illustrate the contributions of individual PCDD/F and PCB congeners to the total WHO-TEQ. The main contributors to the TEQ were PCDFs, particularly 2,3,4,7,8-PeCDF (30–45%) and 2,3,4,6,7,8-HxCDF (
7 to 11%). With regard to PCDDs, two congeners contributed significantly, namely 2,3,7,8-TCDD (2 to 8%) and 1,2,3,7,8-PeCDD (8 to 18%). Although WHO-12 PCBs were detected in much higher concentrations than PCDD/Fs, only PCB 126 contributed significantly to the total TEQ (5 to 12%). The workplace air PCDD/F congener profiles described in this study were very similar to those reported by Chen et al. (2006) for an EAF in Taiwan. However, EAF workplace air congener patterns were different from the workplace air profiles reported in Taiwan, by Shih et al. (2006) for a sinter plant and by Hu et al. (2004) for a municipal solid waste incineration plant (MSWI). With regard to the MSWI plant, 1,2,3,4,6,7,8-HpCDD appeared to be the congener contributing the most to the I-TEQ in workplace air samples (45%), whereas both OCCD and 1,2,3,4,6,7,8-HpCDF were the congeners contributing the most to the I-TEQ in iron ore sintering (20% contribution for each congener).
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Exposure assessment of EAF workers to PCDD/Fs and dioxin-like PCBs
Exposure assessment of workers to PCDD/Fs and dioxin-like PCBs via inhalation was carried out by comparing the estimated daily intake of workers to the TDI and by calculating a potential cancer risk considering a 40-year occupational exposure period. Table 3 summarizes the estimated daily intake of PCDD/Fs and WHO-12 PCBs and the corresponding cancer risk estimates. Three categories of workers were considered. After consultation with plant personnel, it was decided to estimate daily intakes for melting shop workers by assuming that over an 8-h shift, they would typically spend 25% of the time inside the melting shop (mostly during tapping operations) and 75% inside the control cabin. In the casting department, workers would generally spend 50% of the time in the casting area and 50% of the shift inside the control cabin. Finally, workers in charge of furnace operations would spend the entire shift inside the control room. In the melting shop and the casting areas, two intensities of work activities were considered by using two different inhalation rates of 1.3 and 1.5 m3 h–1 for light and moderate activities, respectively. Both the mean and the highest TEQ concentrations were used for calculations. Finally, an inhalation absorption factor of 1 was used assuming 100% absorption of PCDD/Fs and WHO-12 PCBs in the body.
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The highest estimated daily intakes by inhalation of PCDD/Fs and PCBs were found for melting shop workers. These ranged from 0.15 to 0.41 pg WHO-TEQ kg–1 bw and from 0.13 to 0.36 pg WHO-TEQ kg–1 bw for moderate and light activities, respectively (Table 3). For workers in the casting area, estimated daily intakes ranged from 0.09 to 0.24 pg WHO-TEQ kg–1 bw in the case of moderate activities. Finally, the lowest daily intakes were determined for workers inside the control room (
0.06 pg WHO-TEQ kg–1 bw using the highest TEQ concentration). When estimating the dioxin daily intake of workers, it is important to take into account the amount of PCDD/Fs and PCBs from dietary sources. The WHO estimated that >90% of exposure of the general population to these compounds occurs through the diet, with food from animal origin being the predominant source (WHO, 1998). The Food Standards Agency (FSA) carried out several studies of the food supply in the UK based on analysis of retail foods. In the latest available data for total diet survey of food group samples taken in 1997 and reported in 2000 by the FSA (FSA, 2000), the average adult exposure to PCDD/Fs and WHO-12 PCBs was estimated to be 1.8 pg WHO-TEQ kg–1 bw day–1, i.e. for normal consumers and 3.1 pg WHO-TEQ kg–1 bw day–1 for high level food consumers. Based on the average UK adult dietary exposure to PCDD/Fs and WHO-12 PCBs of 1.8 pg WHO-TEQ kg–1 bw day–1, it is estimated that the total daily intake of PCDD/Fs and PCBs from food and from inhalation of air from the EAF workplace would range from 1.95 to 2.21 pg WHO-TEQ kg–1 bw day–1 for melting shop workers and from 1.89 to 2.04 pg WHO-TEQ kg–1 bw day–1 for the casting area workers. The