Litter & microplastics features in table salts from marine origin: Italian versus Croatian brands

Highlights

• Italian and Croatian brands of fine iodate marine salts are studied.

• Total impurities and microplastic levels are correlated.

• Italian and Croatian brands resulted highly polluted than literature.

• Clear PP fibres affect Croatian brands.

Abstract

This study estimates litter content, including microplastics, mesoplastic, and macroplastic in marine table salts coming from Italy and Croatia. Both high (HC) and low (LC) costs commercial brands easily found at the supermarket were analysed. Any macroplastic or mesoplastic were recovered while microplastics and other litter impurities significantly affect table salts of all tested brands. Average microplastic values ranged within 1.57 (HC) – 8.23 (LC) (Italy) and 27.13 (HC) – 31.68 (LC) items/g (Croatia). Microplastics sizes (min-max) ranged within 4–2100 μm (Italy) and 15–4628 μm (Croatia). In samples from both Nations, a significant general positive correlation between the average number of items/g recorded and the total amount of general impurities was recorded. Concerning microplastic shapes, in Italy, fragments dominated even if fibres, granules, films, and foams are frequently recorded. On the contrary, clear PP fibres dominated in Croatian brands even if also other shape classes were recorded.

Introduction

Plastic debris is currently a huge problem of global concern (Hollman et al., 2013) that affects the environment entirely. From sediments (Blašković et al., 2017; Cannas et al., 2017; Renzi et al., 2018a, Renzi et al., 2018b) and water (Eriksen et al., 2013; Zettler et al., 2013) to the animals (Fossi et al., 2016) and humans (EFSA, 2016). Is widely established the transmission of the microplastic through the food chain (Avio et al., 2015). Now more than ever we are aware of the possible action of the plastic litter on human's health. Litter transfer from marine ecosystems to humans represent an important task that should be better described and clarified by the literature to achieve Horizon 2020 targets concerning the Marine Strategy Framework Directive principal purposes (2008/56/EC).

Humans are exposed by diet to plastic litter intake (EFSA, 2016) and seafood represent the most explored source of pollution coming from marine trophic web (Avio et al., 2015).

In coastal area, salt flats represent important coastal areas of great ecological and economical interest at the interface between land and sea and exposed, as coastal transitional ecosystems (Renzi et al., 2012; Renzi et al., 2013), to different kinds of human pressure. That activity could produce significant effects on plastic litter accumulation both in local trophic webs and commercial products. In spite of that, recent literature focuses their research on plastic pollution risks related to natural seafood and maricultured products (Avio et al., 2015; Dehaut et al., 2016; Pellini et al., 2018) and shows that seafood, as well as pelagic and benthonic fish species is affected by microplastics and, in particular, by fibres (Neves et al., 2015). Mussels and other filter feeding bivalves show a large number of individuals affected by the plastic litter (Karlsson et al., 2017; Van Cauwenberghe et al., 2015; Renzi et al., 2018a, Renzi et al., 2018b). There are different types of table salts related to the salt origin as well as sea salt, lake salt, rock salt, river salt, well salt. Production processes are different for different salt types; sea and lake salts are obtained by water evaporation, rocky salt is obtained by mining, while river and well salt is obtained from wells in non-coastal zones (Iñiguez et al., 2017).

Very few studies are performed on table salt from marine origin that represent another important commercial product coming from the sea and potentially affected by marine pollution by plastic litter. Two studies performed recently evaluated levels of plastic litter in table sea salts (Iñiguez et al., 2017; Karami et al., 2017). Karami et al. (2017) performed plastic litter determinations on 17 salt brands from 8 different countries and evidenced that microplastics (171–515 μm) were present in almost all brands at concentrations included between 1 and 10 MPs/kg of salt. Related to shape, authors evidenced that fragments were dominant (63.8%) followed by fibres (25.6%) and films (10.6%). A research performed in Spain by Iñiguez et al. (2017) on 21 different samples of commercial table salts, evidenced ranges within 50–280 MPs/kg salt with any differences between samples due to the origin (sea salts and well salts) and treatments (before and after packaging). Nevertheless, researches on this field are far to be exhaustive.

The aim of this study was to evaluate litter content, including microplastics, in eleven different commercial brands of iodate fine table salts produced in by six different Italian brands and five Croatian brands of sea salt produced locally. Analysed salt samples were easily found at the supermarket and sold in carton (Italian; Croatian) and plastic (Croatian) packs. Total amounts, principal features of recovered litter (including microplastic, mesoplastic, macroplastic), and possible differences among high cost (HC) and low cost (LC) brands were checked.