Initiation/promotion studies with coal-derived liquids

Chemical mixture toxicology: from descriptive to mechanistic, and going on to in silico toxicology

Because of the pioneering vision of certain leaders in the biomedical field, the last two decades witnessed rapid advances in the area of chemical mixture toxicology. Earlier studies utilized conventional toxicology protocol and methods, and they were mainly descriptive in nature. Two good examples might be the parallel series of studies conducted by the U.S. National Toxicology Program and TNO in The Netherlands, respectively. As a natural course of progression, more and more sophistication was incorporated into the toxicology studies of chemical mixtures. Thus, at least the following seven areas of scientific achievements in chemical mixture toxicology are evident in the literature: (a) the application of better and more robust statistical methods; (b) the exploration and incorporation of mechanistic bases for toxicological interactions; (c) the application of physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling; (d) the studies on more complex chemical mixtures; (e) the use of science-based risk assessment approaches; (f) the utilization of functional genomics; and (g) the application of technology. Examples are given for the discussion of each of these areas. Two important concepts emerged from these studies and they are: (1) dose-dependent toxicologic interactions; and (2) "interaction thresholds". Looking into the future, one of the most challenging areas in chemical mixture research is finding the answer to the question "when one tries to characterize the health effects of chemical mixtures, how does one deal with the infinite number of combination of chemicals, and other possible stressors?" Undoubtedly, there will be many answers from different groups of researchers. Our answer, however, is first to focus on the finite (biological processes) rather than the infinite (combinations of chemical mixtures and multiple stressors). The idea is that once we know a normal biological process(es), all stimuli and insults from external stressors are merely perturbations of the normal biological process(es). The next step is to "capture" the biological process(es) by integrating the recent advances in computational technology and modern biology. Here, the computer-assisted Reaction Network Modeling, linked with PBPK modeling, offers a ray of hope to dealing with the complex biological systems.

Epidermal carcinogenesis studies of EDS liquids

A series of liquids representing different potential design options or operating configurations for the EDS direct coal liquefaction process* were evaluated for skin cancer potential. All of the samples that contained substantial amounts of material boiling above 370 degrees C were active dermal carcinogens; tumor yields were near 100% and median times to tumor development generally ranged from 30 to 40 weeks. Two liquids that boiled below ca. 200 degrees C were tested and each produced one squamous cell tumor. These data suggested that high-boiling-point, coal-derived liquids are likely to be relatively potent dermal carcinogens; whereas low-boiling-point liquids do not possess significant carcinogenic potential. Based on a comparison of the carcinogenic potency data, liquids produced by the EDS process apparently do not present a significantly greater dermal carcinogenic hazard than other coal-derived materials of similar boiling range.

Toxicology of coal liquefaction products: an overview

Repeated exposure to coal liquefaction products produces a broad range of systemic effects. Among these, growth suppression, anaemia, leucocytosis and other haematological disorders are most prominent. Bone marrow, liver and kidney are the target organs affected by treatment. The effects are more severe with heavy distillates and male rats are more sensitive than females. Other changes included increased serum transaminases, alkaline phosphatase and cholesterol. Depending on the route of administration, the skin or lung may also be affected. Inhalation exposure produces the most severe changes, and oral exposure the least. Distillates containing N-PAHs and sulphur-containing PAHs are also more biologically active. Teratological effects were only observed if animals were exposed to the heavy distillate. Similarly, heavy distillates have mutagenic or carcinogenic properties. Teratological effects, as well as mutagenicity and carcinogenicity, of the coal liquefaction distillates seem to be linked to their PAH content, especially the N-PAHs. From the data presented in this review, it should become evident that the potential effects of coal liquefaction products on human health could be severe, especially with long-term exposure. Limited information exists on the occupational effects to coal liquefaction materials because most of the work to date has been with pilot plants. Careful and good judgement is required in order to extrapolate data from pilot plants to commercial-scale production. Experience in health effects of workers in the petroleum industry and coke-oven operations can serve as a guide for the implementation of industrial hygiene programmes for coal liquefaction operations. These programmes include engineering controls, health education, personal monitoring and hygienic practices, medical surveillance and long-term epidemiology studies, and they should be implemented to make coal liquefaction a healthy and environmentally sustainable industry.

