Microplastics are plastic particles smaller than 5 millimeters , and can reach much smaller sizes; includes nanoplastics, smaller than 100 nanometers — one ten-thousandth of a millimeter. Microplastics are produced when large pieces of plastic break down, either by physical, chemical or biological processes. The largest source of microplastics is found in garbage.
We find these types of contaminants practically everywhere . Where they have been most studied is in the sea, but they are also scattered in the atmosphere, in rivers, lakes and streams, and of course, in the soil. In this, the particles have less capacity for movement and it can happen that, where they appear, they are increasingly in greater concentration.
Plants can be seriously affected by the presence of microplastics . In general, the effects that they can suffer are related to changes in the soil structure, the immobilization of nutrients and the effects on the microbial communities of the soil, all of which can reduce the correct growth of the plant. However, some microplastics can migrate to plants through the roots and act in terms of toxicity.
Microplastics in our vegetables
The largest particles, spherical and more similar to the particles that make up the soil, tend to be retained on the surface of the root, without penetrating the tissues, and causing little significant damage. However, microplastics with sizes in the order of microns or nanometers, or those in the form of fibers, can enter the plant body through the root system , and even migrate to the aerial part through the vascular system. and accumulate in stem and leaf tissues.
A recent bibliographic review, carried out at the University of Zhejiang, China, has compiled the main studies that analyze the effects of microplastics on different plants, and among them are quite a few related to agriculture.
Microplastic particles have been observed in tissues of lettuce, wheat, spring onion, garlic, carrot and corn , among other products.
In general, as an effect of microplastics, an inhibition of the growth of plants and their fruits is observed; When this happens in agriculture, smaller fruits and vegetables are obtained. Associated with this growth problem, lignification of the roots has been observed, that is, their hardening, preventing their growth and reducing their absorption capacity, or an increase in oxidative stress, which accelerates the decomposition of chlorophyll and reduces photosynthesis .
However, studies related to the phytotoxicity of microplastics and nanoplastics have been studied for a very short time, and we will have to wait for more and better results to be sure which ones and how many harmful effects they cause to plants.
we eat plastic
In much of the food we consume there are microplastic particles. Today, we cannot avoid it.
A recent systematic review, published in February 2022, quantified the amount of microplastics in food. The most contaminated foods are fish and shellfish and beverages, with maximums above 5,600 particles per kilo of product in both cases. In fruit and vegetables they can reach up to 3000 . It is estimated that an adult can consume between 142,000 and 154,000 microplastic particles per year through diet.
The effects of microplastics on human health are not yet well studied , although we already know that, through the digestive system, they can reach the blood, and bioaccumulation has already been observed in the liver, kidneys and intestine.
We need to know more about the toxicokinetics —the set of phenomena that a particle experiences from the time it enters the body— and the toxicodynamics —the set of biochemical and physiological effects it causes— of microplastics in order to establish risk-based food safety regulations.
Food safety authorities face a real challenge in this regard . To date, it is not yet possible to estimate the number or type of adverse effects associated with exposure to microplastics through diet.
REFERENCES:
Bai, C.-L. et al. 2022. Microplastics: A review of analytical methods, occurrence and characteristics in food, and potential toxicities to biota. Science of The Total Environment, 806, 150263. DOI: 10.1016/j.scitotenv.2021.150263
Rubio-Armendáriz, C. et al. 2022. Microplastics as Emerging Food Contaminants: A Challenge for Food Safety. International Journal of Environmental Research and Public Health, 19(3), 1174. DOI: 10.3390/ijerph19031174
Yin, L. et al. 2021. Interactions between microplastics/nanoplastics and vascular plants. Environmental Pollution, 290, 117999. DOI: 10.1016/j.envpol.2021.117999
Yu, Z. et al. 2021. Sources, migration, accumulation and influence of microplastics in terrestrial plant communities. Environmental and Experimental Botany, 192, 104635. DOI: https://doi.org/10.1016/j.envexpbot.2021.104635
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