Warning: wild mushrooms may contain microplastics

Attention: it is important first to understand microplastics

Before delving into the heart of the mycological issue, it is essential to define our "antagonist" with precision: microplastics. Often mentioned in the media, microplastics require a technical understanding to fully assess the scope of the problem. This paragraph provides a solid, scientific foundation on the nature, origin, and spread of these contaminants.

What exactly are microplastics? A technical classification

The term "microplastic" does not refer to a single material, but to a heterogeneous category of solid, water-insoluble, microscopic contaminants. The most widely accepted definition by the scientific community classifies them as particles of synthetic polymeric material with a size smaller than 5 millimeters. However, this classification includes a wide range of subcategories, each with distinct properties and origins.

Primary microplastics are intentionally produced in small sizes. Emblematic examples are the microbeads used until recently in cosmetics like scrubs and toothpaste, pellets (or "nurdles") which are the raw material of the plastics industry, and synthetic fibers that detach from textiles during washing. These enter the environment mainly through water discharges.

Secondary microplastics, instead, originate from the progressive fragmentation of larger plastic items. Exposure to weathering, ultraviolet radiation from the sun, the mechanical action of waves, and physical friction degrade bottles, bags, fishing nets, and other manufactured items, breaking them down into increasingly smaller fragments. This process is relentless and represents the primary source of microplastics in ecosystems.

Sources of microplastic pollution: a continuous and global flow

Global production of plastic has exceeded 400 million tons per year, an enormous amount of which a significant portion is not recycled or disposed of correctly. The pathways for microplastics to enter the environment are multiple and interconnected.

• Urban wastewater: even the most modern treatment plants capture only a portion of microplastics, especially the thinner fibers.
• Agriculture: the use of sewage sludge as fertilizer and plastic mulching films is a direct vector of microplastics into agricultural soils.
• Waste degradation: illegal dumps and mismanagement of plastic waste are primary sources of secondary microplastics.
• Tire wear: has been identified as one of the most underestimated and abundant sources of microplastics, which reach water bodies and soils through runoff.

To understand the pervasiveness of the phenomenon, consider the following table estimating the annual contribution of microplastics from different sources in a European context:

The fungus-microplastic interaction: physiological mechanisms of absorption and accumulation

The kingdom of fungi possesses unique characteristics that make it particularly vulnerable to the accumulation of contaminants, but also extraordinarily useful as a bioindicator. Fungi, unlike plants, are not autotrophic organisms. Their metabolism and nutritional strategy are based on the direct absorption of nutrients from the surrounding environment through the mycelium. It is precisely in this fundamental physiological process that the key to understanding how microplastics enter their system lies.

The mycelium: a non-selective subterranean absorption network

The mycelium is the vegetative part of the fungus, a dense network of hyphae that extends into the substrate (soil, wood, litter). Its primary function is to secrete enzymes to degrade complex organic matter and absorb the resulting simple nutrients. Absorption occurs through the entire surface of the hyphae, a process that is by its nature not entirely selective. While absorbing water, ions, and nutrient molecules, the mycelium can also absorb particles of sizes compatible with its transport mechanisms. Electron microscopy studies have shown that microplastics, especially nanoplastics (smaller than 0.1 micrometers), can be internalized within the hyphae, probably through endocytosis processes or simply physically along with the water flow.

Bioaccumulation and translocation: the journey of microplastics to the sporocarp

Once internalized in the mycelium, microplastics do not necessarily remain confined to the subterranean network. The phenomenon of bioaccumulation occurs when the concentration of a contaminant inside an organism is higher than that present in the surrounding environment.

Fungi, like many other organisms, can bioaccumulate microplastics. Even more relevant for foragers is the process of translocation. To support the growth of the fruiting body (the mushroom we pick), the mycelium mobilizes nutritional resources and water, actively transporting them to the forming sporocarp.

Unfortunately, this internal transport mechanism can also convey the absorbed microplastics, which end up concentrating in the edible mushroom. The concentration in the sporocarp can be several times higher than that detected in the surrounding soil, depending on the fungal species and the type of microplastic.

For an in-depth look at mycological analysis techniques and research on environmental contamination, an authoritative reference in Italy is the Higher Institute for Environmental Protection and Research (ISPRA).

Scientific evidence: data and research on microplastic accumulation in edible mushrooms

The physiological theory now finds solid confirmation in the scientific literature. In the last five years, a growing number of studies have systematically investigated the presence of microplastics in different species of wild and cultivated mushrooms, providing alarming quantitative data. This paragraph reports and analyzes the most significant results of this research, offering a realistic picture of the scope of the phenomenon.

Pioneering studies and subsequent confirmations

One of the most cited studies, published in the journal "Environmental Science & Technology", analyzed mushroom samples collected in different regions of Europe, including woods considered pristine. The researchers detected the presence of microplastics in over 80% of the analyzed samples. Concentrations ranged from a few units to several hundred particles per gram of the mushroom's dry weight. Another study, conducted in China, found microplastics in all analyzed mushroom samples, from both rural and urban areas, suggesting the problem is global and not confined to industrialized zones alone.

