Health effects of Atrazine and Wildlife
Atrazine
One of the most widely used herbicides in the United States has been a topic of concern among environmentalists since its use began in 1958 [i]. Atrazine is used to control weeds in crops such as corn, sugar cane, and sorghum. It eliminates broadleaf weeds by inhibiting photosynthesis, but is absorbed and metabolized/deactivated by crops like corn[ii]. Although its use has decreased in the last few years, it is still purchased yearly between 80-90 million pounds[iii].
The half-life of Atrazine in soil is about 60-150 days, and increases to approximately 660 days when conditions turn anaerobic. Once Atrazine enters water, the half-life increases up to two years, and when it reaches water lacking in oxygen, it can linger for much longer. When it eventually does degrade, it is assumed that the substances it degrades into are equally toxic[iv].
Up until 1994, the Environmental Protection Agency had declared Atrazine to be a human carcinogen. Many studies, including one by Rusiecki et al. on cancer incidence among farmers using Atrazine, found no significant associations between Atrazine exposure and an increase in the incidence of cancer in the farmers[v]. Human exposure (Health effects of atrazine) to Atrazine occurs mainly through contaminated drinking water near farms where Atrazine is used, as well as inhalation and absorption through the skin[vi]. One of the first studies investigating associations between the effects of Atrazine exposure on women aged 18-40 and their menstrual cycles was conducted in 2005 in Illinois farming areas. The study found an association between Atrazine levels well below the EPA defined MCL of 3 ppb in drinking water and fluctuating cycle length, a decrease in reproductive hormones, and an increase in follicular phase[vii].
Amphibian Controversy
The main routes of pollution by Atrazine occur via runoff and erosion into streams and lakes, and have the greatest effect on aquatic organisms[viii].
University of California researcher Tyrone Hayes and his lab study the sexual development and metamorphosis of the model organism Xenopus laevis, or the African clawed frog, in the presence of Atrazine. African clawed frogs and amphibians are very sensitive to environmental change in general, and can be used as environmental monitors. Their studies demonstrate that atrazine reduces testosterone and increases the production of estrogen in frogs. This has been observed in mammals as well following exposure to Atrazine, where an increase in estrogen and decrease in androgens resulted in feminization of male features. Changes occurred in the gonads of frogs at concentrations more than 600 times lower than those used in the mammal studies[ix].
Studies done by Hayes lab indicate that 0.1 ppb Atrazine is sufficient to induce hermaphroditism (or intersex), and 1 ppb causes the larynx to cease growing. These levels were 30,000,000 times lower than the doses administered to rats to cause changes in reproduction[x]. These effective doses suggest that amphibians are more sensitive than mammals, and would serve as appropriate environmental monitors. With this extreme sensitivity, wild frog populations are facing relatively new selective pressures in the form of chemical pesiticides and are thought to be decreasing in part, because of such exposures[xi].
Ecological Implications
Studies in outdoor mescosms have shown that tadpoles exposed to as little as 1.8 ppb of Atrazine (5 ppb the drinking water criteria in Canada and 3 ppb in the United States) during development have major physiological differences compared to unexposed frogs including a 20% increase in the number of phenotypically female frogs, high incidences of testicular oocytes in male frogs reduced metamorphosis rates to under 50%[xii]. (see figure 1) These studies are potentially a cause for concern because frogs are often used as indicator species of ecosystem health.
Frogs play a major role in wetland, forest and riparian ecosystems as nutrient distributors, and ecological assimilators.[xiii] Frogs act as “ecological conveyor belts to pass energy from the bugs and insects they eat on up to larger predators in the ecosystem” [xiv] Frogs also contribute to keeping insect populations in check.[xv] The National Institute of Malaria Research (ICMR), in Delhi, found that mosquito populations decrease in the presence of healthy frog populations, and suggested that the “Overall evaluation of the impact of such introduction of frogs or other predators should be considered for possible benefits to human health.”[xvi]
Atrazine has been implicated in the feminization and demasculinzation of male frogs[xvii],[xviii]. Effects include: reduced levels of testosterone production, decreased breeding gland size, depressed spermatogenesis, altered laryngeal development (altering mating call) suppressed mating behavior and decreased fertility.[xix],[xx]. Several researchers have suggested that the endocrine disruption associate with Atrazine may contribute (along with other factors) to the global amphibian decline.[xxi],[xxii],[xxiii],[xxiv],[xxv],[xxvi]
Collins and Crump sum up the situation "Thus, both because of what they eat and because they serve as food for fish, reptiles, birds, mammals, and other animals, amphibians play a central role in the food web. Cascading effects will be felt throughout both aquatic and terrestrial food webs if large numbers of amphibians disappear”[xxvii]
Sources:
[i] Ribaudo, Marc, and Aziz Bouzaher. United States. Department of Agriculture. Atrazine: Environmental Characteristics and Economics of Management. Washington, DC: , 1994. Print.
