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The present study describes the kinetics of tetrahydronaphthalene in male and female rats (five animals per dose per sex) at three dose levels (15, 50, and 150 mg/kg daily). Plasma concentration measurements were performed in the course of a subacute toxicity study of 28 days duration in an enriched study design. Two blood samples per animal were taken at different time points after application at day 1 and 16 (150 mg/kg daily) and at day 3 and 18 (15 and 50 mg/kg daily), respectively. Tetrahydronaphthalene was assayed by gas chromatography-mass spectrometry (GC-MS) after extraction. The data of plasma concentration time were analysed using non-linear mixed effects modelling as implemented in NONMEM. The structural model with the best fit employed one compartment kinetics with instantaneous drug input. Interindividual variability in both k and V was found to be very small [k, 0.201 h(-1), 0.013; V, 16.19 (kg), 1.77; population mean and SE]. No unequivocal evidence of dose dependence could be found. The kinetic parameter with the highest extent of variability was the extent of bioavailability which showed an coefficient of variation (CV) of 96%. Both gender and dose had no influence on the variability. The present approach is concluded to offer more insight into the relationship between dose, concentration and effect and into factors which explain variability in kinetics without additional testing or additional animals. Proposals for a refined sampling schedule are made.

In a recent 2-year inhalation study with F344 rats and B6C3F1 mice conducted as part of the U.S. National Toxicology Program (NTP, 1989), chloroethane (ECl) at an exposure concentration of 15,000 ppm induced a high incidence of endometrial uterine carcinomas only in female mice but not in rats, leading to the conclusion of "clear evidence of carcinogenicity" for the mouse. In order to elucidate whether a genotoxic effect may be a critical factor for the carcinogenicity of ECl in the mouse, we have performed three genotoxicity tests: (1) in vitro HPRT test with CHO cells according to a specially developed gas protocol, (2) in vivo/in vitro UDS with female B6C3F1 mice at an exposure concentration of 25,000 ppm (6 h/day, 3 days), (3) in vivo micronucleus assay with male and female B6C3F1 mice exposed to 25,000 ppm ECl according to the same schedule. In the in vitro HPRT test a mutagenic potential of ECl was detected in the presence as well as in the absence of S9 mix. In contrast, both in vivo test systems failed to detect any indications of genotoxicity of chloroethane at an exposure concentration even higher than that of the NTP study. It is suggested that in vivo the genotoxic potential of ECl is so low that an assumed genotoxic damage is below the detection limit of the test systems used. This leads to the conclusion that genotoxicity may not be a key factor in the induction of the uterine carcinomas in the B6C3F1 mouse.

The local lymph node assay (LLNA) is the assay of choice in European regulatory toxicology. As with other toxicology/sensitisation assays, it has a potential for false results, the anionic surfactant sodium lauryl sulphate (SLS) representing a classic example. In the work reported here, examples of false positives in the LLNA are compared to published "benchmarks" such as SLS. Clear false positives (e.g. oleic acid) are also contrasted with examples where data interpretation is more challenging. As the LLNA will be applicable to >30,000 chemicals under REACH, and in the light of animal welfare considerations to do no more than the absolute minimum of animal testing, results from a single LLNA often represent the only available data on sensitisation. This reinforces the need to ensure data from this assay are interpreted intelligently, using scientific analysis of results and considering the weight of evidence, before decisions are made on which substances should be classified as representing a skin sensitisation hazard. In chemical classes where the LLNA has been shown to be an inappropriate assay other standardised methods (e.g. the Buehler or Magnusson and Kligman guinea pig tests [OECD 406]) should be employed as the first choice assays.

