Ann. occup. Hyg., Vol. 48, No. 3, pp. 277-283, 2004
© 2004 British Occupational Hygiene Society
Published by Oxford University Press
Dermal Exposure to Chromium in Electroplating
Kuopio Regional Institute of Occupational Health, PO Box 93, FIN-70701 Kuopio, Finland
Received 3 February 2003; in final form 24 April 2003
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Objectives: The aim of the study was to measure the dermal and respiratory exposure levels of hexavalent chromium during electroplating work. Methods: Potential dermal exposure of the body was measured with patch samples and actual exposure of hands with hand-wash samples. For comparison, personal air samples were also collected. Results: The exposure varied widely between workers. The range of body and hand exposure to the electroplating solution was 0.17–28.1 mg/h and 0.04–6.37 mg/h, respectively. Hands and lower limbs were the most contaminated body parts. Conclusions: The results of breathing zone samples and dermal exposure did not correlate with each other. In manual electroplating processes, dermal exposure was higher than in semi-automatic and automatic processes. The amount of hexavalent chromium the workers were exposed to is probably high enough to cause a risk of skin sensitization.
Keywords: chromium; dermal exposure; electroplating; worker exposure
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Chromium is an important component of stainless steel and it is also widely used in electroplating, cement and concrete work, leather tanning, etc. Chromium plating liquid contains mostly Cr(VI), which causes most of the toxic effects, including cancer (Sorahan et al., 1998; Dayan and Paine, 2001). Chromium is a significant cause of occupational allergic contact dermatitis (ACD). In Finland, during a 7 yr period (1991–97) chromium was found to cause 5.6% of all ACD. The incidence rate in electroplating per 10 000 working years was 3.66 (Kanerva et al., 2000). Direct contact with Cr(VI) compounds also causes dermal irritation, slow-healing ulcers and nasal septum lesions (Miksche and Lewalter, 1997). Other adverse health effects of hexavalent chromium include possible kidney dysfunction, respiratory irritation and bronchitis (Miksche and Lewalter, 1997) and asthma (Bright et al., 1997). Cr(VI) enters readily into cells, where it is reduced to highly reactive Cr(V) and then to Cr(III). The reactive ions bind into intracellular proteins and induce DNA damage (Miksche and Lewalter, 1997). Due to this binding, chromium persists at the site of penetration, forming a reservoir (HostÆnek et al., 1993). Hexavalent chromium is a more potent skin penetrant than the trivalent form (Wahlberg and Skog, 1965; HostÆnek et al., 1993). A complete review of chromium toxicity has been published recently by Dayan and Paine (2001).
There are no occupational hygienic limit values for dermal exposure. Chromium is, however, an important contaminant in consumer products and chromated surfaces may release chromium compounds. For that reason some work has been done in order to estimate safe leaching levels or concentrations (Wass and Wahlberg, 1991; Basketter et al., 1993, 2001). For example, the release of Cr(VI) from chromated products has been tested with synthetic sweat. Simultaneously, sensitized patients have been studied. The release was compared to the positive occlusive test results gained from a clinical study of chromium-sensitized persons. It was therefore proposed that an industry standard to minimize the risk of chromate allergy would be 0.3 µg/cm2 (Wass and Wahlberg, 1991). An ECETOC task force recommended 5 p.p.m. as an acceptable contamination level of nickel, cobalt and chromium for consumer products (Basketter et al., 1993). Later, this threshold value was tested and found appropriate in a volunteer study (Basketter et al., 2001).
It has been noticed in a study in The Netherlands that the results of air samples and urinary chromium do not consistently correlate with each other, but observed hygienic behaviour was detected to have a significant impact. As only a small proportion of chromium absorbs through the gastrointestinal tract, it is probable that dermal uptake via at least injured skin may be a relevant route of exposure (Lumens et al., 1993). Kiilunen et al. (1997) have also found a low correlation between nickel in urine and air samples collected from nickel plating workers. The results therefore indicated other routes of exposure, such as ingestion. In the study, a correlation was not found between urinary nickel and workplaces ranked as ‘dirty’ or ‘clean’ in a walk-through survey (Kiilunen et al., 1997). It seems that personal hygienic behaviour might be a more important factor than overall cleanliness.
