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| NIOSH Home > Safety and Health Topics >Skin Exposures and Effects >Occupational & Environmental Exposures of Skin to Chemicals- 2005> Abstracts |
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An occupational hygiene assessment of dermal nickel exposures in primary production industries
G. W. Hughson Background
Nickel is known to cause allergic contact dermatitis in humans and it is possible that nickel may be absorbed through the skin and contribute to overall systemic dose. The permeation rate of nickel ions through the skin is considered to be low, so the main concern is in relation to dermatitis. There is a lack of dermal exposure data for workers involved in production and use of nickel and nickel compounds. Therefore, dermal exposure information was collected for the EU Existing Substances Risk Assessment of nickel and nickel compounds. The object of this study was therefore to measure the levels of nickel in the skin contaminant layer of nickel refinery workers and to facilitate a comparison with predicted exposure levels given by the EASE model and measured dermal exposure data from the zinc and zinc compound producing industries. Workplace surveys were therefore carried out in two different nickel refineries and a range of tasks were studied. These included workers involved in refinery processes such as leaching and electro-winning, plus packaging of the final products which included nickel cathode squares, nickel powder, nickel briquettes, nickel sulphate hexahydrate and nickel hydroxycarbonate. Methods
Dermal exposure samples were collected using a removal method, whereby commercial moist wipes were swabbed over measured areas of the skin to recover nickel and nickel compounds. The sampling method was validated prior to the workplace surveys by measuring the recovery of known quantities of nickel deposited onto surrogate skin media. In addition, background dermal nickel levels were established by studying a group of non-occupationally exposed subjects. Workplace samples were collected from the hands, forearms, neck, face and chest of workers in two different nickel refineries performing different tasks. In the case of the hands and forearms, three sets of samples were collected from each subject periodically throughout the working shift. The skin surface loading for each sample was obtained and an average of each set of three was calculated. The wipes in each sample were analysed for soluble and insoluble forms of nickel and analysed using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). The quantity of nickel in each sample was used to calculate the dermal surface loading for each anatomical area, expressed in terms of mass per unit area (mg/cm2). The dermal exposure measurements for each anatomical area (hands, arms, neck, face and chest) were compared with each other to identify any associations. Results
Method validation The combined nickel recovery efficiency for the sample preparation and analysis procedure was approximately 95% for insoluble nickel and 87% for soluble nickel compounds. There was good recovery at the lowest spike range of 25 µg, corresponding to a dermal exposure level of about 1 µg/cm2, based on a sample area of 25 cm2. The results of the recovery tests carried out using nickel powder showed that the majority of the nickel powder deposits were removed on application of the first wipe, with small remaining percentages being removed by the second and third wipes. The average recovery efficiency for nickel powder using this test was 92%. The procedure was repeated using a solution of nickel sulphate and this gave an average sample recovery of 97%. Controls The background nickel levels for the hands only were in the range 0.01 – 0.09 µg/cm2, with a median value of 0.03 µg/cm2. The results for the forearms were in the range 0.01 – 0.06 µg/cm2, with a median value of 0.01 µg/cm2. A total of 33 complete sets of dermal exposure measurements were collected from 22 different workers. Of the total 792 dermal exposure measurements, 60 were less than the LOD of 0.02 mg/cm2. The highest actual dermal exposures were recorded for nickel powder packing, where the hands, arms, face and neck all received more surface exposure compared with other tasks.
Workplace exposures A total of 33 complete sets of dermal exposure measurements were collected from 22 different workers. Of the total 792 dermal exposure measurements, 60 were less than the LOD of 0.02 mg/cm2. The highest actual dermal exposures were recorded for nickel powder packing, where the hands, arms, face and neck all received more surface exposure compared with other tasks. There was a high level of within-task and between task variability of soluble/insoluble nickel exposure. The between task variability can be explained by the different types of nickel species being handled in the different tasks. The median ratio of soluble/insoluble nickel for metal powder packing was 0.56. The corresponding value for electro-winning, where more soluble forms of nickel are present, was 2.6. The results of the Pearson correlation tests showed a high level of correlation between the various anatomical areas: hand and forearm exposures (r=0.660), hands and neck (r=0.796), hands and face (0.800), and between the hands and chest (r=0.679). All p values were highly significant, with p=<0.001. All upper body exposure measurements (neck, face and chest) were highly correlated with each other. The highest correlation was for neck and chest (r=0.820), with face and chest next (r=0.812) and then face and neck (r=0.798). Again, these associations were all highly significant (p=<0.001).
Conclusions
Overall, the dermal exposures were low, and certainly much less than predicted values generated by the EASE model. In addition, the dermal nickel levels were much lower than levels measured in the zinc industry. It is concluded that this is largely due to the much higher levels of automation and engineering controls applied to the nickel production processes generally, differences in production processes themselves, differences in physical properties of the substances involved, and specific hygiene measures such as the consistent use of personal protective equipment. Although the exposure levels for the electro-winning area were much less than in the nickel powder packing plant the solubility of the nickel was higher, thereby possibly increasing the potential toxicity since it is the amount of available nickel ions that determine toxicity. This illustrates the importance of considering the physical properties of the nickel species, rather than just the skin exposure to total nickel levels in any health risk assessment. The high level of correlation between dermal exposures to the hands, arms, face, neck and chest suggest that it may be possible to extrapolate exposure levels for the main anatomical areas from a relatively limited number of actual exposure measurements but more research is needed to determine if and how this extrapolation could be done.
Content last modified: 15 May 2005 |
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