Appraisal of the human health related toxicological information available on dicyclopentadiene (DCPD) in view of assessing the substance's potential to cause endocrine disruption.

Dicyclopentadiene (DCPD) is an olefinic hydrocarbon which is manufactured and imported into the European Union (EU) at greater than 1000 tons per year. Concerns related to fetotoxic effects observed in reproductive toxicity studies at high doses led the REACH registrants to self-classify DCPD as a Category 2 reproductive toxicant under the EU CLP Regulation. DCPD was also reviewed in the European Union in the frame of an ongoing European Chemical Agency (ECHA) Community Rolling Action Plan (CoRAP) procedure and under the French National Strategy on Endocrine Disruptors (SNPE). To elucidate whether the developmental effects may be triggered by an endocrine mode of action, the Lower Olefins Sector Group (LOSG) of the European Chemical Industry Council (CEFIC) formed an ad hoc expert team to review the available scientific information pertaining to the potential endocrine activity and adversity of DCPD. Existing experimental data was complemented with structure activity modelling using ECHA-recommended (Q)SAR tools. Overall, considering the available information from (Q)SAR, mechanistic in vitro and in vivo studies, no indication of endocrine-mediated adversity was found. Hence, the available evidence supports the conclusion that DCPD does not cause developmental toxicity via an endocrine mode of action. Further work is ongoing to support this conclusion.

A reproductive and developmental toxicity screening study of 1,3-butadiene in Sprague-Dawley rats.

1,3 Butadiene (BD) is an industrial intermediate used primarily in product manufacturing with the greatest exposure potential via inhalation. BD was evaluated for reproductive and developmental effects in a Good Laboratory Practice (GLP)-compliant, extended OECD 421 guideline study (completed 2003). Twelve-week old rats (12/sex/dose) were exposed via whole-body inhalation to BD vapor (0, 300, 1500, 6000 ppm) for 6 h/day, 7 days/week, starting 14 days prior to mating through the day prior to euthanasia (total exposures: 83-84 days for F0 males 60-70 days for F0 females). Select F1 offspring (1/sex/litter) were dosed 7 days (postnatal days 21-27 or 28-34), then necropsied. At 1500 and 6000 ppm, treatment-related facial soiling was seen in F0 males and females with decreased body weights/gains in F0 males. F1 males and females exhibited similar effects at 1500 and 6000 ppm. Importantly, the F0 generation had no evidence of altered sperm production, testicular effects, or ovarian atrophy, which were sensitive responses in mice. The no-observed-adverse-effect-level (NOAEL) is 300 ppm due to decreased body weight/gain and facial soiling at 1500 ppm, whereas 6000 ppm serves as a NOAEL for reproductive and developmental endpoints. This study contributes to the weight-of-evidence of differential BD reproductive toxicity in rats and mice.

A review of the toxicological and environmental hazards and risks of tetrahydrofuran.

We present in this paper a review of the toxicological and environmental hazards, exposures and risks of tetrahydrofuran (THF; CASRN 109-99-9). THF is a polar solvent and monomer that is easily absorbed by all routes of exposure. The acute toxicity of THF is low to moderate by all routes. Irreversible corrosive damage to the eye can result from direct contact. However, THF is neither a skin irritant, nor sensitizer. Studies in vitro and in vivo have shown that THF is not mutagenic. Chronic studies have found benign tumors in the kidneys of male rats and in the livers of female mice. These findings have been examined, and although a mode of action is not known, the weight of evidence suggests that these tumors are likely not relevant to human health, but instead secondary to rodent-specific modes of action. THF produces transient sedative effects in rats at high concentrations but no significant neurobehavioral changes or neuropathology in sub-chronic studies. There were no specific effects reported on reproduction or developmental toxicity in rats or mice, with non-specific developmental toxicity observed only in the presence of significant maternal toxicity. The log K(ow) value for THF is less than 3, indicating a low potential for bioaccumulation. THF is inherently biodegradable, thus is not expected to be environmentally persistent. THF does not present an ecotoxicity hazard based on test results in fish, aquatic invertebrates and plants. Exposures to THF in the workplace, to consumers and via environmental releases were modeled and all found to fall below the derived toxicity thresholds.

Investigation of the potential mutagenicity of ethyl tertiary-butyl ether in the tumor target tissue using transgenic Big Blue Fischer 344 rats following whole body inhalation exposure.

Ethyl tertiary-butyl ether (ETBE) is a fuel oxygenate used for the efficiency of motor vehicle fuels and their octane ratings. ETBE has been reported to induce liver adenomas in male rats in a 2-year bioassay at the highest inhalation concentration tested of 5000 ppm. To investigate the potential mutagenicity of ETBE in the liver, male Big Blue Fischer 344 rats were exposed for 28 consecutive days (6 h/day) to 0, 500, 1500, and 5000 ppm ETBE. The treated rats were sacrificed 3 days post-exposure and the frequencies of cII mutants were evaluated in the liver and bone marrow tissues. The mutant frequency (MF) of the liver in the negative control group was 36.3 × 10-6 and this value was not significantly different in ETBE-exposed animals (39.4, 37.3, and 45.9 × 10-6 in 500, 1500, and 5000 ppm groups, respectively). In the bone marrow, the mean MF in the negative control was 32.9 × 10-6 which was not different from the means of the exposed groups (33.8, 22.6, and 32.0 × 10-6 for groups exposed to 500, 1500 and 5000 ppm, respectively). These data, along with consistent negative response reported in the literature for other apical genotoxicity endpoints informs that mutagenicity is not likely the initial key event in the mode of action for ETBE-induced hepatocarcinogenesis in the rat.

