Population consequences of fipronil and degradates to copepods at field concentrations: an integration of life cycle testing with leslie matrix population modeling.
The predominant data used in ecological risk assessment today are individual-based rather than population-based; yet environmental policies are usually designed to protect populations of threatened species or communities. Most current methods in ecotoxicology are limited by largely logistic/ technology-driven requirements that yield data for a relatively small number of test species and end points that focus on acute lethality or sublethal nonproduction-based parameters (e.g., biomarkers, mutagenesis, genetic change, physiological condition). A contrasting example is presented here showing the predictive ability of meiobenthos-based full life cycle toxicity testing to extrapolate multi-generational effects of chemicals on variables of import to population growth and maintenance. Less than 24-h-old larvae of a meiobenthic copepod were reared individually in 96-well microplate exposures to parent and degradates of the phenylpyrazole insecticide fipronil. Survival, development rates, sex ratio change, fertility, fecundity, and hatching success were tracked daily for 32 d through mating and production of three broods in spiked seawater. These data were then inserted in a Leslie (Lefkovitch) matrix stage-based population growth model to predict relative rates of population increase (lambda) and changes in net population growth with time and toxicant concentration. Field-reported test concentrations produced strong reproductive (52-88%) and net production (40-80%) depressions for parent (at 0.25 and 0.5 microg/L), desthionyl (0.25 and 0.5 microg/L), and sulfide (0.15 microg/L) moieties as compared to controls. Spiked sediment exposures of 65-300 ng of fipronil/g of dry sediment yielded significantly reduced production rates per female that were 67-50% of control production. The consistent reproductively linked impacts of fipronil and its degradation products at the population maintenance levels suggest risks to sediment-dwelling crustaceans at concentrations well below noneffects for most aquatic test species based on risk assessment data from primarily acute and sub-life cycle toxicity tests.
Chandler
G Thomas
GT
Department of Environmental Health Sciences, Norman J Arnold School of Public Health, University of South Carolina, Columbia, South Carolina 29208, USA. tchandler@sc.edu
Cary
Tawnya L
TL
Bejarano
Adriana C
AC
Pender
Jack
J
Ferry
John L
JL
D000818:Animals; D033342:Copepoda / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005298:Fertility / Q000187:drug effects*; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D008018:Life Cycle Stages; D008954:Models, Biological; D011158:Population Growth; D011720:Pyrazoles / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D012098:Reproduction / Q000187:drug effects; D018570:Risk Assessment; D012737:Sex Factors; D013997:Time Factors; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000378:metabolism / Q000633:toxicity*
D007306:Insecticides; D011720:Pyrazoles; D014874:Water Pollutants, Chemical; C082360:fipronil