The sub-chronic toxicity in rats of isoparaffinic solvents

Toxicological Assessment of Higher Olefins in OECD TG 422 Repeated Dose and Reproductive /Developmental Toxicity Screening Tests in Han Wistar Rats

Higher olefins (HO) are used primarily as intermediates in the production of other chemicals, such as polymers, fatty acids, plasticizer alcohols, surfactants, lubricants, amine oxides, and detergent alcohols. The potential toxicity of five HO (i.e., 1-Octene, Nonene, Decene, Hexadecene, and 1-Octadecene) with carbon ranging from C8 to C18 was examined in a combined repeated dose and reproduction/developmental toxicity screening study (OECD TG 422). These five HO were administered to Han Wistar rats by gavage at 0 (controls), 100, 300, and 1000 mg/kg bw/day. As a group of substances, adaptive changes in the liver (liver weight increase without pathological evidence), as well as increased kidney weight in male rats, were observed in HO with carbon numbers from C8 to C10. The overall systemic no observed adverse effect level (NOAEL) for all HO was determined at 1000 mg/kg bw/day. In the reproductive/developmental toxicity assessment, offspring viability, size, and weights were reduced in litters from females treated with Nonene at 1000 mg/kg bw/day. The overall no observed effects level (NOEL) for reproductive toxicity was considered to be 300 mg/kg bw/day for Nonene and 1000 mg/kg bw/day for the other four HO, respectively. These data significantly enrich the database on the toxicity of linear and branched HO, allowing comparison with similar data published on a range of linear and branched HO. Comparisons between structural class and study outcome provide further supportive data in order to validate the read-across hypothesis as part of an overall holistic testing strategy.

Biological effects of inhaled crude oil vapor. III. Pulmonary inflammation, cytotoxicity, and gene expression profile

OBJECTIVE

Workers may be exposed to vapors emitted from crude oil in upstream operations in the oil and gas industry. Although the toxicity of crude oil constituents has been studied, there are very few in vivo investigations designed to mimic crude oil vapor (COV) exposures that occur in these operations. The goal of the current investigation was to examine lung injury, inflammation, oxidant generation, and effects on the lung global gene expression profile following a whole-body acute or sub-chronic inhalation exposure to COV.

MATERIALS AND METHODS

To conduct this investigation, rats were subjected to either a whole-body acute (6 hr) or a sub-chronic (28 d) inhalation exposure (6 hr/d × 4 d/wk × 4 wk) to COV (300 ppm; Macondo well surrogate oil). Control rats were exposed to filtered air. One and 28 d after acute exposure, and 1, 28, and 90 d following sub-chronic exposure, bronchoalveolar lavage was performed on the left lung to collect cells and fluid for analyses, the apical right lobe was preserved for histopathology, and the right cardiac and diaphragmatic lobes were processed for gene expression analyses.

RESULTS

No exposure-related changes were identified in histopathology, cytotoxicity, or lavage cell profiles. Changes in lavage fluid cytokines indicative of inflammation, immune function, and endothelial function after sub-chronic exposure were limited and varied over time. Minimal gene expression changes were detected only at the 28 d post-exposure time interval in both the exposure groups.

CONCLUSION

Taken together, the results from this exposure paradigm, including concentration, duration, and exposure chamber parameters, did not indicate significant and toxicologically relevant changes in markers of injury, oxidant generation, inflammation, and gene expression profile in the lung.

