Population consequences of fipronil and degradates to copepods at field concentrations: an integration of life cycle testing with leslie matrix population modeling.
ABSTRACT 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.
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ABSTRACT: Most demographic studies predict population dynamics from known vital rates. In natural plankton populations, in contrast, the ecologist faces the ‘inverse problem’ to estimate the vital rates from observations of a population's dynamics. Since this problem is complex, many studies only present time series of abundance data from the field and vital rates estimated from laboratory experiments. Here, however, we estimate vital rates of the copepod Arctodiaptomus salinus from a stage‐dependent matrix model developed from time series of abundances.We show how each vital rate contributes to the observed variation in the population growth rate (retrospective analyses) and how potential changes in vital rates could affect this growth rate (prospective analyses). Such perturbation analyses can be expected to become very useful management tools, because they show how sensitive the population is to changes in its different life traits and to detect potential disturbances in its habitat.The models showed that the finite population growth rate (λ) varied seasonally. The population decreased during the summer and was very close to steady state in autumn and winter. The drop in λ in summer was caused mainly by reductions in fertility and in the probability of growth of pre‐adult stages. Fertility and survival of pre‐adult and adult stages were the vital rates contributing most to the variation on λ in autumn. The increment of pre‐adult stage survival determined the increment of λ in winter.During autumn and winter λ was more sensitive to changes to the probabilities of survival than to the probabilities of growth to the following stage, but in summer the opposite was observed. During the whole of the study period, λ was not very sensitive to changes to fertility.Since at high temperatures λ decays and the study pond is warm most of the year, global warming might have dramatic consequences for this A. salinus population even in the short term. Results suggest that pre‐adult stages of A. salinus may over‐summer as quiescence stages, which could be a useful strategy for coping with the warming of the pond and, consequently, global warming.Freshwater Biology 06/2013; 58:1221-1233. · 3.93 Impact Factor
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ABSTRACT: Triplet state excited natural organic matter chromophores (3NOM*) are important reactive intermediates in indirect photochemical processes, yet the impact of salt concentrations relevant to estuarine and marine environments on 3NOM* is poorly understood. The formation rates, pseudo-first order loss rate constants and steady-state concentration of 3NOM* were monitored using the sorbate probe method in synthetic matrices with increasing ionic strength (IS) to seawater values using seawater halides or other salts. The steady-state concentration of 3NOM* was found to increase by ~100% at seawater IS, regardless of the salt used, due to a decrease in the 3NOM* decay rate constant. The electron transfer-mediated degradation of 2,4,6-trimethylphenol (TMP) by 3NOM* was significantly slowed at higher IS. A model is proposed wherein high IS slows intra-organic matter electron transfer pathways, an important 3NOM* loss pathway, leading to longer 3NOM* lifetimes. Although IS did not appear to impact energy transfer pathways directly, the higher 3NOM* steady-state concentrations promotes energy transfer interactions. The observed decrease in decay rate constant and increase in steady-state concentration of 3NOM* at high IS, as well as the inhibition of electron transfer pathways, should be considered when determining the fate of organic pollutants in estuarine and marine environments.Environmental Science & Technology 08/2013; · 5.48 Impact Factor
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ABSTRACT: A scientific advisory panel was convened by the State of California to recommend monitoring for chemicals of emerging concern (CECs) in aquatic systems that receive discharge of municipal wastewater treatment plant (WWTP) effluent and storm water runoff. The panel developed a risk-based, screening framework that considered environmental sources and fate of CECs observed in receiving waters across the State. Using existing occurrence and risk threshold data in water, sediment and biological tissue, the panel applied the framework to identify a priority list of CECs for initial monitoring in three representative receiving water scenarios. The initial screening list of 16 CECs identified by the panel included consumer and commercial chemicals, flame retardants, pesticides, pharmaceuticals and personal care products, and natural hormones. The panel designed an iterative, phased strategy with interpretive guidelines that direct and update management actions commensurate with potential risk identified using the risk-based framework and monitoring data. Due to the ever changing nature of chemical use, technology, and management practices, the panel offered recommendations to improve CEC monitoring, including: development of bioanalytical screening methods whose responses integrate exposure to complex mixtures and that can be linked to higher order effects; development/refinement of models that predict the input, fate and effects of future chemicals; and filling of key data gaps on CEC occurrence and toxicity. Lastly, the panel stressed the need for adaptive management, allowing for future review of, and if warranted, modifications to the strategy to incorporate the latest science available to the water resources community. Integr Environ Assess Manag © 2013 SETAC.Integrated Environmental Assessment and Management 10/2013;