Bioaccumulation of Lanthanum by Two Strains of Marine Diatoms Nanofrustulum shiloi and Halamphora kolbei

TL;DR

This study shows that two marine diatom species can hyperaccumulate lanthanum, a rare earth element, which could help in cleaning up polluted water.

Contribution

The study is the first to demonstrate lanthanum bioaccumulation in diatoms, revealing hyperaccumulation potential for environmental remediation.

Findings

Diatoms bioadsorb lanthanum on their frustule surfaces and hyperaccumulate it within their biomass.

Lanthanum concentration in diatom biomass increased up to 2000-fold compared to surrounding water.

High lanthanum levels negatively affect diatom growth and morphofunctional state.

Abstract

Currently, the mining and use of rare earth elements are steadily increasing. Diatoms are known to absorb various elements from the aquatic environment by adsorbing them onto the surface of their frustules and accumulating them within the cell. While there is a considerable amount of data on the bioaccumulation of various metals by diatoms, there is almost no information on the concentration of rare earth elements in their cells. Thus, the aim of this study was to determine the ability of diatoms to bioaccumulate rare earth elements by the example of lanthanum, one of the most abundant rare earth elements in the marine waters, for two strains of diatoms. As a result, the bioadsorption of lanthanum on the surfaces of frustules and its hyperaccumulation in the biomass of diatoms was revealed. This metal had a significant effect on the growth of diatoms. The results obtained regarding the bioaccumulation of lanthanum by diatoms are important for the further development of methods to treat aquatic environments contaminated with rare earth elements and for the respective bioindication.

Bioaccumulation by diatoms, as the first stage of biomineralisation, has been widely studied for various metals, such as cadmium, copper, zinc, aluminium, gold, silver, etc. However, despite the fact that the mining and utilization of rare earth elements (REEs) are currently increasing, there is almost no data on their bioaccumulation by diatoms. Therefore, the aim of this study was to determine the ability of diatoms to bioaccumulate REEs by the example of lanthanum (La), and to compare this ability for two marine diatoms Nanofrustulum shiloi and Halamphora kolbei. As a result of experiments on the cultivation of diatoms in nutrient media supplemented with La at concentrations of 10 mg·L−1 and 50 mg·L−1, energy-dispersive X-ray spectroscopy revealed the ability of diatoms to bioadsorb La on their frustule surface, as a first stage of its bioaccumulation. The high concentration of La (50 mg·L−1) has a noticeable visual effect on the morphofunctional state of diatoms and causes a decrease in the rate of accumulation. The low concentration (10 mg·L−1) promotes the hyperaccumulation of La by the diatom biomass as a whole, including both bioadsorption and bioabsorption within the cells. This resulted in an increase in La concentration in the biomass by nearly 2000-fold in H. kolbei (6.06 mg·g−1) and by 1000-fold in N. shiloi (6.90 mg·g−1). The results on La bioaccumulation by diatoms are significant for advancing methods to remediate aquatic environments contaminated with rare earth elements and for the bioindication purposes.

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