Pre-treatment effects of trichloroethylene on the dermal absorption of the biocide, triazine
Introduction
Chlorinated solvents and degreasers, such as trichloroethylene (TCE) are frequently used in the metalworking operations to remove cutting oils from the metal surface and there is anecdotal evidence that occupational irritant contact dermatitis (OICD) may be linked to solvent–oil interactions in skin (Goh and Gan, 1994, Zissu, 2002). In addition to being a known carcinogen, TCE has been shown to cause irritant reactions in skin, epidermal necrosis, and more recently, cytotoxicty associated with oxidative stress (Phoon et al., 1984, Zhu et al., 2005). Industrial solvents can potentially compromise the skin barrier by removing lipids from the stratum corneum during the degreasing process, and thereby facilitate penetration of irritants that are components of a cutting fluid formulation. In spite of TCE's multitude of industrial uses and its highly effective fat-solvent properties, the effects of simultaneous TCE exposure or chronic TCE exposure on dermal absorption has not been reported in the literature.
In some metal-machining operations where TCE and related halogenated organic solvents are still being used to wash metal parts once they have been cut or fabricated, it is very likely for the workers’ skin to be exposed to this solvent with simultaneous and/or sequential exposure to cutting fluid components included in many cutting oil and cutting fluid industrial formulations. Although, this degreasing activity can remove cutting fluids from the skin surface, cutting fluid and/or contaminant absorption may be significantly greater in this scenario compared to another scenario when the worker is not involved in degreasing of fabricated metals. There have been numerous reports of solvent effects on skin permeability although the mechanisms have not been investigated (Sherertz et al., 1987, Rosado et al., 2003).
Cutting fluid may be formulated with many performance additives, such as lubricants, emulsifiers, anti-corrosive agents, biocides, and many other chemicals in either a soluble oil or synthetic fluid formulation (Childers, 1994). Many of the formulation additives are known to cause adverse skin and systemic effects. (Al-Humadi et al., 2000), and a more recent epidemiological study suggests that human carcinogenicity is still a major concern amongst workers using aqueous cutting fluids (Mirer, 2003). Cutting fluids can also become contaminated with nitrosamines and metals that can result in dermatitis and systemic effects. In this study, triazine was selected as an absorption marker as it represents one of the many cutting fluid biocides/preservatives that is usually formulated to provide 2% active ingredient in commercial cutting fluids. Not only does triazine cause OCID, rodent studies have demonstrated developmental and maternal toxicity following oral exposure (US EPA, 1997). Furthermore, we recently reported that triazine is more readily absorbed across the skin than most of the other cutting fluid additives (Baynes et al., 2003).
The primary objective of this study was to determine the effect of simultaneous exposure of skin to TCE and cutting fluid components, as well as TCE-pretreated skin on triazine absorption across in vitro porcine skin. It is very likely that TCE can behave as a vehicle or co-solvent in the dermal penetration enhancement of cutting fluid additives, such as triazine. The dermal absorption of TCE in rodents and humans has been widely reported in the literature (Morgan et al., 1991, Bogen et al., 1992, Weisel and Jo, 1996, Poet et al., 2000), and this study allows for simultaneous observation of TCE absorption in the presence of these cutting fluid additives. Porcine skin was used to model human skin as it is anatomically and biochemically similar to human skin (Monteiro-Riviere, 1991).
Section snippets
Reagents and chemicals
The radiolabeled marker component, triazine, more specifically named 1,3,5-triethyl hexahydro-S-triazine [methylene-14C] (specific activity = 10 mCi/mmol, purity = 98.6%) was obtained from American Radiolabeled Chemicals, Inc., St. Louis, MO, USA. Trichloroethylene, TCE, minimum +98.5% A.C.S. reagent grade, was obtained from Aldrich Chemical Company, Milwaukee, WI, USA. Polyethylene glycol (PEG), average MW 200, was obtained from Acros Organics, NJ, USA. Mineral oil, (MO), light white oil, was
Triazine permeability and absorption
The mineral oil (MO)-based cutting fluid resulted in greater permeability in comparison to the polyethylene glycol-200 (PEG) base (Table 2). The 96-h TCE pre-treatment of skin significantly (p < 0.05) enhanced triazine permeability (1.3–1.6-fold) when skin was dosed with (1) only the mineral oil or PEG-based mixtures, and (2) cutting fluids containing NDELA and nickel contaminants. TCE enhancement of triazine permeability in pre-treated skin was slightly greater with PEG than with mineral
Discussion
This study demonstrated that repeated topical exposure to TCE can influence the dermal disposition of the polar biocide, triazine. These observations were with few exceptions reproducible in either mineral oil-based or PEG-based cutting fluid mixtures. These findings are not entirely surprising, as solvents are known to impair skin barrier function by modifying epidermal lipid composition and structure, and thus modulate chemical absorption (Abrams et al., 1993, Tsai et al., 2001). The latter
Acknowledgements
The authors thank the technical staff of CCTRP at NCSU for conducting the perfusion studies and chemical analysis. This research was supported by NIOSH grant R01-OH-03669.
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