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Tonnes of contact lenses flushed down the toilet

12/09/2018By Matthew Woodley
Up to 10 tonnes of contact lenses end up in US wastewater each year, an Arizona State University (ASU) study has found.

The results were derived from a chemical analysis of wastewater and a survey, which led the scientists to estimate that that 15–20% of US contact lens wearers flush their lenses down the sink or toilet.

“This is a pretty large number, considering roughly 45 million people in the US alone wear contact lenses, amounting to 1.8–3.36 billion lenses flushed per year,” ASU researcher and PhD student Mr Charles Rolsky said.

The scientists examined the fate of 13 different contact lens brands made from nine different types of plastic polymers. Team member Mr Varun Kelkar said the flushed lenses end up in wastewater treatment plants, where they are broken down and contribute to microplastic pollution.


“This is a pretty large number, considering roughly 45 million people in the US alone wear contact lenses, amounting to 1.8–3.36 billion lenses flushed per year.”
Charles Rolsky, ASU

“We found that there were noticeable changes in the bonds of the contact lenses after long-term treatment with the plant’s microbes,” Kelkar said.

“When the plastic loses some of its structural strength, it will break down physically. This leads to smaller plastic particles which would ultimately lead to the formation of microplastics.”

The lenses also accumulate in sewage sludge, where a pair of contact lenses can typically be found in each kilogram. As sewage sludge is an abundant material routinely applied on land for sludge disposal and soil conditioning, the presence of contact lenses creates a pathway of macro- and microplastics to enter terrestrial ecosystems where potential adverse impacts are poorly understood.

While flushing lenses is a problem for the environment, the researchers explained it could also have negative effects for people as well. Contact lenses sink as they tend to be denser than water, which could ultimately pose a threat to aquatic life, especially bottom feeders that may ingest the contacts.

Since plastics are indigestible, this dramatically affects the marine animals’ digestive system. As these animals are part of the food chain, some eventually find their way to the human food supply, which could lead to unwanted human exposures to plastic contaminants and pollutants that stick to the surfaces of the plastics.

The findings were presented at the 256th National Meeting and Exposition of the American Chemical Society (ACS), where lead researcher Professor Rolf Halden told reporters the amount of waste created in the US by contact lenses and their plastic packaging was equivalent to around 400 million toothbrushes each year.

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“These are significant pollutants. There are billions of lenses ending up in US wastewater every year. They contribute a load of at least 20,000 kilograms per year of contact lenses,” Halden said.

“Ultimately, we hope that manufacturers will conduct more research on how the lenses impact aquatic life and how fast the lenses degrade in a marine environment.”

Contact lenses recovered from treated sewage sludge could harm the environment. Credit: Charles Rolsky
Contact lenses recovered from treated sewage sludge could harm the environment. Credit: Charles Rolsky

Motivated by the study findings, the researchers have also begun to reach out to manufacturers to limit the effects of unwanted pollution from contact lens disposal.

“A simple first step would be for manufacturers to provide on product packaging, information on how to properly dispose of contact lenses, which is simply by placing them in the trash with other solid waste,” Halden said.

“A desirable long-term outcome would be to create lenses from polymers that are fine-tuned to be inert during use but labile and degradable when escaping into the environment.”

More reading:

B+L contact lens recycling program hits 140k milestone

 

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