Micronucleus assay, which has been used for almost sixty years, is one of the basic methodological approaches of genetic toxicology. This is also evident from more than 10,500 references found in PubMed database. These studies concern the evaluation of cytotoxicity and genotoxicity of numerous chemicals and in the last decade also nanomaterials (NM) and nanoparticles (NP). Surprisingly, no relevant human studies focused on MN formation following the exposure to NP have been reported.In our study we analyzed 4x (in September 2016 and 2017; pre-shift and post-shift each year) samples in a group of workers, working for almost 18 years in nanocomposites research, and matched controls. Detail aerosol exposure monitoring of particulate matter (PM) including nano-sized fractions was completed during working shift in a sampling day. The micronucleus assay using Pan-Centromeric Chromosome Paint was applied to recognize, beside the frequency of total micronuclei (MN) in binucleated cells (BNC), also other types of chromosomal damage (losses and breaks), including the centromere positive (CEN+) and centromere negative (CEN-) micronuclei.The monitoring data showed differences in the risk of exposure to NP related to individual working processes, as well as differences in chemical composition of nano-fraction. Cytogenetic results demonstrated consistently (both years): (i) possible adaptation to long-term exposure of NP (related to total frequency of MN), (ii) short-term (2.5 h) exposure could be a reason for the aberration increase, particularly a chromosomal losses (aneugenic effect).Keywords: Genotoxicity, human, micronucleus assay, nanoparticles, pan-centromeric FISH
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