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Pyrethroids are a class of synthetic insecticides and acaricides, synthetic analogues of pyrethrins, natural constituents of Dalmatian pyrethrum flowers (Tanacetum cinerariifolium (Trevir.) Sch.Bip.).
Thanks to the similarity of the molecule, in fact, they act in the same way as the correspondents of natural origin, however overcoming the main limitation of pyrethrins and that is their photo-lability for which they are much more persistent active ingredients.
The mechanism of action is that of alterations in the nerve transmission of the insect and the action takes place by contact or ingestion. In agriculture, they are exclusively “cover” insecticides, that is, they are unable to penetrate plants to systemically defend them from insect attacks.
However, pyrethroids are widespread in anti-mosquito nebulization systems and in general in all diffusers designed to fight mosquitoes, flies and other insects.
The most common active ingredients of the pyrethroid category are:
– Permethrin;
– Cypermethrin;
– Deltamethrin;
– Fenvalerato.
These are pyrethroids are much more active and stable than those of the previous generation; they are photostable, therefore with a very persistent action, as they are not sensitive to light and heat.

Toxicity for humans –
In case of accidental intoxication, which is much more frequent when spraying is carried out in residential and urban areas, pyrethroids can cause a series of symptoms for humans including, locally: severe paraesthesia to the skin and eyes, irritation to the skin, eyes and mucous membranes.
At a systemic level, i.e. following prolonged and / or repeated exposure over time, the following may occur: chest pain, tachycardia, hypotonia, nausea, abdominal pain, diarrhea, vomiting, dizziness, blurred vision, headache, anorexia, somnolence , coma, convulsions, tremors, prostration, overreaction of the respiratory tract, pulmonary edema, palpitation, muscle fasciculation and apathy.
However, pyrethroids can take on a chronic dangerousness which is well documented on a scientific level.
In fact, the primary action of pyrethroids (as well as pyrethrins) is expressed in the sodium channels of the cell membrane which are responsible for the electrical phenomena underlying the activities of organisms. Pyrethroids are concentrated in tissues with a high lipid content, such as the nervous one. Here they intervene by disturbing the natural transmission of electrical impulses.
Now, the action of pyrethroids is the same in insects and mammals, but in the former it is much more effective. This is because insects have greater sensitivity in the sodium channels, evidently smaller body sizes, and a lower body temperature.
According to various research institutes, including the CNR, mammals are protected from the action of pyrethroids as they have limited skin absorption and are able to rapidly transform substances, making them non-toxic; however, in the event of prolonged or repeated exposure to pyrethroids, there is a real risk that they settle in the adipose tissues, including primarily the brain, whose metabolism is damaged.
Exposure to pyrethroids, however, is increased by ingestion or contact (more frequent than it seems) to substances contained in insecticides such as organ phosphorus which have the ability to limit the natural enzymatic capacity of mammals. In this case, the simultaneous exposure to this type of agents and to pyrethroids increases toxicity, making it more serious and problematic.
It should be borne in mind that the phosphoric organs are very present, at various levels, in the main foods, not produced organically, which we ingest, as they are sprayed to fight phytopathogenic insects.
In this sense, laboratory studies, such as those of the French Center national de la recherche scientifique (CNRS) carried out on mice, have shown that over time many products widely used and considered not very toxic, instead have the ability to alter gene expression, determining chronic damage.
Additional studies conducted by US government agencies such as the US National Library of Medicine and the National Institutes of Health have shown neurotoxicity problems in young subjects exposed to pyrethroids. In some cases, the induction of neuronal death has even been found, and therefore chronic problems on the central nervous system.
Among other things, the generational effects deriving from the continued use of these substances are not fully understood also because many of these pyrethroids bioaccumulate, that is, they tend to accumulate on fatty tissues, including the brain, for which they become a threat to organisms. developing, like children.
Among other things, every year, according to official databases such as ISPRA, public administrations, private companies and individuals carry out repeated treatments with various pesticides to combat the presence of mosquitoes and other insects deemed harmful in man-made areas. Thus large quantities of these active ingredients are widely spread (beyond the thresholds allowed by the indications contained in the same formulations) in the urban environment, both indoors and outdoors, causing damage not only to human health but also to the environment.

