Dermal exposure measurement of the epoxy DGEBA (diglycidylether of bisphenol A)
R. Lindahl*, M. Réhn
National Institute for Working Life, Umeå, Sweden
Epoxy resins are used in very different applications mainly in coatings but also as adhesive, composite, tooling, casting and flooring applications. The most used epoxy resins are diglycidyl ethers of bisphenol A (DGEBA), produced by reacting bisphenol A with epichlorohydrin. The mean molecular weight depends on the ratio of epichlorohydrin to bisphenol A and the general structure is seen in Figure 1.
Figure 1. The general structure of DGEBA resins after production with an excess of bisphenol A. n ³ 0.
Epoxy compounds are known allergens and DGEBA exposure may cause allergic contact dermatitis. The DGEBA with the lowest molecular weight (MW 340) is considered as the main sensitiser. Molecules with higher MW have less sensitising capacity and oligomers with MW above 900 are considered not to induce sensitivity.
For the direct measurement of dermal exposure several different techniques have been used. Methods to remove chemicals deposited or transferred to the skin are hand wash, skin wipes or tape stripping. The tape stripping is performed by removal of stratum corneum cell layers by application of an adhesive tape to the skin after exposure Tapes with an area between 4 and 10 cm2 have often been used. The tape stripping can be used to study not only chemical exposure but also physical and structural properties of stratum corneum. The method may also be used to study penetration of the stratum corneum, were repeated stripping give information from several layers.
Other methods are surrogate skin techniques as patch sampling and whole body sampling. In patch sampling, the patches are located on the skin or on the clothing during exposure. The patches measure the amount deposited directly on the skin or clothing or penetrating outer clothing layers. These methods are intended to collect all substance deposited on them during an exposure period. Various media as cotton, cellulose, polypropylene or glass fibre filters as well as cloths with charcoal have been used for patch sampling methods described. The patches are often about 10 cm2.
In this study we have tested tape stripping and patch sampling for the determination of dermal exposure to DGEBA. The methods were tested in the laboratory and in different occupational settings.
Materials and methods
Sampling
The adhesive used for both tape stripping and patch sampling was Fixomull® (Beiersdorf AG, Germany). The Fixomull® is a self-adhesive gauze with woven polyester backing and a polyacrylate adhesive. The adhesive was cut to size 3 x 3 cm except for measurements on fingers were 2 x 2 cm was used. For the tape stripping measurements the adhesive was applied at the end of a work shift. After one minute, the adhesive was peeled off from the skin using a clean forceps. The adhesive was removed in a 30-45° angle. The forceps was washed in DMF (dimethylformamide) between each stripping. The adhesive was immediately put into a 3.5 mL glass vial containing 3 mL of DMF to stop curing and other reactions with DGEBA. For the patch sampling, the Fixomull® was applied before and removed after the work shift using the same procedure as with tape stripping.
Sample Analysis
For the analysis HPLC with fluorescence detection was used. The column used was a Waters Spherisorb 5µ ODS2, 4.6 x 150 mm. The flow-rate was 0.9 mL/min and the mobile phase was acetonitrile/water (70/30). The injection volume was 10 µL. The wavelengths for excitation and emmitation were 242 nm and 340 nm respectively. For the recovery test and test on using DMF to stop the curing process a UV-detector was used at 210 nm.
Laboratory tests
For the recovery test, 1 µg of DGEBA in 10µL DMF was added to 3 x 3 cm Fixomull®. After 10 min 3 mL of DMF was added. For the tests to stop the epoxy reaction with the hardener 0.25 g of Gilbatherm EP Casting Compound 5010 containing 33% DGEBA (MW 340) and 0.25 g of Gilbatherm EP Hardener 5680 were each dissolved in 50 ml DMF. The two solutions were mixed and analysed immediately and also regularly after storage up to six days.
Results and discussion
By putting the Fixomull® adhesive in DMF (dimethyl formamide) immediately after sampling the epoxy is dissolved and the hardening reaction stopped. The samples were stable after storage for six days in room temperature, and recovery was >97%.
The blank levels of the method were determined with tape stripping on six different positions on two persons at the laboratory. Blank levels were also determined during field sampling with tape stripping on a Monday morning prior to DGEBA exposure on two persons at two different days (N = 8). The amounts of DGEBA were less than 0.3 ng/cm2 for all samples.
The methods have been tested in three companies. In the first two there were only direct contact contamination and no air transport of DGEBA. The work tasks were application of seamless floors and liquid shim application. In the third company the main exposure occurred after air transportation of DGEBA in aerosols produced during spray painting. Parallel tape stripping and patch sampling measurement of the dermal exposure was compared on persons working with the application of seamless floors. The sampling was performed on inside and outside of the wrist, in the palm and on the back of the hand. Leather gloves were used during the work. The amounts varied between 3 and 600 ng/cm2 and the highest values were found on the inside of the wrist and in the palm. The comparison of the two methods showed about three times the amounts for the patch sampling compared to tape stripping, probably due to a too thin stripping layer compared to the permeation rate and sampling time.
Recovery of the stripping method is tested with repeated tape stripping on the same area of the skin. This gives information on thickness of the stripped layer in combination with the amount of the contaminant in the stripped epidermis layers, i.e. information on the permeation rate. Repeated stripping was performed on a person working with application of seamless floors. DGEBA was determined not only in the two first strippings but also in the third stripping (13%) and less than half (48%) of the total amount was found with the first stripping. Although the tape stripping method gives an underestimation of the total exposed amounts of DGEBA it may be used when a relative amount of the exposure is sufficient for the purpose of the measurement, i.e. for a comparison of protective equipment.
The effects of different work routines for dermal exposure were tested on two persons working with liquid shim application using an epoxy adhesive containing DGEBA. Both persons were performing the same work at the same time and were using the same brand of protective gloves. There was no occurrence of DGEBA in the air. One of the persons (A) were considered to work with care and respect for the potential risks. The other person (B) was unhygienic and did not work in a careful way although the health care personnel had informed about the risks. The dermal exposure measurement of DGEBA with patch sampling in palm showed about thirty times higher for worker B (up to1140 ng/cm2) than for worker A (below 30 ng/cm2). This illustrates the importance of good working procedures to reduce the risk of exposure and how the measurement method can be used to motivate to careful work and good hygiene.
Dermal exposure of DGEBA during spray painting was measured on neck, wrists and hands. The person performing the spray painting used leather or disposable gloves. No inhaled exposure occurred as all persons were wearing air supplied breathing equipment. The highest measured amount 670 ng/cm2 was found on the wrist. This exposure was probably due to permeation thru the gloves and/or a contamination during the procedure to take on and off the gloves. Exposure from aerosol deposition on unprotected skin on the neck was also determined, with levels up to 330 ng/cm2.
Conclusions
Both tested methods, tape stripping and patch sampling, are sensitive enough and can be used for dermal exposure measurement of epoxy compounds as DGEBA. The methods can be used in different work tasks and with different exposure situations. An advantage of the tape stripping method is that there is no disturbance to the worker during the work. The patch sampling method gives a better estimate of the exposure. Both methods can be used to evaluate work procedures and/or personal protective equipment.
Content last modified: 24 May 2005