results from this study indicate that for most Corus EAF workers, the estimated daily intake of PCDD/Fs and WHO-12 PCBs via inhalation should not result in the TDI of 2 pg WHO-TEQ kg–1 bw day–1 recommended by COT being exceeded. In the worst case, the results showed that for the most exposed category of workers (i.e. melting shop workers), the estimated daily intake would be 2.21 pg WHO-TEQ kg–1 bw day–1, only slightly above the TDI recommended by COT, but well within the range of 1–4 pg WHO-TEQ kg–1 bw day–1 recommended by the WHO. The potential cancer risk from exposure of Corus EAF workers to PCDD/Fs and PCBs via inhalation was also investigated. Cancer risks were determined by multiplying the inhalation dose by the inhalation cancer potency factor for 2,3,7,8-TCDD. For the calculation of excess cancer risk, no account has been taken of the protection provided by protective respiratory equipment worn by EAF workers, although melting shop workers (the most exposed category of workers) were equipped with masks for use against particles with a low filtration efficiency (Type P1), providing a protection factor of 4 (HSG53, 1998). As may be seen from Table 3, cancer risks from exposure to PCDD/Fs and PCBs via inhalation ranged from 2.05 x 10–5 to 7.54 x 10–5, from 5.69 x 10–6 to 2.14 x 10–5 and from 2.35 x 10–6 to 2.96 x 10–6 for melting shop, casting area and control room workers, respectively. Cancer risks estimated in this study were within the range 1.0 x 10–4 to 1.0 x 10–6 that is acknowledged as acceptable by regulatory agencies such as the US EPA (US EPA, 1989). These data indicated that cancer risks associated with dioxin exposure for Corus EAF workers were acceptable. Furthermore, if the protection factor afforded by the use of personal protective equipment is taken into consideration, the excess cancer risks for EAF workers would be 4-fold lower, and therefore considered as negligible.
PAH concentrations in workplace air and ambient environment of the EAF steelmaking plant
The total 16 US EPA PAHs, B[a]P and B[a]Peq concentrations are summarized in Table 4. Highest concentrations of PAHs were found in the melting shop and the casting areas of the plant, whereas those inside the control cabin were significantly lower. In the melting shop, B[a]Peq concentrations ranged from 3.9 to 62.8 ng m–3 with a mean concentration of 16 ng m–3, but were 0.5 to 5.6 ng m–3 with a mean value of 2.3 ng m–3 inside the control cabin of N furnace (Table 4). PAH concentrations in the workplace were significantly higher than the ambient air concentrations found outdoors where B[a]Peq concentrations ranged only from 0.06 to 0.6 ng m–3.
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Overall, high variability was observed for PAH concentrations between sampling locations and from day to day at the same sampling location. For instance, during the measurement campaign carried out in 2006, markedly higher concentrations of PAHs were detected on the last day of measurements at all sampling sites (Table 4). Figure 3 illustrates typical PAH profiles collected at various locations in the second measurement campaign (September 2006). As may be seen from Fig. 3, four PAHs, phenanthrene, fluoranthene, pyrene and anthracene were particularly predominant, and their concentrations varied significantly over the sampling campaign and were particularly high on the last day. It is likely that these variations were associated with process factors or the quality of scrap used. High molecular weight PAHs such as B[a]P were also detected, but at much lower concentrations than the four PAHs cited previously (Fig. 3). Relatively, few studies have been carried out on PAH concentrations in the workplace air of EAF plants and insofar as is known, Bergamaschi et al. (2005) carried out the only noteworthy survey. In the latter study, pyrene and B[a]P concentrations in workplace air ranged from 2 to 530 and 1 to 148 ng m–3, respectively. Overall, B[a]P exposures of workers were three orders of magnitude lower than typical B[a]P exposure associated with cokemaking in the UK (Unwin et al., 2006) or aluminium manufacture (Ronneberg and Romundstadt, 1997). The B[a]P concentrations determined at the EAF steelmaking plant were all below the threshold limit value of 150 ng m–3 (8-h time-weighted average) specified for workplace exposure in France.
