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Brazil - Final Regulatory Action
Methamidophos CAS number:
Date circular:

Chemical name: O,S-dimethyl phosphoramidothioate

Final regulatory action has been taken for the category: Pesticide

Final regulatory action: The chemical is Banned

Use or uses prohibited by the final regulatory action:

All formulations containing Methamidophos and all uses of this active ingredient will be prohibited in the end of the phase-out described below:
I - 31 December 2011 - prohibition of the sale
II - 30 June 2012 - prohibition of the use
III - 31 December 2012 - Cancel the registration of all products containing methamidophos.

Pesticide use or uses that remain allowed:


The final regulatory action was based on a risk or hazard evaluation: Yes

Summary of the final regulatory action:

Gradual reduction in methamidophos use until the ban of this pesticide.
*ban of use, sale, import and export

The reasons for the final regulatory action were relevant to: Human health

Summary of known hazards and risks to human health:

Methamidophos is an extremely toxic organophosphate (Class I, Brazil 1992), which causes serious adverse effects to human health, especially related to neurotoxicity, immunotoxicity and to the endocrine, reproductive systems and fetal development.
Toxicity studies observed symptoms of poisoning consistent with cholinesterase (AChE) inhibition, a typical effect caused by organophosphates.
All animals tested had loss in their organ weights, such as thyroid, heart, lung, pancreas liver kidneys, adrenals, spleen, thymus, testes and ovaries. The decrease in the concentration of AChE was observed in all groups treated with different doses.
The endocrine disruption caused by methamidophos in experimental studies should be valued, because they have the potential to interfere with reproduction, although few epidemiological studies have been reported in the literature. Endocrine disruption is a very worrying adverse effect because it can trigger serious debilitating effects and even death. Endocrine disruptors have the potential to interfere with reproduction, thus change the number of individuals of a given population. Studies showed that this substance can damage the sperm morphology and interfere with the fertility. It can lead to changes in reproductive performance of males and females and also cause infertility, causes pronounced effects in fetuses, such as embryolethality, malformations, change on the physical landmarks of development and on the behavior of puppies.
Methamidophos is also immunotoxic, inducing a number of immunological effects, including decreased numbers of lymphocytes, monocytes and inhibition of antibody formation. In parallel to the potential immunosuppressive effects, methamidophos induces genotoxic effects. Several studies report mutations, chromosomal aberrations and DNA damage.
Although few studies found on the carcinogenicity of methamidophos, it is important to note that the association of pesticide exposure and cancer induction is difficult because the lack of specific models for this purpose. It is noteworthy that the DNA mutation is a genuine indicator of the carcinogenesis process. Data indicate that methamidophos induces metaphases with chromosomal aberrations at low doses.
Psychiatric disorders such as depression, which can lead to suicide, cognitive impairment, and parkinsonism are correlated with exposure to organophosphates. The neurotoxicity of methamidophos is also a consequence of the inhibition of acetylcholinesterase, essential enzyme for the transmission of nerve impulses. The main chronic neurotoxic effect manifested is delayed polyneuropathy.

Expected effect of the final regulatory action in relation to human health:

Remove the human exposure to methamidophos.

Date of entry into force of the final regulatory action: 17/01/2011