240 Abstracts and comments--Fd Chem. Toxic. Vol. 20. No. 2

fibrosis were slightly (but not significantly) higher. The authors suggest that these tissue changes might indicate differences in the pattern of dust deposition in the rat lung between 'even' dosing and intermittent dosing and might warrant further investigation.

There would appear to be little evidence that inter- mittent high doses of asbestos present a significantly greater hazard than more constant low levels, but it is difficult to satisfactorily emulate the very large differ- ences in levels that can be found in the industrial environment.

Inorganic fibre migration Lee, K. P., Barras, C. E., Griffith, F. D. & Waritz, R. S. (1981). Pulmonary response and transmigration of inorganic fibers by inhalation exposure. Am. J. Path. 102, 314.

Both the capacity to produce mesotheliomas in vivo and the in vitro cytotoxic activities of fibrous mineral dusts such as potassium octatitanate seem to be deter- mined by the number of long fine fibres in the dust (Cited in F.C.T. 1980, 18, 321). Potassium octatitanate fibres are similar to asbestos in their physical con- figuration and size distribution. It is therefore not sur- prising that there is now limited evidence that potas- sium octatitanate produces mesothelioma after intrapleural implantation in rats (Stanton & Layard, National Bureau of Statutards Special Publication 505, 1978). The toxicology of potassium octatitanate itself has generated some interest because of its potential use, as a substitute for asbestos in filters, by the food industry. Although potassium octatitanate and asbestos fibres have strong physical similarities, the former are much more easily detected in tissues because of their dark colour and birefringence in polarized light. In the present study Lee et al. used potassium octatitanate (known commercially as Fybex) to study the fate of inhaled inorganic fibres.

Groups of 19-25 young adult male rats (Charles River-CD, Sprague-Dawley-derived), 12-18 Syrian male hamsters and 11-18 albino male guinea-pigs were exposed by inhalation to an average gravimetric concentration of 0'079mg Fybex/litre of air in one experiment, and to concentrations of 0.039mg/litre, 0.082 mg/litre and 0-37 mg/litre of air in another ex- periment; the numbers of Fybex fibres greater than 5/am in length per litre of air were 2.9 x 106/litre, 2'9 x 106/litre, 13"5 × 106/litre and 41'8 x 106/litre respectively. In both experiments the animals were exposed for 6 hr/day, 5 days/wk for 3 months. They were killed for autopsy and comparison with controls after a further 15-24 months.

The exposed animals showed dose-related depo- sition of Fybex dust in the lungs and pulmonary fibrosis mainly in the respiratory bronchioles, alveolar ducts, and adjoining alveoli, Pulmonary fibrosis was most prominent in the rats. There was some evidence to suggest that inhalation of Fybex was directly related to the production of mesothelioma in ham- sters. In the two lower dose groups exposed at the 2.9 x 106/litre level, one of the 30 hamsters developed epithelial-type pleural mesothelioma whereas none of

the 20 control hamsters had tumours. One of 13 ham- sters at the 13"5 x 106/litre dose level had a biphasic- type pleural mesothelioma and 1 of 16 hamsters in the high-dose group showed epithelial-type pleural mesothelioma with metastasis to the mediastinal lymph nodes. No mesotheliomas were found in the control or Fybex-treated rats or guinea-pigs.

In the lungs of each species, most short fibres (< 5/am) were phagocytosed by alveolar macrophages but long fibres (< 10/am) were phagocytosed by for- eign-body giant cells. The Fybex-laden macrophages had entered the walls and lumina of the lymphatic and blood vessels in the lungs. In addition, large numbers of dust cells had reached the thoracic lymph nodes where they had also entered into the lumina of lymphatic and blood vessels. There was some migra- tion of fibres into the liver and other organs and tissues. Giant cells loaded with long fibres were oc- casionally observed in the liver. The hearts of some hamsters revealed dust-cell infiltration with mesothe- lial hyperplasia and fibrosis. Intra- and extracellular migrating fibres were found in the gastro-intestinal tract, kidneys, pancreas, salivary gland, brain, men- inges, pituitary gland, thyroid, adrenals, extraorbital gland and pineal body, without apparent effects. Since dust-cell accumulation was considerable in the lymph nodes draining the lung but minimal in the spleen and liver, it was suggested that the main route of dust-cell migration was via the lymphatic vessels.

The authors considered these results in relation to the migration of inhaled asbestos fibres. Some Fybex particles were found in the mucosa or submucosa of the gastro-intestinal tracts of the experimental ani- mals, but not in the muscle layers of the gut. The authors therefore considered it unlikely that fibres of asbestos, ingested as contaminants of food or bever- ages, or from lung clearance mechanisms following inhalation exposure, can penetrate the gastro-intesti- hal tract and induce either gut cancer or peritoneal mesothelioma.

Heavy metal levels in pigeons Hutton, M. & Goodman, G. T. (1980). Metal con- tamination of feral pigeons Columba livia from the London area: Part 1--Tissue accumulation of lead, cadmium and zinc. Envir. Pollut. (Ser. A) 22, 207.

The abundance of alkyllead compounds due to high traffic densities in urban areas is a matter of continuing concern, and attention has recently been paid to the possible risks arising from the ingestion of lead-rich street dust, especially by children. Similarly, motor-vehicle tyres may be the source of elevated cadmium levels found in the air and dust of urban areas. In the study reported here, levels of lead, cad- mium and zinc were determined in the tissues of feral pigeons caught in Chelsea, Mortlake or Heathrow Airport (4, 8 and 18 km from the centre of London, respectively). Control birds were obtained from rural Cambridgeshire.

Tissue lead concentrations increased progressively with proximity to the city centre. The highest levels were found in bone, and females from all of the Lon- don sites contained higher bone levels of lead than