Dicofol is a synthetic organic compound historically used as a pesticide, specifically as an acaricide or miticide. Its journey from widespread agricultural use to global restriction highlights the complex interplay between pest control, environmental effects, and human health considerations. This substance, once a common tool for farmers, has drawn significant scientific and regulatory scrutiny over time.
What is Dicofol?
Dicofol is an organochlorine acaricide, primarily used to control mites on various crops, including fruits, vegetables, ornamentals, and field crops. Its chemical formula is C14H9Cl5O, and it is also known by the trade name Kelthane®. Structurally, dicofol is similar to DDT, differing by the replacement of a hydrogen atom with a hydroxyl group on one of its carbon atoms.
This relationship is significant because dicofol was historically produced using DDT, leading to DDT impurities in older formulations. Technical grade dicofol typically consists of about 80% p,p’-dicofol and 20% o,p’-dicofol isomers. It is generally found as a white crystalline solid that is practically insoluble in water but dissolves in organic solvents.
Environmental Impact
Dicofol exhibits environmental persistence, breaking down slowly in certain conditions. Its half-life in acidic solutions (pH 5) can range from 47 to 85 days, though it degrades more rapidly in alkaline conditions or when exposed to ultraviolet light. This slow degradation allows it to remain in the environment for extended periods, including in soil and on treated plants.
The compound has a high potential for bioaccumulation, meaning it can build up in the tissues of living organisms. Bioconcentration factors (BCFs) in aquatic organisms have been reported to be very high, often ranging from 6,100 to 10,000. This bioaccumulation can lead to higher concentrations at ascending levels of the food chain, affecting non-target organisms. Dicofol is toxic to aquatic life, including fish, aquatic invertebrates, and algae. It has also been linked to reproductive issues in birds, such as eggshell thinning and reduced offspring survival, similar to the effects observed with DDT.
Health Concerns
Exposure to dicofol can occur through various routes, including ingestion, dermal contact, and inhalation. Acute exposure in humans and other mammals can lead to symptoms such as nausea, dizziness, weakness, vomiting, skin irritation, rash, and conjunctivitis. Neurological effects, including nervousness and hyperactivity, headache, and unusual sensations, have also been reported.
Beyond acute effects, chronic exposure to dicofol raises concerns for more severe health impacts. It has been shown to affect the liver, kidneys, and central nervous system in mammals. Studies indicate potential for liver toxicity, reproductive issues, and endocrine disruption. Dicofol has been identified as a possible human carcinogen. It is classified as a “moderately hazardous” pesticide by the World Health Organization.
Global Regulatory Status
Due to its persistence, bioaccumulation, and toxicity, dicofol has faced significant global regulatory actions. Many countries have banned or severely restricted its use. The U.S. Environmental Protection Agency (EPA) temporarily canceled its use in 1986 due to high levels of DDT contamination.
Dicofol is also listed in Annex A of the Stockholm Convention on Persistent Organic Pollutants (POPs), which aims for the elimination of its production and use. This international treaty legally binds signatory countries to reduce or eliminate the production, use, and release of listed POPs. The European Union has also adopted the Stockholm Convention into its legislation, further restricting dicofol within its member states. These global efforts reflect a collective recognition of dicofol’s adverse effects on human health and the environment.