title: Use of vegetated agricultural drainage ditches to decrease toxicity of irrigation runoff from tomato and alfalfa fields in California, USA.
abstract: The current study investigated the potential of vegetated drainage ditches for mitigating the impact of agricultural irrigation runoff on downstream aquatic ecosystems. Water column toxicity to larval fathead minnow (Pimephales promelas),and the amphipod Hyalella azteca was measured for 12 h or less at the ditch inflow and outflow, using custom-built in situ exposure systems. In addition, water and sediment samples were subject to standard toxicity tests with Ceriodaphnia dubia and H. azteca, respectively. No acute toxicity to larval fathead minnow was observed; however, runoff was highly toxic to invertebrates. Passage through a 389- to 402-m section of vegetated ditch had a mitigating effect and reduced toxicity to some degree. However, runoff from an alfalfa field treated with chlorpyrifos remained highly toxic to both invertebrate species, and runoff from a tomato field treated with permethrin remained highly toxic to H. azteca after passage through the ditch. Predicted toxic units calculated from insecticide concentrations in runoff and 96-h median lethal concentration (LC50) values generally agreed with C. dubia toxicity measured in the laboratory but significantly underestimated in situ toxicity to H. azteca. Sediments collected near the ditch outflow were toxic to H. azteca. Results from the current study demonstrate that experimental vegetated ditches were unable to eliminate the risk of irrigation runoff to aquatic ecosystems. In addition, protective measures based on chemical concentrations or laboratory toxicity tests with C. dubia do not ensure adequate protection of aquatic ecosystems from pyrethroid-associated toxicity.
authors.affiliation: Aquatic Toxicology Laboratory, School of Veterinary Medicine, University of California, Davis, California 95616, USA. iwerner@ucdavis.edu
authors.forename: Inge
authors.initials: I
authors.lastname: Werner
authors.forename: Linda A
authors.initials: LA
authors.lastname: Deanovic
authors.forename: Jeff
authors.initials: J
authors.lastname: Miller
authors.forename: Debra L
authors.initials: DL
authors.lastname: Denton
authors.forename: David
authors.initials: D
authors.lastname: Crane
authors.forename: Abdou
authors.initials: A
authors.lastname: Mekebri
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Moore
authors.forename: Jeanette
authors.initials: J
authors.lastname: Wrysinski
mesh_terms: D057914:Agricultural Irrigation / Q000379:methods*; D002140:California; D004787:Environmental Pollution / Q000517:prevention & control*; D018551:Solanum lycopersicum; D000455:Medicago sativa; D014481:United States; D014874:Water Pollutants, Chemical / Q000737:chemistry; D014876:Water Pollution / Q000517:prevention & control*
chemical_list: D014874:Water Pollutants, Chemical