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

Abstract

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.

Urinary naphthols as an indicator of exposure to naphthalene

“…Our results show that most naphthalene is metabolized to 1-and 2-naphthol and 1,4-naphthoquinone (figure 2). Small amounts of 1-naphthol and 2-naphthol are excreted in the urine after the dermal application of naphthalene (4). In an earlier study it has been shown that there is a good statistical correlation between 1-naphthol excretion and naphthalene exposure in the concelltration range of 0.2-6 mg/m3.…”

A review of the current state of the art of physiologically-based tests for measuring human dermal in vitro bioavailability of polycyclic aromatic hydrocarbons (PAH) in soil

“…Unlike the Turkall et al(1994) and Kadry (1995) studies, the sandy soil with higher organic matter had higher dermal bioavailability. This is probably due to the autoclaving step used in soil preparation which may have broken down the organic matter in the soil.…”

“…Metabolites of hydroxylated PAH (pyrene, phenanthrene, naphthalene and fluorene) have been analysed by Turkall et al (1994); Elovaara et al, (2006);McClean et al,, (2012); Serdar et al, (2012);and, Choosong et al, 2014). Pliel et al (2000) quantified exposure of marker compounds (e.g.…”

“…The in vivo animal studies which relate specifically to PAH dermal bioavailability from soils have used monkeys, rats and guinea pigs (Yang et al, 1989;Wester et al, 1990;Turkall et al, 1994;Kadry et al, 1995;Moody et al, 1995;Roy et al, 1998a). These tests take the general form of applying the test chemical to a designated area of skin in an appropriate vehicle (for the purposes of this review this is soil).…”

“…Again, it is unclear if the dermal bioavailability includes the amount of BaP in the skin as well as in the receptor fluid. Turkall et al, (1994) and Kadry (1995). The same soils (a sandy soil: 90% sand, 2% clay, 4.4% organic matter; a clay soil: 50% sand, 22% clay, 1.6% organic matter) were autoclaved and deionised water added to achieve a moisture content of 11%.…”