Analysis of sea salt sold in markets on the Indonesian island of Lombok has found microplastics in every sample, suggesting that this global staple carries signs of ocean pollution.
The study's findings also show that plastic waste is contaminating common foods, including such basic items as salt.
Here's what you need to know.
In a study reported by Mongabay, a research team led by Anna Ida Sunaryo Purviyanto collected 20 sea salt samples from vendors at 10 markets on Lombok Island.
The researchers separated the suspected particles from the salt and then examined them using a stereo microscope.
Because sea salt is produced by evaporating seawater, plastic fragments in the water can end up in the final product.
Microplastics are pieces of plastic smaller than 0.2 inches (5 millimeters) that result from the breakdown of larger plastic waste.
The researchers found differences between the products. Coarse-grain sea salt contained more microplastics than fine-grain salt, likely because fine-grain salt undergoes additional washing and filtering.
However, contamination was detected in all samples, "indicating widespread contamination in the markets surveyed," the study noted.
Additional information
Taken together, the results point to microplastic pollution in the waters around Lombok Island and reveal another way that pollution enters everyday life: through salt.
This is consistent with earlier studies showing the presence of microplastics in seafood, drinking water and many other places, highlighting how widespread plastic pollution has become.
However, this study is not presented as evidence that salt itself poses a new, serious threat to human health.
Tamara Galloway, a microplastics researcher at the University of Exeter in the UK who was not involved in the study, said: "The risk to human health from microplastics in sea salt is very low, especially compared to many other sources of microplastics and associated contaminants in our diets and everyday lives.".
Instead, salt appears to be a relatively small part of a much broader public health problem, even as researchers and regulators take a closer look at how plastic gets into the food system.
What can be done?
For producers, one of the first options is more thorough washing and filtering, especially of coarse-grained sea salt, to reduce the amount of residual microplastics. This won't solve the ocean pollution problem, but it can reduce contamination in the final product.
The researchers also identified a gap in legislation. Salt products are generally not covered by standardized microplastic regulations, making it difficult to compare results and ensure quality standards are met.
Including microplastic testing in food safety and salt quality standards could provide regulators and producers with a clearer way to respond.
The study's authors articulated the problem clearly: "From a regulatory perspective, the lack of standardised guidelines for microplastic content in salt products remains a key limitation [to reducing microplastic pollution].".
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