The presence of microplastics in agricultural soils has become one of the greatest environmental challenges of our time, with consequences that go far beyond simple visual pollution. Although we used to think of the oceans as the great sinks for plastic waste, the reality is that agricultural lands are accumulating alarming levels of tiny plastic particles that threaten both soil fertility and human health.
In recent years, several international and European studies have focused on the "silent spread" of microplastics and nanoplastics, not only in the soil but also through the food chain until they reach our plates. From crops as common as lettuce and carrots to the proven presence of microplastics in human organs, this phenomenon raises urgent concerns for farmers, consumers, and regulators.
What are microplastics and where do they come from?
Microplastics are plastic fragments smaller than 5 millimeters, while nanoplastics are even smaller. There are two main types: primary, manufactured in this size for products such as cosmetics or cleaning products, and secondary, which are the result of the degradation of larger plastic objects, such as bags, bottles, agricultural films, or textile fibers.
In agriculture, the main source of this waste is plastics used for mulching, irrigation, containers, sludge fertilizers, and the use of plastic machinery. The use of plastic films in fields—known as agricultural mulch—leaves a persistent trail in the soil, as between 10% and 20% of these materials are not properly removed and continue to fragment year after year. Other sources include atmospheric dust, irrigation water, and even rain contaminated with wind-borne microplastics.
Why are microplastics in the soil a problem?
Agricultural soil is not just an inert support, but a complex ecosystem teeming with microorganisms essential for plant fertility and health. The accumulation of plastics alters both physical (aeration, water retention) and chemical properties, as additives and components in plastics can be released over time, altering soil pH, nutrients, and structure.
One of the most worrying aspects is that microplastics act as sponges for unwanted contaminants: They are capable of absorbing and transporting heavy metals, pesticides, herbicides, and other persistent organic pollutants. This property makes microplastics vectors that facilitate the accumulation of toxins in plants and, therefore, their entry into the food chain.
Impact on soil microorganisms
Recent research in Spain has shown that the microbial biodiversity of agricultural soil is seriously altered by the presence of microplastics. Studies conducted on conventional and organic farms in the Mediterranean region have shown that, although certain bacteria (such as those of the Solirubrobacterales and Acidobacteriotas orders) appear to find advantages in adhering to plastic fragments, other communities essential to soil health, such as Clostridiales, decline significantly.
Fungi, on the other hand, mostly ignore the presence of plastic, but the total number of beneficial microorganisms ends up being reduced. This results in reduced nutrient flow and less positive interaction between bacteria and plant roots, directly affecting agricultural production and soil resilience to disease and environmental stress.
Furthermore, pesticide residues that cling to plastic fragments do not discriminate and eliminate both pathogenic and beneficial microorganisms. This double attack – on the one hand chemical and on the other physical-biological – alters the ecological balance of the soil.
Absorption of microplastics by plants and their passage into the food chain
Various experiments have confirmed that microplastics and nanoplastics can be absorbed by the roots of crops such as lettuce, wheat, or carrots, and transported to their edible organs. Scientific evidence indicates that these particles do not remain on the soil surface, but can end up in our bodies on a continuous and chronic basis, which is causing growing concern.
Microplastics have also been shown to act as carriers of antimicrobial resistance genes (ARGs). Microbial biofilms that form on plastic surfaces facilitate the horizontal transfer of these genes, increasing the spread of antibiotic resistance, a serious public health problem worldwide.
Human health: What risks exist?
The discovery of microplastics in vital human organs such as the lungs, blood, brain, heart, and placenta has set off alarm bells. Although the precise toxicity at ambient doses is not yet known, the potential for bioaccumulation and the presence of chemical additives such as phthalates or flame retardants (PBDEs)—linked to endocrine disruption, cardiovascular disease, and neurodegenerative diseases—indicate that the health risk may be significant.
Added to this is the lack of knowledge about the potential effects of bisphenol A (BPA) substitutes, such as BPF or BPS, which are already present in agricultural materials and also exhibit hormone-disrupting activity. The lack of specific regulations on the presence of microplastics and additives in agricultural soil exacerbates the situation and leaves the population unprotected.
Methodological challenges: Why is it so difficult to measure microplastics in soil?
One of the barriers to progress in managing the problem is the technical difficulty of detecting, quantifying, and characterizing microplastics in matrices as complex as agricultural soil. Unlike water or air, where filters or nets can be used, soil sampling requires much more laborious and costly extraction and analysis techniques.
Plastic content can vary greatly between plots, and protocols are not yet standardized. Furthermore, the presence of high organic matter in the soil makes it difficult to identify the smallest plastic fragments. In 100 grams of soil, only a few particles are detectable microplastics.
What alternatives exist in agriculture to curb the microplastics crisis?
The solution to the problem requires a multidisciplinary approach and the collaboration of researchers, farmers, industries, and regulators. Among the most urgent measures are:
- Develop and use truly biodegradable bioplastics capable of disappearing under real-world field conditions without leaving toxic residues.
- Promote agroecological strategies that minimize the use of plastics and replace chemical pesticides and fungicides with biological alternatives.
- Develop more effective detection technologies and establish standard protocols that allow for realistic comparison of studies and pollution monitoring.
Projects like Smart Sprays are already working on non-toxic bioplastic barriers that can be easily applied to the soil and retain water without contaminating it. Furthermore, research into composting and biodegradable mulch films is key to reducing the amount of plastics entering farmland.
Legal limitations and lack of regulations
One of the major shortcomings identified by the scientific community is the almost total absence of specific regulations regarding the presence of microplastics in agricultural soils. This makes it difficult to control, monitor, and penalize bad practices, perpetuating the continued entry of plastic waste into agriculture and, therefore, into human food.
At the international level, concern is beginning to be reflected in forums such as the UN, which has already included plastic pollution among the ten most serious environmental problems on the planet. However, regulation lags far behind technological advancements and the advancement of the plastics industry, leaving significant legal loopholes.
Challenges and future of research
Research on microplastics in agricultural soils is still in its early stages, but the impact on fertility, the soil microbiome, and food safety is increasingly being identified. Experts are calling for greater toxicological rigor, long-term field analysis, and the integration of ecological, health, and socioeconomic data to understand the true scope of this global challenge.
International collaboration and the development of more sustainable and responsible technologies are key to preventing agriculture from transforming from a source of food into a source of chronic plastic pollution.