In order to assess occupational exposure to chromic acid, dermal and respiratory exposure to chromium were measured. Processes and tasks were observed and the working conditions documented with a structured questionnaire (Hebisch and Auffarth, 2001; RISKOFDERM, 2001, 2002). New measurement methods and valid models are needed for dermal exposure assessment. An EU-funded Risk Assessment for Occupational Dermal Exposure to Chemicals (RISKOFDERM, QLK4-CT-1999-01107) project will provide new information about the subject (van Hemmen, 1997; Marquart et al., 2001). The survey reported in this article is one of the sub-studies enhancing the knowledge about the features of occupational dermal exposure. An introductory article describing the project in detail is published in this issue.
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MATERIALS AND METHODS |
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Description of workplaces and work practices
The study was conducted in six electroplating (nickel and chromium plating, hard chromating) shops. The number of workers varied between 3 and 1300. The total number of workers participating the study was 16 and the number of measurements was 29. Consequently, the exposure of most of the workers was measured twice. All workers were skilled male employees or entrepreneurs. The average sampling time was 267 min, and it varied between 81 and 483 min. The study protocol was approved by the Ethical Committee of the Finnish Institute of Occupational Health and the workers participating in the study gave their informed consent.
Five of the factories plated small furniture parts, tools, etc., attached to hangers or put into drums. The baths in these factories were relatively small, the average size being 4 m3. The hard chromating factory handled large cylinders for paper-making machines. The average volume of the baths was 10 m3. The baths contain washing and degreasing solutions, nickel plating solution and chromating solution containing CrO3. In 22 cases, the process was categorized as manual or semi-automatic, which means that the workers carried the hangers or drums manually or with the assistance of jigs to the baths. In seven cases, a pre-programmed, automatic process was studied. In all cases, workers also hung the pieces or drums to be plated and took them off after drying. Sometimes the pieces were rinsed with running water. A typical semi-automatic plating works is shown in Fig. 1.
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A structured questionnaire was developed in the RISKOFDERM project (Hebisch and Auffarth, 2001; RISKOFDERM, 2001, 2002). This questionnaire was also used to gather information during the occupational hygienic measurements. Trained occupational hygienists interviewed and observed the workers during the measurements and filled out the questionnaire forms.
In one of the factories, there was no ventilation at all, except a hole in the wall. In one place, there was only general ventilation. In the rest of the workplaces (four companies), local ventilation systems existed, but they were classified in the questionnaire as inadequate. When the direction of the airflow was checked with a smoke tube, it was found that either there was no airflow at all, or it had no specific direction.
Eight electroplaters wore overalls and eight had long trousers and a jacket or a T-shirt. Four workers wore a cap. Half of the workers changed their work clothes once a week, the other half less often. Eleven workers wore rubber boots and five had safety shoes. Gloves were usually worn (in 27 measurements), but in 13 cases only part time. One worker did not wear gloves at all. In five cases the only gloves used were cotton liners. Twelve workers wore PVC gloves and 10 used cotton gloves impregnated with rubber. Only one worker complained about dryness of hands, which he related to his work.
Sampling
Potential dermal exposure of the body was studied with a modified patch method described in the OECD sampling protocol for pesticide sampling (OECD, 1997). The method measures the mass of contaminants on the outer clothing contaminant layer (Schneider et al., 1999). Ten 
-cellulose patches (Schleicher & Shüll, technical filter paper 0860, 74 g/m2) were attached to chest, back, left and right forearm, left and right upper arm, left and right upper leg, and left and right lower leg to sample potential dermal exposure. The size of each of the patches was 100 cm2. No patches were attached to the head of the worker, but the potential exposure was taken into account in the measurements of the torso area. Actual exposure and the transfer through the protective clothing were assessed with one patch attached to the chest under the work clothing (measuring contamination of inner clothing and the proportion reaching the skin). To prevent possible contamination of the inner side of the patches due to dirty clothes, all 11 were taped onto a piece of polyethylene (PE) plastic, which was then attached to clothes with safety pins. After the sampling, the patches were removed hygienically from the clothes of the worker, detached from the plastic background and folded carefully. The patches were transferred to PE bags (Minigrip®) for transport and storage.
