Oil spills, a serious environmental issue

The discharge of oils and organic solvents into water bodies is a serious environmental issue that can cause harm to marine and freshwater ecosystems and threaten the livelihoods of communities depending on them informs a recent paper titled 'Azolla Pinnata: Sustainable floating oil cleaner of water bodies' published in ACS Omega.

Oils spell doom for biodiversity and can destroy the protective capability of animals such as otters and birds who depend on water by losing the water-repellent character of their skin and feathers, resulting in their deaths. Besides, oil leaks have deadly toxic substances that can stay for long periods in the waters harming the aquatic organisms such as fish living in the waters leading to their deaths, reducing biodiversity and altering community structures.

Traditional techniques to deal with oil spills can be harmful to the environment

Traditionally techniques for oil spill cleanup vary based on factors like spill size, location, oil type, and weather and currently used nonbiodegradable oil cleaners, such as pads, socks, and booms made of foam, rubber, or plastic can prove to be a threat to the environment. Techniques such as in situ burning emit harmful substances, and vacuum trucks, while efficient in extraction, produce harmful emissions during the process. 

These limitations highlight the need for exploring more environmentally friendly alternatives to cope with the adverse impacts of oil spill on ecosystems. Plant-based materials like coconut coir/or biochar are known to absorb oil and clean up oil spills as they have high absorption rate, are biodegradable and ecofriendly, making them a more sustainable alternative to traditional oil cleaning methods.

Azolla fern too is known to have such properties, but continues to be understudied in terms of its mode of action and effectiveness. The paper discusses the findings of a study that explores the suitability of Azolla fern (Azolla pinnata) found in large numbers in lakes and ponds for its  oil-absorbing properties. 

Azolla, a unique floating fern may provide an answer

Azolla is a rapidly growing aquatic fern that freely floats on surface of lakes and ponds as a small, flat, compact green mass. Under ideal conditions it can grow very fast doubling its biomass every three days. There are eight species of Azolla namely A. caroliniana, A. circinata, A. japonica, A. mexicana, A. microphylla, A. nilotica, A. pinnata and A. rubra. The common species of Azolla in India is Azolla pinnata.

This fast growing fern can be grown and used in areas affected by oil spills to accelerate the natural biodegradation process. In addition to their potential remediation capabilities, living floating species offer other benefits. They can help restore damaged ecosystems by providing a food source for animals living in the waters and can also be useful for bioremediation beyond oil spills such as in treating wastewater or other pollutants.

Unique Azolla leaves that attract and repel water at the same time

The unique qualities of Azolla can be attributed to its leaf structure. The floating fern has a unique hierarchical leaf surface design. This gives the fern exceptional characteristics such as superhydrophobicity, high water adhesion, and oil or organic solvent absorption capabilities. The leaf is made up of hydrophilic spots (which attract water drops) on a superhydrophobic base (that cause water to bounce and roll off as if it were mercury), which results in high water adhesion on the superhydrophobic surface. 

Thus when a water droplet comes in contact with the fern’s surface, the superhydrophobic base shapes the droplet into a spherical form due to its low surface energy. At the same time, the hydrophilic spots pin the water droplet on the leaf surface (even in an upside-down position) because of their high surface energy. This phenomenon is known as the rose-petal effect. When submerged in water, Azolla leaves absorb light oils at the air−water interface, and can extract high-density organic solvents thus cleaning water droplets of oil.

The authors argue that Azolla thus has a tremendous potential to act as a natural biodegradable material for oil remediation in  rivers, lakes, and springs because it can absorb oil and organic solvents at the air/water surface and underwater. Azolla is easily available and is economical and environmentally friendly to use showing quick growth in moving waters.

Moreover, it shows rapid growth even in flowing waters and can serve as a sustainable alternative to traditional synthetic oil-cleaning materials that affect the environment negatively. Azolla could thus pave the way for more environmentally friendly approaches to mitigate the negative impacts of oil spills and promote a cleaner water ecosystem.