A discovery by researchers from Flinders University enables the removal of mercury from water & soil
ABC TV’s “Catalyst” program recently discussed mercury levels in fish. They reported that fish are a healthy source of protein and omega-3 fatty acids, but high mercury levels in fish can be a problem.
At very high concentrations, mercury has a profound toxic effect on human beings. It is hoped that a new invention can help with the mercury problem.
One of the most toxic forms of mercury is methylmercury. It consists of one mercury atom bonded to one carbon and three hydrogen atoms, and it can be created as a by-product of bacteria consuming mercury in sediments.
According to Dr Hugh Jones, “From the sediments, it can then be transported to the food chains. Eventually it ended up in the fish and those are fish we eat.”
According to Dr Simon Apte, “Methylmercury is one of the most toxic forms of mercury and one of the most commonly encountered forms of mercury that human beings will be exposed to. It can cause all sorts of neurological problems like shaking, memory loss, change in behaviour, numbness, lack of sensation, all those sorts of things, and ultimately, at very high concentrations, it can cause death.”
Dr Simon Apte has been researching mercury contamination for almost 30 years. He says, “We routinely test a variety of different specimens for mercury concentrations. We look at the total mercury concentration and, importantly, we also analyse the methylmercury concentrations.”
There is an exciting new invention for dealing with mercury problems. Dr Justin Chalker and student researcher, Max Worthington, from Flinders University in South Australia began a research project intending to make a new type of plastic from sustainable materials. That material was sulphur, an abundant waste product.
According to Dr Chalker, “Sulphur is produced in more than 70 million tonnes per year. There is so much sulphur produced each year that it’s incredibly cheap. They’ll pay you to take it away. The first experiment using sulphur to make a polymer was a very simple one where we simply melted sulphur and it becomes polymeric. The problem is, after it cools down, this material is very brittle. It falls apart very easily. And so we had to go back to the drawing board and figure out a way to make polymeric sulphur, but a way in which it can stay as a polymer. To meet this challenge, we considered different molecules that could react with sulphur and hold it in the polymeric state.
One of them that struck our attention was one that’s derive from plant sources – limonene. Limonene is the main component of orange oil. The citrus industry makes more than 70,000 tonnes of limonene per year, and it’s used as a solvent and you may have smelt it yourself in some cleaning products.
At this stage in the research, mercury wasn’t even on our radar. But it occurred to us, because our plastic has very high sulphur content, it should bind to certain types of metals. It’s known that sulphur does have a high affinity for metals like mercury. And so the next experiment that was the logical progression in this research was to see how our sulphur-limonene polysulfide interacted with mercury.”
Max and Justin set out to experiment and characterise the properties of the new polymer. Dr Chalker says, “The first time we did this experiment, we took a sample of our polysulfide and we added a solution of mercury chloride to it. Mercury chloride is a type of inorganic mercury that’s soluble in water.” Max and Justin applied just a drop of the mercury chloride solution to the surface of the polysulfide and then left it for a while. After 30 minutes or more, something interesting happened. The mercury in the water seemed to be absorbed by Justin and Max’s polymer. When they removed the excess water with a pipette, they could see that the mercury left behind had turned the polymer yellow.
“Typically when we measure the amount of mercury left in this water, we find that 50% has been removed”, says Max. On discovering that the polysulfide could remove mercury from water, they thought to try a more complex solution. They went on to try a soil sample spiked with mercury and found that, again, the polysulfide turned yellow. This result verified that it had been successful in removing mercury from the soil sample.
They anticipate that their material will also bind to methylmercury, but they haven’t yet been able to verify that in the laboratory. “We have a polysulfide that can remove mercury from water . . . and we’re hoping that this technology can be adapted to improve the environment”, they say. Justin and Max’s invention still has a lot of development ahead of it.
Steve Reynolds is the current President of MLSSA and is a long-standing member of the Society. Steve is a keen diver, underwater explorer, photographer and is chief author of the Society's extensive back catalogue of newsletters and journals.