Fipronil
[CAS# 120068-37-3]

Identification

• Classification: Chemical pesticide >> Insecticide >> Organochlorine insecticide
• Name: Fipronil
• Synonyms: 5-Amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazole-3-carbonitrile
• Molecular Formula: C₁₂H₄Cl₂F₆N₄OS
• Molecular Weight: 437.15
• CAS Registry Number: 120068-37-3
• EC Number: 424-610-5
• SMILES: C1=C(C=C(C(=C1Cl)N2C(=C(C(=N2)C#N)S(=O)C(F)(F)F)N)Cl)C(F)(F)F

Properties

• Density: 1.9±0.1 g/cm³, Calc.^*
• Melting point: 196-202 °C (Expl.)
• Index of Refraction: 1.618, Calc.^*
• Boiling Point: 510.1±50.0 °C (760 mmHg), Calc.^*
• Flash Point: 262.3±30.1 °C, Calc.^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS06;GHS08;GHS09 Danger
• Risk Statements: H331-H311-H301-H372-H400-H410
• Safety Statements: P260-P261-P262-P264-P270-P271-P273-P280-P284-P301+P316-P302+P352-P304+P340-P316-P319-P320-P321-P330-P361+P364-P391-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H311
Acute toxicity	Acute Tox.	3	H301
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Acute toxicity	Acute Tox.	3	H331
Acute toxicity	Acute Tox.	2	H330
Eye irritation	Eye Irrit.	2	H319

Discovery and Applications

Fipronil is a broad-spectrum insecticide belonging to the phenylpyrazole class, developed for the control of a wide range of pests, including insects that affect agricultural crops, household pests, and even fleas and ticks on pets. First synthesized in the late 1980s by the pharmaceutical company Rhône-Poulenc (now part of Bayer), fipronil is known for its high efficacy and relatively low toxicity to humans and animals when used according to recommended guidelines. Its discovery was driven by the need for a new type of insecticide with a novel mechanism of action, distinct from the organophosphates and carbamates that were commonly used at the time.

The compound is characterized by its ability to interfere with the nervous system of insects. Fipronil acts as a blocker of the gamma-aminobutyric acid (GABA)-gated chloride channels in the central nervous system of insects, leading to uncontrolled nervous stimulation and eventually the death of the pest. This action is selective to insects, as the structure of the GABA receptors in mammals differs significantly. As a result, fipronil has become one of the most important tools in modern pest control, with applications ranging from agriculture to veterinary medicine.

In agriculture, fipronil is widely used for the protection of crops such as rice, maize, and wheat. It is applied in the form of soil treatments, seed coatings, and foliar sprays to combat various insect pests, including termites, ants, and root-feeding insects. Its persistence in the environment makes it effective over extended periods, reducing the need for frequent reapplication. Additionally, fipronil has been used in combination with other insecticides in integrated pest management programs to reduce the development of resistance among pest populations.

In veterinary medicine, fipronil is commonly used to control ectoparasites, including fleas, ticks, and lice, in companion animals. It is typically applied topically, and the compound binds to sebaceous glands in the skin, where it is slowly released into the bloodstream. Fipronil’s ability to remain active for several weeks makes it highly effective in providing long-lasting protection to pets, particularly against fleas and ticks, which are difficult to manage. Fipronil-based treatments have become a cornerstone in pet healthcare, providing a critical tool in the management of parasitic infestations.

In addition to its agricultural and veterinary uses, fipronil has also found application in the control of termites, which are known to cause significant structural damage to buildings. Fipronil is often used as a liquid treatment for subterranean termite control, where it acts as both a repellent and a lethal agent. Termites are exposed to the compound through direct contact or by consuming the treated wood, and because fipronil remains active in the environment for a long period, it provides extended protection against termite infestations.

However, the widespread use of fipronil has raised concerns about its environmental impact. While it is effective in controlling pests, the compound has been shown to be toxic to aquatic organisms, including fish and amphibians, and can accumulate in water bodies if not applied carefully. There have been reports of fipronil contamination in water supplies, leading to regulatory scrutiny in some countries. Additionally, its persistence in the environment has contributed to concerns about its potential to harm non-target species, including beneficial insects such as honeybees. As a result, there have been efforts to develop safer alternatives and improve application techniques to mitigate its environmental impact.

Fipronil also plays a role in resistance management, as pests can eventually develop resistance to the chemical. This has led to the exploration of integrated pest management strategies that combine fipronil with other control methods, such as biological controls, crop rotation, and the use of other insecticides with different modes of action. These strategies aim to slow the development of resistance and ensure the continued efficacy of fipronil in pest control.

In conclusion, fipronil is a highly effective insecticide with broad applications in agriculture, veterinary medicine, and pest control. Its unique mechanism of action and effectiveness against a wide range of pests make it a valuable tool in modern pest management. However, its environmental impact and potential for resistance development highlight the need for careful and responsible use, alongside the development of alternative strategies to reduce its negative effects.

References

2015. Determination of Residues of Fipronil and Its Metabolites in Cauliflower by Using Gas Chromatography-Tandem Mass Spectrometry. Bulletin of Environmental Contamination and Toxicology.
DOI: 10.1007/s00128-014-1447-7

2017. Nosema ceranae, Fipronil and their combination compromise honey bee reproduction via changes in male physiology. Scientific Reports.
DOI: 10.1038/s41598-017-08380-5

2016. Persistence of fipronil residues in Eucalyptus seedlings and its concentration in the insecticide solution after treatment in the nursery. Environmental Monitoring and Assessment.
DOI: 10.1007/s10661-016-5304-5