Inhibition Effects of Cobalt Nano Particles Against Fresh Water Algal Blooms Caused by &amp;lt;i&amp;gt;Microcystis&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Oscillatoria&amp;lt;/i&amp;gt;

Anusha L

doi:10.11648/j.ajasr.20170304.12

Abstract

Cyanobacterial blooms deplete nutrients, reduce water clarity, exhaust carbon di oxide and produces secondary metabolites which negatively affect aquatic organisms and water quality. Control of algal blooms using metal nano particles is one effective method for the safety of water environment. Cobalt nano particles (CoNPs) were synthesized and tested against microalgae isolated from fresh water cyanobacterial blooms by assessing the effects on growth rate, biomass concentration, photosynthetic pigments concentration and antioxidant enzyme activity. Microcystis and Oscillatoria were identified as the predominant isolates from algal blooms and treated with varying concentrations (1, 2, 3, 4 and 5 mg·L-1) of CoNPs. Steady decline in the growth rate of microalgae was observed at the end of 5 days indicating the toxicity of CoNPs on microalgal growth. At the end of cultivation period, 78% and 88% of reduction in biomass concentration of Microcystis and Oscillatoria were observed at 5 mg·L-1 of CoNPs. The chlorophyll content was reduced from 1.53 to 0.24 mg·L-1 in Microcystis and 1.63 to 0.29 mg·L-1 in Oscillatoria. There was a 69.3% and 73.2% decrease in carotenoid content of Microcystis and Oscillatoria respectively. Both protein and carbohydrate contents of the microalgae were reduced with increasing concentration of nano particles. The decrease in Super oxide dismutase (SOD) activity with increased nanoparticle concentration reveals the formation of stress in the microalgae. The increasing GSH activity proved the effect of CoNPs on the activation of antioxidative enzymes to protect the cells. This study demonstrates the efficiency of cobalt nano particles (CoNPs) on inhibition of fresh water algal blooms thereby reducing the eutrophication problem.

Highlights

Microalgae utilize light, carbon di oxide and nutrients to produce biomass in water bodies which is consumed by planktonic herbivores
In order to evaluate the effect of cobalt nanoparticle on growth of Microcystis and Oscillatoria strains, 3 ml of microalgal suspension with exponential growth phase was harvested from stock cultures and was added to 150 ml of BG11 medium
Growth medium without nano particles was served as control and the experiments were performed in triplicates

Summary

Introduction

Microalgae utilize light, carbon di oxide and nutrients to produce biomass in water bodies which is consumed by planktonic herbivores. Blooms due to rapid growth, division rates, stable water column and higher nutrient upload leads to adverse tastes, odours and toxicity of affected water bodies [4]. Higher cell densities of blooms rapidly deplete nutrients, increase turbidity, and exhaust CO2 causing decline in biomass leading to decaying, odoriferous, unsightly scums. These scums contain variety of microorganisms which produce significant chemical and biological changes, release of toxic compounds, accelerated release of nutrients from sediments that aggravates eutrophication and blooms [5, 6]

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