title: Mixture effects of the nonylphenyl polyethoxylate, R-11 and the insecticide, imidacloprid on population growth rate and other parameters of the crustacean, Ceriodaphnia dubia.
abstract: The toxicity of the nonylphenol polyethoxylate, R-11 and the neonicotinoid insecticide, imidacloprid were evaluated on the crustacean, Ceriodaphnia dubia Richard. These compounds were evaluated separately and as a mixture because they are applied for pest control and may exist as a binary mixture in surface water. Acute mortality estimates (48h) were developed followed by population-level studies after chronic exposure. LC50s and 95% CL for R-11 and imidacloprid were 9241 (8521-9842)microg/l and 2.1 (1.1-3.4)microg/l, respectively. In the population study, C. dubia were exposed to concentrations equivalent to the acute LC25 for R-11 (8090microg/l) and imidacloprid (0.3microg/l) separately and as a mixture for 8d. The results of the chronic study indicated that R-11 had a greater impact on population parameters than imidacloprid and the mixture had a greater impact than either compound alone. For example, the total number of individuals at the end of the chronic study was 73%, 19%, and 6% of the control for imidacloprid, R-11, and the binary mixture, respectively. Additionally, exposure to R-11, imidacloprid, and the mixture resulted in 52%, 10%, and 91% reductions in population growth rate compared to the control, respectively. The results of this study indicate that when combined, R-11 and imidacloprid act in a more than additive manner. Therefore, it is important that their potential effects on aquatic organisms be evaluated together.
authors.affiliation: Ecotoxicology Program, Department of Entomology, Washington State University, Puyallup Research and Extension Center, Puyallup, WA 98371, USA.
authors.forename: Xue Dong
authors.initials: XD
authors.lastname: Chen
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Culbert
authors.forename: Vince
authors.initials: V
authors.lastname: Hebert
authors.forename: John D
authors.initials: JD
authors.lastname: Stark
mesh_terms: D000818:Animals; D033361:Cladocera / Q000187:drug effects* / Q000254:growth & development; D004305:Dose-Response Relationship, Drug; D004784:Environmental Monitoring; D007093:Imidazoles / Q000633:toxicity; D007306:Insecticides / Q000633:toxicity*; D007928:Lethal Dose 50; D009026:Mortality; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000633:toxicity; D017137:Nonoxynol / Q000633:toxicity*; D011158:Population Growth; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D014874:Water Pollutants, Chemical; D017137:Nonoxynol; C082359:imidacloprid