Atrazine population-level effects

These high levels were sporadic and transitory. However, some of them were high enough to have caused phytotoxicity, and more work needs to be done to establish whether herbicides are having adverse effects upon populations of aquatic plants in areas highlighted in this study. It should also be borne in mind that there may have been additive or synergistic effects caused by the combinations of herbicides found in these samples. For example, urea herbicides such as diuron and chlortoluron act upon photosynthesis by a common mechanism, so it seems likely that any effects upon aquatic plants will be additive. Similarly, simazine and atrazine share a common mechanism of action. 

In terrestrial ecosystems, atrazine effectively inhibits photosynthesis in target weeds and can also affect certain sensitive crop plants. Atrazine metabolites are not as phytotoxic as the parent compound. Degradation is usually rapid, although atrazine can persist in soils for more than one growing season. Soil fauna may be adversely affected shortly after initial atrazine application at recommended levels, but long-term population effects on this group are considered negligible. 

Reviews by the Australian Pesticides and Veterinary Medicines Authority (APVMA) in 1997 and again in 2004 concluded that properly used and applied, atrazine and simazine are safe for humans and the environment [Australian Pesticides and Veterinary Medicines Authority (APVMA), 1997, 2004], The APVMA also reviewed additional data on potential effects of atrazine on amphibians and concluded that taken together, these data indicate that it is unlikely that atrazine is impacting adversely on populations of Australian amphibians at current levels of exposure (APVMA, 2004). 

At 2.5 mg atrazine/kg soil, equivalent to 2 kg/ha in the top 10 cm, field and laboratory studies demonstrated that mortality in arthropod coUembolids Onchiurus apuanicus) was 47% in 60 days however, fecundity was not affected at dose levels up to 5.0 mg/kg soil. It was concluded that atrazine applications at recommended treatment levels had negligible long-term population effects on sensitive species of soil fauna. At 5.0 or 8.0 kg atrazine/ha, all species of soil fauna tested, except some species of nematodes, were adversely affected. One month post-application, population reductions of 65-91% were recorded in protozoans, mites, various insect groups, and collem-bolids at 5.0 kg/ha after 4 months, populations were still depressed by 55-78%. At 8.0 kg atrazine/ha, soil faun populations... 

If and when consistent and robust responses to atrazine are identified in frogs, the mechanisms by which these effects are mediated should be elucidated. This will better allow the application of biomarkers to assess the significance of responses in the field situations and increase the precision and accuracy of extrapolation of effects to other an hibians and assessment of their relevance at the level of the population. 

---