title: The influence of simulated immigration and chemical persistence on recovery of macroinvertebrates from cypermethrin and 3,4-dichloroaniline exposure in aquatic microcosms.
abstract: BACKGROUND
  Chemical dissipation and organism immigration are considered important factors that influence recovery potential from perturbation of aquatic macroinvertebrates. Experiments were conducted to investigate the effect of simulated immigration on recovery of aquatic macroinvertebrates exposed in outdoor microcosms to ecotoxicologically similar concentrations of the rapidly dissipating pyrethroid insecticide cypermethrin (70 ng L(-1)) or the more persistent herbicide intermediate and degradate 3,4-dichloroaniline (10 mg L(-1)). Microcosms were covered with light-permeable mesh to prevent recolonisation. Immigration was simulated by the regular addition of organisms after treatment.
  
  
  RESULTS
  Microcosms exposed to 3,4-dichloroaniline treatment suffered substantial loss of taxon richness and by 10 months after treatment had only recovered where invertebrates had been added. Those treated with cypermethrin underwent an initial decline in certain crustacean and insect populations. These populations showed some signs of recovery over a period of 5 months through internal processes alone. However, rate of recovery was further enhanced where immigration was simulated, and in this case recovery had occurred around 100 days after treatment.
  
  
  CONCLUSIONS
  Although not the only factors involved, simulated immigration and chemical fate clearly influence the ability of communities to recover from chemical exposure. Consideration of immigration processes and development of models will help to increase the realism of risk assessments.
authors.affiliation: Syngenta Crop Protection AG, Basel, Switzerland. steve.maund@syngenta.com
authors.forename: Steve
authors.initials: S
authors.lastname: Maund
authors.forename: Jeremy
authors.initials: J
authors.lastname: Biggs
authors.forename: Penny
authors.initials: P
authors.lastname: Williams
authors.forename: Mercia
authors.initials: M
authors.lastname: Whitfield
authors.forename: Thomas
authors.initials: T
authors.lastname: Sherratt
authors.forename: Will
authors.initials: W
authors.lastname: Powley
authors.forename: Phil
authors.initials: P
authors.lastname: Heneghan
authors.forename: Paul
authors.initials: P
authors.lastname: Jepson
authors.forename: Nigel
authors.initials: N
authors.lastname: Shillabeer
mesh_terms: D000814:Aniline Compounds / Q000494:pharmacology*; D025041:Animal Migration; D000818:Animals; D017753:Ecosystem; D004784:Environmental Monitoring; D006540:Herbicides / Q000494:pharmacology; D007306:Insecticides / Q000494:pharmacology; D007448:Invertebrates / Q000187:drug effects* / Q000502:physiology; D008954:Models, Biological; D011722:Pyrethrins / Q000494:pharmacology*; D014874:Water Pollutants, Chemical / Q000494:pharmacology*
chemical_list: D000814:Aniline Compounds; D006540:Herbicides; D007306:Insecticides; D011722:Pyrethrins; D014874:Water Pollutants, Chemical; C017160:cypermethrin; C014464:3,4-dichloroaniline