FAQs - Human Safety
Q. What evidence is there that paraquat doesn’t cause Parkinson’s disease, as associations and correlations have been found?
The view that paraquat does not cause Parkinson’s disease is prompted by the absence of evidence that paraquat is causally related with this disease in humans. This absence of evidence comes after more than 40 years of product usage around the world. An analysis by independent senior medical and epidemiological scientists under the guidance of Professor Sir Colin Berry (Emeritus Professor at Queen Mary, University of London, and former member of the UK Medical Research Council) and Professor Pierluigi Nicotera (Founding Director of the German Center for Neurodegenerative Diseases, Bonn) has found no causal link between exposure to paraquat and Parkinson’s disease (Berry, C., La Vecchia, C. & Nicotera, P., (2010). Paraquat and Parkinson’s Disease. Cell Death and Differentiation ,17, 1115–1125). You can find more information here
Taking all relevant factors into account, there is no evidence that the number of new cases of Parkinson’s disease (PD) is increasing. In fact the available data indicate that the incidence of PD has remained unchanged over the last 70 years (during which time modern synthetic pesticides were first used in U.S. and European farming). Because the incidence increases with age, it can be expected that as the population ages in Western society, more individuals with this disease will be present in the general population. Additionally, modern medicine has greatly prolonged life expectancy so that individuals with PD have the same life expectancy as unaffected people of the same age. The diagnosis of the disease is also becoming more sophisticated with the use of new technology.
A. The neurotoxic potential of paraquat has been extensively studied in laboratory animals. No clinical signs of neurotoxicity or consistent neuropathological changes have been reported following long-term exposures of dietary administration of paraquat to rodents or dogs in regulatory-compliant studies. Paraquat did not result in neurotoxic effects in modern US EPA guideline-compliant oral acute and sub-chronic (90 day) neurotoxicity paraquat studies conducted in 2006. In 2006 US EPA stated “Paraquat does not inhibit cholinesterase activity, produce cholinergic-like toxic signs, or affect morphology of the central or peripheral nervous systems. Furthermore, the molecular structure is not similar to those of compound classes known to have effects on the nervous system. Clinical signs of toxicity did not indicate neurotoxicity. As there is limited concern for neurotoxicity resulting from exposure to paraquat, neurotoxicity studies, including a developmental neurotoxicity study, are not required at this time.” We have extensive data on the safety of our products in use and there is no evidence of neurotoxic effects in humans associated with paraquat.
A. Under normal use conditions (i.e. as recommended on the label) paraquat is safe to users and bystanders. Using eye protection and gloves when handling concentrated product and wearing normal work wear like long-sleeved shirts, long trousers, and waterproof shoes are advised for spraying pesticides generally. Following this recommendation already provides a high and sufficient level of safety for the agricultural use of paraquat. In 2004, paraquat was again reviewed by leading international organizations, including the FAO (Food and Agricultural Organization) and the UN Joint Meeting on Pesticide Residues (JMPR), which is comprised of experts from the WHO (World Health Organization) and the FAO. These experts support that, when used as directed, there is no safety hazard associated with the use of paraquat. Its physical properties make it safe to handle, when used according to label directions. Europe’s Scientific Committee on Plants (SCP) stated: “Based on the field exposure studies, corroborated by information on health surveys on operators, the SCP is of the opinion that when paraquat is used as a plant protection product as recommended under prescribed good working practices, its use does not pose any significant health risk to the operators.” (SCP, 2002) The conclusion derived from more than four decades of use and various reviews by international regulatory bodies, is that paraquat is safe to users, the environment, consumers and wildlife when used for its intended purpose as herbicide. Its safety has been confirmed by its registration for use in nearly 90 countries all around the globe including those with the most stringent regulatory requirements such as the US.
A. The potential long-term hazard associated with the use of paraquat has also been studied. The World Health Organization concluded (Environmental Health Criteria, 1984) that there were no significant differences in all health parameters measured between paraquat users and non-paraquat users, which led the authors to suggest that the long-term use of paraquat was not associated with harmful effects on health. This has been confirmed in detailed surveys comparing the health of long-term users of paraquat with unexposed people.
A. No. The current EPA registration documentation for paraquat (EPA ‘RED’, August 1997) clearly indicates that the EPA does not consider neurotoxicity to be an issue with the compound. The EPA also stated that a developmental neurotoxicity study was not required. According to the World Health Organization (Environmental Health Criteria 39, 1984) paraquat has not been found to be teratogenic (to cause birth defects) or carcinogenic (to cause cancer) in long-term studies on rats and mice.
A. An endocrine disruptor is a synthetic chemical that when absorbed into the body either mimics or blocks hormones and disrupts the body's normal functions. Like all crop protection products, paraquat has been subjected to a full regulatory toxicological evaluation, including the required mammalian studies. Such studies allow for the examination of toxicological affects following repeated exposure of a range of species to paraquat. Studies such as these evaluate the ability of materials to cause significant adverse effects through endocrine disruption and no evidence linking endocrine disruption to paraquat has been found.
A. No. Paraquat is not volatile and vapor from the product cannot enter into the respiratory system. Additionally, the spray droplets produced by knapsack or tractor sprayers used to apply products containing paraquat, or any other CPP, are too large to be respired. Most droplets emitted from spray equipment are between 100 and 200 microns in diameter, but a particle must be 10 microns or less to enter the air spaces in the lungs. The large spray droplets cannot be inhaled into the respiratory system. The US EPA concluded that, “particles used in agricultural practices are well beyond the respirable range and therefore inhalation toxicity is not a toxicological endpoint of concern” (US EPA, 1997).
A. Like many readily available chemicals, paraquat is harmful and fatalities have occurred when the concentrated product has been swallowed in sufficient quantity, usually in an attempt to commit suicide. The label for products containing paraquat states that the product should always be kept in its original container and never stored in food, drink, or other containers. Products containing paraquat should also be locked away when not in use. According to the FAO specification paraquat technical material as well as SL and SG formulations must contain an effective emetic at minimum levels. These materials may also include colorants and olfactory alerting agents. Syngenta’s paraquat products comply with the FAO specification most recently updated in 2003 and 2008. Syngenta has added the three 'safening' agents into all of its SL (soluble concentrate) paraquat formulations to avoid accidental ingestion and to deter misuse: A blue dye to avoid confusion with beverages, an olfactory alerting agent (a strong and deterring odor), and an emetic to induce vomiting after ingestion. It is widely believed that these developments have contributed to a reduction in accidents. The WHO International Program for Chemical Safety classification system of pesticides classifies over 500 chemicals.
Paraquat is classified as “moderately hazardous” (WHO class II) along with more than 100 other AIs. Information about the full classification system is available here.
|Class||Number of AIs|
|“Extremely hazardous, class Ia”||29|
|“Highly hazardous, class Ib”||61|
|“Moderately hazardous, class II”||123|
|“Slightly hazardous, class III”||122|
|“Unlikely to present acute hazard”||246|