The NRA Review of ATRAZINE - Forward, Contents, Summary

Volume 1, November 1997

Foreword

The National Registration Authority for Agricultural and Veterinary Chemicals (NRA) is an independent statutory authority with responsibility for the regulation of agricultural and veterinary chemicals.

The NRA's Existing Chemicals Review Program (ECRP) systematically examines agricultural and veterinary chemicals registered in the past to determine whether they continue to meet current standards for registration. Chemicals for review are chosen according to pre-determined, publicly available selection criteria. Public participation is a key aspect of this program.

In undertaking reviews, the NRA works in close cooperation with advisory agencies including the Department of Health and Family Services (Chemicals and Non-Prescription Drug Branch), Environment Australia (Risk Assessment and Policy Section), Worksafe Australia (Chemical Assessment Division) and State Departments of Agriculture.

The NRA has a policy of encouraging openness and transparency in its activities and community involvement in decision-making. The publication of evaluation documents for all ECRP reviews is a part of that process.

The NRA also makes these reports available to the regulatory agencies of other countries as part of bilateral agreements or as part of the OECD ad hoc exchange program. Under the OECD program it has been proposed that countries receiving these reports will not utilise them for registration purposes unless they are also provided with the raw data from the relevant applicant.

This report provides full details of the review of atrazine that has been conducted by the NRA and its advisory agencies. The review's findings are based on information collected from a variety of sources, including data packages and information submitted by the registrant, information submitted by members of the public, questionnaires sent to key user/industry groups and government organisations, and literature searches.

The information and technical data required by the NRA to review the safety of both new and existing chemical products must be derived according to accepted scientific principles, as must the methods of assessment undertaken.  Details of required data are outlined in various NRA publications.

Other publications explaining the NRA's requirements for registration can also be purchased or obtained by contacting the NRA. Among these are: Ag Manual:  The Requirements Manual for Agricultural Chemicals; Vet Manual: The Requirements Manual for Veterinary Chemicals and Volume II of Interim Requirements for the Registration of Agricultural and Veterinary Chemical Products.

The NRA welcomes comment on this review and the review program. They can be addressed to Manager, Chemical Review, National Registration Authority for Agricultural and Veterinary Chemical, PO Box E240, Kingston ACT 2604, Australia.

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Abbreviations and Acronyms

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Summary

The NRA has reviewed the registration of atrazine. Atrazine is a selective, systemic herbicide which provides knockdown and residual action for control of many broad leaved weeds and some grasses in tree plantations and a variety of crops such as sorghum, maize, canola and sugarcane. Atrazine is one of the most widely used herbicides in Australian agriculture.

The review, conducted under the NRA's Existing Chemicals Review Program, found that atrazine continues to demonstrate the potential to contaminate ground and surface water and that safety margins for aquatic organisms are, in some circumstances, narrow. The NRA, therefore, recommends that measures be taken to reduce aquatic contamination, and that levels of atrazine and its major metabolites in the environment be monitored to determine trends in atrazine contamination of surface and ground waters and to establish whether current and future restrictions are effective in maintaining or improving safety margins.

Product details

Label directions for the majority of its uses in agriculture require atrazine to be applied pre-planting at rates between 1.8 and 3.0 kg active ingredient (a.i.) per hectare, depending on soil type, or 1.25 kg a.i. per hectare when used in combination with metalochlor. Lower rates are applied to other crops such as lupins and lucerne. Post-planting rates are 0.5 kg active ingredient per hectare.

Application is mostly by tractor- or 4WD vehicle-mounted boomspray, with some aerial application (fixed wing) occurring when soils are wet. Some application by helicopter occurs in plantation forestry. In plantation forestry, annual application rates are 4.5 kg a.i. per hectare for sandy and highly erodible soils and 8 kg a.i. per hectare for clay loams and heavier soils. For the home garden, label application rates are given as product (g) per m² and correspond to 2.5 and 5.0 kg atrazine /ha.

In Australia, 34 registrations for products containing atrazine and 4 approvals for active constituents currently exist.

Low hazard to members of the community and users

Atrazine is of low acute toxicity and is not a skin sensitiser in humans. Toxicological evidence suggests that atrazine is not a genotoxic carcinogen. In the Sprague Dawley (SD) strain of rats, the earlier onset of mammary tumours (a common tumour type in these rats, with a high background incidence in ageing females) observed in some toxicology studies at high doses of atrazine was due to a strain-specific hormonal effect. The pattern of oestrogen levels in ageing SD rats differs from that of other rat strains tested, and from that in humans. The atrazine effect in this particular strain of rats is not considered to be an appropriate model for the assessment of mammary tumour development in humans. Atrazine is not considered to be teratogenic or toxic to reproduction.

The 1992 Australian Market Basket Survey conducted assays for atrazine and simazine in meat and cereal foods. No residues of either herbicide were detected. This finding is in agreement with US data; in over 30 years of use, atrazine has not been detected in edible portions of plants or livestock nor has it been detected in market-basket surveys. Therefore, exposure of the population to atrazine in food is considered very unlikely.

Exposure to atrazine is more likely to occur through drinking water. It is estimated that intake at 10 ppb in water would result in an intake approximately 5.7% of the current acceptable daily intake (ADI) for atrazine.

