Dimefox is a highly toxic organophosphate insecticide and acaricide that serves as a key historical example of why rigorous chemical regulation and legacy-stock management matter. First synthesized in 1940 by Gerhard Schrader’s group at I.G. Farben, it was once promoted as a powerful systemic pesticide but is now globally obsolete and banned due to extreme human and environmental toxicity.  

Today, the World Health Organization and most national authorities classify dimefox as an obsolete pesticide with no acceptable uses. For EHS professionals, it mainly appears as forgotten legacy stock that demands immediate hazard recognition, robust controls, and specialist disposal.  

 

Dimefox: Chemical Identity and Key Properties 

Names and Identifiers 

Dimefox is chemically known as tetramethylphosphorodiamidic fluoride and has appeared under trade names such as TL-792, Terra-Sytam, and Pestox XIV. Its primary identifiers include:  

  • CAS Number: 115-26-4 
  • EC Number: 204-076-8 
  • UN Hazard Class: 6.1 (acute toxicity), Packing Group I (extremely dangerous)  

Structural Classification 

Dimefox is an organophosphate in the phosphor diamide subclass. The molecule features a phosphorus atom bound to fluorine and two dimethyl amino groups, a configuration that drives its high insecticidal potency and severe mammalian toxicity.  

Physical-Chemical Profile 

In pure form, dimefox is a colorless to pale yellow liquid with a fishy odor and relatively high volatility, contributing to significant inhalation risk. It is highly soluble in water and moderately soluble in common organic solvents, and it decomposes more rapidly under alkaline conditions and elevated temperatures.  

 

Mechanism of Toxicity 

1) Acetylcholinesterase Inhibition

Dimefox’s toxicity is driven by irreversible inhibition of acetylcholinesterase (AChE), the enzyme that normally terminates acetylcholine signaling at synapses. Once dimefox phosphorylates AChE, acetylcholine accumulates, causing continuous stimulation of muscarinic and nicotinic receptors and resulting in cholinergic crisis.  

2) Toxic Pathway in Humans

After inhalation, dermal absorption, or ingestion, dimefox rapidly distributes to target organs, especially the nervous system. It forms a stable phosphorylated AChE complex, leading to neurotransmitter buildup, uncontrolled nerve firing, respiratory failure, cardiovascular collapse, seizures, and potentially death.  

3) Extreme Potency

Estimated lethal doses range roughly from 5–50 mg/kg in humans, meaning even a few drops to about a teaspoon could be fatal for a 150‑lb adult. The narrow margin between symptomatic and lethal exposures leaves virtually no practical “safe” exposure threshold.  

 

Historical Use and Current Legal Status 

➢ Past Agricultural Uses

Dimefox was once used as a systemic insecticide and acaricide on hops, fruit trees, vegetables, ornamentals, and various field crops. It was typically applied as a foliar spray, with systemic movement through plant tissues providing long-lasting pest control.  

Beyond agriculture, dimefox served as a reference compound in toxicology and pharmacology research to study AChE inhibition and organophosphate poisoning mechanisms, including antidote efficacy.  

➢ Why It Was Abandoned

Dimefox was phased out as regulators, and toxicologists recognized that its acute mammalian toxicity, inhalation hazard, and environmental risks far outweighed its agronomic benefits. Concerns included worker fatalities, groundwater contamination potential, bioaccumulation risk, and impacts on beneficial insects.  

➢ Global Regulatory Status

  • European Union: Not approved under plant protection regulations; all authorizations expired and use is prohibited.  
  • United States: Not registered by EPA; no legal pesticide uses allowed.  
  • WHO/FAO: Listed as an obsolete, highly hazardous pesticide subject to international restriction procedures.  

Overall, dimefox meets criteria as a Highly Hazardous Pesticide, and international consensus supports complete prohibition and strict control of legacy material.  

 

Routes of Exposure and Health Effects 

✔️ Main Exposure Routes

  • Inhalation: Volatile at room temperature; vapors in poorly ventilated spaces pose severe acute inhalation risk.  
  • Dermal: Penetrates intact skin efficiently, with small spills on skin or contaminated clothing capable of causing fatal poisoning.  
  • Eye contact: Causes severe irritation and burns and allows systemic absorption through ocular tissues.  
  • Ingestion: Rapidly lethal route, with efficient GI absorption and systemic distribution.  

Secondary contamination via contaminated clothing, tools, and surfaces is a significant concern, particularly in older facilities with legacy residues.  

✔️ Acute Symptoms

Acute poisoning presents a classic cholinergic syndrome: excessive salivation, tearing, urination, defecation, gastrointestinal distress, vomiting, bronchorrhea, bronchospasm, miosis, muscle fasciculations, weakness, and CNS effects ranging from confusion to seizures and coma. Without rapid intervention, respiratory paralysis is a leading cause of death.  

