Prospects in Cadmium-Contaminated Water Management Using Free-Living Cyanobacteria (Oscillatoria sp.)

Iván Carralero Bon,Jordi Morató,Leonardo M Pérez,Lucas M Salvatierra,Luciana D Lario

doi:10.3390/w13040542

Abstract

In this study, the removal of cadmium (Cd) by free-living Oscillatoria sp. was studied. Our results showed that maximal Cd removal efficiency (~60%) by the cyanobacterial culture was achieved within 12–24 h in the presence of 5.0 or 25.0 mg/L of Cd. The mechanisms underlying this phenomenon were explored by elemental analysis and FTIR-ATR spectroscopy. It was found that metal adsorption by negatively charged functional groups in the cyanobacterial biomass was the main mechanism used by Oscillatoria sp. to remove metal from the aqueous medium, followed by Cd bioaccumulation into living cells. Additionally, Cd-exposed microalgae showed increased oxidative stress (MDA formation), a decreased dehydrogenase activity, a higher amount of soluble carbohydrates and a decreased total carotenoid concentration, as compared to the control cells. These results suggest that Oscillatoria sp. improved its antioxidative defense system under stressful conditions, through carotenoid-mediated ROS quenching and induction of carbohydrate catabolism, in order to counteract the oxidative damage and preserve the photosynthetic machinery and cellular energetics. In fact, no significant reduction in Oscillatoria sp. cell density, total protein amount, and chlorophyll a content was observed after 24-h Cd exposure, even at the highest metal concentration tested (i.e., 25.0 mg/L). Hence, the presented results are the first to describe some new insights about the metabolic and physiological behavior of living Oscillatoria sp. during Cd remediation, and open up the possibility of finding an equilibrium that maximizes metal removal performance with an active cyanobacterial metabolism, to achieve a rewarding and sustainable management of industrial metal-polluted wastewater.

Highlights

IntroductionHeavy metal pollution of fresh-water reservoirs is one of the most relevant environmental issues since toxic metal persistence in water poses a serious risk to both aquatic organisms and human beings [1]
Our results showed that an increase in Cd accumulation was detected when metal Our results showed that an increase in Cd accumulation was detected when metal concentration increased from 5.0 to 25.0 mg/L, suggesting the induction of some response concentration increased from 5.0 to 25.0 mg/L, suggesting the induction of some response mechanisms
Attenuated Total Reflectance (ATR) spectroscopy revealed that distinct functional groups present at the surface of the cyanobacterial cell walls play a significant role on metal adsorption

Summary

Introduction

Heavy metal pollution of fresh-water reservoirs is one of the most relevant environmental issues since toxic metal persistence in water poses a serious risk to both aquatic organisms and human beings [1]. Most metals are waste products of industrial and metallurgical processes and their environmental impact is largely increased due to the continuous release of aqueous effluents containing heavy metals without an appropriate treatment. This malpractice is somewhat frequent in poor and developing countries where sanitary solutions are weak and scarce, and toxic metals are often discharged into natural water sources without adequate handling, and poses a major health risk [2,3].

Methods

Results

Conclusion