Nanoparticle Fertilizer Could Improve CO2 Capture by Phytoplankton

In addition to lowering CO₂ emissions, capturing and sequestering carbon dioxide to remove it from the atmosphere is a useful approach to mitigating climate change. The oceans play an important role in this due to their potential to store large amounts of CO₂. Phytoplankton, for example, consists of microscopic organisms in the oceans that perform photosynthesis and can, thus, capture CO₂. They ultimately sink to the deep sea or even the ocean floor, where the captured carbon is then stored for long periods of time.

Artificial ocean fertilization (AOF) could stimulate phytoplankton growth and CO₂ uptake in the oceans by introducing an additional source of a limiting nutrient, such as iron. However, the added nutrients can suffer from low bioavailability and the “export” of captured carbon to the ocean floor can be slow.

Michael F. Hochella Jr., Pacific Northwest National Laboratory, Richland, WA, USA, and Virginia Tech, Blacksburg, VA, USA, and colleagues have investigated whether engineered nanoparticles (ENPs) can help to overcome these problems. The team analyzed 123 existing studies. They found several positive aspects of the use of ENPs. For example, ENPs can attach to the plankton’s cell surfaces, which could help with nutrient uptake and allow the use of lower overall concentrations than when soluble “fertilizer” is employed.

Nanoparticles can also be designed as composites that include secondary nutrients such as trace metals. Adsorbed nanoparticles could also repel animals that feed on the plankton and improve the rates at which the phytoplankton sinks to the deep sea after carbon capture. The team found that ENP concentrations that induce phytoplankton growth are mostly below toxic ranges. Nevertheless, the potential toxicity of ENPs to marine ecosystems under realistic conditions and unknown long-term impacts need careful consideration in the further development of this concept.