Publication of toxicology report
Key points
- The APVMA commenced a reconsideration of paraquat in 1997 due to human health and environmental concerns. Paraquat products are highly restricted, and only available for commercial use by trained professionals. They are not available for use by the general public in home garden or domestic situations.
- The APVMA has published a paraquat toxicology assessment report which determined that there is no data which would impact the approval status of paraquat.
- The APVMA will continue assessing the occupational health and safety, residues and environmental related aspects of paraquat use before deciding whether any regulatory changes are required.
What is paraquat
Paraquat is a broad spectrum, non-selective, contact herbicide belonging to the bipyridinium class of compounds. It acts by inhibiting photosynthesis in green plants, specifically photosystem 1, by reacting with free electrons to form highly reactive super-oxides, which cause rapid cell death and desiccation of foliage.
Paraquat use in Australia
Paraquat has a long history of use in Australia and overseas for the effective control of various weeds in fruit, vegetable and cereal crops, pastures, fallows, and non-agricultural situations such as fire breaks, around roads, paths and other structures. It is also used for the desiccation of cotton and hay freezing.
Paraquat products are available as liquid formulations and are only applied as ground-based sprays.
Regulation of paraquat
Paraquat is classified as a dangerous poison, and must not be used in home garden or domestic situations. Paraquat products are strictly for commercial use only by trained professionals and subject to stringent storage, packaging and labelling restrictions. Paraquat liquid formulations must be coloured and contain an effective stenching agent to reduce the risk of accidental ingestion.
All paraquat products registered for use in Australia are subject to a rigorous pre-market assessment by the APVMA to ensure they meet contemporary safety standards.
APVMA reconsideration of paraquat
The APVMA commenced a reconsideration of paraquat in 1997 due to human health and environmental concerns. The reconsideration involves component toxicology, occupational health and safety, residues and environment assessments.
Toxicology assessment
The APVMA commissioned a toxicology assessment of paraquat which has been published as a 3–part series as follows:
These reports have been developed to incorporate the most contemporary scientific literature, including reports of neurological effects in mice. The main findings of the report are as follows:
- there are no data or findings which would impact the approval status of paraquat
- current Australian health based guidance values remain appropriate
- the weight-of-evidence is that paraquat does not cause adverse neurological effects (including Parkinson’s disease).
Paraquat and Parkinson’s disease
A comprehensive assessment of the neurotoxicity of paraquat has been completed, following reports of neurological effects resembling Parkinson’s disease in mice after being injected with paraquat. The assessment considered all available published and unpublished studies including recent epidemiological studies and concluded that there is no link between paraquat exposure and Parkinson’s disease. It was noted that several of the earlier studies reporting effects have been found to be unreliable and not reproducible in more recent studies. Furthermore, exposure via injection is not a relevant exposure route for humans. More recent and appropriately designed studies found no evidence of neurotoxicity after oral administration of paraquat.
Next steps for the APVMA reconsideration of paraquat
The APVMA will continue assessing the occupational health and safety, residues and environmental related aspects of paraquat use before publishing a proposed regulatory decision planned for June 2017. After a period of public consultation, a final regulatory decision for paraquat is anticipated for January 2018.