Atrazine poses no undue hazard to most users. Predicted exposures and worker exposure studies, extrapolated to Australian conditions, indicate acceptable risk for the majority of users. Faggers involved in aerial spraying are considered to be at risk. The use pattern for atrazine indicates that workers entering treated areas will not be exposed to levels likely to have a detrimental effect on health.

Minor efficacy concerns

Minor issues concerning the efficacy of atrazine have been reported to the NRA. Reports of variable performance in the Northern Territory over the 1995-96 season have raised concerns over the possible development of resistance to atrazine by a major weed of sorghum and maize, Penniseteum peddicellatum. An unconfirmed report of resistance in Johnson grass (Sorghum halepense) has also been received in Victoria.

New uses

Consideration should be given to extending the registration of atrazine in certain areas, to reflect current use patterns. The area planted to triazine-tolerant (TT) canola is rapidly expanding, and atrazine use on this crop is currently allowed under NRA permit. Atrazine is used off-label on chick peas in north-west Victoria. Chick peas are a major pulse crop for Victoria with significant export potential. Atrazine registration for use on Parthenium weed in Queensland should be extended to other States now infested with the weed, namely parts of the Northern Territory and northern NSW.

Residue information incomplete

Information provided on residues indicated no change to the current residue definition of atrazine parent for crops and animal commodities is necessary. However, data are required on forage and fodder residues for sorghum, pastures and lucerne to confirm the primary animal feed commodity maximum residue limit (MRL) and those of animal commodities. Certain MRLs should be deleted because there is no current Australian use pattern.

Potential hazard to aquatic ecosystems

Atrazine is a mobile chemical with the potential to contaminate water at low levels as a result of normal use. Evidence indicates that, in the Australian aquatic environment, atrazine exposures are generally below the threshold for ecosystem effects, which is about 20 ppb. Groundwater samples often contain detectable levels of atrazine and its metabolites around the level of 1 ppb. Higher levels have been detected but these were known to be of point-source origin, arising from improper pesticide handling practices or accidents. General historical levels in natural surface waters are less than 10 ppb (and in most cases below 1 ppb) although higher levels may occur briefly in lower order streams receiving storm runoff. However,  safety margins are narrow.

The NRA has already taken steps to eliminate some sources of aquatic contamination by restricting maximum annual application rates of atrazine and withdrawing certain uses with a high potential for aquatic contamination. The NRA has also established a broad-based taskforce to conduct a three-year program of trials and monitoring to establish whether revised conditions of use in plantation forestry will reduce aquatic contamination to acceptable levels. A number of trials are in progress.

Reducing potential hazard to the environment

While it is acknowledged that low level aquatic contamination by atrazine is unavoidable, due to its widespread use, every effort should be made to minimise its occurrence. Poor agricultural practices such as tailwater release from excessive irrigation, application shortly before heavy rains or storms or to waterlogged soils, and use in irrigation channels need to be stopped. Users should also be re-educated on the review recommendations to ensure they are adopted fully.

Monitoring levels of atrazine in surface and ground water

The NRA considers that monitoring of atrazine levels in the environment needs to continue to determine trends in atrazine contamination of Australian surface and ground waters. In addition, future monitoring needs to be conducted to investigate levels in natural waterways as well as the irrigation drainage systems that have been the main focus to date. Monitoring of residue levels in water should also be linked to biological monitoring to determine the ecological significance of atrazine levels found in Australian waterways. This monitoring will help determine whether current and future restrictions are effective in maintaining or improving current safety margins. The monitoring will initially include testing for metabolites, but only until more information has been obtained on the current levels of metabolites, as well as parent atrazine to metabolite ratios.

However, should monitoring be inadequate, or should it demonstrate that environmental safety margins continue to be narrow, the NRA will consider restricting the use of atrazine further.

Proposals for water quality guidelines

The current Australian Drinking Water Guideline is based on the measurement of atrazine alone. Metabolites, when measured, have commonly been detected at levels of the same order of magnitude as parent atrazine. Since the metabolites are, in general, no less toxic than atrazine, these metabolites should be considered in the standard. Therefore, while there is no basis for concern about human health effects at current, reported levels of contamination, consideration should be given to amending the standard to measure the combined total of atrazine plus its closely related metabolites. This action would have the equivalent effect of lowering the guideline value (currently 0.5 ppb) and the health value (currently 20 ppb) for atrazine alone since, in water samples in which atrazine is detected, one or more metabolites are commonly detected but disregarded in the current standard. This issue has been referred to the National Health and Medical Research Council (NHMRC) for consideration by a joint committee of the NHMRC and the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ).

Australia has yet to establish a water quality guideline for protecting aquatic ecosystems, but the Environmental Research Institute of the Supervising Scientist (ERISS) is currently reviewing the Australian guidelines. A guideline value of 2 ppb for atrazine operates overseas and has been proposed locally. The NRA will provide a copy of its review of atrazine to ERISS to aid deliberations.

The NRA proposes that:

• certain measures be taken to minimise aquatic contamination by atrazine;
• atrazine levels in the environment be monitored to determine trends in atrazine contamination and whether the measures are effective;
• the definition of atrazine for the Australian Drinking Water Guideline be amended to include atrazine plus its major metabolites; and
• some registrations and MRLs be amended in line with current use patterns.

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