Friedrich Pott

Results of current intraperitoneal carcinogenicity studies with mineral and vitreous fibres

The study includes some 50 groups of male or female Wistar rats tested in three series. Except for one untreated group and 3 vehicle control groups, the animals were injected intraperitoneally (i.p.) once or repeatedly with dust suspensions and then examined, after lifetime observation up to 30 months, for tumours in the abdominal cavity. 1 granular dust (silicon carbide), 2 asbestos dusts (crocidolite, tremolite) and 11 vitreous fibre dust samples were administered. 5 of the vitreous fibre types were fine fibre fractions from 4 commercial insulation wools and 1 experimental wool, the others were prepared by milling glass microfibres, which have, per se, a small diameter range. The dosage per rat differed over a wide range in accordance with experience from earlier studies. The lowest dose was 0.04 x 10(9) crocidolite fibres in 0.5 mg dust, and the highest amounted to 20 x 10(9) glass fibres in 1000 mg divided into 40 weekly injections. Two mesotheliomas were found in a total of 395 rats treated with saline or granular silicon carbide (250 or 1000 mg). Eleven fibre dusts produced dose-dependent mesotheliomas at rates of up to 97 %, but the calculated fibre number > 5 micrometers in length required for inducing a 25 % tumour risk differed between the fibre samples tested in the relation of 1 to about 1000. UICC-like crocidolite heads the ranking order; the glass fibre B-01, which possesses a low durability in the body, ends it together with a rather thin sample of glass fibre type B-09. The stone fibre MMVF-21 takes a high place in the ranking order, similar to the tremolite sample. The results correspond to those of earlier i.p. tests.

Tumours by the Intraperitoneal and Intrapleural Routes and their Significance for the Classification of Mineral Fibres

In 1967, the first author of this paper started intraperitoneal studies on the carcinogenicity of asbestos. Later Wagner and coworkers (1974) published their large inhalation experiment with five asbestos types and this provided the incentive to perform similar inhalation studies with man-made mineral fibres. This aim was achieved in 1983 after some years of planning and the construction of the facilities for inhalation toxicology at the Fraunhofer Institute in Hannover. It was a great disappointment that Muhle and coworkers (1987) at the new facilities could not even find a clear carcinogenic effect in the groups exposed to chrysotile or crocidolite. Even in a parallel injection study with about 109 chrysotile fibres there was no clear carcinogenic effect. In these experiments Californian chrysotile was used as a positive control following the recommendation of NIOSH. The crocidolite sample used gave an unequivocally positive result after intraperitoneal injection of a relatively low number of fibres but no significant carcinogenic effect could be detected in the inhalation study. This compares with the work of Wagner and others (1985, 1987) who also failed to reproduce the high tumour rates observed with crocidolite in their previous inhalation study.

Urinary and faecal excretion of pyrene and hydroxypyrene by rats after oral, intraperitoneal, intratracheal or intrapulmonary application

The urinary and faecal excretion of pyrene and 1-hydroxypyrene after oral (53.4%), intraperitoneal (3.1%), intratracheal (30-37%) and intrapulmonary application (0.003%) to rats has been determined by means of gas chromatography/mass spectrometry and the excretion rates were found to depend on the mode of application. With regard to the low urinary excretion rates, 1-hydroxypyrene seems not to be very suitable as a biological marker for PAH exposure to man.

Estimation of a lifetime unit lung cancer risk for benzo(a)pyrene based on tumour rates in rats exposed to coal tar/pitch condensation aerosol

