EPR, TEM and cell viability study of asbestiform zeolite fibers in cell media

tHuman monocyte U937 cell line was used as a model to verify the toxicity of erionite and offretiteasbestiform zeolite fibers. As a presumed non-toxic reference, a fibrous scolecite zeolite was also used.To analyze the process of fiber ingestion into cells and the cells-fibers interactions, a spin-probe electronparamagnetic resonance (EPR) analysis was performed supported by transmission electron microscopy(TEM) and cell viability measurements as a function of the incubation time. Erionite fibers were fastinternalized in the membrane mainly as aggregates with radical-solution drops trapped inside, and werefound in the cytosol and at the nucleus. In 24 h, first erionite fibers rich in sodium and potassium, and thencalcium-rich erionite fibers, induced cell necrosis. The offretite fibers formed rounding electron-densefilaments which transformed in curved filaments, initially perturbing the cell structure and interacting atthe external surface more than erionite fibers. Such interactions probably diminished the toxic effect ofoffretite on cells. Interestingly, the presumed non-toxic scolecite fibers were partially internalized, induc-ing formation of swollen mitochondria and squared cells. Overall, the toxic effect of the fibrous zeoliteswas related to fiber morphology, chemical distribution of sites, structural variations and formation ofaggregates.