Abstract
Aim:
To evaluate the toxic effects of nano-zeolites on soil beneficial
microorganisms.
Methodology: This study involved dry milling of zeolites at
varying parameters to obtain dry-milled zeolites of four size regimes such as
10-100 nm, 200-400 nm, 500-1000 nm and 1000-2000 nm that were tested at incremental
concentrations such as 100 ppm, 1000 ppm and 2000 ppm along with control on
various soil beneficial microorganisms. Three replications were done for each
treatment with factorial completely randomized design. The poison food
technique, growth curve assessment followed by cytotoxicity and genotoxicity
studies on all four bacterial genera treated with zeolites of varying sizes
and doses were undertaken. The effects of zeolite on average linear growth
rate (ALGR) of biocontrol agent, Trichoderma viride were also studied.
Results:
The effect of zeolites tested on four bacterial genera viz. Azotobacter
chroococcum, Rhizobium leguminosarum, Bacillus megaterium and Pseudomonas
fluorescens using poison food technique and growth curve revealed that
zeolites regardless of size or concentration had positively influenced the
growth dynamics of all four bacteria tested. The effect of zeolite on average
linear growth rate (ALGR) of Trichoderma viride also indicated that
incremental dose of zeolite had a positive effect. Lactose dehydrogenase
revealed that 2000 ppm nano-zeolite exhibited cytotoxic effects on soil
beneficial micro-organisms tested. On the other hand, comet assay
demonstrated no quantifiable DNA damage in nano-zeolite treated cells in
comparison to control cultures.
Interpretation: This study unequivocally demonstrated
that zeolites of size greater than 200-400 nm, irrespective of doses even up
to 2000 ppm are quite safe for soil beneficial microbes.
Key words: Bacteria, Comet assay, Cytotoxicity, Nano-zeolite, Trichoderma
viride
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