An investigation of the main mutagenic components of a carcinogenic oil by fractionation and testing in the modified Ames assay

A low-viscosity carcinogenic oil was extracted with dimethylsulphoxide (DMSO) and the extract fractionated into 1-3 ring aromatic components, 4-6 ring polycyclic aromatic compounds (PCAs) and polar materials. Each of these fractions was tested in the Mobil modified Ames assay at the same concentration as in the DMSO extract, alongside unfractionated DMSO extracts from the same oil and two reference oils. In addition the fractions were combined in various ways to examine inhibitory or additive effects. Clear positive findings were obtained with the DMSO extract of the main test oil, with some reduction in activity in a sample (the starting material for fractionation) that was back-extracted to remove DMSO. Of the three fractions tested on their own and assessed in terms of mutagenicity index, the 1-3 ring aromatic fraction had the greatest mutagenic activity, showing similar activity to the starting material, whereas the 4-6 ring PCA fraction had much lower activity and the polar fraction showed the lowest activity with an absence of doubling in one of the tests. The polar fraction showed signs of an inhibitory effect on the response to the 1-3 ring aromatic fraction and to a questionable extent on that of the 4-6 ring PCA fraction. Although a low level of the 4-6 ring PCA fraction showed some inhibitory effect on the response to the 1-3 ring aromatic fraction, a low level of the 1-3 ring aromatic fraction added to the 4-6 ring PCA fraction enhanced the response.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nitrosation on the chemical composition and epidermal carcinogenicity of the nitrogen-rich fraction of a high-boiling coal liquid

An 800-850 degrees F solvent-refined coal-II liquid was fractionated into chemical classes to obtain the aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAH), nitrogen-containing polycyclic aromatic compounds (NPAC), and hydroxy-substituted PAH (hydroxy-PAH). The isolated NPAC fraction was refractionated by chemical class both before and after undergoing a nitrosation reaction. The nitrosated and non-nitrosated refractionated NPAC fractions were further subfractionated into secondary amine (pyrroles), primary amine-enriched (amino-PAH), and tertiary amine (azaarene) classes. The PAH and hydroxy-PAH composition of the NPAC fraction increased upon nitrosation, whereas the amino-PAH fraction composition decreased upon nitrosation. Nitrosation of standards indicated the amino-PAH compounds reacted to form parent PAH, chloro-substituted PAH, and methoxy-substituted PAH when analyzed by high-resolution gas chromatography (GC) and GC/mass spectrometry (MS). Some easily oxidized PAH compounds reacted to form ketones and quinones. All other standard reference compounds, chosen to be representative of the major chemical classes of compounds present in coal liquefaction materials, were unchanged by the nitrosation reaction. The amino-PAH of the nitrosated NPAC fraction reacted to form parent and some chloro-substituted PAH when analyzed by low-voltage direct-probe MS in addition to the methods given above. Epidermal carcinogenesis studies with the PAH, NPAC, nitrosated NPAC, and hydroxy-PAH fractions isolated from the 800-850 degrees F coal liquid indicated the PAH and NPAC were the most important determiners of skin carcinogenesis, with the PAH giving a higher response than the NPAC. The tumorigenicity of the NPAC was drastically reduced by nitrosation, probably due to the destruction of the amino-PAH upon nitrosation.

Toxicological studies of chemical mixtures of environmental concern at the National Toxicology Program: health effects of groundwater contaminants

In cooperation with the Agency for Toxic Substances and Disease Registry, the National Toxicology Program is participating in a Public Health Service activity related to the Comprehensive Environmental Response, Compensation and Liability Act (Superfund Act) by conducting toxicology studies on chemicals found in high-priority hazardous waste sites and for which adequate toxicological data are not available. As part of this effort, a project on the toxicology of chemical mixtures of groundwater contaminants was initiated. The first study, centered on the health effects of groundwater contaminants, is at the contractual stage. Nineteen organic and six inorganic chemicals, selected from more than 1000 known groundwater contaminants, will be given in drinking water to Fischer 344 rats and B6C3F1 mice for 3 or 6 months. Controls and five dose levels, based on average concentrations (i.e., baseline level) of individual component chemicals, or 0.1-, 10-, or 1000-fold of the baseline level, will be used. Toxicological end points include mortality, clinical signs, water and food consumption, body and organ weights, clinical pathology analytes (e.g., hematology, clinical chemistry, and urinalysis), gross and histopathology, neurobehavioral tests, sperm morphology and vaginal cytology evaluations (SMVCE), and cytogenetics. This paper summarizes the rationale behind our experimental design and the factors one must consider when designing studies of complex chemical mixtures.