Development of updated RfD and RfC values for medium carbon range aromatic and aliphatic total petroleum hydrocarbon fractions

Using total petroleum hydrocarbon (TPH) measurements as a tool for assessing potential human health risks associated with exposures to petroleum products in the environment poses unique challenges, as TPH represents highly variable and complex mixtures containing hundreds of individual chemicals with wide-ranging chemical and physical properties. Current risk assessment practice generally involves analysis of environmental samples for various TPH fractions and summation of risk across those fractions. The United States Environmental Protection Agency (USEPA) derived provisional toxicity criteria for low, medium, and high carbon range aromatic and aliphatic hydrocarbon fractions over a decade ago. These criteria have been used, in whole or in part, to derive risk-based cleanup levels for TPH contamination in soil and groundwater. Herein, we evaluate and update oral and inhalation toxicity criteria for two of these fractions - medium carbon range aromatics and aliphatics - using, where applicable, newer data, updated modeling techniques, and new/alternative analyses of certain endpoints, human relevance, and uncertainty. The results of the analyses support an ~10-fold increase in the USEPA provisional reference concentration (p-RfC) values from 0.1 mg/m³ to 1 mg/m³ for both medium carbon range aromatics (different uncertainty factor) and aliphatics (new study and different judgment of toxicity data from existing study). Compared to the USEPA provisional oral reference dose (p-RfD) values for the medium carbon range aromatics and aliphatics of 0.03 mg/kg-day and 0.01 mg/kg-day, respectively, the present analyses suggest the RfD for medium carbon range aromatics could be increased >6.6-fold to 0.2 mg/kg-day (updated modeling and different uncertainty factors), and the RfD for medium carbon range aliphatics could be increased ~20-fold to 0.2 mg/kg-day (new study). These updated toxicity criteria could be used by regulatory agencies to reevaluate risk-based screening levels or by risk managers to support cleanup levels for medium carbon range aromatics and aliphatics, while still ensuring adequate health protection.Implications: Petroleum products represent complex mixtures of hydrocarbons broadly comprised of aliphatic compounds (straight-chain, branched-chain, and cyclic alkanes and alkenes) and aromatic compounds such as benzene, alkylbenzenes, and polycyclic aromatic hydrocarbons. The complex nature of petroleum products presents challenges for assessing potential health risks associated with exposure to petroleum hydrocarbon contamination in the environment. It has been over ten years since the U.S. Environmental Protection Agency derived provisional toxicity criteria for low, medium, and high carbon range aromatic and aliphatic hydrocarbon fractions. In that time, risk assessment guidance and tools have evolved, and new studies have been published. Our analyses indicate that current provisional toxicity criteria for medium carbon range aromatics and aliphatics fractions are overly conservative by approximately an order of magnitude.

An investigation of the acute central nervous system effects of n-decane

Acute central nervous system (CNS) depression is the most sensitive toxicological effect associated with aliphatic hydrocarbon exposure. No observed effect levels for the CNS effects of aliphatic constituents decrease with increasing carbon number to C10 (Lammers et al., 2011; McKee et al., 2011), whereas constituents with carbon numbers > C10 do not produce CNS effects at maximally attainable vapor concentrations (Nilsen et al., 1988). Accordingly, as n-decane appeared to be the "worst case" for acute CNS effects among aliphatic hydrocarbon solvent constituents, experimental studies were conducted to more precisely define the no effect level. Rats were exposed for 8 h to n-decane, either constantly at 3000 mg/m³ or at higher levels using a discontinuous exposure protocol to assess the influence of fluctuating exposures. Neurobehavioral testing methods including visual discrimination performance and motor activity were used to assess performance, and concentrations of n-decane in blood and brain were measured to obtain pharmacokinetic data. No statistically significant differences were observed in the neurobehavioral tests, establishing 3000 mg/m³ as the no effect level for CNS effects in rats. These data support the recommended guidance value of 1050 mg/m³ for C9-C15 aliphatic hydrocarbons for use in calculating occupational exposure levels for complex hydrocarbon solvents and provide empirical evidence that advice from the ACGIH^® that within a working day there should be no more than 3 fluctuations, not longer than 15 min and not exceeding 3 times the Threshold Limit Value (TLV^®), is reasonable for this group of substances.

