Microplastics are variously shaped plastic particles with a size of 0.1-5,000 µm (0.1 µm - 5 mm). 100 µm, i.e. 1000 times 0.1 µm, roughly corresponds to the thickness of a sheet of paper, while 5 mm corresponds to the average length of a red ant.

A basic distinction is made between primary and secondary plastic microparticles. Primary microparticles are produced specifically in the size intended for use, such as for shower gels, hand-washing soaps and toothpaste. They are used here for mechanical cleaning of the skin or teeth. Secondary microparticles are formed unintentionally from ordinary articles made of plastic as a result of aging and decomposition processes, such as abrasion from production equipment or environmental pollution. They occur much more frequently than primary plastic microparticles and are a problem in the oceans in particular. Microplastics can enter the food chain via fish and seafood.

The polymers most commonly found in microplastics include polyethylene, polypropylene and polystyrene.

Microplastics are found in soils, sediments, plants, animals, in the air and in the sea and can consequently enter the food chain. It is unintentionally introduced into the environment by humans, for example via textiles, tire wear, products such as cosmetics and detergents containing microplastics, waste, fisheries, agriculture and industry. For example, microplastics enter the sewage system via rinse water from the use of cosmetics, textile fibers from washing machine wastewater, or tire abrasion. Although wastewater treatment plants remove microplastics from wastewater, they enter the soil when sewage sludge is used as fertilizer.

According to the Austrian Federal Environment Agency, tire abrasion is the largest contributor to the release of microplastics into the environment, followed by waste disposal and textile washing.

In the course of some studies, it has already been proven that microplastics are mistaken for plankton by marine animals such as fish, mussels and shrimps, which are then ingested as food. In addition, it has already been shown that this microplastic can also be found in the gastrointestinal tracts of these animals. Nevertheless, an extremely low intake of microplastics from fish and seafood is to be expected here, since usually only gutted fish are consumed. In addition to the detection of microplastics in fish, there are also reports of the presence of microplastics in foods such as seafood, salt, sugar, honey, fruits, vegetables, rice, drinking water and beer.

Absorption of microplastics from cosmetics through healthy skin is not expected. Even through accidental swallowing of toothpaste, these particles can only be absorbed in extremely small quantities through the gastrointestinal tract due to their size, while the majority is excreted again through the stool.

The exact toxicological effects of microplastics on humans have not yet been comprehensively investigated. Both the BfR (German Federal Institute for Risk Assessment) and the EFSA (European Food Safety Authority) have already published recommendations to conduct further investigations with regard to microplastics. Due to the lack of relevant robust data, toxicological studies regarding the uptake and effect of microplastics in the human body as well as studies on the degradation of microplastics and the possible formation of nanoplastic particles in the human digestive tract, among others, are necessary for a better assessment of the health risk.

In the area of the use of microplastics in cosmetic products, there are already some producers who voluntarily refrain from adding microplastics, for example in products bearing the EU Ecolabel for "rinse-off" cosmetic products (products that are rinsed off; 2014/893/EU).

Regarding secondary microplastics from pollution, there are numerous projects as well as legislative initiatives within the EU that aim to address and reduce marine pollution, which will also reduce the generation of microplastics. In January 2018, the European Commission issued the European Strategy for Plastics in the Circular Economy, which includes numerous measures to deal with and reduce plastic/microplastics. In this context, legal framework conditions for reducing the environmental impact of certain plastic products are defined at EU level. For example, the European Commission published Directive 2019/904/EC of June 5, 2019, on reducing the impact of certain plastic products on the environment, on the basis of which a ban on the marketing of oxo-degradable plastic (= plastic containing additives that cause the plastic to break down into microparticles or chemically degrade by oxidation) has been in effect since July 3, 2021.

Investigation of microplastics in salt

As part of a priority action in 2021, we examined twenty selected samples of salt for microplastics in cooperation with the Austrian Federal Environment Agency. The aim was to obtain an overview of the composition and number of microplastic particles in table salt. Only one of the 20 samples was free of microplastics. Eight samples had microplastic contents below 500 pieces per kg, in seven samples microplastic contents between 500 and 5000 pieces per kg were determined, four samples had a content of more than 5000 particles per kg. Ten different types of plastics were identified. The results showed that in the ready-to-eat salt samples without grinders, the most abundant plastic types were polypropylene (PP), polyethylene (PE) and polyethylene terephthalate (PET). On the other hand, in samples from pre-filled salt mills, the plastic types most commonly identified were polycarbonate (PC) and polystyrene (PS), followed by polypropylene (PP). These originate predominantly from the abrasion of the grinding mills. The three salt samples from Austria showed little to no microplastics.

Avoiding the formation of further microplastics, for example by:

• Using reusable instead of disposable products (containers, bags, etc.), e.g. storage containers made of glass and cloth carrier bags made of natural fibers
• Correct disposal of plastic products that are no longer needed via recycling collection points or household waste
• Preference for textiles made of natural fibers
• Preference for cosmetics and detergents that do not contain microplastics

If microplastics are ingested orally, either by swallowing toothpaste or by eating contaminated seafood, the actual uptake via the gastrointestinal tract into the body's cells is low. Here, the respective particle size plays a role above all. According to EFSA, only particles with a size of less than 150 µm can be absorbed, and of these only a maximum of 0.3%. The toxicological relevance of the uptake of such small quantities of microplastics into the body's cells is still largely unclear.

Microplastics can also be a source of pollutants, which are either added during plastic production (additives) and may contain plasticizers, for example, or which are adsorbed during their residence time in the sea or in the environment. Organic and inorganic pollutants found in seawater that can adhere to microplastics and subsequently accumulate there include, in particular, compounds such as organic chlorine compounds (e.g. polychlorinated biphenyls (PCBs), pesticides) or polycyclic aromatic hydrocarbons (PAHs).

In a worst-case scenario calculation, EFSA concludes that 225 g of mussel meat (1 serving of mussels) would ingest around 7 µg of plastic. At the same time, this would correspond to less than 0.01% of the estimated daily intake of the contaminants PCBs and PHAs, and less than 2% of the estimated daily intake of bisphenol A. Accordingly, EFSA concludes that even excessive consumption of seafood does not have a significant impact on the intake of pollutants associated with plastics.

Soil Plastic App: Colorful Soil - How much plastic is hiding in our soils?

Minagris: Micro- and Nanoplastics in Agricultural Soils: Sources, Environmental Behavior, and Ecosystem Impacts.