[Peroral toxicological assessment of bentonite nanoclay used in the food industry].

Bentonite nanoclay (NC) manufactured from the natural sedimentary mineral bentonite contains more than 90% montmorillonite. Currently, it is widely used in food industry as processed aids - adsorbents for the purification of vegetable oils and beverages. Clay minerals have also applications as food additives and components in composite package materials. In vitro studies have shown that various forms of NC exerted cytotoxicity in many cell lines, whereas in vivo evidence of NC oral toxicity is contradictory. Therefore, this study aimed to assess the acute oral toxicity of NC and to evaluate its toxicological characteristics in a subacute 92-day experiment on Wistar rats with a daily oral administration in doses of 1, 10, and 100 mg/kg body weight (bw). Material and methods. The NC acute toxicity was evaluated in 8 male and 8 female rats with the initial bw 236±10 and 203± 10 g, respectively. NC was administered as an aqueous dispersion intragastrically at a dose of 5 g/kg bw. On the 14th day (end of the experiment), an autopsy of the chest and abdominal organs was performed. The subacute experiment was carried out on 64 male rats with an average initial bw of 117±7 g. During the experiment the levels of anxiety and memory function were evaluated using the test "Conditional reflex of passive avoidance". On the 90th day of the experiment, diurnal urinary excretion of creatinine and selenium was evaluated. At the end of the experiment, the integral parameters, the state of the intestinal wall permeability were assessed. Hematological and biochemical parameters were examined in blood, the content of non-protein thiols and the number of cells in apoptosis were determined in liver, and the state of cultivated microbiome populations was studied in cecum. Results. The results of the determination of NC acute toxicity showed the absence of rat's mortality and specific pathological changes in the internal organs at a dose as large as 5000 mg/kg bw, which allowed attributing NC to the V hazard class. Nevertheless, under the conditions of the 92-day experiment, NC caused some adverse biological effects on rat's organism. So, even at an NC dose of 1 mg/kg bw, there was a sharp inhibition of the symbiotic bifidobacterium growth, an increase in platelet count, in LDL and the LDL/HDL ratio, together with the presence of hypertriglyceridemia. At a dose of 10 mg/kg bw, an increase in spleen mass and a decrease in the de Ritis coefficient (AsAT/AlAT) were established. At a dose of 100 mg/kg bw there were shifts in the leukocyte blood count, an excessive enterococci growth in the cecum, significantly increased animal bw, along with the decrease of AsAT/AlAT and the level of serum nitrogen metabolites, indirectly indicating inhibition of catabolic processes. However, at the highest dose of NC, intestinal absorption of the protein antigen - ovalbumin, was apparently completely blocked. Conclusion. The data obtained have shown that NC has potentially adverse effects on the rats mainly at a dose of 100 mg/kg bw, nevertheless, its NOAEL in the 92-day daily oral exposure experiment is probably less than 1 mg/kg bw.