title: The fungicide chlorothalonil is nonlinearly associated with corticosterone levels, immunity, and mortality in amphibians.
abstract: BACKGROUND
  Contaminants have been implicated in declines of amphibians, a taxon with vital systems similar to those of humans. However, many chemicals have not been thoroughly tested on amphibians or do not directly kill them.
  
  
  OBJECTIVE
  Our goal in this study was to quantify amphibian responses to chlorothalonil, the most commonly used synthetic fungicide in the United States.
  
  
  METHODS
  We reared Rana sphenocephala (southern leopard frog) and Osteopilus septentrionalis (Cuban treefrog) in outdoor mesocosms with or without 1 time (1×) and 2 times (2×) the expected environmental concentration (EEC) of chlorothalonil (~ 164 μg/L). We also conducted two dose-response experiments on O. septentrionalis, Hyla squirella (squirrel treefrog), Hyla cinerea (green treefrog), and R. sphenocephala and evaluated the effects of chlorothalonil on the stress hormone corticosterone.
  
  
  RESULTS
  For both species in the mesocosm experiment, the 1× and 2× EEC treatments were associated with > 87% and 100% mortality, respectively. In the laboratory experiments, the approximate EEC caused 100% mortality of all species within 24 hr; 82 μg/L killed 100% of R. sphenocephala, and 0.0164 μg/L caused significant tadpole mortality of R. sphenocephala and H. cinerea. Three species showed a nonmonotonic dose response, with low and high concentrations causing significantly greater mortality than did intermediate concentrations or control treatments. For O. septentrionalis, corticosterone exhibited a similar nonmonotonic dose response and chlorothalonil concentration was inversely associated with liver tissue and immune cell densities (< 16.4 μg/L).
  
  
  CONCLUSIONS
  Chlorothalonil killed nearly every amphibian at the approximate EEC; at concentrations to which humans are commonly exposed, it increased mortality and was associated with elevated corticosterone levels and changes in immune cells. Future studies should directly quantify the effects of chlorothalonil on amphibian populations and human health.
authors.affiliation: Department of Integrative Biology, University of South Florida, Tampa, Florida 33620, USA. tamcmaho@mail.usf.edu
authors.forename: Taegan A
authors.initials: TA
authors.lastname: McMahon
authors.forename: Neal T
authors.initials: NT
authors.lastname: Halstead
authors.forename: Steve
authors.initials: S
authors.lastname: Johnson
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Raffel
authors.forename: John M
authors.initials: JM
authors.lastname: Romansic
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Crumrine
authors.forename: Raoul K
authors.initials: RK
authors.lastname: Boughton
authors.forename: Lynn B
authors.initials: LB
authors.lastname: Martin
authors.forename: Jason R
authors.initials: JR
authors.lastname: Rohr
mesh_terms: D000663:Amphibians / Q000276:immunology* / Q000378:metabolism*; D000818:Animals; D003345:Corticosterone; D005659:Fungicides, Industrial / Q000633:toxicity*; D007109:Immunity / Q000187:drug effects*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D009026:Mortality; D009570:Nitriles / Q000633:toxicity*; D011894:Rana pipiens / Q000276:immunology / Q000378:metabolism; D011898:Ranidae / Q000276:immunology / Q000378:metabolism; D014874:Water Pollutants, Chemical
chemical_list: D005659:Fungicides, Industrial; D009570:Nitriles; D014874:Water Pollutants, Chemical; C005806:tetrachloroisophthalonitrile; D003345:Corticosterone