title: Mixture toxicity of the antifouling compound irgarol to the marine phytoplankton species Dunaliella tertiolecta.
abstract: This study examined the toxicity of irgarol, individually and in binary mixtures with three other pesticides (the fungicide chlorothalonil, and the herbicides atrazine and 2,4-D), to the marine phytoplankton species Dunaliella tertiolecta. Standard 96-h static algal bioassays were used to determine pesticide effects on population growth rate. Irgarol significantly inhibited D. tertiolecta growth rate at concentrations > or = 0.27 micro g/L. Irgarol was significantly more toxic to D. tertiolecta than the other pesticides tested (irgarol 96 h EC50 = 0.7 micro g/L; chlorothalonil 96 h EC50 = 64 micro g/L; atrazine 96 h EC50 = 69 micro g/L; 2,4-D 96 h EC50 = 45,000 micro g/L). Irgarol in mixture with chlorothalonil exhibited synergistic toxicity to D. tertiolecta, with the mixture being approximately 1.5 times more toxic than the individual compounds. Irgarol and atrazine, both triazine herbicides, were additive in mixture. The toxicity threshold of 2,4-D was much greater than typical environmental levels and would not be expected to influence irgarol toxicity. Based on these interactions, overlap of certain pesticide applications in the coastal zone may increase the toxicological risk to resident phytoplankton populations.
authors.affiliation: US Department of Commerce/NOAA, National Ocean Service, Coastal Center for Environmental Health and Biomolecular Research, Charleston, SC 29412-9110, USA. marie.delorenzo@noaa.gov
authors.forename: Marie E
authors.initials: ME
authors.lastname: DeLorenzo
authors.forename: Lorimar
authors.initials: L
authors.lastname: Serrano
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000633:toxicity; D000818:Animals; D001280:Atrazine / Q000633:toxicity; D001681:Biological Assay; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004357:Drug Synergism; D005659:Fungicides, Industrial / Q000633:toxicity*; D006540:Herbicides / Q000633:toxicity*; D007928:Lethal Dose 50; D009570:Nitriles / Q000633:toxicity; D010839:Phytoplankton / Q000187:drug effects* / Q000254:growth & development*; D011156:Population Density; D011158:Population Growth; D014227:Triazines / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D004338:Drug Combinations; D005659:Fungicides, Industrial; D006540:Herbicides; D009570:Nitriles; D014227:Triazines; D014874:Water Pollutants, Chemical; D015084:2,4-Dichlorophenoxyacetic Acid; C103341:irgarol 1051; C005806:tetrachloroisophthalonitrile; D001280:Atrazine