US Fish & Wildlife Service


Date of this Version



Eisler, R. 1989. Atrazine hazards to fish, wildlife, and invertebrates: a synoptic review. U. S. Fish Wildl. Servo Biol. Rep. 85(1.18). 53 pp.


The herbicide ·atrazine (2-chloro-4-ethylamino-6-isopropylamino-I,3,5- triazine) is the most heavily used agricultural pesticide in North America. In the United States alone, more than 50 million kg (110 million pounds) are applied annually to more than 25 million ha (62 million acres), primarily to control weeds in corn and sorghum. Residues have been detected at phytotoxic concentrations in groundwater, lakes, and streams as a result of runoff from treated fields. Atrazine degrades rapidly, usually by way of hydrolysis, nitrogen dealkylation, and splitting of the triazine ring to less toxic compounds not normally inhibitory to plants and animals. The half-time persistence of atrazine in soils is usually about 4 days, but may range up to 385 days in dry, sandy, alkaline soils, under conditions of low temperature and low microbial densities. Half-time persistence is about 3 days in freshwater, 30 days in marine waters, 35 days in marine sediments, and less than 72 hours in vertebrate animals.

Sensitive species of aquatic plants experience temporary, but reversible, adverse effects at concentrations in the range of 1 to 5 ug atrazine/l. However, potentially harmful phytotoxic concentrations of atrazine, i.e., >10 ug/l for extended periods, have not been documented in the environment, and are probably unrealistic under current application and degradation rates. Aquatic fauna are indirectly affected at atrazine concentrations of 20 ug/l and higher, partly through reduction of the food supply of herbivores, and partly through loss of macrophyte habitat. Direct adverse effects to aquatic invertebrates and fishes were measured at 94 ug/l and higher. Bioaccumulation of atrazine. is limited, and food chain biomagnification is negligible in aquatic ecosystems. Birds are comparatively resistant to atrazine, having a low probability for uptake and retention. Known acute oral lD-50 values for birds are >2,000 mg/kg body weight, and dietary lD-50s are >5,000 mg/kg ration. However, indirect ecosystem effects of atrazine on seed- and insect-eating birds are unknown, and should be investigated. Data are lacking for atrazine toxicity to mammalian wildlife, but tests with domestic livestock and small laboratory animals indicate that this group is also comparatively resistant. Acute oral lD-50s for mammals are >1,750 mg/kg body weight; no adverse effects were measured at chronic dietary levels of 25 mg/kg (about 1.25 mg/kg body weight) and, for some species, 100 mg/kg diet.

Proposed criteria for aquatic life protection include <5 ug atrazine/l for sensitive species of aquatic flora, and <11 ug/l for most species of aquatic plants and animals. No criteria have been promulgated for human or animal health protection, although it has been suggested that <7.5 ug/l in drinking water, and <0.0375 mg atrazine/kg body weight (<2.25 mg daily for a 60 kg adult, <1.5 mg/kg diet based on consumption of 1.5 kg food daily) would pose a negligible risk to human health. Additional data are needed on toxicity, environmental fate, and chemistry of atrazine and its metabolites in order to maintain existing registrations or to permit new registrations. In particular, more research is needed on possible synergistic or additive effects of atrazine with other agricultural chemicals in aquatic environments.