Assessment of the potential reproductive and subchronic toxicity of EDS coal liquids in Sprague-Dawley rats

The EDS direct coal liquefaction process is one of several methods of producing liquid fuels from coal which have reached the pilot or demonstration stage of development. Relatively high levels of polycyclic aromatic hydrocarbons are present in distillate fractions boiling above approximately 370 degrees C, and unrefined coal-derived liquids which contain substantial amounts of material from this boiling range are relatively potent dermal carcinogens. Because coal-derived liquids containing high boiling (i.e., greater than 370 degrees C) material may pose a variety of toxic hazards, efforts have been made to evaluate the potential effects on biological endpoints other than cancer. The present studies assessed the potential for reproductive and subchronic toxicity following repeated oral administration of 2 coal-derived liquids, recycle solvent and fuel oil, which contained substantial amounts of high boiling material. Few biologically important differences were found in any of the experimental parameters. In the reproductive toxicity study, frequency of fertilization and implantation, mean number of live births, fraction of litter surviving through the lactation period and mean weight gain of the litters during the lactation period were not affected by treatment; in addition, there was no evidence of increased frequency of malformation. In the subchronic toxicity study, weight gain was reduced in animals from the high dose groups, but was not significantly different from controls. Liver weights were significantly elevated, but there was no microscopic evidence of pathologic changes. Erythrocyte counts, hemoglobin levels and hematocrits were significantly reduced suggesting a tendency towards anemia. These findings suggested that repeated exposure to EDS recycle solvent and fuel oil at levels of up to 0.5 g/kg per day had no detectable effect on reproductive capacity or performance and did not induce substantial systemic toxicity.

Developmental toxicity of EDS recycle solvent and fuel oil

Direct coal liquefaction is one of several technologies currently under development as alternative means to produce liquid fuels. Relatively high levels of polycyclic aromatic hydrocarbons are present in distillate fractions boiling above approximately 370 degrees C. Coal-derived liquids containing substantial amounts of material from this boiling range were genotoxic in in vitro tests and carcinogenic in mouse skin. Some of the liquids were also teratogenic in rodents. The present report describes studies which assessed the potential effects of 2 coal-derived liquids, recycle solvent (nominal boiling range 200-427 degrees C) and an experimental industrial fuel oil (nominal boiling range 204-538 degrees C) on prenatal development in the rat. The test materials were produced by the EDS direct coal liquefaction process and contained substantial amounts of material boiling above 370 degrees C. Test materials were administered by gavage to pregnant female Sprague-Dawley rats from days 6 to 19 of gestation (G). Animals were sacrificed on day 20G and the uterine contents were removed and examined. Results of both studies were similar. The number of live fetuses declined in a dose-related manner, and there was evidence of intrauterine growth retardation in fetuses which survived to day 20G. Statistically significant effects were noted at doses which did not appear to be maternally toxic. The frequency of malformation was not significantly elevated in either study; however, a thorough evaluation of this endpoint was precluded by embryo lethality at the high doses. It was apparent that both of the EDS liquids examined affected prenatal survival and growth. However, in contrast to studies of other coal-derived liquids, there was no evidence of teratogenic effects at non-toxic doses.

Epidermal carcinogenesis studies of synthetic fossil fuel materials in mice

Skin tumor response in mice to solvent fractions of heavy distillate (HD) from a solvent-refined coal (SRC-II) process indicated that the basic tar and neutral tar were the most carcinogenically potent fractions. Assays of another SRC-II coal liquid that had been fractionally distilled indicated that the carcinogenicity of this material for mouse skin is due to that portion boiling above 371 degrees C (700 degrees F), and that the carcinogenic potency of the material increased with boiling point. Samples of the 399-427 degrees C (750-800 degrees F) distillate were nitrosated to destroy primary aromatic amines and were chemically fractionated to assess the carcinogenicity of chemical class fractions of these complex mixtures. Data from these assays indicated that neutral polycyclic aromatic hydrocarbons (PAH) and nitrogen-containing polycyclic aromatic compounds (NPAC) both contribute to the carcinogenicity of this distillate.

