What are natural pyrethrum (pyrethrins) and pyrethroids? What are the most commonly used insecticides in agriculture today and what risks do they pose to health and the environment? In the context of organic farming, we cannot avoid asking these questions. In this article, therefore, we will focus on the risks posed by common insecticides, which are unfortunately still widely used in traditional agriculture.
We will also make an important distinction between products derived from natural pyrethrum, the pyrethrins, whose use is permitted in organic farming with certain limitations, and pyrethroids, synthetic chemical products that make up a large part of the active ingredients in the most commonly used insecticides, including those commonly used in home gardens.
Natural Pyrethrum and Pyrethrins
Pyrethrum is a flower belonging to the Asteraceae (or composite) family, with the scientific name Chrysanthemum cinerariifolium. In appearance, it is similar to common daisies, although it has nothing to do with them. The flowers of the pyrethrum are harvested, dried, and then ground to obtain a natural insecticide. The insecticidal action is due to pyrethrins, substances of plant origin that represent its active ingredient.
Today, pyrethrum is mainly cultivated in countries such as Kenya, Tanzania, and Australia, from where it is exported.
How Do Pyrethrins Work as Insecticides?
Pyrethrins exert their insecticidal action on contact. They affect the insect’s nervous system, causing initial difficulty in movement, followed by paralysis, and, in most cases, death.
However, here lies the first problem with pyrethrins: the natural extracts of pyrethrum, with their potent insecticidal action, are NOT selective and affect all insects they come into contact with, including beneficial insects such as pollinators and natural predators.
To understand the problem with pyrethrins, we can make a comparison with another product that is highly selective: Bacillus thuringiensis. The latter is capable of targeting only specific insect species and is entirely harmless to others.
Another negative characteristic of natural pyrethrum and its first-generation extracts, pyrethrins, is the high toxicity to aquatic organisms such as fish, amphibians, and reptiles, which must never be exposed to these treatments.
Positive Characteristics of Pyrethrins
Products based on natural pyrethrum are not systemic, meaning they cannot penetrate the plants’ sap. This limitation prevents them from expressing their action for an extended period.
Pyrethrins are photolabile and thermolabile, leading to their rapid degradation when exposed to sunlight and heat. The active ingredient degrades quickly and leaves no trace in the environment. To overcome these characteristics, which are positive for the environment but negative for those selling these products, commercial formulations are usually added with synergizing substances. These substances improve the absorption of pyrethrins in the insect’s body by slowing down their metabolism. They also increase the persistence of action by reducing photolability and thermolability, making pyrethrins more stable.
The most well-known and widely used synergizing substance is piperonyl butoxide (Ppbo). When added to pyrethrum, it significantly increases its effectiveness but also its toxicity.
One positive note is the non-toxicity of pyrethrins to warm-blooded organisms (humans and other animals). Unfortunately, this characteristic does not apply to felines, which cannot metabolize pyrethrins and suffer neurological damage.
Use of Pyrethrum in Organic Farming
Under Regulation (EC) No. 834/2007, integrated with EC Regulation (EC) No. 889/2008, on the organic production and labeling of organic products, pyrethrins are included among the substances of animal and plant origin allowed in organic farming. Their use is that of natural insecticides.
However, as we have explained, there are several problems related to the use of first-generation derivatives of natural pyrethrum. Among these, the issue that concerns us most is the non-selectivity of pyrethrins. If we genuinely want to practice organic farming, we cannot overlook the protection of beneficial insects in the garden. The action of pollinators and predators is essential in an organic garden.
Using products that kill beneficial insects is not acceptable. A cultivation without bees or ladybugs cannot be called organic.
The non-selectivity of pyrethrins also leads to the development of insect resistance. Repeated treatments only increase their resistance. Following this path leads to a vicious circle that requires the product to be used more frequently and intensively, with all the consequences that follow.
