Sea Salt Contaminated with Microplastics
Tiny plastic bits, collectively known as microplastics, are showing up in bodies of water around the world, and are accumulating in aquatic creatures, including fish and shellfish. Now scientists, after testing a sampling of commercial products in China, have reported for the first time that they could be contaminating sea salt.
Microplastics are defined as plastic particles smaller than five millimeters in size. They come from a variety of sources, including industrial waste, personal care products and plastic litter that degrade in the environment. What this pollution means for aquatic life and people who consume seafood isn’t clear, but experts have raised concerns about potential health effects.
Some lab tests have shown nano-sized plastic fragments can enter cells and cause tissue damage. With increasing reports on this issue, Huahong Shi and colleagues from the East China Normal University wanted to see whether microplastics might also be in sea salt. The seasoning is made by evaporating sea water and is now a popular alternative to regular table salt, which comes from underground deposits.
The researchers tested 15 brands of sea salts, lake salts and rock and well salts from underground deposits purchased at Chinese supermarkets. The sea salts contained the highest concentrations of microplastics from 550 to 681 particles per kilogram. Rock and well salts had the lowest amounts ranging from 7 to 204 particles per kilogram, suggesting these salts from dry deposits likely get contaminated during processing.
If adults were to consume sea salt at the recommended nutritional level for the seasoning, they could potentially ingest 1,000 microplastic particles every year (about three a day). For the sake of comparison, another study has estimated that many Europeans consume about 11,000 of these particles every year by eating contaminated shellfish.
The study, published in the American Chemical Society (ACS) journal Environmental Science & Technology, follows another one by Shi published in Environmental Pollution which surveyed nine species of Chinese bivalves including mussels, scallops, oysters and clams. That analysis turned up two to 10 microplastics, mainly fibers, per gram of edible bivalve tissue.
Eating a lot of these animals tainted at this level could add 100,000 particles of microplastics to the human diet each year, Shi’s team estimates. This value is much higher than the 11,000 particles per year to which the top shellfish-consumers in Europe might be exposed.
Other recent studies have shown that fragments of plastic now make up a significant proportion of the sand on beaches around the world, and plastic debris has been found in some of the deepest parts of the world’s oceans. Planktonic animals have been filmed eating microplastics, suggesting their impact on the food chain may be greater than anticipated.