Evaluation of the teratogenic potential and reproductive toxicity of coal-derived naphtha

Liquids which are derived from coal liquefaction processes and boil above approximately 250 degrees C have induced terata in rats. However, few studies have addressed the teratogenic potential of coal liquids which boil below 250 degrees C. The present studies evaluated the reproductive and teratogenic potential of EDS hydrotreated naphtha, a refined coal liquid boiling below 177 degrees C. These studies were conducted by inhalation exposures with Sprague-Dawley rats at target vapor concentrations of 0.2, 1.0, and 5.0 g/m3. The first study assessed teratogenesis. There was no evidence that inhalation exposures for 6 hr per day between Days 6 and 19 of gestation induced maternal toxicity, fetal toxicity, or malformation. In a second study, rats were exposed for 6 hr per day, 5 days per week for 13 weeks, and then mated to assess reproductive toxicity. There was little evidence that inhalation exposure to EDS hydrotreated naphtha adversely affected reproductive performance or fetal development in Sprague-Dawley rats. A low incidence of malformations was observed in treated groups, but these malformations were probably not treatment related.

Lung development and postnatal survival for rats exposed in utero to a high-boiling coal liquid

Previous studies performed in this laboratory indicated that exposure of rat fetuses to high-boiling coal liquids from 12-14 days of gestation (dg) induced a number of major malformations, including cleft palate, diaphragmatic hernia and small lungs. The study reported here was designed to determine postnatal viability and development of survivors following in utero exposure to Harmarville process solvent (HPS), a wide-boiling-range (150 to greater than 455 degrees C) coal liquid. For this study, 0.74 g kg-1 of the coal liquid was administered (by intragastric intubation) to rats from 12 to 14 dg. Offspring were evaluated for postnatal survival, growth and lung and thymus weights. Randomly selected pups from control and treated litters were killed and necropsied at 1, 3, 7 and 21 days postpartum. In addition, data for control pups were obtained at 0.25 and 0.5 days postpartum for comparison with body, lung and thymus weights of pups that died during this interval. Fifty-four per cent of the exposed pups and 9% of the control pups died between birth and 3 days postpartum. Of the treated pups that died, 10% (6/5; pups/litters) had cleft palate, 27% (17/9) had small lungs and 33% (21/8) had both cleft palate and small lungs. No gross malformations were observed in the remaining 30% of the dead pups. Microscopic examination of lungs from HPS-treated pups revealed no evident histological abnormalities. Body, lung and thymus weights for treated animals that died were significantly less than those of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of inhalation exposure to a high-boiling (288 to 454 degrees C) coal liquid

Coal liquids have been evaluated in a variety of short-term toxicological assays; however, few studies have been conducted to determine the systemic effects after inhalation exposure to these materials. To extend the data base on potential health effects from coal liquefaction materials, we performed a study with solvent refined coal (SRC)-II heavy distillate (HD). Fischer-344 rats were exposed for 6 hr/day, 5 days/week for 5 or 13 weeks to an aerosol of HD (boiling range, 288 to 454 degrees C) at concentrations of 0.69, 0.14, 0.03, or 0.0 mg/liter of air for the high, middle, low, and control groups, respectively. Survival through 13 weeks of exposure was greater than 90% for all groups; body weights for exposed animals were decreased in a dose-dependent manner. Significant increases in liver weights and decreases in thymus and ovary weights were observed for treated animals compared with controls. There were also significant treatment-related decreases in erythrocytes, hemoglobin, volume of packed red blood cells, lymphocytes, eosinophils, and total white blood cells. After 5 weeks of exposure serum cholesterol concentrations increased in a dose-dependent manner for both sexes and serum triglyceride amounts decreased for males but not for females. After 13 weeks of exposure, high-dose animals had significant increases in cholesterol (males only), triglycerides, blood urea nitrogen, and serum glutamic pyruvic transaminase (SGPT; males) and significant decreases in albumin, SGPT (females), and lactate dehydrogenase (LDH). Examination of bone-marrow preparations from exposed animals demonstrated consistent decreases in the degree of cellularity, suggesting that this organ is a target for HD. Microscopic evaluation of organ sections indicated exposure-related changes for nasal mucosa, pulmonary macrophages, thymus, liver, kidney, bone marrow, ovaries, and cecum. Results from this study indicated dose-dependent increases in the severity of the lesions observed, with few effects in the low-exposure group that were attributable to the exposure.