Hand exposure was studied by hand washing. The washing was done according to the procedure described in EN 1499 to equalize the washing efficiency as much as possible (CEN, 1997). Washing solution was poured onto workers’ hands held over a beaker for 30 s, and during that time the worker rubbed his/her hands in a specific way described in the standard. Deionized water (200 ml) containing 1.0 ml/l hypoallergenic liquid soap was used for hand-wash sampling. The beaker was rinsed with 2 x 25 ml of unused washing solution. The solutions were combined and poured into PE bottles for transportation and storage.
Inhalable aerosols were collected simultaneously with dermal exposure measurements on Millipore® cellulose-acetate filters (0.8 µm) with IOM® samplers attached to portable, pre-calibrated SKC 224® pumps (SKC Inc., Eighty Four, PA) at a flow rate of 2.0 l/min.
Analysis
The patch samples were burned to ash in porcelain pots at 500°C overnight or for at least 6 h. The samples were digested with nitric acid (65%, 2.5 ml, Merck 411 Suprapur®) and hydrochloric acid (30%, 2.5 ml, Merck 318 Suprapur®), and dried on a warming plate. The residues were dissolved with 2 x 5 ml of acid solution containing 5.5% HNO3 and 2.1% HCl. The solutions were filtered through Macherey-Nagel 640m filter paper® to 25 ml volumetric flasks and filled with the acid solution.
Hand-wash samples were transferred into 250 ml glass beakers in the laboratory. Acid solution containing 5 ml of 65% HNO3 and 5 ml of 30% HCl was added. PE bottles were rinsed with the acid solution and 5 ml of deionized water, which were combined with the samples. The samples were evaporated to dryness in a water bath. The residues were diluted and the solutions filtered in the same way as the patch samples.
The limit of detection (LOD) and the limit of quantification (LOQ) were determined on the basis of five blank samples at average blank signal plus three and ten times the standard deviation, respectively. For patch samples the LOD was 2.32 µg and LOQ 7.72 µg. For hand-wash samples the LOD was 4.02 µg and LOQ 13.4 µg.
The concentration of inhalable aerosols was measured gravimetrically. Afterwards, the filters were transferred into Teflon jars with tweezers for metal analysis. HNO3 (1.5 ml), HCl (1.5 ml) and ultrapure water (5 ml) were added to filters, which were then digested in a microwave oven. Cooled liquid was transferred into a volumetric flask (25 ml) and filled with ultrapure water.
All chromium samples were analysed with an atomic absorption spectrometer (Perkin Elmer 2100® and later Perkin Elmer AAnalyst 800®) using the flame technique. Total chromium was analysed, as it was assumed that all chromium present in plating liquid is in hexavalent form. The random error of the analysis method was estimated to be 2.0% and the systematic error calculated from external quality control samples was 6.9%. All laboratory equipment and containers were tested for any metal residues and pre-washed with nitric acid. External standards (1–3 mg/l), control samples (ICP Multi Element Standard 15474®, Merck), and field and laboratory blanks were analysed as the other samples. Standard curves were linear between LOQ and 2.0 mg/l. The highest standard concentration was 3.0 mg/l, which was corrected by the equipment’s programme. Samples with higher concentrations were diluted to concentrations within the linear area.
SAS v. 8.02 (SAS Institute, Cary, NC) and SPSS-PC v. 10.0.7 (SPSS, Inc., Chigago, IL) statistical softwares were used to analyse the results.
Quality assurance
The laboratory of the Occupational Hygiene and Toxicology section of the Kuopio Regional Institute of Occupational Health is accredited by the Finnish Centre for Metrology and Accreditation according to the standard SFS-ISO/IEC 17025. The fields of testing consist, for example, of sampling and analysis of inhalable dust and airborne metals.
The recovery of the patch method was tested with four different concentrations (4–7 parallel samples). The average recovery was 70%. The within-day repeatability varied from 7.9 to 1.7% depending on the concentration.
