‘Sea Salt as an Indicator of Seawater MP Pollution’ Factsheet
A recent study “Global Pattern of Microplastics (MPs) in Commercial Food-Grade Salts: Sea Salt as an Indicator of Seawater MP Pollution” co-designed by Professor Kim, Seung-Kyu at Incheon University and Greenpeace East Asia found positive correlations between microplastics in seawater and microplastics in sea salts which people consume everyday. It is a global pattern that the sea salt containing higher microplastic numbers were mostly located at coasts polluted by microplastics. Greenpeace is urging corporations around the world to reduce and eventually phase out single-use plastics.
Definition of Microplastics
Microplastics are small plastic pieces less than five millimeters long which come from a variety of sources of plastics. Primary microplastics are tiny pieces of manufactured plastic including microbeads. And secondary microplastics are created from larger plastic debris that degrades into smaller pieces. Microplastics can be harmful to our ocean, aquatic life and human health.
Global implications of this research
- Building on earlier studies of microplastic pollution in salt, this research is the first study of its kind in terms of scale and approach that looks at contaminant levels of a geographical spread of sea salt, and its correlation with environmental discharge and pollution levels of plastics.
- Total 39 different salt brands produced at geospatially different sites were investigated. Based on raw material and production location, the sampled salt products consist of 28 sea salts from 16 countries/regions, 9 rock salts from 8 countries/regions, and 2 lake salts from two countries/regions.
- 28 sea salt brands produced from 16 countries/regions of six continents.
Global distribution of sea salt microplastics as an indicator of seawater plastic pollution
- Among 39 different salt brands, A wide range of microplastics contents was found: zero – 1,674 n/kg (excluding one Indonesian outlier(IN-S1) of 13,629 n/kg) in sea salts, zero – 148 n/kg in rock salt, and 28 – 462 n/kg in lake salt.
- The samples of sea salt produced in Asia contained relatively higher microplastics content than those from other continents: 1,028±3,169 n/kg in Asian sea salt brands versus 39±9 n/kg in brands from other continents. While nine of the top 10 sea salts with higher microplastic contents were produced in Asian regions. No significant difference in microplastic content was observed between rock salts from Asia and the others.
- Amongst all, extremely high microplastics content was observed in one Indonesian sea salt(over 3,000 microplastic particles per 250 g sample), that suggests the sea salt can be an alternative compartment for seawater pollution monitoring. Indonesia is considered to be the second-largest plastic emitter to the ocean in the world after China mainland.
- When excluding Indonesian sea salt, 75.7% of total 3,879 particles were microplastics followed by unidentified particles (15.4%), natural polymers (7%), and mineral particles (1.9%).
- Only three brands of investigated salts –Taiwan(refined sea salt), China mainland(refined rock salt), France (unrefined sea salt produced by solar evaporation)– did not contain any microplastic particles in both replicate samples. All other salt samples contained microplastic particles.
- Abundance of microplastics in unrefined sea salts (n=25) exhibited significant linear correlations with plastic emissions via worldwide rivers as well as with microplastics pollution levels in surrounding sea waters in published literature.
- The results support not only that Asia is the hot spot of global plastic pollution as previous studies suggest, but also that sea salt can be a good indicator of the magnitude of microplastics pollution in the surrounding marine environment.
- 39个不同的食盐品牌普遍被发现含有微塑料：每公斤海盐中含微塑料0-1674个(其中不包括印度尼西亚微塑料含量异常高的海盐样本(IN-S1)，每公斤海盐含13629个微塑料)，岩盐每公斤微塑料含量在0-148 个，湖盐每公斤含量在28-462 个。
Difference from previous microplastics in salt studies
- This study gives a much broader insight than previous studies into the variation of microplastic levels in salts from different geographical regions, and how those may be influenced by regional differences in plastic pollution of the environment.
- This study compared 28 sea salt brands produced from geospatially different sites, i.e., 16 countries/regions of six continents, to reveal any relationship with marine plastic pollution. Also, rock and lake salts were also investigated for comparison.
Implication to human exposure
- The purpose of this research is not to reveal harmful effects of sea salt ingestion on the human body, but to identify linear correlations between abundance microplastics in sea salts, riverine plastic emissions and microplastic pollution levels in seawater. Through the exhibition, this research highlighted that fundamental preventive measures such as controlling environmental discharge of mismanaged plastics are required to limit human exposure to microplastics.
- Considering global mean salt-equivalent intake of 10.06 g/day, and assuming the average level of microplastics in salt determined in this investigation (including an Indonesian salt that had a particularly high level of MP), an average adult consumer of salts could take in almost 2,000 microplastics each year through salt alone. Even if we discount that highly contaminated sample, the average adult could still be consuming many hundreds of microplastics every year with their salt.
- Microplastics intakes can be largely different among different citizens in the same country/region dependent on which brand of salt they consume. Based on investigated salts, much higher exposures are expected for the consumers of salts produced in Asia.
- Microplastics are also ingested by humans via various pathways and salt ingestion might be a minor contributor, accounting for approximately 6% of total exposure.
Due to corporations’ indiscriminate and unsustainable plastic production, low possibility of recycling and lack of regulations, plastic waste has polluted the global ocean and is affecting human health. Only 9% of the world’s plastic has been recycled and 79% remains in natural environment including ocean. Greenpeace demands corporations to take responsibility for the life of its products and their potentially negative environmental and social impacts by committing to immediately reduce and ultimately moving towards a phase-out of single-use plastic packaging and items, rather than putting it on consumers.
 National Ocean Service. https://oceanservice.noaa.gov/facts/microplastics.html
 Science Advances. http://advances.sciencemag.org/content/3/7/e1700782.full