Battle against mercury pollution using fake sponges.

Mercury exists in nature at low concentrations. Normally mercury is not harmful, but due to human emission the quantities become harmful. Researchers at the Zhejiang University (China) have developed a fake sponge that can absorb mercury from the oceans. 

Where does mercury come from?

Long before humans started releasing mercury, there was already mercury present in the atmosphere and in the oceans. This is caused by natural processes such as earthquakes and volcano eruptions. Mercury is released from the inside of the earth and is released into the atmosphere. As long as the amount of mercury remains low, there is not much to worry about. However, processes such as burning fossil fuels and gold mining have increased the amount of mercury. Rain and snow take the mercury from the atmosphere into the oceans, increasing the concentrations. Since the beginning of the industrial revolution, this has resulted in a tripling of mercury in the oceans.

Mercury, a danger for human and animal.

When mercury ends up in the oceans, it can turn into methylmercury via a chemical reaction. Methyl mercury is a very toxic compound. It penetrates plankton and bacteria. It then accumulates in fish through the food chain. As a result, the amount of mercury can reach up to 13000x the amount in water! When eating fish, the mercury enters the body. This happened in 1956 in Minamata Bay (Japan), where high concentrations of methylmercury had been observed and the population mainly ate locally caught fish. Especially in the young this led to serious ailments such as muscle weakening, kidney failure and memory loss.

Wisdom comes with age.

An ancient group of animals comes to rescue for removing mercury from the oceans. Sponges are one of the oldest group of animals on earth, the first sponges lived about 640 million years ago! The sponges have been through a lot, which makes them immune to almost all dangers. Wherever there is water, there is sponges living at the bottom, in rivers, in seas and in the oceans. Sponges can easily reach the age of 1000 years. According to Anna de Kluijver, ecologist and biochemist at Utrecht University, sponges are ‘super-survivors’. But it is actually not the sponges, but the bacteria that live on the skeleton of the sponge that provide protection, she continues. The biggest disadvantage of purifying water with living sponges is that they only live at the bottom, and thus only filter water there.

Sponges from the laboratory.

Researchers at China’s Zhejiang University have attempted to recreate sponges to purify mercury from the water. The synthetic sponges do not resemble the organic sponges in shape. The similarity is in the skeleton. Both the biological sponge and the fake sponge have a silica skeleton. In the biological sponge, bacteria live on this skeleton. While for the synthetic sponge, iron sulphide nanoparticles have been placed on the skeleton.

Nanoparticles are like sand grains. They are 100 nanometres, about 800x thinner than a human hair! The sand grains are extremely porous, which means that there is a lot of open space on the inside. There is also a layer of aluminiumoxide on the inside, which helps in the breakdown of methylmercury. The methylmercury is sucked into the granules. Here it sticks to the sulphide so that is no longer harmful. It can also no longer be absorbed by bacteria in this way. The synthetic sponges can absorb mercury for up to 30 days before they have to be washed and can be reused.

The synthetic sponges can absorb large amounts of mercury. And if they are placed on the surface of the oceans they can also purify the water there, unlike biological sponges. Obviously, it will be better if we find alternatives to reduce mercury emissions, but before we find those we can use sponges to lower the current mercury levels in the oceans.

References.

Minamata Disease » Sustainability » Boston University. (z.d.). Boston University Sustainability. Geraadpleegd 14 oktober 2020, van https://www.bu.edu/sustainability/minamata-disease/

Sun, Y., Lou, Z., Yu, J., Zhou, X., Lv, D., Zhou, J., Baig, S. A., & Xu, X. (2017). Immobilization of mercury (II) from aqueous solution using Al 2 O 3 -supported nanoscale FeS. Chemical Engineering Journal, 323, 483–491. https://doi.org/10.1016/j.cej.2017.04.095

Staff, I. (2014, 8 augustus). Ocean Mercury Levels Have Tripled Since the Industrial Revolution. Inhabitat – Green Design, Innovation, Architecture, Green Building. https://inhabitat.com/ocean-mercury-levels-have-tripled-since-the-industrial-revolution/#:%7E:text=According%20to%20a%20letter%20published,than%20in%20the%20deep%20ocean.