[ii] Solomon, Kieth, James Carr, Louis Du Preez, John Giesy, Ronald Kendall, Ernest Smith, and Glen Van Der Kraak. "Effects of Atrazine on Fish, Amphibians, and Aquatic Reptiles: A Critical Review." Critical Reviews in Toxicology. 38. (2008): 721–772. Print.
[iii] Ribaudo, Marc, and Aziz Bouzaher. United States. Department of Agriculture. Atrazine: Environmental Characteristics and Economics of Management. Washington, DC: , 1994. Print.
[iv] Ribaudo, Marc, and Aziz Bouzaher. United States. Department of Agriculture. Atrazine: Environmental Characteristics and Economics of Management. Washington, DC: , 1994. Print.
[v] Rusiecki, Jennifer A., Anneclaire De Roos, Won Jin Lee, Mustafa Dosemeci, Jay H. Lubin, Jane A. Hoppin, Aaron Blair and Michael C. R. Alavanja. “Cancer Incidence Among Pesticide Applicators Exposed to Atrazine in the Agricultural Health Study.” Journal of the National Cancer Institute 96.18 (2004): 1375-1382.
[vi] Ribaudo, Marc, and Aziz Bouzaher. United States. Department of Agriculture. Atrazine: Environmental Characteristics and Economics of Management. Washington, DC: , 1994. Print.
[vii] Cragin, Lori A., James S.Kesner, Annette M.Bachand, Dana BoydBarr, Juliana W.Meadow, Edward F.Krieg, and John S.Reif. “Menstrual cycle characteristics and reproductive hormone levels in women exposed to atrazine in drinking water.” Environmental Research. 111. 8 (2011): 1293-1301.
[viii] Solomon, Kieth, James Carr, Louis Du Preez, John Giesy, Ronald Kendall, Ernest Smith, and Glen Van Der Kraak. "Effects of Atrazine on Fish, Amphibians, and Aquatic Reptiles: A Critical Review." Critical Reviews in Toxicology. 38. (2008): 721–772. Print.
[ix] Hayes, Tyrone, Atif Collins, Melissa Lee, Magdelena Mendoza, Nigel Noriega, A. Ali Stuart, and Aaron Vonk. "Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses." PNAS. 99.8 (2002): 5476-5480. Print.
[x] Wetzel, Lawrence. T, Louis G. Luempert III, Charles B. Breckenridge, Merrill O. Tisdel, James T. Stevens, Ajit K. Thakur, Pamela J. Extrom and J. Charles Eldridge. “Chronic effects of atrazine on estrus and mammary tumor formation in female Sprague?Dawley and Fischer 344 rats.” Journal of Toxicology and Environmental Health. 43.2 (1994): 169-182
[xi] Hayes, Tyrone, Atif Collins, Melissa Lee, Magdelena Mendoza, Nigel Noriega, A. Ali Stuart, and Aaron Vonk. "Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses." PNAS. 99.8 (2002): 5476-5480. Print.
[xii] Langlois, Valérie S. , Amanda C. Carew, Bruce D. Pauli, Michael G. Wade, Gerard M. Cooke, and Vance L. Trudeau. "Low Levels of the Herbicide Atrazine Alter Sex Ratios and Reduce Metamorphic Success in Rana pipiens Tadpoles Raised in Outdoor Mesocosms." Enviromental Health Perspectives. 118.4 (2010): n. page. Web. 13 Oct. 2011. <http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info:doi/10.1289/ehp.0901418>.
[xiii] NAMOS, . "Importance of Amphibians." Northern Amphibian Monitoring Outpost Society . NAMOS, 2011. Web. 1 Nov 2011.
