Are oranges the key to removing toxic mercury from the environment?
While the fruit alone is not enough, a team at Flinders University has developed an inexpensive, non-toxic polymer that can absorb hazardous mercury compounds out of water and soil.
The polymer material is made from sulfur and limonene, a colorless liquid hydrocarbon extracted from the peel of citrus fruits such as oranges and lemons, through a process of centrifugal separation or steam distillation. This compound is what gives citrus fruits their odor.
The limonene is combined with industrial waste sulfur and synthesized to form a sulfur-limonene polysulfide compound. This material can potentially be processed into functional coatings or molded into solid objects and used to remove palladium and mercury salts from water and soil.
When initially produced the polymer is a dark red colour, but will react chemically to the presence and absorption of mercury and turn a bright yellow.
The polymer is cheap to produce due to the global abundance of waste sulfur and limonene. Limonene is abundantly available as it is produced commercially for a number of uses including cleaning solvents, food flavouring and perfume or cosmetics.
“More than 70 million tons of sulphur are produced each year by the petroleum industry, so there are literally mountains of it lying, unused, around the globe, while more than 70 thousand tons of limonene are produced each year by the citrus industry,” said Justin Chalker, one of the researchers on the project.
“So not only is this new polymer good for solving the problem of mercury pollution, but it also has the added environmental bonus of putting this waste material to good use while converting them into a form that is much easier to store so that once the material is ‘full’ it can easily be removed and replaced,” said Chalker.
The affordability of production makes this an appealing prospect for large-scale environmental cleanup of mercury contamination in soil and large bodies of water.
It also shows promise for commercial applications such as coating domestic and waste water-carrying pipes or testing the mercury content of food products such as fish, many species of which are known to have high mercury contamination levels.
Mercury is a known toxic compound that causes illness in humans with health effects ranging from vision, speech and hearing impairment, lack of coordination and sensory impairment to damage to internal organs such as the brain, lungs and kidneys.
Mercury poisoning can also result in several diseases including acrodynia, Hunter-Russel syndrome and Minamata disease. Depending on the mercury compound, method and duration of exposure and the dose, it can also result in death.
“Mercury contamination plagues many areas of the world, affecting both food and water supplies and creating a serious need for an efficient and cost effective method to trap this mercury,” says Dr. Chalker. “Until now, there has been no such method, but the new sulfur-limonene polysulfide addresses this urgent need.”
If commercial production of this polymer material is doable, it could mean an affordable and easy way not only for industrial cleanup of mercury such as spills and environmental contamination, but also consumer-level uses.
Even small amounts of the polymer are useable as a mercury detector in areas where pollution is suspected, as the color change is a bright indicator of contaminants.
Can you imagine being able to test for mercury in a lake or public drinking water supply as easily as tossing in some rubber balls, or testing contamination levels in fish before processing or eating it?
Can you imagine cleaning up the environment around sites of mercury mining or processing facilities by mixing soil and water with mercury-absorbing objects, which can later be removed after their bright yellow color indicates their job is done?
Whether high-volume commercial production or this material would be feasible is still unknown, but the potential benefits speak loudly in favor of pursuing the option.
A paper detailing the Flinders University team’s sulfur-limonene polysulfide material is published in the journal Angewandte Chemie International Edition and can be read here.