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Exposure assessment to PAHs for Corus EAF workers
As may be seen from Table 5, cancer risks from exposure to PAHs via inhalation ranged from 3.66 x 10–6 to 1.64 x 10–5, from 1.59 x 10–6 to 1.10 x 10–5 and from 5.23 x 10–7 to 1.27 x 10–6 for melting shop, casting area and control room workers, respectively. The cancer risks determined in this study were well within an acceptable range of excess cancer risk of 1.0 x 10–4 to 1.0 x 10–6 defined by the US EPA (US EPA, 1989), suggesting a very limited risk for Corus EAF workers from PAH exposure via inhalation. By comparison, higher estimated lifetime cancer risks (within the range 0.4–4.7 x 10–5) have been reported for the general population of localities with aluminium smelting activities (Vyskocil et al., 2004).
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Surveys were carried out at an EAF steelmaking plant to determine workplace air concentrations of PCDD/Fs, WHO-12 PCBs and PAHs and investigate potential exposure of workers to these compounds.
Highest concentrations of PCDD/Fs and PCBs were found in the melting shop area, followed in order by the casting area and control cabin. Total TEQ concentrations were 0.29–8.62 pg WHO-TEQ m–3, 0.48–2.45 pg WHO-TEQ m–3 and 0.25–0.39 pg WHO-TEQ m–3, in the melting shop, the casting area and the control cabin, respectively. When considering the average UK adult dietary exposure to PCDD/Fs and WHO-12 PCBs of 1.8 pg WHO-TEQ kg–1 bw day–1, the results indicated that the total daily intake of PCDD/Fs and PCBs from both diet and workplace exposure would range from 1.95 to 2.21 pg WHO-TEQ kg–1 bw day–1 for melting shop workers, well within the range of 1–4 pg WHO-TEQ kg–1 bw day–1 recommended by the WHO.
The potential exposures of EAF workers to PCDD/Fs and PCBs via inhalation were also investigated by estimating cancer risks. Estimated excess cancer risks ranged from 2.05 x 10–5 to 7.54 x 10–5 for the most exposed category of workers (i.e. melting shop area), well within the acceptable range (of excess cancer risk) of 1.0 x 10–4 to 1.0 x 10–6 proposed by the US EPA. For the calculation of excess cancer risks, no account has been taken of the protection provided by protective respiratory equipment worn by EAF workers inside the melting shop. When taking into account appropriate personal protective equipment, the excess cancer risks for EAF workers would be lower and are considered as negligible.
With regard to PAHs, the highest concentrations were found in the melting shop and the casting areas of the plant. In comparison, PAH concentrations inside the control cabin were significantly lower. High variability was observed for PAH concentrations from day to day at identical sampling locations, which may be attributed to process factors or the quality of scrap used. In the melting shop, B[a]P concentrations ranged from 1.4 to 24.5 ng m–3 with a mean value of 7 ng m–3. Exposure assessment of workers to PAHs was carried out by calculating a potential cancer risk over a 40-year occupational exposure period. Both the mean and the highest B[a]Peq concentrations were used for calculations. Estimated cancer risks for the most exposed category of workers (i.e. melting shop area) ranged from 3.66 x 10–6 to 1.64 x 10–5. The excess cancer risks were well within the acceptable range (of excess cancer risk) of 1.0 x 10–4 to 1.0 x 10–6 defined by the US EPA, suggesting a very limited risk for Corus EAF workers.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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The authors would like to thank Pretash Patel and Shelley Richardson for their help in preparing the samples. The authors would like to thank Simon D. Ellis, Amanda Horne and Ken Burnett for their significant work in collecting the samples during both sampling campaigns. The authors would like to thank P. D. E. Brooks and V. Kisnah for helpful comments in improving the manuscript and support throughout the project.
Received November 29, 2007; in final form February 8, 2008
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