The phototoxic and allergenic potential of EDS liquids

Liquid fuels derived by direct coal liquefaction may be similar in boiling range and chemical composition to coal tar products. In the past, phototoxicity, an occupational skin disorder, has been associated with coal distillation. Consequently, the phototoxic properties of 5 materials representing the full boiling range of liquids derived from the EDS process were characterized utilizing a guinea pig model. Results with low boiling, coal derived liquids (less than 200 degrees C) were not different from unirradiated controls; however, liquids boiling above 200 degrees C induced phototoxic effects. These results suggest that high boiling EDS liquids may possess phototoxic potential. Differences in the phototoxic activities of liquids of similar boiling range may be related to chemical composition. A study of the allergenic potential of the EDS liquids described above was conducted utilizing the guinea pig maximization test. None of the test materials produced positive responses, suggesting that EDS liquids are low in allergenic potential.

Comparative chemical and biological analysis of coal tar-based therapeutic agents to other coal-derived materials

In this study, methodologies developed for the analysis of synthetic fuel products were applied to the coal tar fractions isolated from coal tar-based pharmaceutical products. A pharmaceutical stock solution of 20% coal tar in alcohol, a 50% coal tar bath emulsion and a 4.3% coal tar shampoo were studied. The toxicology and chemical composition of the coal tar fractions isolated from these materials were compared with an industrial coal tar and with a direct-liquefaction coal liquid product. The coal tars and coal liquid product were fractionated into chemical classes by alumina column chromatography and individual components were identified and quantitated by high-resolution gas chromatography. The microbial mutagenicity of these materials was measured against S. typhimurium, TA 98. In addition, the industrial coal tar, coal-liquid product, and coal tar isolate from the 20% coal tar in alcohol solution were tested for initiating activity in an initiation/promotion mouse skin painting assay for carcinogenicity. The chemical compositions of the coal tar-based therapeutic agents, the industrial coal tar and direct-liquefaction coal liquid were similar. With the exception of the 50% bath emulsion, the microbial mutagenicity and tumor-initiating activity in mouse skin for those materials tested were also similar.

The distribution of dermal tumorigens in coal liquids: relationship of tumorigenicity and microbial mutagenicity

Polycyclic aromatic hydrocarbons and/or their pyrolle derivatives were found to be the primary contributors to the skin tumorigenicity of the neutral fractions of two coal oils. Mutagenicity of the neutral fraction in Salmonella test strains was found to be due primarily to polycyclic aromatics containing polar substituents. Thus, the chemical classes responsible for skin tumorigenicity differ from those responsible for mutagenicity.

Mutagenic and carcinogenic activity of a hydrotreated coal liquid

A fuel-oil blend (FOB) and its hydrotreated product from the solvent-refined coal (SRC) II process were evaluated for their mutagenic and carcinogenic potential. The FOB was highly active in both cellular assays, as well as in animal (skin-painting) studies. Cell-transforming and mutagenic activities of hydrotreated FOB were consistently found to be lower than for untreated FOB. Finally, while most of the initiating activity (in the animal assay) was lost following hydrotreatment, the data indicate that the hydrotreated FOB still had significant skin-tumor-promoting activity.

Transformation of Syrian hamster embryo cells by synfuel mixtures

Existing Syrian hamster embryo (SHE) cell-transformation assay methods were modified to allow the assay of complex synfuel mixtures. A shale oil, high-molecular-weight, high-boiling distillates from two different solvent-refined coal (SRC) processes, and two crude petroleum samples caused transformation of SHE cells. Chemical fractionation of SRC-II heavy distillate and assay of resultant fractions allowed detection of significant transforming activity in chemical fractions, where such activity had not previously been observed. The polyaromatic-hydrocarbon-enriched fraction, neutral aliphatic hydrocarbon fraction, and neutral tar fraction all showed a positive response in the SHE assay. In addition, we confirmed earlier data showing that both the tar fractions (basic and neutral) and the soluble basic fractions from both SRC processes and shale oil contained genetically active materials.