Alternatives to Pyrethrum
What we strongly recommend to organic growers is to explore other methods for pest control. The goal should be to establish an ecosystem compatible with the presence of beneficial insects. Natural macerates, Bacillus thuringiensis, pheromone traps, mechanical defense, natural predators, trap crops, and more are all techniques and natural remedies that allow us to implement a strategy of biological defense without disrupting the ecosystem balance.
Pyrethrins and Pyrethroids, Further Information
At this point, we could conclude our discussion on pyrethrum and its natural derivatives, namely pyrethrins. However, we feel obligated to delve further and talk about pyrethroids. They represent a large family of chemically synthesized active ingredients found in many pesticides used in traditional agriculture. There is often confusion between pyrethrins, which despite their limitations are of natural origin with limited toxicity, and pyrethroids, which are entirely synthetic and pose a real danger to human health and the entire ecosystem.
What are Pyrethroids
Pyrethrum and its natural extracts have been used since the early 20th century as natural insecticides. Their effectiveness was influenced by pyrethrum’s characteristics, such as low persistence and high photolability. In the post-war period, chemical companies recognized the potent insecticidal capabilities of pyrethrum and modified its molecule, creating synthetic chemical products known as pyrethroids.
Pyrethroids are molecules, chemically derived active ingredients capable of reproducing the action mechanism of pyrethrum, but with much more potent and, at the same time, more dangerous effects.
Development of Pyrethroids
The development of pyrethroids can be divided into two subsequent stages. From the late 1940s to the late 1960s, first-generation pyrethroids were developed with action mechanisms very similar to pyrethrins, characterized by high photolability. These included active ingredients such as:
These substances are currently present in many insecticides used against mosquitoes, flies, wasps, etc., and can be found in aerosol sprays, powders, coils, and mosquito-repellent devices.
Starting from the early 1970s, chemical industry advancements allowed further manipulation of the molecule of natural pyrethrum, specifically, chrysanthemic acid. This gave rise to a new generation of active ingredients known as second-generation pyrethroids.
Some of the most widely used second-generation pyrethroids include:
These pyrethroids are much more active and stable than their first-generation counterparts, and they are photostable, meaning they have a persistent action as they are not sensitive to light and heat. These active ingredients can be found in the most common insecticide-pesticide products available commercially to combat major pests in the garden (or in pet parasite control products).
It is essential to note that none of the commercial products with pyrethroids as active ingredients can be used in organic farming. Now let’s explore the actual dangers posed to human health and the environment. First, we will investigate the most widely used pyrethroid, namely deltamethrin, and then look into studies on the chronic hazards of pyrethroids that have been published so far.
Deltamethrin, the Most Widespread Pyrethroid
Let’s continue our examination by focusing on deltamethrin, currently the most widely used pyrethroid. It was synthesized in the early 1970s and later patented in 1981 by a well-known German multinational company. Presently, it is found in as many as 21 commercial formulations.
A quick glance at photos of home gardens posted by enthusiasts (even on social networks) reveals how widespread this product is, even in DIY cultivation.
In traditional agriculture, deltamethrin is used against aphids, whiteflies, certain bugs, caterpillars, and more. However, it has a particular characteristic that makes its use quite unique: it attracts mites, especially the red spider mite.
Thus, while it eliminates harmful insects, it also attracts some that are highly destructive to crops. Naturally, this aspect is not disclosed on the label.
Deltamethrin is toxic to aquatic organisms and all beneficial insects in the garden. In 2013, Greenpeace raised an alarm including deltamethrin among the seven active ingredients that should be eliminated and banned from the market to protect bees.
Dangers to Humans and Main Symptoms
Let’s now examine the dangers to humans in case of accidental poisoning (which is not difficult when spraying the product on plants, especially for inexperienced users who do not use all the necessary personal protective equipment).
Without adding anything invented, we report what is written on the label and, therefore, legally required by the manufacturer.
