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Chemistry

Please Pass the Plastic

Microplastics for Dinner

Scientists from the State Key Laboratory in Shanghai, China found microplastics in 15 randomly selected table salts bought in supermarkets across China. Image sources: Chesapeake Bay Program on Flickr (right) and Wikimedia Commons (left)

 

The Paper:

Yang, D.; Shi, H.; Li, L.; Li, J.; Jabeen, K.; Kolandhasamy, P. Microplastic pollution in table salts from China. Environ. Sci. Technol. 2015, 49, 13622-13627. DOI: 10.1021/acs.est.5b03163

 

Microplastics

Sea salt

An example of harvesting sea salt via evaporation ponds in India. Source: wikipedia.org

Tiny shards and fibers of plastic termed “microplastics” have been found to accumulate in seafood with unknown consequences for human health. Now, they’re turning up in a product even more difficult to avoid: Scientists from the State Key Laboratory in Shanghai, China found microplastics in 15 randomly selected table salts bought from supermarkets across China. They found that sea salts, which are usually harvested via evaporation from coastal waters, contained at least 3 times as much microplastic as salt from lakes or underground deposits.

Microplastics are tiny (less than 5 millimeters, or 0.2 inches, in size). The most common microplastics are of the very, very small variety and are difficult to see without a microscope. Some microplastics come from the degradation, abrasion, and aging of larger plastic products, whereas others, like microbeads from soaps and creams, are released as small particles.

 

This Study

Researchers collected 15 brands of table salt at random from supermarkets across China and looked at the salts under a microscope. The salts were divided into three categories depending on their origin: sea salts (harvested from evaporating sea water), lake salts (harvested from evaporating lake water), and rock/well salts (harvested from underground). Figure 1 shows the plastic particles found in some of the samples after other forms of debris (like sand and organic matter) were separated from the sample.

How Much Plastic is in Table Salt?

Yang et al. Plastics

Figure 1. Plastic particles, as seen through a microscope, collected from three different types of table salt bought from supermarkets in China. D: sea salt; E: lake salt; F: rock salt Adapted with permission from Yang et al. 2015. Copyright 2015 American Chemical Society.

Clearly, sea salts contained more microplastic than salts collected from other sources. The researchers counted about 550-681 particles per kilogram of sea salt, compared to 43-364 particles in a kilogram of lake salts, and 7-204 particles in a kilogram of rock/well salts. They found no clear differences among different brands of sea salt. The majority of microplastics found were less than 200 micrometers in size
(for reference, that’s about twice the average width
of a human hair – pretty small!).

The scientists who conducted this study noted that sea salts sold in China typically come from coastal areas with high population density, whereas lake salts typically come from remote mountainous areas and rock/well salts come from underground. This might explain, to some extent, why sea salts were much more impacted by microplastics than salts harvested from other areas.

What Kinds of Plastic are in Table Salt?

Yang et al FTIR Matches

Figure 2. FTIR absorption spectra for some of the particles identified in this study. The spectra show absorbance as wavelength of light is varied. These spectra act as fingerprints to identify the type of plastic a particle is made of. The abbreviations stand for different types of plastics and other synthetic particles, and the number in parentheses represents how well the samples matched to known spectra. Reprinted with permission from Yang et al. 2015. Copyright 2015 American Chemical Society.

After they established that the amount of microplastics was different in salts from different origins, the researchers wanted to know whether the types of microplastics found in the salts differed as well. They used a technique called Fourier Transform Infrared Spectroscopy (FTIR) to identify the materials the microplastics were made of based on differences in the way these materials absorb infrared light. They used a sort of “fingerprinting” technique to identify the plastics — they compared results from their study to spectra for known materials to see if they could find matches and identify the types of plastics present. Some of the results are shown in Figure 2.

The most common materials making up particles isolated from sea salts were PET (polyethylene terephthalate – a common plastic used in polyester clothing and food containers), PE (polyethylene – another common plastic used in plastic shopping bags, water bottles, and other food containers), and cellophane (used in fiberglass and food wrappers). Cellophane was most common in the lake and rock/well salts.

 

Why Do We Care?

They’re probably in your table salt, too:

So far, the presence of microplastics in table salt has only been reported in this one study on Chinese products. However, because salts in other parts of the world are harvested and prepared similarly, it’s very likely we’ll soon see similar studies confirming that microplastics are present in salts around the world.

Who doesn’t eat salt?

This isn’t the first time that these synthetic particles have been found in things that humans eat – they’ve also been found in various forms of seafood, including fish and shellfish. However, this is the first time they’ve been found in something that everyone, regardless of their dependence on seafood for sustenance, consumes.

It’s not just microbeads:

This study emphasizes how crucial it is for scientists to better understand the effects of microplastics on human health, as well as their effects on marine ecosystems. While usage of some microplastics, like plastic microbeads used in exfoliants, has recently been banned as their environmental repercussions are better understood, microplastics also enter the environment as larger plastic products are degraded, or plastic-containing textiles are laundered, so we’re likely to continue releasing them to the environment for many years to come. We need to keep reducing our plastic usage if we want to stop eating plastic particles.

Human health impacts:

Using the World Health Organization (WHO)’s guidelines on safe salt consumption, the authors of this study estimated that someone who consumes salt responsibly could end up ingesting about 1000 microplastic particles per year via their salt consumption. This is a low estimate, seeing as many people consume twice as much salt as WHO recommends.

The health risk associated with eating microplastics is currently unknown. Many researchers are concerned because plastics absorb harmful synthetic chemicals from the environment, concentrating them and possibly facilitating their accumulation in humans. Scientists are currently working to determine whether this is happening, and what it means for human health.

 

How do you feel about having microplastics in your body? Do you have plans to reduce your plastic usage? Let us know in the comments!

I am the founder and editor-in-chief of oceanbites, and a 5th year doctoral candidate in the Lohmann Lab at the University of Rhode Island Graduate School of Oceanography. My research focuses on how toxic chemicals like flame retardants end up in our lakes and oceans. Before graduate school, I earned a B.Sc. in chemistry from MIT and spent two years in environmental consulting. When I’m not doing chemistry in the lab, I’m doing chemistry at home (brewing beer).

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