Occupational and Environmental Medicine 1994;51:492-499 Biological effects of inhaled magnesium sulphate whiskers in rats

Male Wistar rats were exposed to two types ofmagnesium sulphate whiskers by inhalation for six hours a day, five days a week, for four weeks (sub-chronic study), or for one year (chronic study) to clarify the biological effects of the whiskers. There were few whiskers detected in the rat lungs even at one day after the exposure, suggesting that they are dissolved and eliminated rapidly from the lungs. To measure the clearance rate of the whiskers from the lungs, an intratracheal instillation was performed in golden hamsters. The half life of the whiskers in the lung was determined as 17-6 minutes by temporally measuring the magnesium concentration up to 80 minutes after the instillation. A histopathological examination indicated a frequent occurrence of adenoma and carcinoma in the year after chronic exposure, but it was not significantly different between exposed and control rats. (Occup Environ Med 1994;5l:492-499) cal properties of fibres, as well as their geometric characteristics, are important factors for biological effects. For example, the fibres that have lower solubility will persist longer in the body. The surface charge might be associated with pathogenicity,"2 and acid treatment was effective in decreasing pathogenicity of the fibres,"3 suggesting that differences in chemical characteristics could cause different interactions between the tissues and fibres even when the geometrical sizes are the same. The purpose of the present study was to investigate biological effects of magnesium sulphate whisker. As it is important to know the basic characteristics of the whiskers, some physical and chemical properties that may be associated with biological effects were measured in advance of animal experiments. Then, rats were exposed to the whiskers by inhalation to establish the durability and histopathological effects of the whiskers. The clearance rate of the whiskers in the lungsthat is, an index of durability-was determined by temporally measuring the amounts ofmagnesium in the lungs after intratracheally injecting the whiskers into hamsters. Department of Environmental Health Engineering, Institute of Industrial Ecological Sciences H Hori S Ishimatsu T Oyabu H Yamato I Tanaka Department of Pathology and Oncology, School of Medicine T Kasai J Haratake Department ofWork Systems and Health, Institute ofIndustrial Ecological Sciences, University of Occupational and Environmental Health, Japan, Kitakyushu 807, Japan T Higashi Correspondence to: Dr Hajime Hori, Department of Environmental Health Engineering, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Japan, 1-1 Iseigaoka Yahatanishi-ku, Kitakyushu 807, Japan. Accepted for publication 18 March 1994 Many kinds of manmade mineral fibres (MMMFs) have been developed in recent years as asbestos substitutes or as reinforcements, insulators, and friction materials. Magnesium sulphate whisker is an MMMF synthesised from magnesium sulphate and magnesium hydroxide by hydrothermal reaction at 100-300'C. It is used as a reinforcement for plastics and rubbers and a thickener of paint materials and epoxy adhesives. In general, not only asbestos but also respirable long fibres with a small diameter have been suspected of exerting strong biological effects-for instance, acting as carcinogens. l 2 To verify this hypothesis, many in vivo'-5 and in vitro68 studies have been reported for MMMFs, especially for glass fibres, ceramic fibres, and slug/rock fibres. Magnesium sulphate whisker is a fibrous material with a large aspect ratio, so that some biological effects might be suspected. The effects of magnesium sulphate whisker have not been established yet, however, because it is a newly developed material. Adachi et a19-"1 showed an increase in tumours in hamsters that were given magnesium sulphate whisker by intratracheal instillation, but there is no report available on inhalation studies that resemble actual exposure in the work environment. Recently, it has been shown that the chemiMethods MEASUREMENT OF PHYSICAL AND CHEMICAL CHARACTERISTICS OF WHISKERS Materials Whiskers studied consisted of magnesium sulphate and magnesium hydroxide (MgSO4 5Mg(OH)2 3HO), commercial name; MOSHIGE (UBE industries, Japan). Two types of whiskers, short whiskers (USW) and long whiskers (ULW) were examined. Length and diameter of the whiskers A scanning electron microscope (Hitachi, S700, Japan) was used to obtain the distribution of whisker lengths and diameters. The measurements were taken in accordance with the WHO method.'4 Because MOS-HIGE is soluble in water, the whiskers were suspended in cyclohexane and collected on a nucleopore filter (25 mm diameter, pore size 0-25,um). Photos were taken at a magnification of 2000. The magnification was increased up to 20 000 to obtain a higher accuracy for measuring whiskers with a small diameter. The diameter and the length of the whiskers were measured with a backlight digitiser (Graphtec, Japan, KD-3030D). The diameter was measured at the centre of the whisker and the length was measured along the curve on the developed negative films or enlarged photos. 492 group.bmj.com on July 4, 2017 Published by http://oem.bmj.com/ Downloaded from