Pesticide Mixtures, Endocrine Disruption, and Amphibian Declines: Are We Underestimating the Impact?
By T. Hayes, P. Casé, Sarah Chui, Duc Chung, C. Haeffele, K. Haston, Melissa Lee, V. P. Mai, Youssra Marjuoa, J. Parker and 1 more. Environmental Health Perspectives, 2006
677 citations recorded by the source corpus.
Amphibian populations are declining globally at an alarming rate. Pesticides are among a number of proposed causes for these declines. Although a sizable database examining effects of pesticides on amphibians exists, the vast majority of these studies focus on toxicological effects (lethality, external malformations, etc.) at relatively high doses (parts per million). Very few studies focus on effects such as endocrine disruption at low concentrations. Further, most studies examine exposures to single chemicals only. The present study examined nine pesticides (four herbicides, two fungicides, and three insecticides) used on cornfields in the midwestern United States. Effects of each pesticide alone (0.1 ppb) or in combination were examined. In addition, we also examined atrazine and S-metolachlor combined (0.1 or 10 ppb each) and the commercial formulation Bicep II Magnum, which contains both of these herbicides. These two pesticides were examined in combination because they are persistent throughout the year in the wild. We examined larval growth and development, sex differentiation, and immune function in leopard frogs (Rana pipiens). In a follow-up study, we also examined the effects of the nine-compound mixture on plasma corticosterone levels in male African clawed frogs (Xenopus laevis). Although some of the pesticides individually inhibited larval growth and development, the pesticide mixtures had much greater effects. Larval growth and development were retarded, but most significantly, pesticide mixtures negated or reversed the typically positive correlation between time to metamorphosis and size at metamorphosis observed in controls: exposed larvae that took longer to metamorphose were smaller than their counterparts that metamorphosed earlier. The nine-pesticide mixture also induced damage to the thymus, resulting in immunosuppression and contraction of flavobacterial meningitis. The study in X. laevis revealed that these adverse effects may be due to an increase in plasma levels of the stress hormone corticosterone. Although it cannot be determined whether all the pesticides in the mixture contribute to these adverse effects or whether some pesticides are effectors, some are enhancers, and some are neutral, the present study revealed that estimating ecological risk and the impact of pesticides on amphibians using studies that examine only single pesticides at high concentrations may lead to gross underestimations of the role of pesticides in amphibian declines.
Subfields: Global and Planetary Change, Health, Toxicology and Mutagenesis, Insect Science
View Paper: https://www.semanticscholar.org/paper/041d4b38e34094788631793e0e27996fe839bf53
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Citations in the corpus
- Occurrence of Azoxystrobin, Propiconazole, and Selected Other Fungicides in US Streams, 2005–2006 (2011, background): “Finally, some pesticide mixtures can have adverse effects on aquatic communities even when no individual compound occurs at toxic levels (Castillo et al. 2006; Hayes et al. 2006; Relyea 2009).”
- Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses. (2012, neutral): “that samples collected from humans and the environment typically contain hundreds of contaminants, usually in the parts-per-billion (ppb) range (90, 91).”
- High Levels of Miticides and Agrochemicals in North American Apiaries: Implications for Honey Bee Health (2010, background): “Pesticides have been implicated in the declines of other bioindicator species including the altering of olfactory behavior in western US salmon [19], disrupting signaling required for recruitment of nitrogenfixing bacterial symbionts [20], and causing endocrine disruption, increased disease suscepti”
- The Hidden and External Costs of Pesticide Use (2016, background): “The effects of such mixtures of pesticides have probably played a major role in the global decline of amphibians (Hayes et al. 2006 ).”