Atrazine in freshwater and marine water

​​​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’ of the ANZECC & ARMCANZ (2000) guidelines.

The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.

Description of chemical

Atrazine (CAS 1912-24-9) is a triazine herbicide developed by Ciba-Geigy, with a selective systemic mode of action, being absorbed mainly through the roots (Tomlin 1994). It inhibits photosynthesis and other enzyme processes (Tomlin 1994). A comprehensive draft review of atrazine by NRA (1997b) indicated that a complete set of data was available.

Its IUPAC name is 6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine, molecular formula is C8H14ClN5 and molecular weight is 215.7. Atrazine is soluble in water at 33 mg/L at 20°C (Tomlin 1994). It has a pKa of 1.7. The current analytical practical quantitation limit (PQL) for atrazine in water is 0.5 µg/L (NSW EPA 2000).

Uses and environmental fate

Atrazine is used widely against grasses and broad-leaved weeds in a variety of vines, orchards, plantations and crops, particularly maize and sorghum (NRA 1997a). In Australia, atrazine has over 1600 registered uses as 30 registered products. It is often used in conjunction with other herbicides.

Atrazine is relatively stable in water and persists in groundwater with a DT50 greater than 100 days (Tomlin 1994). Atrazine breaks down only slowly in sunlight with a half-life of around 1 year. Its half-life in fresh water systems is around 2 months, or more at lower temperatures, but is more rapid (<1 month) in estuarine systems (NRA 1997b). It does not bioaccumulate significantly. Atrazine is highly mobile and it has been commonly detected in surface and groundwater samples in Australia (Cooper 1996) usually at less than 1 µg/L. In fact, it is one of the most commonly detected pesticides in the Murray–Darling Basin.

Aquatic toxicology

Freshwater algae: two species, 48 to 96-hour EC50 (growth) of 21 to 377 µg/L. The lowest figure was for Scenedesmus subspicatus but another figure of 110 µg/L was also reported for that species.

Freshwater fish: 14 species; 96-hour LC50 between 500 (Rasbora heteromorpha, 48-hour LC50) and 71,000 µg/L (Poecilia reticulata). A 35-day mortality NOEC of 300 µg/L was obtained for Brachydanio rerio; a 21-day mortality NOEC of 60 µg/L for trout Oncorhynchus mykiss; a 274-day growth NOEC of 250 µg/L for Pimephales promelas but no effect on reproduction at 2000 µg/L (highest concentration). An acute-to-chronic ratio (ACR) of 300 was reported.

Freshwater crustaceans: five species, 48 to 96-hour EC50 of 5700 to 54,000 µg/L.

Microcosms and mesocosms: NRA (1997b) reviewed a number of aquatic microcosm and mesocosm studies with different composition and test end-points (Moorhead & Kosinski 1986, Pratt et al. 1988, Stay et al. 1989, Neugebaur et al. 1990, Detenbeck et al. 1996, Gruessner & Watkin 1996). Most reported just LOEC values between 50 and 300 µg/L but eight NOEC values were reported; 3.2, 5, 17.5, 20, 20, 20 and 80 µg/L. The lowest figure was a stimulation effect and was not considered. None of these fully satisfied the requirements but they do give added confidence in the trigger value.

Marine fish: two species, 96-hour LC50 between 2000 and 16,200 µg/L.

Marine crustacean: four species, 96-hour LC50 of 94 µg/L (Acartia tonsa) to 13,200 µg/L; 8-day NOEC (mortality) between 4200 and 17,500 µg/L for the copepod Eurytemora affinis, depending on salinity. Two species of adult crabs were insensitive to atrazine up to its solubility.

Marine diatom: one species, 48 to 72-hour EC50 of 50 to 265 µg/L (PSR, photosynthesis).

Australian and New Zealand data

The 96-h LC50 to the introduced fish Gambusia holbrooki was 18,900 µg/L and to Hypseleotris gallii (firetail gudgeon) was 258,000 µg/L, well above the solubility level. The 48-hour LC50 to the water flea Ceriodaphnia dubia was 18,300 µg/L. The 72-hour EC50 to the alga Selenastrum capricornutum was 359 µg/L. All of those figures were within the range of overseas species, except for the gudgeon, which was particularly insensitive.

Factors that modify toxicity of atrazine

The NRA (1997b) review did not identify any factors modifying atrazine toxicity. Synergy was not demonstrated with the pyrethroid bifenthrin. Hall et al. (1995) demonstrated varying chronic toxicity of atrazine to an estuarine copepod, Eurytemora affinis, under different salinity regimes. It was most sensitive (14.6 mg/L) at 5 ppt salinity and of lowest sensitivity (20.9 mg/L) at 15 ppt. Mixtures of atrazine and metribuzin have additive toxicity to algae (Altenburger et al. 1990).

Guidelines

A freshwater moderate reliability trigger value of 13 µg/L was derived for atrazine using the statistical distribution method with 95% protection and an ACR of 20.2.

Although there are marine data on fish, crustaceans and algae (OECD MPD) it was considered preferable to adopt the freshwater figure as a marine low reliability trigger value (13 µg/L). This should be used only as an indicative interim working level.

References

Altenburger R, Bodeker W, Faust M & Grimme LH 1990. Evaluation of the isobologram method for the assessment of mixtures of chemicals. Ecotoxicology and Environmental Safety 20, 98-114.

ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

Cooper B 1996. Central and north west regions water quality program 1995/96 Report on pesticides monitoring. Department of Land and Water Conservation, TS 96.048, Parramatta, NSW.

Detenbeck NE, Hermanutz R, Allen K & Swift MC 1996. Fate and effects of the herbicide atrazine in flow-through wetland mesocosms. Environmental Toxicology and Chemistry 15, 937-946.

Gruessner B & Watkin MC 1996. Response of aquatic communities from a Vermont stream to environmentally realistic atrazine exposure in laboratory microcosms, Environmental Toxicology and Chemistry 15, 330-336.

Hall LW, Ziegenfuss MC, Anderson RD & Tierney DP 1995. The influence of salinity on the chronic toxicity of atrazine to an estuarine copepod: Implications for development of an estuarine chronic criterion. Archives of Environmental Contamination and Toxicity 28, 344-348.

Moorhead DL & Kosinski RJ 1986. Effect of atrazine on the productivity of artificial algal communities. Bulletin of Environmental Contamination and Toxicology 37, 330-336.

Neugebaur K, Zieris F-J & Huber W 1990. Ecological effects of atrazine on two outdoor artificial freshwater ecosystems. Zeitschrift fur Wasser-Abwasswer-Forschung 23, 11-17.

NRA 1997a. Database extraction of selected pesticides: Registered uses in Australia, National Registration Authority, July 1997, Canberra.

NRA 1997b. Technical report on the NRA review of Atrazine. Draft for public comment, National Registration Authority, July 1997, Canberra.

NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.

Pratt JR, Bowers NJ, Niederlehner BR & Cairns J Jr 1988. Effects of atrazine on freshwater microbial communities. Archives of Environmental Contamination and Toxicology 17, 449-457.

Stay FS, Katko A, Rohm CM, Fix MA & Larsen DP 1989. The effects of atrazine on microcosms developed from four natural plankton communities. Archives of Environmental Contamination and Toxicology 18, 866-875.

Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.