TOXICOLOGICAL INVESTIGATIONS ON SILICON-CARBIDE .2. IN-VITRO CELL TESTS AND LONG-TERM INJECTION TESTS

Silicon carbide (SiC) dust and other dusts for comparison were injecte d intratracheally at a high dose (50 mg) into rats and the response of the lungs and the lymph nodes was studied after an appropriate experi mental period. The indices studied were: histological changes in the l ung and lymph nodes, organ weights, the formation of collagenous fibre s, and the appearance of quartz typical areas. According to several ep idemiological investigations and previous experimental animal studies, SiC produces silicogenic (fibrogenic) effects. No changes in the tiss ues studied in terms of damaging fibrogenic effects could be found aft er eight months (first series) and three and 12 months (second series) . In particular, the histological findings and the absence of quartz t ypical areas as well as the quantitative determination of collagen fib res show that SiC had no harmful effects on tissues. Based on these re sults, the extent to which other exposures during the production of Si C can be responsible for the established radiological alterations is d iscussed. Without doubt the following may be confounders: SiC fibres, crystalline SiO2 (quartz, cristobalite, tridymite), and possibly gasli ke emissions (SO2). From the hygienic medical point of view the workpl aces during SiC manufacture should be examined carefully. The substanc e SiC dust as such can be considered as inert from the experimental re sults based on qualitative and extremely sensitive procedures. A revis ion of the present threshold value for SiC in the German MAK list is c alled for.