Effects of soil on percutaneous absorption of toluene in male rats

Dermal absorption of environmental contaminants from soil and sediment: a critical review

Risk assessment of hazardous wastes sites may require characterization of the dermal availability of chemical contaminants in soil and/or sediment. Current U.S. Environmental Protection Agency guidance for assessment of dermal exposures to contaminants in water and soil was finalized in 2004 as a supplement (Part E) to the Risk Assessment Guidance for Superfund (RAGS). The soil protocol presented in RAGS Part E is less sophisticated than the water protocol and is supported by less empirical data. Investigations of dermal absorption of soil and sediment-borne contaminants that have been conducted to date include in vitro and in vivo experiments using both human and surrogate skin. A review of that literature was conducted with attention to relevant criteria including consideration of layering effects, degree of chemical saturation of soil, appropriateness of particle size distribution employed, soil-chemical contact time, and continuity of soil-skin contact (in in vivo studies). Most studies published to date are deficient by virtue of execution or reporting on one or more of the selected criteria. In addition the lack of methodological standardization evident in the literature hinders systematic evaluation of results. Since additional experimental work is needed, general agreement on acceptable approaches would be useful. Recommendations for good practice are presented.

Exhalation behavior of four organic substrates and water absorbed by human skin

The simultaneous measurement of several volatile organic compounds and water released from the human skin can be achieved successfully by using a modified gas chromatographic system. After the thumb of each subject was dipped in aqueous solution containing acetone, diethyl ether, ethanol, and toluene, it was dried in the air. Then the thumb attached to the sampling probe for measuring the released gases. It is found that 90% of all these chemical substrates were desorbed after 20 min. The initial exhalation rate factor for each chemical substrate was determined in every subject. Correlation factors of the linear relationships between the initial exhalation rate for hydrophilic substrates (acetone and ethanol) and the total amount of water (TAW) released from the skin were 0.94 and 0.92, respectively. However, the rate of hydrophobic toluene was not dependent on the TAW. Therefore, the exhalation rate of substrates is greatly influenced by both their hydrophilicity and TAW. Additionally, an interesting personal specific character among the 6 subjects was observed on plotting the exhalation rate of organic substrates and water during the elapsed time. With the released water mostly due to insensible perspiration, the exhalation rate of all simultaneous organic substrates decreased monotonically over the elapsed time. On the contrary, when subjects sweated emotionally, the exhalation rate of organic substrates showed some variation, namely a higher of exhalation rate compared to the case of mostly due to insensible perspiration. Therefore, emotionally-induced sweating can enhance the release of organic substrates.

A comparative study of the kinetics and bioavailability of pure and soil-adsorbed naphthalene in dermally exposed male rats

The aim of this study was to utilize pharmacokinetic techniques to assess the bioavailability of sandy or clay soil-adsorbed naphthalene vs chemical alone following dermal treatment of male rats. Animals were exposed to 43 micrograms total of 14C-naphthalene (pure or adsorbed to one of two soils) introduced into a shallow glass cap covering a 13-cm2 area on the skin of each rat. While both soils delayed the time to reach maximum plasma concentration of radioactivity and significantly increased the half-life of plasma absorption, only sandy soil significantly decreased the peak plasma concentration of radioactivity versus the pure compound. Within 12 h after dermal application, approximately 50% of the naphthalene dose was excreted in the urine of the pure and clay soil-adsorbed groups. However, when naphthalene was adsorbed to sandy soil, the percentages of the initial dose excreted in the urine collected between 0-12 h and 12-24 h were nearly equal (33-39%). Furthermore, sandy soil adsorption shifted the secondary excretion route from expired air to feces and significantly lowered the amount of radioactivity in expired air relative to naphthalene alone. In the presence of sandy soil, a significantly larger amount of radioactivity washed off of the skin application sites. In all groups the predominant urinary metabolites determined by high performance liquid chromatography were 2,7- and 1,2-dihydroxynaphthalenes.

Soil adsorption alters kinetics and bioavailability of trichloroethylene in orally exposed female rats

Soil contamination with dangerous toxic chemicals remains one of the most difficult problems in this era. Bioavailability of a chemical absorbed through gastrointestinal tract exposure from contaminated soil may differ from that seen following exposure to the pure chemical. In this study 4.6 microCi of 14C-TCE (trichloroethylene) alone, or adsorbed to clay or sandy soil, was administered to female Sprague-Dawley rats. Maximum plasma levels of radioactivity were highest in the presence of clay soil. However, they were similar for TCE alone and sandy-soil-adsorbed chemical. The half-life (t1/2) of absorption was statistically longer and the half-life of elimination was statistically shorter in the presence of sandy soil compared with TCE alone. There were no differences in the area under the plasma concentration-time curves between groups. Liver and kidney exhibited the highest tissue concentrations of radioactivity in all groups. Urine was the primary route of excretion followed by expired air in the pure- and clay-soil-adsorbed groups. However, equal amounts of the dose were excreted in both urine and expired air of the sandy-soil-adsorbed group with a significant increase of radioactivity in expired air throughout the 72-h study period. Trichloroethanol was the major urinary metabolite of TCE.