Female Wistar rats were exposed to coal tar/pitch condensation (CTP) aerosol containing either 20 or 46 micrograms/m3 benzo(a)pyrene (BaP) among other polycyclic aromatic hydrocarbons (PAH) 17 h/day and 5 days/week for 10 or 20 months followed by a clean air period of up to 20 or 10 months, respectively. Based on the inhaled BaP, given as BaP exposure concentration multiplied by the total exposure time, the cumulative dose of inhaled BaP of the 4 exposure groups was 71, 142, 158 and 321 mg BaP/m3 x h and the corresponding lung tumour rates were 4.2, 33.3, 38.9 and 97.2%. There was no lung tumour in the control group. Using the US Environmental Protection Agency (EPA) linearized multistage model, the lifetime lung tumour risk for rats exposed to 1 microgram/m3 BaP as a constituent of a complex PAH mixture may be 2% or correspondingly 2 per 100,000 with a BaP concentration of 1 ng/m3. The estimation of the unit lung cancer risk for BaP based on epidemiological data from coking plants was 7-9%.

Lung Tumor Risk Estimates from Rat Studies with Not Specifically Toxic Granular Dusts

Abstract:  Since 1985 several carcinogenicity studies have been published about lung tumors in rats after exposure to respirable granular biodurable particles without known significant specific toxicity (abbreviation of this complex definition by the three letters GBP to substitute the former term inert dusts). During this time, the relevance of the carcinogenicity of GBP in rats was questioned, for example, because no lung tumors from GBP were found in hamsters and carcinogenicity in mice was questionable. However, the carcinogenesis and the tumor risk from quartz appear similar in men and rats, and the effects of GBP in rats appear not to differ, on principle, from that of quartz, but at a much higher dose level. We calculated the excess risk (ER) of GBP in rats from the final results of an instillation study with 16 GBP types in connection with results of inhalation experiments with carbon black, titanium dioxide, and diesel particles. Retained particle volume together with some indicator of particle size was identified as the best suitable dose metric and the dose‐response relationships were analyzed on the basis of the multistage model. By relating the results to the available dose–response slopes after inhalation, ER for workplace‐like exposure were calculated for three particle size classes and an exposure to 0.3 mg/m3 (density 2–2.5 g/mL); mean diameter 1.8–4 μm (GBP‐fine‐large): ER 0.1%; 0.09–0.2 μm (GBP‐fine‐small): ER 0.2%; 0.01–0.03 μm (GBP‐ultra‐fine): ER 0.5%.

Intraperitoneal Injection Studies for the Evaluation of the Carcinogenicity of Fibrous Phyllosilicates

A review of the inhalation studies performed with crocidolite shows that, in the case of mineral fibres, realistic exposure can lead to irrelevant (false negative) results. The intraperitoneal test with mineral dusts in rats is much more sensitive and the qualitative analogy to the carcinogenicity found in the lung is good. Evaluation of the carcinogenicity of different fibre types according to their activity after i.p. injection may be justified. New measurements of fibres tested in earlier experiments indicate that at least 0.5 to 1 × 109 fibres longer than 5 pm should be injected for a negative result to become valid. About 109 fibres of chrysotile Calidria did not show a clear carcinogenic effect in contrast to 4 × 107 fibres of UICC chrysotile from Canada which induced tumours in about 30% of the rats.

Comparison of primary lung tumor incidences in the rat evaluated by the standard microscopy method and by multiple step sections