The sub-chronic toxicity of a naphthenic hydrocarbon solvent in rats

Cycloalkanes/naphthenes are constituents of complex hydrocarbon solvents, and hence an understanding of their toxicological profile is critical to establish safe limits for occupational exposures to these solvents. Although naphthenes are structurally related to and share a common metabolic fate with the straight and branched chain analogues, some toxicokinetic differences have been noted. The acute central nervous system response to volatile naphthenes in rodents has been shown to be slightly different compared to other alkane analogues. To determine whether these differences may extend to systemic effects with less volatile naphthenes, rats were exposed to 1500, 3000 or 6000 mg/m³ of a C₉-C₁₁ aliphatic solvent containing 70% naphthenes, for 90 days. Effects were limited to adaptive liver enlargement in both sexes and kidney toxicity in the male rat. For comparative purposes, the results from this study were compared to published reports of a complex hydrocarbon solvent with a higher proportion of volatile C₅/C₆ naphthenes and a mono-constituent naphthene (decahydronaphthalene). The results indicate that the systemic effects of naphthenes are similar to the straight and branched chain analogues and that the effects that are most relevant for human health evaluations of alkanes are acute central nervous system effects.

The sub-chronic oral toxicity of dearomatized hydrocarbon solvents in Sprague-Dawley rats

Dearomatized hydrocarbon solvents in the C9-C14 aliphatic carbon number range were developed as alternatives to traditional solvents such as mineral spirits, but with lower aromatic content. Previous subchronic toxicity studies (both published and unpublished) have shown minimal to no systemic effects with exposure to dearomatized solvents, with the exception of rat-specific renal effects that have no relevance to humans. In this study, Sprague-Dawley rats were exposed to 0, 500, 2500 and 5000mg/kg/day of a C10-C13 dearomatized solvent for 90days by oral gavage. Liver enlargement and centrilobular hypertrophy were observed in all treated groups but were considered adaptive consequences of hydrocarbon-induced microsomal enzyme induction. Clinical chemistry data showed elevations of alanine aminotransferase (ALT), gamma glutamyltransferase (GGT) and total bilirubin in mid (ALT alone) and high dose groups, suggesting potential hepatobiliary effects with high dose exposure. Increased absolute kidney weight changes were restricted to male rats and associated with renal lesions indicative of alpha-2u globulin-mediated nephropathy. One limitation of the NOAEL/LOAEL approach in selecting points of departure for exposure limits is its dependence on dose selection/study design. Hence, a more robust approach that incorporates all data points on the dose-response curve, such as bench mark modeling, is preferred. Overall, benchmark dose analysis estimated a BMDL of 1857mg/kg/day based on increased serum ALT. This value is consistent with studies of similar hydrocarbon substances showing a lack of systemic effects at doses up to 1000mg/kg/day in the same rat strain.

The sub-chronic toxicity of regular White Spirit in rats

Hydrocarbon solvents are mostly complex substances (UVCB) with carbon numbers in the range of approximately C5-C20. One of the most common types is a C9-C14 aliphatic solvent containing approximately 20% aromatics and commonly known as White Spirit in Europe and mineral spirits in the US. In previous repeated inhalation toxicity studies, White Spirit was reported to cause minimal systemic effects in most animal species with few effects other than male rat-specific kidney changes at levels up to approximately 2000mg/m(3). In the present study male and female rats were exposed to White Spirit vapors, 6h/day, 5days/week for 13weeks at levels of approximately 2000, 4000, or 8000mg/m(3) to assess the potential for effects at higher exposure levels. All of the rats survived the treatment period. In life observations were largely restricted to acute central nervous system (CNS) effects in the high exposure group. Terminal body weights of high exposure groups animals were significantly below control values. Statistically significant differences in the clinical and hematological observations were small and within normal physiological limits. Weights of some organs including liver, spleen and kidneys were elevated, but microscopic examination indicated that the only pathological effects were changes in the kidneys of the male rats, consistent with an α2u-globulin-mediated process, which is gender and species-specific and not relevant to humans. The overall no observed adverse effect level (NOAEC) was 4000mg/m(3).