Global Pattern of Microplastics (MPs) in Commercial Food-Grade Salts: Sea Salt as an Indicator of Seawater MP Pollution

Abstract

Previous studies have identified microplastics (MPs) in commercial table salts but could not exactly address the origin of the MPs because of several limitations. The present study is based on the hypothesis that commercial sea salts can act as an indicator of MP pollution in the surrounding environment unless the MPs are filtered out during the manufacturing process. A total of 39 different salt brands produced at geospatially different sites, including 28 sea salt brands from 16 countries/regions on six continents, were investigated. A wide range of MP content (in number of MPs per kg of salt; n/kg) was found: 0−1674 n/kg (excluding one outlier of 13 629 n/kg) in sea salts, 0−148 n/kg in rock salt, and 28−462 n/kg in lake salt. Relatively high MP content was identified in sea salts produced in Asian countries/regions. The abundance of MPs in unrefined sea salts (n = 25) exhibited significant linear correlations with plastic emissions from worldwide rivers (r 2 = 0.33; p = 0.003) and with the MP pollution levels in surrounding seawater (r 2 = 0.46; p = 0.021) in the published literature. The results indicate that not only is Asia a hot spot of global plastic pollution, as previous studies have suggested, but also that sea salt can be a good indicator of the magnitude of MP pollution in the surrounding marine environment.

Microparticles in Table Salt: Levels and Chemical Composition of the Smallest Dimensional Fraction

“…On the basis of the absence of statistical significance with the geographical origin evidenced by this study, we cannot support that table salt can be considered a good indicator of the magnitude of the microplastic pollution in the sea of origin as previously evidenced by Kim et al [38] testing 25 samples from sampling sites worldwide. Our results could be explained by different causes: (i) tested samples come from the same marine basin (Mediterranean Sea) and evidence a narrow and low range of magnitude of microplastic pollution; (ii) we tested a minor number of samples (11 vs. 25) compared to the previous research performed by literature [38]; (iii) the geographical scale explored in this study is not relevant to evidence significant differences among tested samples; (iv) production process could contribute to the product pollution by microplastics. Further researches should be performed to evaluate how much the production process could affect marine salt pollution compared to the original pollution levels recorded in marine water to better focus this not yet clarified aspects.…”

“…Levels reported by the literature ranged within 1-806 items/kg (number of particles per kg of salt) [31,36]. Kim et al [38] suggested the occurrence of a strong relationship among pollution of marine water and pollution observed in derived table salt. In the same study, a wide range of microplastic levels 0-1674 items/kg (one outlier of 13,629 items/kg) was reported.…”

“…In the same study, 171-515 µm of particle size (min-max: 160 -980 µm) was the principal range detected; almost all of the tested brands had 1-10 items/kg within this size range. Recent research performed on 25 unrefined marine salt trademarks worldwide evidenced that sea salt can be considered a good indicator of the magnitude of microplastic pollution in the marine environment [38]. In fact, they observed that levels positively correlated with both plastic inputs from rivers (r = 0.57; p = 0.003) and pollution levels in seawaters (r = 0.68; p = 0.021) near the production area of table salt.…”

Toxicity of Microplastics and Nanoplastics in Mammalian Systems

“…While plastics are generally perceived to pose minimum risk to human, several recent scientific findings, picked up by the popular press, have heightened the worry of possible tissues penetrance and adverse effects of MPs/NPs due to their small sizes. Humans could accumulate MPs/NPs from different food sources [53,54] as well as drinking water [55,56]. Plastic water containers [57,58] and plastic teabags [59] are, perhaps unsurprisingly, common sources for human ingested MPs/NPs.…”

Microplastics generated when opening plastic packaging

“…Once introduced into the environment, the fate and transportation of microplastics can be fuelled through wind advection, stormwater runoff, drainage systems and wastewater 18 . Previous studies suggested that the environmental distribution of microplastics can consequences in food contamination via the processing and packaging of the products, as well as the geospatial location of their sources 19,20 . However, the sources of microplastics…”