Biological Alternative to the Ecological Threat Posed by Cadmium and Lead

Abstract

Aquatic cyanobacteria are gaining importance as biological alternatives for the remediation of heavy metal–contaminated waters due to their natural abundance, rapid kinetics and metal-binding ability. The present study evaluates the abatement efficiency of lead (Pb) and cadmium (Cd) by three unicellular cyanobacterial species, Synechocystis salina, Synechococcus elongatus and Gloeocapsacrepidinum, commonly occurring in aquatic environments in and around Cochin, India. Metal removal was assessed at different concentrations using Atomic Absorption Spectrophotometry (Perkin Elmer AAS 3110). Results revealed a clear concentration-dependent abatement, with significantly higher removal at lower metal concentrations. Among the species tested, Gloeocapsacrepidinum exhibited the highest tolerance and abatement efficiency for both Pb and Cd. Time-course studies showed that maximum metal removal occurred within the first 15–30 minutes, followed by a gradual reduction in abatement rate, reaching near equilibrium within 24 hours. The study demonstrates the potential of cyanobacteria, particularly G. crepidinum, as eco-friendly and cost-effective agents for the bioremediation of Pb- and Cd-contaminated aquatic systems.

Introduction

Heavy metals in aquatic environments are dangerous because they persist in water and accumulate in the food chain, causing harmful effects even at very low concentrations. Conventional treatment methods such as precipitation and filtration are expensive, generate waste, and are often ineffective for removing trace amounts of heavy metals. Therefore, researchers are exploring biological remediation methods that use microorganisms to remove metals from water.

Cyanobacteria, a group of photosynthetic microorganisms, have strong potential for heavy metal removal because they grow rapidly and contain metal-binding functional groups in their cell walls and extracellular substances. These characteristics allow them to absorb and accumulate heavy metal ions such as lead (Pb) and cadmium (Cd) from water. This study evaluated the heavy metal removal ability of three cyanobacterial species: Synechocystis salina, Synechococcus elongatus, and Gloeocapsa crepidinum.

The organisms were cultured under controlled laboratory conditions and exposed to different concentrations of lead and cadmium. The remaining metal concentrations were measured using Atomic Absorption Spectrophotometry (AAS). Results showed that metal removal was higher at lower metal concentrations, because high concentrations negatively affect the physiological activity of the organisms.

Among the tested species, Gloeocapsa crepidinum showed the highest efficiency in removing both lead and cadmium. Time-dependent studies also showed that most metal removal occurred in the initial minutes of exposure, after which the removal rate gradually slowed down.

Conclusion

The present investigation demonstrates that heavy metal abatement by cyanobacteria is strongly influenced by metal concentration and exposure time. Reduced abatement at higher concentrations may be attributed to metal-induced physiological stress. Among the species studied, Gloeocapsacrepidinum showed superior tolerance and abatement capacity for both Pb and Cd, indicating species-specific resistance mechanisms. The lower efficiency of cyanobacteria at higher concentrations of lead and cadmium is mainly due to the saturation of available metal-binding sites and the toxic effects of these metals on cellular functions. Elevated metal levels can interfere with photosynthetic processes, trigger oxidative stress, and disrupt key enzymes and transport systems involved in metal uptake. In addition, at higher concentrations, the bioavailability of lead and cadmium decreases, which further restricts biosorption and bioaccumulation, ultimately resulting in reduced removal efficiency [11] The rapid removal observed during the initial exposure period suggests a predominantly passive biosorption mechanism involving ion exchange and surface complexation. Similar fast kinetics have been reported for cyanobacteria and microalgae by Inthorn et al. (2001). Compared to conventional physicochemical methods, cyanobacterial remediation offers advantages such as low cost, eco-friendliness, and high selectivity [10]. The study emphasizes the potential of cyanobacteria as effective biosorbents for the removal of lead and cadmium, especially at lower concentrations typical of contaminated natural waters.Among the three species selected for the study, Gloeocapsacrepidinum emerged as the most promising cyanobacterium species for bioremediation applications due to its dose-dependent and time-dependent abatement efficiency for both lead and cadmium. This may be due to the adsorption of heavy metals by the characteristic mucilage layers on cell walls of algae.

References

[1] S. E. Manahan, Environmental Chemistry. Boca Raton, FL, USA: CRC Press, 1993, 811 pp. [2] International Journal of Environmental Science and Technology, “Aims and scope,” Springer, 2025. [Online]. Available:https://www.springer.com/journal/13762. [Accessed: Mar. 4, 2026]. [3] L. Lourembam, M. Singh, and R. K. Sharma, “Cyanobacterial extracellular polymeric substances and their role in heavy metal biosorption,” Journal of Applied Phycology, vol. 36, no. 1, pp. 145–158, 2024. [4] M. Hossain and T. Okino, “Comparative evaluation of cadmium and lead removal by live cyanobacterial strains,” Environmental Pollution, vol. 345, p. 123456, 2024. [5] M. Ciani and A. Adessi, “Cyanoremediation and phyconanotechnology: Cyanobacteria for metal biosorption toward a circular economy,” Frontiers in Microbiology, vol. 14, May 2023. [6] D. Inthorn, N. Sidtitoon, S. Silapanuntakul, and A. Incharoensakdi, “Sorption of mercury, cadmium, and lead by microalgae,” ScienceAsia, vol. 27, pp. 253–261, 2001. [7] J. Wang and C. Chen, “Biosorption of heavy metals by microbial biomass,” Biotechnol. Adv., vol. 27, pp. 195–226, 2009. [8] K. S. Kumar, H. U. Dahms, E. J. Won, J. S. Lee, and K. H. Shin, “Microalgae as a promising tool for heavy metal remediation,” Ecotoxicol. Environ. Saf., vol. 190, pp. 110–114, 2020 [9] S. K. Mehta and J. P. Gaur, “Use of algae for removing heavy metal ions from wastewater,” Crit. Rev. Biotechnol., vol. 25, pp. 113–152, 2005. [10] R. B. Genter, “Bioremediation of inorganic contaminants,” Environ. Sci. Technol., vol. 30, pp. 231–238, 1996. [11] B. Volesky, “Biosorption and metal removal,” Hydrometallurgy, vol. 59, pp. 203–216, 2007.

Copyright

Copyright © 2026 Newby Joseph, Newly Joseph. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.