Simazine - Update on Review Status
Updated 28 July 2010
Simazine, a herbicide and algaecide, is either exempt from scheduling or is in Schedule 5 of the Uniform Scheduling of Drugs and Poisons (SUSDP). In the latter case its products bear the signal heading ‘Caution’.
Current registration status
Seventy six simazine products are registered in Australia. They are available in a variety of formulations for the control of a large number of weed species, both broadleaf and grasses in fruits, vegetables, lentils and vineyards, home garden and non-agricultural situations. They are also used to control algae in pools, aquariums and ponds.
Simazine was placed on the APVMA Priority Candidate Review List as a priority 2 chemical in the mid 1990s in order to reconsider environmental and human health aspects. The health concerns that prompted this nomination at that time related to fears that simazine might promote cancer in humans. These concerns have since been discounted.
In addition to approved uses on labels, there are currently 14 permits issued for the application of simazine products typically for use in specialty crops.
Review Status
The review will commence once preliminary work is completed to determine the scope of the review. Work to determine the scope of the forthcoming review of simazine/cyanazine is underway, including collation and organisation of data holdings by APVMA’s advisory agencies (including DSEWPC and OCSEH). The review will commence once this preliminary work is completed. The timeframe for this work has not been fixed but the APVMA is satisfied that the work now underway is appropriate, as it will help ensure that the forthcoming review is appropriately targeted and will facilitate timely review outcomes.
Generally, comprehensive reviews can take several years to complete. Review outcomes are developed following assessment of the data and other relevant information. However, if there is new information suggesting a previously unrecognised risk exists that cannot be managed, the APVMA can implement regulatory actions before the review is finished (e.g. product suspensions).
The Swimming Pool Issue
The media has recently reported claims that the use of simazine as an algaecide in swimming pools exposes children, in particular, to health risks. A recent story in the The Australian presents many of these claims.
Key among these is that simazine is a common ingredient in swimming pool anti-algae treatments, that children swimming in pools treated with simazine could be exposed to five or six times the acceptable daily intake (ADI), that children may ingest levels of simazine in pool water that are higher than those allowed in domestic water supplies, and the suggestion that simazine promotes cancer.
These claims do not accurately reflect the facts.
Simazine is not ‘a common ingredient’ in swimming pool anti-algae products. It is present in only eleven of over 500 currently registered pool algaecide products. Information available to the APVMA reveals that, in terms of sales, simazine pool products account for only 0.6% of the total value of all pool product sales. It is predominantly used by commercial pool operators to treat outdoor pools over winter, when the pool is not used for swimming. It is, therefore, unlikely that children will be exposed to the chemical in practice.
The use of the Acceptable Daily Intake (ADI) measure to assess risk to children using a simazine treated pool is not the best comparative tool to use in this context. The ADI seeks to quantify the whole-of-life daily intake that could be experienced without causing any adverse effect. It is typically used to evaluate residues in foodstuffs. It is a conservative measure based on long-term animal studies with large, built-in safety margins over doses that cause no effects in laboratory test species. For these reasons, exceedences of the ADI once or several times over a period of time are unlikely to cause any health impacts. Beyond this, the claims that were made were based on a range of doubtful assumptions such as multiple simazine treatments in the one pool and that children as young as three would be regular swimmers in the pool for long periods of time.
Be that as it may, APVMA calculations suggest that a six year old child undertaking an average swim in a simazine treated pool would ingest and absorb around 30% of the ADI. Advice from the Office of Chemical Safety and Environmental Health in the Department of Health and Ageing confirms there is no cause for concern. The APVMA is not aware of any incidents of harmful effects to swimmers associated with the use of simazine as a pool chemical.
The argument that children potentially exposed to higher concentrations of simazine in pool water than is permitted in drinking water is spurious. Pool water is not suitable to be used as drinking water and should not be drunk. It is treated to prevent and control the growth or bacteria, protozoa, viruses and algae, which can cause very significant human health problems. Similarly, drinking water is specifically regulated and managed for its intended purpose.
The cancer concerns that led some regulatory jurisdictions such as the United States to discontinue the use of simazine in swimming pools prior to 1994 have since been discounted by competent national and international scientific and regulatory authorities. These concerns are no longer current.
On the present evidence, the APVMA does not believe that the use of simazine products as algaecides in swimming pools presents any significant health risk. Nonetheless, this question will be formally considered in the context of the forthcoming simazine review.