[xiv] NAMOS, . "Importance of Amphibians." Northern Amphibian Monitoring Outpost Society . NAMOS, 2011. Web. 1 Nov 2011.
[xv] "TED case studies." Frog Trade. N.p., 1/11/1997. Web. 1 Nov 2011. http://www1.american.edu/TED/frogs.htm
[xvi] Raghavendra, K, P. Sharma , and A. P. Dash. "Biological control of mosquito populations through frogs: Opportunities & constrains." Indian J Mes Res. 128.July (2008): 22-24. Print. <http://www.ncbi.nlm.nih.gov/pubmed/18820354>.
[xvii] Hayes, Tyrone B, Vicky Khoury, Anne Narayan, Mariam Nazir, Andrew Park, Travis Brown, Lillian Adame, and Elton Chan. "Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis) ." PNAS. 107.10 (2010): 3612-4617. Web. 16 Oct. 2011. <http://www.pnas.org/content/107/10/4612.full>.
[xviii] Template:31 HayesTyrone B. Stuart, A. Ali, Mendoza Magdalena, Collins Atif, Noriega Nigel, Vonk Aaron, Johnston Gwynne ,Liu Roger , Kpodzo Dzifa 2006;
[xix] Hayes, Tyrone B, Vicky Khoury, Anne Narayan, Mariam Nazir, Andrew Park, Travis Brown, Lillian Adame, and Elton Chan. "Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis) ." PNAS. 107.10 (2010): 3612-4617. Web. 16 Oct. 2011.
[xx] Hayes, Tyrone B, Vicky Khoury, Anne Narayan, Mariam Nazir, Andrew Park, Travis Brown, Lillian Adame, and Elton Chan. "Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis) ." PNAS. 107.10 (2010): 3612-4617. Web. 16 Oct. 2011. <http://www.pnas.org/content/107/10/4612.full>.
[xxi] Beebee, Trevor J.C., and Richard A. Griffiths. "The amphibian decline crisis: A watershed for conservation biology?." Biological Conservation. 125.3 (2005): 271-285. Web. 16 Oct. 2011. <http://www.sciencedirect.com/science/article/pii/S0006320705001825
[xxii] Collins, ames P., and Martha L. Crump. Extinction In Our Times, Global Amphibian Decline. Oxford University Press, USA, 2009. 8-15. eBook. http://books.google.ca/books?id=PIwMWjcjqGoC&printsec=frontcover&dq=Extinction in our times: global amphibian decline By James P. Collins, Martha L.
[xxiii] Rohr, Jason R., Tyler Sager, Timothy M. Sesterhenn, and Brent D. Palmer. "Exposure, Postexposure, and Density-Mediated Effects of Atrazine on Amphibians: Breaking Down Net Effects into Their Parts." Enviromental Health Perspectives. 114.1 (2006): 46-50. Web. 16 Oct. 2011.
[xxiv] Hayes, Tyrone B, Vicky Khoury, Anne Narayan, Mariam Nazir, Andrew Park, Travis Brown, Lillian Adame, and Elton Chan. "Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis) ." PNAS. 107.10 (2010): 3612-4617. Web. 16 Oct. 2011. <http://www.pnas.org/content/107/10/4612.full>.
[xxv] Langlois, Valérie S. , Amanda C. Carew, Bruce D. Pauli, Michael G. Wade, Gerard M. Cooke, and Vance L. Trudeau. "Low Levels of the Herbicide Atrazine Alter Sex Ratios and Reduce Metamorphic Success in Rana pipiens Tadpoles Raised in Outdoor Mesocosms." Enviromental Health Perspectives. 118.4 (2010): n. page. Web. 13 Oct. 2011. <http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info:doi/10.1289/ehp.0901418>.
[xxvi] Raloff, Janet. "Frogs: Clues to how weed killer may feminize males ." Science News. 02/03/2010: n. page. Web. 13 Oct. 2011. <http://www.sciencenews.org/view/generic/id/56867/title/Science_+_the_Public__Frogs_Clues_to_how_weed_killer_may_feminize_males>.
[xxvii] Collins, ames P., and Martha L. Crump. Extinction In Our Times, Global Amphibian Decline. Oxford University Press, USA, 2009. 8-15. eBook. http://books.google.ca/books?id=PIwMWjcjqGoC&printsec=frontcover&dq=Extinction in our times: global amphibian decline By James P. Collins, Martha L.