A consistent and transparent approach for calculation of Derived No-Effect Levels (DNELs) for petroleum substances.

The REACH legislation introduced Derived No-Effect Levels (DNELs) which are defined as 'the levels of exposure above which humans should not be exposed'. DNELs were required for several categories of petroleum substances and CONCAWE developed a consistent approach for their derivation. First, the No-Observed Effect Level from a relevant study was corrected for pattern and route of exposure to obtain a modified Point-of-Departure (POD(modified)). Subsequently, the DNEL was calculated by dividing the POD(modified) by Assessment Factors (AFs) to adjust for inter- and intraspecies differences. If substance-specific information allowed, Informed Assessment Factors (IAFs), developed by CONCAWE were utilised. When little or no substance-specific information on those differences was known, default AFs from the guidance provided by ECHA were used. Some hazard endpoints did not lend themselves to calculation of DNELs (e.g. aspiration, dermal irritation, mutagenicity). DNEL calculation was considered not appropriate if adverse effects were not observed in tests conducted at a limit dose or if meaningful dose-response curves could not be developed. However, DNELs were calculated when hazards were identified, regardless of whether or not risk characterisation was required under REACH. Examples for gasoline, Lubricating Base Oils, gas oils and bitumen are provided to illustrate CONCAWE's approach.

Concept of assessing nanoparticle hazards considering nanoparticle dosemetric and chemical/biological response metrics.

Engineered nanoparticles (NP) are being developed and incorporated in a number of commercial products, raising the potential of human exposure during manufacture, use, and disposal. Although data concerning the potential toxicity of some NP have been reported, validated simple assays are lacking for predicting their in vivo toxicity. The aim of this study was to evaluate new response metrics based on chemical and biological activity of NP for screening assays that can be used to predict NP toxicity in vivo. Two cell-free and two cell-based assays were evaluated for their power in predicting in vivo toxicity of eight distinct particle types with widely differing physicochemical characteristics. The cell-free systems comprised fluorescence- and electron spin resonance-based assays of oxidant activity. The cell-based systems also used electron spin resonance (ESR) as well as luciferase reporter activity to rank the different particle types in comparison to benchmark particles of low and high activity. In vivo experiments evaluated acute pulmonary inflammatory responses in rats. Endpoints in all assays were related to oxidative stress and responses were expressed per unit NP surface area to compare the results of different assays. Results indicated that NP are capable of producing reactive species, which in biological systems lead to oxidative stress. Copper NP had the greatest activity in all assays, while TiO(2) and gold NP generally were the least reactive. Differences in the ranking of NP activity among the assays were found when comparisons were based on measured responses. However, expressing the chemical (cell-free) and biological (cells; in vivo) activity per unit particle surface area showed that all in vitro assays correlated significantly with in vivo results, with the cellular assays correlating the best. Data from this study indicate that it is possible to predict acute in vivo inflammatory potential of NP with cell-free and cellular assays by using NP surface area-based dose and response metrics, but that a cellular component is required to achieve a higher degree of predictive power.

Derivation of an occupational exposure limit for benzene using epidemiological study quality assessment tools.

This paper derives an occupational exposure limit for benzene using quality assessed data. Seventy-seven genotoxicity and 36 haematotoxicity studies in workers were scored for study quality with an adapted tool based on that of Vlaanderen et al., 2008 (Environ Health. Perspect. 116 1700-5). These endpoints were selected as they are the most sensitive and relevant to the proposed mode of action (MOA) and protecting against these will protect against benzene carcinogenicity. Lowest and No- Adverse Effect Concentrations (LOAECs and NOAECs) were derived from the highest quality studies (i.e. those ranked in the top tertile or top half) and further assessed as being "more certain" or "less certain". Several sensitivity analyses were conducted to assess whether alternative "high quality" constructs affected conclusions. The lowest haematotoxicity LOAECs showed effects near 2 ppm (8 h TWA), and no effects at 0.59 ppm. For genotoxicity, studies also showed effects near 2 ppm and showed no effects at about 0.69 ppm. Several sensitivity analyses supported these observations. These data define a benzene LOAEC of 2 ppm (8 h TWA) and a NOAEC of 0.5 ppm (8 h TWA). Allowing for possible subclinical effects in bone marrow not apparent in studies of peripheral blood endpoints, an OEL of 0.25 ppm (8 h TWA) is proposed.

Mode of action and human relevance of THF-induced mouse liver tumors.

In a National Toxicology Program (NTP) bioassay, inhalation of tetrahydrofuran (THF) induced liver tumors in female B6C3F1 mice but not in male mice or rats of either sex. Since THF is not genotoxic, the NTP concluded this carcinogenic activity was likely mediated via non-genotoxic modes of action (MOA). Based on evidence that THF and phenobarbital share a similar MOA, female Car/Pxr knock-out mice were orally exposed to THF to evaluate the potential role of CAR activation in the MOA for THF-induced liver tumors. Because data from this oral study with Car/Pxr knock-out mice (C57Bl/6) and the inhalation studies with wild type mice (B6C3F1) reported by NTP and others were derived from different strains, oral studies with wild type B6C3F1 and C57Bl/6 mice were conducted to ensure THF responses in both strains were comparable. As seen in inhalation studies with THF, oral exposure of wild type female mice to a maximum tolerated dose of THF increased total P450 content, CAR-related P450 activities, and hepatocyte proliferation; these effects were not observed in Car/Pxr knock-out female mice. This finding supports the hypothesis THF-induced carcinogenicity is likely mediated via CAR activation that has limited, if any, relevance to humans.