title: An assessment of direct and indirect effects of two herbicides on aquatic communities.
abstract: Herbicides are often detected in watersheds at concentrations that are toxic to phytoplankton, potentially causing indirect effects on higher trophic organisms. The long-term effects of 5 applications over 30 d of binary mixtures of the herbicides diuron and hexazinone were assessed at "low" and "high" concentrations typically found in the environment, using mesocosms. Sixteen of 95 phytoplankton taxa, 3 of 18 zooplankton taxa, and 6 of 14 macroinvertebrate taxa responded negatively to contaminant exposures. Herbicide applications altered the phytoplankton community structure. Relative abundance of Cyanophyceae decreased following 5 applications from 52.1% in the control to 37.3% in the low treatment and to 25.9% in the high treatment, while Chlorophyceae increased to 50.6% in the low treatment and to 61.7% in the high treatment compared with the control (39.7%). Chlorophyceae had the greatest number of affected species (8), whereas 1 species within the Cyanophyceae was negatively affected on more than 1 sampling day. Further, chlorophyll a was reduced on 4 and 5 d out of the 8 total sampling days in the low and high treatments, respectively, compared with the control. These results highlight that integrating multiple taxa and contaminants with long-term exposures in ecological risk assessments of herbicides can facilitate the ability to make predictive and mechanistic generalizations about the role of herbicides in shaping patterns of species abundance in natural systems. Environ Toxicol Chem 2017;36:2234-2244. © 2017 SETAC.
authors.affiliation: Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, California, USA.
authors.forename: Simone
authors.initials: S
authors.lastname: Hasenbein
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, California, USA.
authors.forename: Sharon P
authors.initials: SP
authors.lastname: Lawler
authors.affiliation: Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, California, USA.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Connon
mesh_terms: D033304:Amphipoda / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D059001:Aquatic Organisms / Q000187:drug effects* / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D004237:Diuron / Q000633:toxicity*; D004784:Environmental Monitoring / Q000379:methods*; D006540:Herbicides / Q000633:toxicity*; D010839:Phytoplankton / Q000187:drug effects / Q000378:metabolism; D014227:Triazines / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D015048:Zooplankton / Q000187:drug effects / Q000378:metabolism
chemical_list: D006540:Herbicides; D014227:Triazines; D014874:Water Pollutants, Chemical; D002734:Chlorophyll; D004237:Diuron; C025641:hexazinone; D000077194:Chlorophyll A
keywords: Algae; Aquatic toxicology; Chlorophyll a; Food web; Mesocosm