Background
The global issue of microplastics
It is undeniable that we live in a “plastic age”: plastic items are used worldwide, resulting in a wide-spread dispersal and accumulation of plastic fragments in lands, air, and waters. Once in the environment, plastic particles slowly break into smaller fragments, namely microplastics (0.1µm to 5mm), through physical degradation, photodegradation, and biodegradation. Recent studies have shown that microplastics are ubiquitous in air, soil, and water, even reaching remote areas. Some reports have worryingly estimated that humans may consume up to 52,000 particles per year and inhale up to 74,000 particles per year.
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In this scenario, several effects of microplastics on aquatic organisms have been reported, while terrestrial ecosystems are still less studied, and especially pollinating insects.
Toxic effects on plants
Microplastic pollution in soil inevitably have an impact on plants through multiple potential mechanisms due to the large variety of plastic materials and the complexity of the soil environment. A wide range of effects has been reported in different plant species, including growth impairment, reduction in germination rates, genotoxic and oxidative damage, reduction in the photosynthetic activity and alterations in the plant nutrient assimilation and metabolic profile.
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Microplastic contamination in agricultural soils can also represent a crucial problem in terms of yield and economic losses for crops and human food safety: smaller particles are taken up by the plant, potentially accumulating in edible plant tissues and entering the food chain, leading to human exposure.
Pollinators at risk from microplastics
Pollinators, such as honeybees and wild solitary and social bees, interact with plants, air, soil, and water basins, and are therefore directly exposed to microplastics when foraging. Microplastics have been found in honey, in several plant species foraged by bees and on the cuticle of honeybees.
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Laboratory studies have investigated toxicity of microplastics, reporting varying effects on individual and population health of several insect species, as example; reduction of the body size, disruption of the gut microbiota, increase of susceptibility to pathogen infestation, and a general reduction of survival.
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Most of the available studies have the limitations to use unrealistic and artifact conditions: insects are exposed to sucrose solutions containing extremely high concentrations of microplastics. There is still little information on the effects of microplastics on pollinators under realistic conditions and field exposure scenarios, particularly on their behavior and cognition.
Let's keep safe pollinators
Pollinators are inextricably linked to plant biodiversity and the health of ecosystems, beeing essential for the sexual reproduction of 87.5% of all seed plants. Pollinating insects provide fundamental benefits also to the human population, considering that, globally, 1500 crops need insect pollination.
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In recent years, several factors are posing at risk the abundance and distribution of several pollinator species, causing the decline of the worldwide pollinator populations, especially bees and bumblebees: change in agricultural landscape, pathogens and parasites, climate change, indiscriminate use of synthetic and broad-spectrum pesticides, introduction of invasive species, and habitat destruction.
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Wide research is necessary to understand how microplastics may represent an additional hazard for pollinating insects and to keep safe these organisms as important as they are at risk.