An environmental assessment of hydrotropes was conducted under the Organisation for Economic Co-operation and Development (OECD) Screening Information Data Sets (SIDS) for High Production Volume (HPV) Program via the Global International Council of Chemical Associations (ICCA) Hydrotropes Consortium. The assessment and its conclusions were presented at a meeting of the OECD member countries in Washington, DC in 2005. The SIDS Initial Assessment Report (SIAR) was accepted by the membership. Their conclusion was “The chemicals in this [hydrotropes] category are of low priority for further work because of their low hazard profile.” Hydrotropes are used to solubilize the water-insoluble ingredients of cleaning and personal care products including, for example, powder and liquid laundry detergents, hard-surface cleaners, machine dishwashing rinse aids, hand dishwashing liquids, body washes, shampoos, hair conditioners, and liquid hand and face soaps. Global production equals approximately 46 500 metric tons, a little more than half of which is used in the United States. The 8 chemicals accounted for in the “hydrotropes category” include ammonium, Ca, K, and Na salts that are described by 10 Chemical Abstract Service (CAS) registration numbers. The 8 chemical entities are generally comparable and predictable in their chemical behavior and that measured and/or modeled data for members from one subgroup can be applied to other subgroups and to the hydrotropes category as a whole. The assessment is based on a search for and evaluation of available data on physical–chemical properties, biodegradability, removal by wastewater treatment, and aquatic toxicity. Reliable ecotoxicity and environmental fate data were found for selected members of the category. Partitioning, once released into the environment, and exposure in surface waters were modeled for consumer use and manufacturing scenarios relevant to the United States, Europe, and Australia. The models indicate 99+% of the hydrotropes will partition to water. Furthermore, given the low potential for hydrotropes reaching the terrestrial environment and their lack of persistence or bioaccumulation, the focus of the assessment is on the aquatic environment, specifically the water compartment. Aquatic risks were assessed in each scenario using what is referred to as the PEC/PNEC ratio. The modeled predicted environmental concentration (PEC), accounting for volume released and wastewater treatment, is divided by the predicted no effect concentration (PNEC) derived from the aquatic toxicity tests. The closest a predicted environmental concentration came to the toxicity threshold is 0.125 (or 12.5% of the no effect concentration) and that is for a hypothetical manufacturing facility that produces the entire annual volume of hydrotropes and discharges to a small (10%ile) stream under low flow (7Q10) conditions. PEC/PNEC ratios were considerably smaller for consumer use scenarios. The ratios were 0.0002 for a low flow (7Q10) stream scenario in the United States, 0.026 to 0.089 for regional and local water bodies, respectively, in Europe, and 0.004 to 0.036 for oceans and rivers, respectively, in Australia. In conclusion, aquatic hazard levels are not expected to be reached under exaggerated conditions of manufacture or normal consumer use of hydrotropes. Hydrotropes are neither persistent nor bioaccumulative in the environment. Integr Environ Assess Manag 2010; 6:155–163. © 2009 SETAC

Female DA/Han rats were administered p-tert-octylphenol [OP; p-(1,1,3,3-tetramethylbutyl)-phenol], either intravenously (5 mg/kg body wt.) or orally by gavage (50 or 200 mg/kg body wt.). After i.v. administration the blood concentration-time curve of OP was fitted to a tri-exponential model, resulting in a final half-life (gamma-phase) of 36.1 h. This contrasts to much more rapid eliminations previously reported in male Wistar rats. The oral bioavailability of 50 mg/kg OP was 12.3% and of 200 mg/kg 8.4%. The higher dose (200 mg kg) was absorbed slower than the smaller dose, probably due to low solubility of OP in aqueous media. Maximal OP blood levels in female DA/Han rats receiving 50 and 200 mg OP/kg body wt, were 4.5 and 3 times higher than previously reported in male Wistar rats. The blood concentration-time curves after oral administration of OP to female DA/Han rats revealed pronounced interindividual differences, indicating extensive enterohepatic circulation of OP in this rat strain. In contrast to male Wistar rats, after application of high doses of OP to female DA/Han rats the compound was not completely eliminated within 48 h: under these conditions some bioaccumulation might therefore occur. The experimental toxicokinetics of OP appears as a relevant subject to be integrated into extrapolation of toxicological data, from in vitro to in vivo, and into systems of risk assessment of endocrine modulating activity which are currently being developed.