Toxicity of toner dusts

Status:

completed 02/2003

Aims:

In the past, the Ames test has been used for toxicological assessment of toner dusts. The use of this test for the assessment of toners is controversial since, whilst it is suitable for detecting mutagenicity of soluble substances from the toner coating, it does not permit assessment of the inhalation toxicity caused by particle effects. In conjunction with the Fraunhofer Institut for Toxicology and Experimental Medicine (ITEM), studies were performed regarding the toxicity of toner particles following intratracheal instillation in rats (intratracheal screening test, IST; for measurement of the inflammatory potential of dusts, in order to permit for the first time a comparison between toner dusts). An assessment of the effects was performed against a reference toner which has been subjected to comprehensive toxicological testing and which gave negative results in carcinogenicity studies with rats and golden hamsters. In the course of certification by BG-PRÜFZERT, this procedure was to improve evaluation of the pulmonary toxicological hazard of toner dusts compared to the in vitro methods used in the past.

Activities/Methods:

The test toner and the reference toner were screened in the ITEM and instilled intratracheally in rats in a particle size respirable by rats (mass median aerodynamic diameter < 5 µm). Following monitoring over seven days, a bronchoalveolar lavage was performed on the rats, and the bronchoalveolar lavage fluid obtained characterized by the differential cell count (macrophages, neutrophiles, lymphocytes) and a range of biochemical parameters (lactate dehydrogenase, ß-glucuronidase, total protein). The wet weights of the lungs were also determined. The inhalation toxicological potential of the test toner could then be assessed by comparison with the reference toner. Parallel to the intratracheal screening test (IST), an in vitro macrophage test was performed with the toners in order to permit an in vivo/in vitro comparison.

Results:

Following intratracheal instillation of very high toner doses, the test and reference toners exhibited virtually identical effects of an inflammation reaction in the lung which was clearly distinguishable from the negative controls. Minor but significant differences were observed in the differential cell count between the reference and test toners. The result of intratracheal instillation of toner can be considered indicative of a probable similarity between the particle effect of the reference and test toners. Earlier results with the test toner support the assumption that on the basis of existing findings, the particle effect alone of the toners is not toxic if a respirable dust concentration of 1.5 mg/m³ is not exceeded. The actual dust exposure arising during the operation of printers and photocopiers is substantially below this value. Higher exposures to toner dust may however arise for brief periods during changing or refilling of toner cartridges or during cleaning of the equipment. In the in-vitro macrophage test on rat cells, the reference and test toners did not differ noticeably from the negative control. Macrophages from guinea pigs exhibited a heightened release of tumour necrosis factor alpha following exposure to unsifted test toner in comparison with the medium control and the cells treated with corundum; this can be considered an indication of inflammatory characteristics of the toner in the lung. An increase in the release of lactate dehydrogenase at higher toner doses is indicative of damage to the cell membrane of the macrophages. If the results of measurement for quartz and corundum are taken as the reference, the potency of the toner is however clearly inclined much more closely towards that of corundum, which is generally regarded as being toxicologically safe. Surface constituents of the toner soluble in dimethyl sulphoxide exhibited no mutagenic action in the Ames test. The intratracheal instillation of toner should be regarded as an extension of the macrophage test, as possible toxic effects upon other cell species in the respiratory tract are detected in addition to the action of the dust upon alveolar macrophages. As screening tests, both methods permit conclusions regarding the inflammatory potential of toners in the lung. The screening methods employed do not however yield information regarding a possible sensitizing potential or the possible incidence of chronic toxic effects (due to additives on the particle surface). This method can be supplemented by the Ames test for study of the mutagenic action of surface constituents of the toner particles which are soluble in dimethyl sulphoxide. In order to rule out a dermal sensitizing potential, the toner should be tested in accordance with OECD Guidelines 406/429.

Further informations:

Last Update: