Chemicals in the News: Atrazine
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Last updated 30 June 2010 - Atrazine Mode-of-Action report completed
What is atrazine?
Atrazine is a triazine herbicide currently registered in Australia for the control of grass and broadleaf weeds in crops such as sorghum, maize, sugarcane, lupins, pine and eucalypt plantations, and triazine tolerant (TT) canola.
Current registration status in Australia
The APVMA concluded an extensive review of atrazine in 2008 and continues to be satisfied that it can be safely used in Australia, subject to those conditions outlined on product labels.
Tighter regulations for the use of atrazine have been introduced by the APVMA since 1997, including the cancellation of industrial and non-agricultural uses and a range of label instructions designed to reduce the risk of atrazine entering waterways.
For more information, see the full details of the atrazine review.
Current issues
Human health
In 2008, in conjunction with the publication of its Final Review Report and Regulatory Decisions on Atrazine (PDF, 1.09Mb), the APVMA commissioned the Office of Chemical Safety and Environmental Health in the Australian Department of Health and Ageing to assess data published at that time suggesting that atrazine might be responsible for adverse reproductive and developmental effects in humans through an endocrine mode-of-action (MOA). This report was published in June 2010 (PDF, 633kb) to provide a technical update for consideration by the community, to articulate current thinking and to identify areas where future work may be forthcoming.
The report considered three potential modes of action and provided preliminary information on a possible fourth. It concluded that adequate information to establish a plausible link between atrazine exposure and an identified endpoint was found for only one MOA but the MOA was considered not to be relevant to human health risk assessment. In relation to the other proposed MOAs, it was found that further studies are need to explore whether these MOAs can be established as plausible, and then their relevance to human health risk assessment.
The results of this analysis do not suggest that a further scientific review of atrazine toxicity is warranted or provide a basis to undertake a re-evaluation of the existing health values.In February 2010, at the annual meeting of the United States Society for Maternal-Fetal Medicine held in Chicago, Dr Sarah Waller from the University of Washington presented the results of an epidemiology study (external site) suggesting that exposure to atrazine was associated with the birth defect, gastroschisis. The APVMA has referred the study to the Australian Government Department of Health and Ageing for assessment.
While a causal link of atrazine and birth defects would be of serious concern if proven, the APVMA notes that atrazine has been very extensively tested and reviewed, both nationally and internationally. For example, in 2007 a World Health Organization (WHO) committee concluded that atrazine is not teratogenic (does not cause malformations of an embryo or a foetus).
Initial advice from DoHA was that there is no evidence of any significant exposure of the population to atrazine in drinking water in any state or territory of Australia or unusual trends in the incidence of birth defects. To date, no link of birth defects to atrazine use has been made by researchers in Australia. Every year, a number of epidemiological studies describing correlations between certain human health or environmental findings and pesticide use are published. Because of the relatively low rate of occurrence of birth defects, epidemiological studies of this type offer some useful information and hypotheses. In the regulatory context, any causal link has to be established by more extensive investigations and targeted follow-up studies.
Water quality issues
There are infrequent low-level atrazine detections in river systems in Tasmania and Queensland; however, levels, when found, are consistently hundreds of times less than the health-based Guideline Value for atrazine.
Amphibians
There is a body of research (first published after 2002), most closely associated with the work of Professor Tyrone Hayes, that suggests that atrazine disrupts sex differentiation and organogenesis in amphibians. This work was assessed by the Department of the Environment, Water, Heritage and the Arts (DEWHA) at the request of the APVMA prior to finalisation of the atrazine review. The conclusion of the APVMA at that time, based on advice from DEWHA, was that atrazine is unlikely to have an adverse impact on frogs at existing levels of exposure. This advice was consistent with findings by the US EPA in 2007 (see below) that atrazine does not adversely effect amphibian gonadal development.
Most recently, in March 2010, Professor Hayes was the lead author on a paper published in the Proceedings of the National Academy of Sciences of the United States of America (external site) that argued that atrazine demasculinised frogs exposed to a single laboratory controlled, low dose of atrazine throughout all life stages (egg, tadpole and adult). The APVMA submitted this and a number of similar papers to DEWHA for assessment. DEWHA found that these papers do not provide sufficient evidence to justify a reconsideration of current regulations which are based on a very extensive dataset.
Registration status in other national jurisdictions
Atrazine is widely used throughout the world. There have been no adverse human health or environmental findings to date by any regulator.
United States of America
The United States Environment Protection Authority (U.S. EPA) reviewed atrazine in 2003 and re-affirmed its registrations.
In June 2003 the United States Environment Protection Authority (U.S. EPA) requested further studies to assess whether atrazine affected amphibian gonadal (sexual) development. The EPA received and assessed the requested studies and other available research and in 2007, concluded that atrazine does not adversely affect amphibian sexual development. For more information, see EPA Atrazine Updates (external site).
In October 2009, the EPA announced a further review of atrazine (external site) to reconsider existing data and evaluate new studies published since their last review, focusing mainly on risks to human health. For more detailed information see Atrazine Science Reevaluation: Potential Health Impacts (external site).
Canada
The Canadian regulatory authority, the Pest Management Regulatory Agency (PMRA) concluded in 2004 that the use of atrazine did not entail an unacceptable risk to human health, provided that the required mitigation measures were implemented. See Atrazine Re-Evaluation Decision Document (external site).
European Union
The European Commission (EC) excluded atrazine from a re-registration process in 2003 because the registrants did not supply sufficient water monitoring data.
Specifically, the commission found that the data was ‘insufficient to demonstrate that in large areas concentrations of the active substance and its breakdown products will not exceed 0.1 μg/l in groundwater. Moreover it cannot be assured that continued use in other areas will permit a satisfactory recovery of groundwater quality where concentrations already exceed 0.1 μg/l in groundwater.’ See the European Commission decision document (external site).
It is frequently asserted that atrazine has been banned in the EU. This is an incorrect interpretation of the EC decision. Atrazine has not been assessed and de-registered because of a human health or environmental concern. It is not on any EU ‘banned list” and could theoretically be reregistered in the EU should the product registrant provide all the required data. Terbuthylazine, a herbicide very closely related to atrazine is registered in the EU.
Evaluations by international agencies
International Agency for Research into Cancer
The IARC published a detailed evaluation of atrazine in 1999 (external site) in which they concluded that earlier onset of tumours in one strain of female rats dosed with atrazine was unique to that strain and not relevant to humans. Thus it downgraded its earlier classification of atrazine from Group 2B ‘possible human carcinogen’ to Group 3 ‘not classifiable’.
WHO/FAO Joint Meeting on Pesticide Residues (JMPR)
The Joint Meeting on Pesticide Residues (JMPR), a joint committee of the World Health Organization (WHO) and the Food and Agriculture Organization (FAO), re-assessed atrazine in September 2007 and published the final report in October 2009. The JMPR established a higher Acceptable Daily Intake (ADI) than the Australian standard.