Solvent Warning

Soak Your Hand
Soak Your Head

Photo 1: Women in an auto assembly smooth sealer on a car body. Materials should be carefully screened and proper gloves should be used to prevent skin absorption of solvents.

A recent paper clarifies the importance of skin absorption of common solvents to evaluation of total exposure. The dermal absorption of 1,1,1-trichloroethane (methyl chloroform), trichloroethylene, tetrachloroethylene (perchloroethylene), toluene and xylene was studied in groups of volunteers. The solvents were applied for 3 minutes on the forearm over an area of 27 cm2 (approximately a square that is 2 inches by 2 inches). An inhalation exposure with a known input rate served as a reference exposure. Concentration of solvent in exhaled air was measured. Permeation rates were calculated from exhaled air time courses.

Permeation time courses showed fast and slow patterns. Fast permeation was seen in three of six subjects for trichloroethylene, 1,1,1-trichloroethane and toluene. Slower permeation was seen for the other three subjects with these solvents, and for all subjects exposed to perchloroethylene and xylene. The maximum permeation rate occurred 15-25 minutes after exposure (see Figure 1).

Skin irritation was reported by many subjects, varying from tingling to pain, for exposure to toluene and 1,1,1-trichloroethylene. Reddening of the skin was associated with these complaints. Skin irritation was observed in all subjects with fast permeation.

Rates of permeation of the skin were calculated for each solvent. The investigators then calculated the airborne exposure equivalent to exposing 360 cm2 of skin – equivalent to stretched palm and fingers— for 3 minutes, repeated eight times during a working day.

What Local Unions Should Do
There are a number of practical lessons from this study. MSDS sheets and work practice, must be carefully screened. The women pictured in photo 1: is using a sealer that contains VM & P Naptha (Case #8034-32-4). VM & P Naptha contains 12% alkyl benzene, a chemical family that includes toluene and xylene. Gloves that are chemically resistant to these chemicals must be provided. Workers need to be trained on hazard recognition. Alternative application procedures should be investigated. Chemical suppliers should be contacted to determine the specific chemicals contained in the materials used. Any reports from workers of dermatitis caused by using this chemical should be recorded in the injury/illness log.

1S Kezic;A C Monster;I A van de Gevel;J Kruse;et al; “Dermal absorption of neat liquid solvents on brief exposures in volunteers,” AIHAJ; 62: 12-18(2001)

UAW Commentary

This paper demonstrates that substantial amounts of solvent soaks through the skin into the blood, even for solvents with no “skin” notation. Once absorbed, the solvent circulates to all the organs of the body. The majority of the skin absorption was found to happen after the skin contact had ended, because the solvent soaks into the outer layer of the skin and is absorbed from there. Absorption rates are highly variable between individuals, as much as four-fold within this small group of volunteers. This variability suggests that the permeation rates calculated in the paper understate the average permeation rates in the general population, and that the differences in permeation rates between solvents may be an artifact of the small sample size. The health significance of these findings depends on whether the exposure limits in the table are protective. In general, worker exposures of 10-50 ppm, the range observed in this study, will produce significant complaints of symptoms of solvent exposure.

The National Toxicology Program has designated trichloroethylene and perchloroethylene as “reasonably anticipated to cause cancer in humans.” This would suggest that systemic exposures equivalent to those predicted here would have health significance. Commercial xylene contains about 1/3 ethyl benzene. The International Agency for Research Against Cancer (IARC) has designated ethyl benzene “possibly carcinogenic to humans.” 1,1,1,-trichloroethane is on test for carcinogenicity at NTP.

FIGURE 1: Exposure ends after 3 minutes, close to the left axis of the graph. However, solvent which has soaked into the skin continues to enter the bloodstream, circulates to the lungs, and is exhaled. The maximum blood concentration was observed in this subject at 15 minutes, but measurable xylene remained in the blood for nearly two hours.

 

Inhalation Equivalent to Skin Absorption Rate Values in ppm, 8 hour TWA
Solvent	Inhalation Equivalent	OSHA PEL	NIOSH REL	ACGIH TLV
1,1,1-trichloroethane	18	350	350	350
trichloroethylene	60	100	25	50
perchloroethlene	12	100	ca	25
toluene	26	200	100	50
xylene	5	100	100	100
Extrapolated from permeation values in this study to estimate the amount of solvent absorbed through a 360 cm/2 patch of skin (approximately 55 sq. inches, the surface of a hand) exposed for 3 minutes, 8 times per day. Note that trichloroethylene is absorbed at a rate greater than the TLV.

 

 

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