Microplastics act as “Trojan horses” carrying toxic metals in food chain, warns study
12 Aug 2021 --- Researchers from Helmholtz Zentrum Hereon, Germany, have discovered microplastics might be transporting toxic metals into the food chain. According to the study, the smaller the plastic particles, the larger the harmful cargo they can carry.
Some metal ions, such as chromium, iron and tin attached themselves almost entirely to the microplastics. Others, such as cadmium, zinc and copper, showed almost no accumulation on the plastic over the entire test period.
In addition, the polyethylene (PE) particles showed significantly greater accumulation than the polyethylene terephthalate (PET) particles.
More concerningly for human health, the Hereon scientists showed the particles carrying metals or semi-metals released nearly all of them again under chemical conditions, such as those that prevail in the digestive tract.
Why this matters
An Australian study revealed last year that opening plastic packages can catapult up to 75,000 microplastics across three meters. Tearing open chocolate bags, cutting sealing tapes and twist-opening bottle caps generated microplastics from broken junction and cap abrasion.
In 2019, researchers warned it is “not yet totally clear just how dangerous microplastics are for living organisms.” Consequently, a “wait and see” approach should be avoided.
The Hereon research results were published in the Journal of Hazardous Materials Letters.
Periodic tables: Categorization of metals and metalloids according to the sorption extent to PE and PET microplastic particles.Selecting plastics for analysis
The team studied the accumulation of 55 different metals and semi-metals on PE and PET particles, measuring 63 to 250 micrometers in size.
“In regard to water polluted by plastics, the two types of plastics we studied play a vital role,” says first author Dr. Lars Hildebrandt, environmental chemist at Hereon.
“This is due to their wide range of applications and the associated high production volumes. Most shopping bags, for example, are made of PE and plastic drinking bottles are almost without exception made of PET.”
A study from two years ago also identified PE as one of the three most abundant microplastics in the Mediterranean coastal waters, where up to 1.9 million pieces cover one square meter of seafloor.
Microplastics all around
Two years ago, the World Health Organization posited chemicals and biofilms associated with microplastics in drinking water pose a low concern for human health. However, the organization acknowledged it was working with “limited evidence available” and encouraged more research.
Since then, researchers have flagged the persistence of microplastics in F&B applications, even in infant-feeding bottles.
The researchers also found other types of plastic, such as polyurethane, measured via digital methods (Picture: Hereon/Inorganic Environmental Chemistry).Not all is lost?
Some efforts to combat microplastics have surfaced by means of nanocellulose structures and membrane filtration technologies. In March, PackagingInsights spoke with South Korean start-up Real Water about its reusable bottle cap that filters out microplastics from water.
For future studies on microplastics as a vector for metals, the Hereon researchers advocate investigating pellets in the millimeter range, for which sorption is mostly low.
“Future studies should also consider different environmental factors, for example the presence of different natural ligands, and conservatively choose microplastic and elemental concentrations,” the study concludes.
By Anni Schleicher