Differences between species: hyperaccumulators and low-absorption species

Not all mushroom species accumulate microplastics to the same extent. Research is beginning to identify specific patterns. Mycorrhizal fungi, which live in close association with tree roots, seem to be particularly efficient at absorbing microplastics from the rhizosphere soil. Species such as Boletus edulis (porcini) and some Lactarius have been found with high concentrations. In contrast, saprophytic fungi, which feed on dead organic matter, and parasitic fungi might show different accumulation dynamics, although data are not yet conclusive. The following table summarizes preliminary results of microplastic concentrations (particles/g dry weight) in some common species, based on a meta-analysis of recent studies:

Implications for human health: what does it mean to ingest mushrooms containing microplastics?

The spontaneous question, which directly interests every forager and consumer, is: what are the health risks associated with ingesting mushrooms containing microplastics? At the moment, there are no long-term epidemiological studies that have established a direct causal link. However, toxicology allows us to formulate hypotheses based on the known mechanisms of action of microplastics and data from other areas of food research.

The physical and chemical risk associated with microplastics

The risk can be divided into two main categories: physical and chemical. The physical risk is linked to the presence of the particles themselves in the digestive system. Microscopic-sized particles could, in theory, cause localized inflammation at the intestinal epithelium level, translocate through the intestinal barrier and enter the lymphatic and circulatory systems, with effects that are still largely unknown.

The chemical risk is perhaps even more insidious. Plastic materials are not pure polymers: they contain additives such as phthalates, bisphenol A (BPA), brominated flame retardants, and UV stabilizers, many of which are known endocrine disruptors. These substances can migrate from the plastic particle into the mushroom's tissues and, subsequently, into our bodies. Furthermore, microplastics act as "vectors" for other environmental contaminants (e.g., pesticides, hydrocarbons) that can adsorb onto their surface.

Exposure assessment and the precautionary principle

The extent of the risk for a consumer depends on the exposure dose. Occasional consumption of wild mushrooms likely poses a negligible risk compared to our total exposure to microplastics from other sources (bottled water, seafood, sea salt, air). However, for professional foragers, communities that base a significant part of their diet on mushrooms, or for "heavy consumer" enthusiasts, exposure could be significant and deserves particular attention.

In the absence of definitive data, applying the precautionary principle is the wisest choice. This does not mean stopping mushroom foraging, but adopting behaviors that minimize risk, as illustrated in the next paragraph.

For official updates on food safety and contaminants, the institutional reference is the Website of the European Food Safety Authority (EFSA).

Risk prevention and mitigation: practical guidelines for foragers and mycoculturists

Faced with this evidence, the approach should not be one of indiscriminate alarm, but of awareness and informed action. There are practical strategies that foragers and cultivators can implement to reduce exposure to microplastics present in mushrooms. This paragraph is dedicated to providing concrete guidelines based on ecological and scientific common sense.

Choice of foraging location: the first and most important barrier

The concentration of microplastics in the soil is not uniform. Avoiding areas with evident anthropogenic impact is the first step. It is essential to pay attention not to pick mushrooms near busy roads (due to tire wear), agricultural fields where plastic mulching or sewage sludge is used, illegal dumps, and watercourses that could receive urban discharges.

Prefer mature and intact woods, as far as possible from pollution sources. Protected areas and natural parks, although not immune, generally offer better conditions.

Cleaning and preparation practices: can the microplastic load be reduced?

Cleaning the mushroom begins in the woods, by removing as much soil attached to the stem as possible. At home, thorough cleaning is essential. Washing mushrooms is a debated topic among purists, but in the context of microplastics, a quick rinse under cold running water, followed by brushing with a soft-bristled brush, can help remove surface particles. Prolonged washing or soaking is not recommended, as it could promote hydration and the absorption of any water-soluble contaminants.

Cooking, although it does not destroy microplastics, remains a fundamental practice for eliminating bacteria, parasites, and for degrading many other natural toxins present in some species.

The future of mycoculture: pure substrates and state-of-the-art filters

For mycoculturists, control of the growth substrate is the most powerful weapon. The choice of high-quality, certified raw materials, such as untreated straw, sawdust from sustainable sources, and contaminant-free supplements, is crucial. Using irrigation water filtered with micro-filtration or reverse osmosis systems can prevent the introduction of microplastics into the cultivation cycle.

Research is also exploring the use of fungi themselves (for example, species of Pleurotus) for the bioremediation (mycoremediation) of soils contaminated by plastics, exploiting their ability to absorb and partially degrade them.

Attention: the future leads towards conscious foraging and cultivation

The discovery that wild mushrooms accumulate microplastics represents a further, powerful signal of the profound imprint that humans are leaving on the planet. Even the purest and wildest products of nature are no longer immune to the consequences of plastic pollution. However, this awareness must not lead to resignation, but to action.

For the forager, it means adopting a new ethics of foraging, made of careful choice of locations and an even deeper respect for the ecosystem. For the mycoculturist, it means investing in the quality and traceability of substrates. For the researcher, it means deepening studies on hyperaccumulator species, translocation mechanisms, and potential health effects.

Mycology today finds itself having to integrate microplastic contamination among the parameters for evaluating the quality and safety of mushrooms. It is a complex challenge, but facing it with scientific rigor and passion is the only way to preserve the pleasure and tradition of foraging for future generations.