Effect of Al2O3 nanoparticles on soil microbiocenosis, antioxidant status and intestinal microflora of red californian worm (Eisenia foetida)

With the accumulation of experimental data it is evident that nanomaterials, which are widely used in human activity, look promising for agronomy. However, available publications on a comprehensive assessment of biological risks arising from nanoherbicides, nanofertilizers, etc., in particular on how the metal nanoparticles affect geobionts, are very limited. In the model experiments with California red worms Eisenia foetida as test organisms we studied the influence of aluminum oxide nanoparticles on soil biocoenosis and their biodegradation. We found an increase in mortality of worms up to 20 % at the maximum dosage of aluminum oxide nanoparticles introduced into the soil. Assay of antioxidant defense enzyme activity in the E. foetida revealed an increased superoxide dismutase and catalase level as influenced by the studied nanoparticles. The positive effect of their vermicomposting was shown. At increasing content of aluminum oxide nanoparticles (the nanoparticle dosage of 50, 100, 300, and 3000 mg/kg in the groups 1, 2, 3, and 4, respectively), the 61.7-67.6 % reduction in soil microorganism counts was found without vermicomposting vs. 55.6-61.3 % under vermicomposting. The number of microorganisms in the soil decreased in the groups 1, 2, 3 and 4 by 42.8, 52.4, 61.9 and 76.2 % for fungi, by 64.3, 77.9, 78.6 and 85.7 % for nitrogen-fixing bacteria, and by 22.7, 38.6, 84.1 and 86.4 % for bacteria cultured on starch-and-ammonia agar. The number of cellulolytic bacteria increased by 6.9 % in the group 1 and decreased by 16.7, 12.5 and 25.0 % in the groups 2, 3 and 4, respectively. A similar trend was observed under the influence of aluminum oxide nanoparticles on the E. foetida intestinal microflora. As the soil content of aluminum oxide nanoparticles increased from 50 to 3000 g/kg, the total number of microorganisms in the E. foetida intestine decreased by 9.7 to 43.2 %. In this, fungi decreased in the groups 1, 2, 3 and 4 by 18.0, 20.0, 39.0 and 40.0 % as compared to control. The number of nitrogen-fixing bacteria was insignificant in the control samples and decreased in the E. foetida intestine in the groups 1, 2, 3 and 4 by 16.0, 60.0, 78.8 and 80.0 %. The cellulolytic bacteria counts increased in the intestine of E. foetida (by 16.0 %) at minimum nanoparticle dosages, whereas in the groups 2, 3 and 4 this index was lower by 8.0, 32.0, 25.0 and 40.0 %. The number of bacteria cultured on starch-and-ammonia agar decreased in the E. foetida intestine in groups 1, 2, 3 and 4 by 13.3, 46.7, 60.0 and 73.3 %. Therefore, our data indicate dose-dependent effects of aluminum oxide nanoparticles and gradual development of their toxicity toward soil and intestinal microflora at increasing levels in the soil. The negative impact of the aluminum oxide nanoparticles on soil biocenosis was shown that was manifested in its depletion, leading to soil degradation and decreased fertility. We confirmed the necessity for complex assessment of nanoparticle biotoxicity in a variety of habitats. The antioxidant system activity in the presence of Al2O3 nanoparticles is indicative of E. foetida adaptability to stress caused by these agents.