Fungi Digest Plastic Trash : Discovery News
Chemicals like BPA that leach from plastic waste have been linked to reproductive, developmental and other health issues.
With help from a little ultraviolet light, fungi can break down worrisome plastics.
The technique might help scientists develop environmentally friendly ways of disposing of "bad" plastics.
Ordinary fungi can safely break down polycarbonate plastic -- an omnipresent material that contains the worry-inducing chemical bisphenol A, or BPA.
BPA, which has been linked to a growing number of reproductive, developmental and other health issues, appears in a huge variety of plastic products, including CDs, screwdriver handles, eyeglasses frames, water bottles and toys. Worldwide, some 2.7 million tons of polycarbonate plastic is produced each year.
In experiments, three types of fungi were able to break down about 5 percent of the plastic in their lab dishes over the course a year, as long as the plastic was first zapped with ultraviolet light.
It's a small amount, said lead researcher Mukesh Doble, a chemical engineer at the Indian Institute of Technology in Madras. But the results are encouraging, he said, because no BPA leached into the solution in the process. Down the line, fungi and UV light might be part of an environmentally friendly solution for degrading BPA-containing plastic waste.
"The ultimate goal is to have a sustainable way of disposing of these polymers after they've completed their life that doesn't harm the environment," Doble said. "I think this is a good start in that direction."
As plastic waste piles up, a major fear is that sun, rain and other elements are degrading the material, causing BPA and other chemicals to leach into the environment. These chemicals eventually contaminate our water and food, and threaten our health.
To find a way to break the material down in a safer way, Doble and a colleague started experimenting with three types of fungi, which had been shown in previous work to be capable of degrading some environmental pollutants. Two of the fungal types were extracted from soil. The third is a commercial organism called white-rot fungus. It is commonly used for bioremediation.
In their laboratory, the researchers placed thin sheets of polycarbonate plastic in a liquid solution, which was fortified with some nutrients for the first 10 days to help the fungi grow. When the scientists added fungi to the mix, not much happened.
But when the researchers pre-treated the polycarbonate films by exposing them to ultraviolet light, the fungi started digesting the plastic. A year later, they reported in the journal Biomacromolecules, the fungi had broken down more than 5 percent of the plastic by weight.
"The numbers are small," Doble said. "But the most important part is that BPA is not seen in the solution at the end of one year. That means that the fungi are making use of it."
The fungi use enzymes to cut the plastic into pieces, and Doble suspects that these proteins selectively bite into regions between BPA molecules. That would prevent the chemical from leaching out into the solution. The UV light probably weakens the material enough to let the fungi in.
Someday, a system of bioreactors might use fungi to eat up UV-treated plastics, envisioned Kartik Chandran, a chemical engineer at Columbia University in New York. Further research combined with engineering, he added, could lead to synthetic versions of the fungal proteins that are doing the work.
Polycarbonates aren't the only plastics that contain BPA. And BPA isn't the only chemical of concern in the environment. Studies like this one offer hope that nature might provide answers to some of our stickiest chemical problems.
"Anywhere you look -- shaving cream, toothpaste -- you're bound to find something harmful," said Chandran, who encouraged people to seek out alternative materials, like stainless steel instead of plastic water bottles. "As we find more and more chemicals, we absolutely need to come up with biological solutions for treatment of these compounds."