Most sea salt contains microplastics, study finds
Salt samples from 8 different countries revealed the presence of plastic contaminants from ocean pollution.
Oh, we are a special species. Not only did we figure out how to make something as ridiculously durable as plastic, but then we decided to use it for things that don't require durability – things like single-use shopping bags and the grit in face scrubs. And best yet? Once plastic's short use for our needs is complete, we allow ourselves to let 13 million metric tons of the stuff find its way into the oceans each year. According to a 2014 study, there are more than 5 trillion pieces of plastic in the sea, 92 percent of which are microplastics less than five millimeters (0.2 inches) in size.
Back in 2015, a study looking at salt in China found plastic in salt purchased in supermarkets there. It was thought possible that this could be found elsewhere as well. And sure enough, such seems to be the case as has been revealed in new research published in Scientific Reports.
Aquatic toxicologist Ali Karami and his team from the Universiti Putra Malaysia analysed sea salt extracted from eight different countries: Australia, France, Iran, Japan, Malaysia, New Zealand, Portugal, and South Africa.
In their lab they removed suspected microplastic particles larger than 0.149 mm (0.0059 inches) from 17 different salt brands. Microplastics were found in all but the French salt; of the 72 extracted particles they found, 41.6 percent were plastic polymers, 23.6 percent were pigments (from plastic), 5.50 percent were amorphous carbon, and 29.1 percent remained unidentified. The unidentified particles were likely unable to be determined because of photo-degradation, weathering and/or additive. The authors write:
The most common plastic polymers were polypropylene (40.0%) and polyethylene (33.3%). Fragments were the primary form of MPs [microplastics] (63.8%) followed by filaments (25.6%) and films (10.6%). According to our results, the low level of anthropogenic particles intake from the salts (maximum 37 particles per individual per annum) warrants negligible health impacts. However, to better understand the health risks associated with salt consumption, further development in extraction protocols are needed to isolate anthropogenic particles smaller than 149 μm.
Microscopic images of some of the extracted particles. A (a) polyisoprene/polystyrene, (b) polyethylene, and (c) pigment (phthalocyanine) fragment. Image d is a nylon-6 filament. Photo: Karami et al./CC BY 2.0
An expert in global ocean circulation and plastic pollution, Erik van Sebille from Utrecht University in the Netherlands, tells Hakai magazine that the findings are at once surprising and not. “Over the last few years, whenever scientists have gone out to look for plastic in the ocean, they have almost always found it. Whether on the remote ocean floor, in the ice in the Arctic, in the stomachs of seabirds and fish, or now in sea salt.
“Plastic in the ocean is an atrocity," he adds, "a testament to humanity’s filthy habits, but we don’t know exactly what harm it does to marine life or to us.”
Noting that sea salt is not the only vehicle that microplastics hitch upon to enter our diet, Karami says that small doses from multiple sources could add up.
“If we suspect these microplastics are toxic – if we suspect they might pose some health concerns – we have to be worried about them, until we are sure that they are safe,” he says.
Not to be taken with a grain of salt; read the study at Scientific Reports.