Environmental Toxicity –
Pyrethrins, as well as pyrethroids (which, as mentioned, are however more persistent) are active ingredients, which due to their characteristics and as explained above, are not selective and therefore they affect, in addition to mammals and other living beings (such as amphibians and fish ) all insects with which they come into contact, therefore also useful insects, such as pollinators and natural predators.
In the last quarter of a century, the toxicity of 381 pesticides to bees, other pollinating insects and aquatic invertebrates has more than doubled. The discovery is contained in a study developed by the universities of Koblenz and Landau in Germany that focused attention on products used in agricultural activity in the United States.
According to German research, based on data from the United States Geological Survey and the Federal Environmental Protection Agency (EPA), overall pesticide use has decreased. But the use of both neonicotinoids, insecticides chemically related to nicotine, particularly toxic to bees, and that of pyrethroids, which particularly damage aquatic invertebrates such as crustaceans, mayflies and dragonflies, has increased.
Among other things, pyrethroids, not being selective, damage entire ecosystems as, by indiscriminately hitting the entomological fauna (therefore also bees and various pollinators), it leads to the degradation of entire ecosystems, which are intimately connected to each other.
Unfortunately, the collapse of the population of this species of insects (such as Apis, Linnaeus, 1758) or of other hymenoptera, such as those of the Halictidae family, where the decrease has reached 41% due to gaps in species, is neither a fact nor isolated. nor rare.
We are facing a generalized phenomenon that entomologists have baptized with the term “windshield phenomenon”. That is, a progressive disappearance of insects recorded through the sharp decrease, especially in the summer months, of insects that squash on the car windshield.
This extermination marches at an annual rate; according to studies published in Biological Conservation, it is 2.5 percent, but this is an absolutely approximate number. 40 percent of known insect species are in constant decline, one third of the species are critically endangered.
Among other things, in a detailed article of 2014, the journal Science tried to quantify the decline by calculating a synthesis of the results of several scientific studies already concluded: the result, for some monitored species, was a collapse of 45 per hundred. More specific and circumscribed researches have given even more alarming numbers. For example, the number of flying insects in German nature reserves has fallen by 75 percent in the last quarter of a century. In the last twenty years, the monarch butterfly population in the United States has decreased by 90 percent, with a loss of approximately 900 million individuals. In England, 58 per cent of butterflies in cultivated fields disappeared in less than ten years, from 2,000 to 2009.
In this regard, we recall that many of the 20,000 species of existing insects pollinate 85% of food and fruit crops around the world: everything from garlic to grapefruit, from coffee to cabbage.
The avifauna are especially intimately connected to insects. Birds (which feed mainly on insects) have dramatically decreased over the past 40 years. This data comes from a study by BirdLife International, the Ornithological Society of the Czech Republic and the Royal Society for the Protection of Birds (RSPB) who analyzed and compared data from 378 of the 445 native species in European countries and Great Britain.
According to this research, there was a numerical decline in bird populations, from 17 to 19% of species, between 1980 and 2017. In 40 years they have become less and less numerous in our skies, in addition to the house sparrow (Passer domesticus Linnaeus, 1758), also the yellow dancer (Motacilla cinerea Tunstall, 1771); 97 million less; starlings, down by 75 million and larks down by 68 million.
Unfortunately, the use of pesticides, including pyrethroids, dealt with in this text, negatively affect the entire ecosystem.
These active ingredients, among others, are highly dangerous for other living beings such as amphibians and fish.
Fish deaths are events that can lead to suspicion of the pollution of rivers and seas. In reality they are often due to natural events, such as low oxygen levels in the water; however, the causes can be difficult to identify and often remain unknown.
However, in this regard, the deaths of fish that occurred in October 2014 in a drainage channel in the south of the province of Padua are known and documented. The researchers of the Experimental Zooprophylactic Institute of the Venezie (IZSVe), in collaboration with the laboratories of the Regional Agency for Environmental Prevention and Protection of the Veneto (ARPAV), have in fact identified the cause of the death in the presence in the water of pesticides belonging to the class of pyrethroids.
Following a report, the ARPAV technicians collected samples of the contaminated water, although initially they did not find any dead animals near the spill. In the following days, however, numerous fish carcasses of different species were found along the canal, up to a distance of 6 km from the point of the original report.
ARPAV analyzes showed the presence of relevant concentrations of cypermethrin, permethrin, deltamethrin and tetramethrin in the water samples. On the tissues of fish analyzed by the IZSVe contaminants and biomonitoring laboratory, the presence of cypermethrin and permethrin was found at concentration ranges respectively between 476 and 2834 μg / kg and between 346 and 2826 μg / kg.
This data, if ever it were needed, has “certified” the sensitivity of fish (with entire aquatic ecosystems) to pyrethroids.
In this sense, the report on the analyzes conducted by the IZSVe, published in the international journal Forensic Science International, contributed significantly to the available literature on the mortality of fish fauna caused by pesticides, and in this case linked to pyrethorides.

Conclusions –
This fact sheet could be drastically prolonged, there is so much scientific evidence on the subject, both for toxicity on mammals (including humans) and on the entire world fauna.
This is linked to a factor very little paid attention to by the mass media, namely the interference of the collapse of ecosystems on global warming.
Biodiversity represents the planetary dissipative system par excellence, that is, that complex ecological apparatus capable of dispersing solar heat, transforming it into energy accumulated in the form of organic substance and capable, therefore, of constantly cooling our planet.
According to what was highlighted at the time by the Russian chemist and physicist Ilya Prigogine (Moscow, January 25, 1917 – Brussels, May 28, 2003), Nobel Prize for chemistry in 1977, dissipative structures (such as ecological systems are) allow not only the life on earth but also to keep it in constant and lasting conditions.
The loss of biodiversity (of all kinds and species, including insects, birds, plants, etc.) is one of the main factors in the rise in temperatures due to a decrease in the ecosystem to dissipate solar radiation.
It is no coincidence that in the UN 2030 Agenda for Sustainable Development, the goal of “Protecting, restoring and promoting sustainable use of the earth’s ecosystem” appears as goal number 15.
Not for nothing, the recent 2022 reform of the Constitution of the Italian Republic introduced, with Articles 9 and 41, the concept of protecting the environment and ecological systems.

Guido Bissanti

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