Main local symptoms include:
- Severe skin and eye paresthesia
- Irritation to the skin, eyes, and mucous membranes
- Coughing and sneezing
Main systemic symptoms, resulting from prolonged and/or repeated exposure, include:
- Chest pain
- Abdominal pain
- Blurred vision
- Hyperreactivity of the respiratory tract
- Pulmonary edema
- Muscular fasciculation
After this list, there is little else to add. It is also worth considering that deltamethrin is considered one of the safest products on the market among operators. Imagine the rest!
Fortunately, since November 25, 2015, the purchase of such products requires a certification of qualification, as discussed in this article on pesticides.
The Chronic Toxicity of Pyrethroids
Fortunately, the scientific community has extensively investigated the chronic and long-term effects of pyrethroids. However, it is unfortunate that legal authorizations do not always align with scientific evidence.
Let’s take a step back and talk about the action mechanisms of pyrethroids. The primary action of pyrethroids (as well as pyrethrins) occurs in the sodium channels of the cell membrane, responsible for the electrical phenomena underlying the activities of organisms. Pyrethroids concentrate in tissues with a high lipid content, such as nervous tissue, where they disrupt the natural transmission of electrical impulses.
Now, the action of pyrethroids is the same in insects and mammals, but it is much more effective in insects. This is because insects have greater sensitivity in their sodium channels, smaller body sizes, and lower body temperatures.
According to various research institutions, including the Cnr, mammals are protected from the action of pyrethroids because they have limited skin absorption and can quickly metabolize and render these substances non-toxic.
However, in case of prolonged exposure to pyrethroid chemicals, there is a real risk that they may accumulate in adipose tissues, including the brain, where their metabolism is impaired.
Another problem in this regard is the presence of other substances contained in insecticides, such as organophosphates, which limit the natural enzymatic capacities of mammals. The simultaneous exposure to these types of agents and pyrethroids increases toxicity, making it more severe and problematic.
Another critical aspect is the laboratory toxicity tests usually performed on mice. It is known that some mammals are more sensitive than others, resulting in different reactions to pyrethroid exposure. Mice are known for their high capacity for cellular recovery.
Studies conducted by the French Cnrs and the association Antidote Europe using toxicogenomics have shown over time that many commonly used and considered low-toxicity products can actually alter gene expression, leading to chronic damage. For example, cats’ livers are very sensitive to certain pyrethroids like permethrin. This active ingredient has been eliminated from agricultural use but is still present in dog parasitic products. Cats exposed to this agent have experienced severe poisoning symptoms.
Additional studies conducted by US government agencies such as the US National Library of Medicine and the National Institutes of Health have demonstrated neurotoxicity problems in young subjects exposed to pyrethroids. In some cases, neuron death was induced, leading to chronic issues in the central nervous system.
We could provide more examples of such studies, but it seems appropriate to stop here. For further in-depth information, you can study this document from Ispra (the Institute for Environmental Protection and Research), which explains in detail the action of individual pyrethroids and all harmful effects on humans and the environment.
- Pyrethrins General Fact Sheet from Oregon State University: This resource discusses pyrethrins, which are highly toxic to fish, lobster, shrimp, oysters, and aquatic insects.
- PYRETHRINS AND PYRETHROIDS – EXTOXNET PIP from Oregon State University: This resource provides information about pyrethrin, which is extremely toxic to aquatic life, such as bluegill and lake trout, while it is slightly toxic to bird species, such as mallards.
- Pesticide Information about pyrethrin from University of California Agriculture and Natural Resources: This resource discusses pyrethrin, an active ingredient in many insecticides. It mentions that absorbed runoff toxicity risk to fish rating is low.
- Potential Health Effects of Pesticides from Penn State Extension: This resource discusses the potential health effects of pesticides, including symptoms such as headache, excessive salivation and tearing, muscle twitching, nausea, diarrhea, respiratory depression, seizures, and loss of consciousness.
- Long-Term Insecticide Exposure Tied to Heart Disease from University of Iowa: This resource discusses a study that links long-term exposure to pyrethroids, found in mosquito repellents, pet sprays, and lice shampoos, to increased cardiovascular risks.