The recovery of the hand-wash method was tested in the laboratory by spiking the washing liquid with four different chromium concentrations (n = 4–7) and by spiking the hands of three volunteers (three samples/volunteer, total n = 9). The recovery was over 100% in all cases, and therefore 100% was used in further calculations. The within-day repeatability was between 1.2 and 0.8% when the washing solution was spiked, and 3.2% when the hands were spiked. The stability of spiked (200 µg) hand-wash samples was tested for one month. For that time the recovery was 113% (n = 4).
The efficiency of the hand-wash method was also tested in the field by repeated washings and tape stripping samples (modified from the procedure described by Surakka et al., 1999). Fixomull tape®, cut into 2.5 x 4 cm pieces, was used to sample residues from the right palm. Stripping was repeated twice and the tape pieces were combined. On average, 83% of chromium was found from the first washing (72–93%). All the results of the tape-stripping samples were under the limit of detection (<7 µg). Due to these results, it was decided to use only one washing.
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RESULTS |
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Dermal exposure
Dermal exposure of electroplaters to hexavalent chromium solution varied widely between workers, as can be seen from the standard deviations and ranges presented in Table 1 and in Fig. 2. The results in Table 1 have been calculated from the concentrations found in patches or hand-washing solutions. The area of the body part in question has been taken into account in addition to sampling time, chromium concentration of the solution used, and the sampling and analytical recoveries. ‘Analyte’ refers to the chromium concentration measured, whereas ‘formulation’ is the total amount of the electroplating liquid handled. With the results of analyte measurements, it is possible to estimate the chromium exposure as such. When the amount of formulation is calculated, the results can be used in a more universal way to assess exposure to liquids in this type of task in general. US EPA Exposure Factors Handbook body region areas were used in calculations (US EPA, 1997). The total area of the body (excluding hands) was 18 720 cm2. In all calculations, values below LOQ are presented as a half of LOQ and values below LOD (not detected) as a half of LOD. Hands and right lower limbs were the most contaminated body parts, when expressed as mass per square centimetres (Fig. 2).
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Spatial and temporal variation of exposure, e.g. within- and between-worker variances, were estimated with analysis-of-variance (ANOVA) from log-transformed exposure values. The procedure has been described in detail by, for example, Kromhout et al. (1993). The total variances of body and hand exposure (TS2y) was 1.83 and 1.67, respectively. Between-worker exposure dominated in both cases. The proportion of between-worker component of variance (BS2y) was 76% for body exposure and 64% for hand exposure (P < 0.01).
The electroplating processes varied from each other in different companies and sometimes also within a shop. Most tasks were considered semi-automatic, which means that the workers moved the hangers, etc., with help of jigs. In manual processes, the pieces to be plated had to be lifted manually from one bath to another. Automatic processes followed a pre-programmed procedure and the workers mainly supervised the process and fixed the positions of the hangers when needed. The effect of the level of automation was studied by comparing the medians of dermal exposure levels. The sample size was small; there were six results from manual processes, 16 from semi-automatic processes and seven from automatic processes. The exposure was highest in the manual processes (median exposure, body and hands 13.6 mg/h). Semi-automatic processes exposed the workers least (2.2 mg/h). Automatic processes were placed in between (4.9 mg/h). The differences were significant according to the Kruskall–Wallis test (P = 0.034).
The actual hand exposure was, on average, highest for workers using PVC gloves (1.3 mg/h). Cotton gloves and rubber-coated cotton gloves provided approximately the same protection, the mean concentrations measured were 0.7 and 0.5 mg/h, respectively. These differences were not statistically significant.
Residues of chromium in the inner patch were found only from three workers. The highest measured actual exposure was 0.5 µg/cm2.
Respiratory exposure
The results of the breathing zone measurements have been presented in Table 2. The Finnish occupational exposure limits for inorganic dust and chromium(VI) compounds are 10 and 0.05 mg/m3, respectively. No significant correlation was found between respiratory exposure and dermal exposure.
