Glyphosate-based formulations are among the most commonly used herbicides. For many years, glyphosate was considered a substance with relatively low toxicity to mammals that does not possess the long-term effects. However, in 2015, IARC classified glyphosate as “probably carcinogenic to humans", triggering ongoing discussions about its safety to human health. The EFSA and EPA did not share the IARC's position. Based on their opinion, glyphosate is unlikely a carcinogen to humans. Currently, there are many questions regarding the safety of glyphosate to humans, especially the long-term effects, which is an important reason for additional research. We have studied the cytogenetic effect of glyphosate in a chronic experiment using a micronucleus test on mammalian peripheral blood erythrocytes. The research was carried out in accordance with the OECD guideline No. 474 "Mammalian Erythrocyte Micronucleus Test" on outbred adult male albino rats which were fed diets containing 0, 0,15, 20, 200, 2000 and 20 000 ppm of glyphosate. The samples of peripheral blood from the tail vein of animals were taken after 3, 6 and 12 months (the end of study). Two microscope slides per animal were prepared and examined microscopically (Nikon Eclipse Ci-L, Japan). 4000 polychromatic erythrocytes (PChE) were counted per animal for the assessment of micronucleated PChE (PChEMN) incidence. No inhibition of erythropoiesis was observed in all exposure groups. After 1-year glyphosate exposure the maximum frequency of PChEMN ± SD (%) was 0,04 ± 0,03 at a dose of 0,15 ppm and 0,06 ± 0,02 at a dose of 20 000 ppm. The average frequency of PChEMN in all groups receiving the glyphosate did not significantly exceeded that ones for animals of the concurrent negative control group at α = 0.05 at all experimental time points. The frequency of PChEMN in all treatment groups was inside the Poisson based 95%-control limits. Using the Mantel-Henzel method, no dose related trends were found (p > 0,05). Thus, the chronic exposure of glyphosate at doses of 0,15–20,000 ppm did not cause an increase in the frequency of PChEMN in the peripheral blood erythrocytes of animals. The results of the micronucleus test in vivo indicate the absence of the genotoxicity of glyphosate at the 1-year chronic exposure.

Conflicts of Interest:
The authors declare no conflicts of interest. Abstract was not submitted elsewhere and published here firstly.

Funding:
The study had no sponsorship.