✔️ Chronic and Systemic Effects

Evidence from animal studies and other organophosphates suggests that repeated low‑level exposure can lead to peripheral neuropathy, cognitive changes, mood disturbances, and potential liver and kidney effects. Delayed neurotoxicity with weakness and ataxia has also been associated with organophosphate exposure patterns similar to dimefox.  

 

First Aid and Medical Management 

Immediate Field Actions

For any suspected exposure: 

  • Remove the victim from the contaminated area and prevent further contact. 
  • Strip and bag contaminated clothing in a controlled manner. 
  • Flush affected skin or eyes with copious water for at least 15 minutes. 
  • Provide respiratory support, including artificial respiration and oxygen as needed, and activate emergency medical services and poison control immediately.  

Inducing vomiting after ingestion may be considered only under professional direction and within very narrow criteria; activated charcoal and cathartics may be used in appropriate, conscious patients. These decisions must be made by medical professionals or poison control.  

Antidotal Therapy

Atropine is the primary antidote used to block muscarinic effects of accumulated acetylcholine, while pralidoxime (2‑PAM) is administered to reactivate AChE if given before the phosphorylated enzyme complex “ages.” Both are typically delivered intravenously or intramuscularly, alongside airway management, oxygen therapy, seizure control, and cardiovascular support.  

Because of dimefox’s potency, aggressive supportive care and early antidote use are crucial, and treatment should occur in a facility experienced with organophosphate poisoning.  

 

Handling, Storage, and Decontamination 

a) Personal Protective Equipment

Any handling of dimefox—typically limited today to emergency response for legacy containers—requires full chemical protection: 

  • Respiratory: Positive pressure supplied air respirator or SCBA for emergencies. 
  • Skin: Chemical-resistant full-body suit, double nitrile or butyl gloves, and chemical-resistant boots. 
  • Eyes/Face: Chemical splash goggles plus face shield and, ideally, a hooded suit.  

Clothing that may be contaminated must never be reused until decontaminated under controlled conditions or disposed of as hazardous waste.  

b) Engineering Controls and Work Practices

Work with suspected dimefox containers should occur in well-ventilated areas, preferably inside fume hoods or other containment systems. Negative pressure rooms, local exhaust, and monitored exhaust discharge help maintain airborne concentrations as low as reasonably achievable.  

Activities such as opening old containers, transferring contents, or attempting in‑house neutralization are typically inappropriate in non-specialist settings. The safer approach is to isolate the material and engage a licensed hazardous waste contractor.  

c) Storage of Legacy Stock

If temporary storage is unavoidable before disposal: 

  • Keep containers sealed, upright, and in secondary containment at cool, stable temperatures. 
  • Segregate from incompatible materials, ignition sources, and occupied spaces. 
  • Maintain clear labeling, access control, and immediate availability of SDS and emergency procedures.  

Routine inventory checks and documentation are essential to avoid re-forgetting these materials.  

 

Environmental and Disposal Considerations 

1) Environmental Fate and Ecotoxicity

High water solubility means dimefox can migrate into groundwater and surface water if spills or improper disposal occur. Although hydrolysis and biodegradation do occur, data on exact degradation rates are limited, and the compound is highly toxic to fish, aquatic invertebrates, birds, and beneficial insects such as honeybees.  

Its lipophilic character suggests some potential for tissue accumulation and food-chain transfer, especially in aquatic systems, even though organophosphates generally bioaccumulate less than organochlorines.  

2) Disposal Requirements

Dimefox and contaminated materials must be treated as hazardous waste and managed by licensed disposal contractors. High‑temperature incineration with appropriate exhaust scrubbing is the preferred destruction method; controlled alkaline hydrolysis may be used for smaller, specialized treatments, followed by appropriate handling of breakdown products.  

Discharge to drains, standard landfills, burial, or ad hoc burning is unsafe and typically illegal. Empty containers require thorough triple-rinsing (with rinsate captured as hazardous waste) or professional decontamination before final disposal.  

 

Safer Modern Alternatives and EHS Best Practices 

Modern pest management relies on less toxic chemistries, such as neonicotinoids and pyrethroids, combined with integrated pest management and biological controls to reduce reliance on highly hazardous pesticides like dimefox. These alternatives still require careful stewardship but offer substantially wider safety margins for workers and the environment.  

For EHS teams, the key responsibilities regarding dimefox are: 

  • Recognize and identify legacy containers using labels and CAS numbers, without opening or disturbing them. 
  • Ensure GHS-compliant SDS coverage and accessible emergency procedures for any suspected stock. 
  • Maintain established organophosphate response plans, including access to atropine, pralidoxime, and trained responders where appropriate. 
  • Use only licensed hazardous waste contractors with organophosphate experience for removal and destruction, documenting the entire process for regulatory compliance.  

Dimefox’s regulatory history illustrates how rapidly “innovative” chemistries can transition to banned substances once full hazard profiles are understood. Its continued appearance in legacy inventories keeps it relevant as a powerful teaching tool for risk assessment, precautionary regulation, and long-term stewardship of hazardous chemicals.