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DISCUSSION |
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Patch sampling can be reliably used in situations where the contaminants distribute uniformly on skin and clothes (Fenske, 1993). During electroplating, the exposure is partly due to generation of metal containing aerosol, which may be assumed to distribute evenly at least to the upper body. Enhancing the ventilation or putting lids on the baths could reduce both dermal and respiratory exposure. In addition, high exposures may be due to splashes, touching of contaminated surfaces (edges of pools, hangers, etc.) and immersion of hands in the plating solution. It was also found that the breathing zone measurements do not predict the dermal exposure.
There was large variability in the dataset, especially between workers. Estimation of within-worker variability is, however, limited, as at most only two repetitive samples were taken. Personal working habits and/or the conditions at the workplaces seem to affect the exposure and cause differences.
The level of automation did not unambiguously affect the exposure. The simplest explanation is that the automatic processes, often considered as less exposing for the workers, seemed to have more problems and interruptions which had to be solved at the baths touching the contaminated surfaces, also unintentionally with other parts of the body than hands. The dataset was also quite small, so this finding remains only a preliminary one.
Some gloves were not impermeable (cotton, cotton and rubber) and it was possible that those gloves could increase the exposure when they got wet. It could be observed that when the workers had impermeable gloves, they were more careless in touching wet surfaces and the solution itself. In most workplaces, smoking was allowed during work, and then the gloves were always taken off. The material of the protective gloves did not, however, affect positively the level of actual hand exposure, possibly due to the unhygienic habits mentioned. The impermeable gloves were also changed less often than lighter gloves, which were changed daily or even several times per day.
If the cotton glove method had been used in sampling for potential exposure as described in the OECD protocol (OECD, 1997), it would have vastly overestimated the exposure due to constant saturation in the plating liquid. Soaked gloves would also have to be changed immediately to new ones, which technically would have been extremely difficult. For this reason, the hand-wash method, even though measuring actual instead of potential exposure, had to be used.
In the study of the chromium-sensitized patients, a ‘threshold value’ for safe exposure of 0.3 µg/cm2 was proposed (Wass and Wahlberg, 1991). When the results of that study are compared with the measured hand exposures of this study (average actual exposure 4 µg/cm2/h), it might be concluded that a sensitization risk exists if the contaminated surfaces are touched with bare hands. The patch measurements done under the protective clothes in this study do not reliably estimate the extent of actual exposure, as the chest is not usually the area of greatest contamination.
Measurements of potential exposure do not give enough information to assess dermal uptake, which would require biological monitoring of the workers. However, with the results of dermal exposure measurements it is possible to evaluate the sites and sources of exposure, the effect of personal behaviour, and to give instructions on personal protective equipment and other exposure reduction techniques (Fenske, 1993). A conceptual model describing the processes of dermal exposure and uptake with consistent terminology has been introduced by Schneider et al. (1999). They point out the fact that most of the current methods used to assess dermal exposure determine the mass of contaminant depositing on the skin (e.g. patch sampling) or remaining on the skin at the end of the exposure period (e.g. hand washing). However, the risk of dermal uptake can only be estimated if the time-dependent concentration is measured on the skin (Schneider et al., 1999). Therefore, it is most important to emphasize that the measurements done in this study do not take into account all important processes associated with the dermal exposure process. The aim of the study was mainly to focus on finding the parameters that determine dermal exposure.
Acknowledgements—The authors wish to thank all the plating shops and their employees for their participation in the study. We are especially grateful to Professor Juhani Kangas, FIOH, Dr Joop van Hemmen, TNO, Dr Bob Rajan, HSE, and Professor Hans Kromhout, University of Utrecht for their constructive comments, Mrs Sirkka Roivainen, laboratory technician, for her skilful assistance in field surveys and analysis of the samples, and Maria Hirvonen, MSc, for the statistical analyses. Study was part of the RISKOFDERM project (Risk Assessment for Occupational Dermal Exposure to Chemicals, QLK4-1999-01107). We want to thank the European Commission and the Finnish Work Environment Fund for financial support.
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FOOTNOTES |
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* Author to whom correspondence should be addressed. E-mail: milja.makinen@ttl.fi
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