The data presented in this paper have been derived from a carcinogenicity experiment with rats as part of a comprehensive research project focused on experimental studies on the toxicity and carcinogenicity of intratracheally instilled granular dusts [Ernst H, Rittinghausen S, Bartsch W, Creutzenberg O, Dasenbrock C, Görlitz B-D et al. Pulmonary inflammation in rats after intratracheal instillation of quartz, amorphous SiO(2), carbon black, and coal dust and the influence of poly-2-vinylpyridine-N-oxide (PVNO). Exp Toxicol Pathol 2002; 54: 109-26; Ernst H, Kolling A, Bellmann B, Rittinghausen S, Heinrich U, Pott F. Pathogenetische und immunbiologische Untersuchungen zur Frage: Ist die Extrapolation der Staubkanzerogenität von der Ratte auf den Menschen gerechtfertigt? Teil II: Histologie. Abschlussbericht. Umweltforschungsplan des Bundesministeriums für Umwelt, Naturschutz und Reaktorsicherheit. November 2005. http://www.umweltdaten.de/publikationen/fpdf-l/3033.pdf]. The results of the standard approach to histological sampling in rodent carcinogenicity inhalation studies were compared to those obtained after supplemental evaluation of step sections at intervals of 250microm through the entire lung. Seven lung tissue specimens (six sections) each of 251 rats (55 rats of the control group, 53 rats of the group treated with quartz DQ 12, 56 rats of the group treated with quartz DQ 12 and PVNO (poly-2-vinylpyridine-N-oxide), 53 rats of the group treated with amorphous SiO(2), and 17 rats each of the groups treated with coal dust and carbon black) were evaluated by light microscopy. At least 60 hematoxylin and eosin (H&E)-stained sections per lung were evaluated of 99 female rats (30 rats of the control group, 7 rats each of the groups treated with quartz, quartz and PVNO, and carbon black, 31 rats of the group treated with amorphous SiO(2), and 17 rats treated with coal dust). For the neoplastic and pre-neoplastic lesions detected in the serial slides an approximate value of the whole tumor volume was calculated. The detection of tumors with a diameter of 0.25mm was possible. Based on the size distribution of 75 tumor volumes, the probability of detecting a tumor was 86% when using 12 sections. The addition of step sections enhanced the tumor detection rate from 17 to a total number of 44 lung tumors in the quartz-treated rats, from 6 to 10 in the quartz- and PVNO-treated rats, from 4 to 11 in the amorphous SiO(2)-treated rats, and from 4 to 10 in the carbon black-treated rats. Both the tumor multiplicity and the number of rats with pre-neoplastic lesions increased. These additional data corroborated the initial findings in all experimental groups and provided statistically significant results confirming the equivocal evidence of carcinogenic activity of amorphous SiO(2) in female Wistar rats. This technique offered accurate information on the incidence, histological type, size, and location of proliferative lesions in the entire lung, but the benefit must be balanced against the extra financial effort.

Detection of mineral fibre carcinogenicity with the intraperitoneal test—Recent results and their validity

The general experimental design of intraperitoneal (i.p.) carcinogenicity studies with inorganic fibres in rats is described. In a current study, in addition to glass microfibres, size-separated fine respirable fractions of commercial insulation wools (MMVF-11 and MMVF-21) also induced mesotheliomas after i.p. injection of 0.4 x 10(9) fibres. These fibre samples were also tested in inhalation studies. A special glass fibre type (B-01), which is of interest because of its low biodurability, induced tumours with 25- and 50-fold higher doses. The i.p. model has been proved to be much more specific and sensitive for testing the carcinogenicity of inorganic fibres than the inhalation model. Objections to this conclusion are cited and discussed with alternative arguments.

Polycyclic aromatic hydrocarbons in human bronchial carcinoma

A study was made to determine whether and to what extent polycyclic aromatic hydrocarbons (PAH) are present in human bronchial carcinoma. Twenty-four carcinomas, obtained from surgical operations and autopsies, were examined. The samples were tested for 12 PAH; these were determined by direct fluorescence analysis on thin-layer plates. Only 4 of the 12 PAH were detected in the cancerous tissue: benzo(a)pyrene, fluoranthene, benzo(ghi)perylene. Beno(a)pyrene was found in all carcinomas. The reasons for increased concentration of the detected PAH in cancerous tissue are discussed with respect to deposition and elimination of inhaled particles as well as the metabolism of these compounds.

Durability of Various Mineral Fibres in Rat Lungs

The durability of crocidolite, glass fibres, and wollastonite in rat lungs was examined after intratracheal instillation. Experiments were based on the assumption that thin ( 5 µm) and durable fibres are of special importance for the carcinogenic potency of these materials. After serial sacrifices up to two years after administration of the test materials, the retained fibres in lungs were analysed by scanning or transmission electron microscopy. Retention half times of between 10 and more than 500 days were calculated for the various fibre types investigated.