In the European registration procedure for pesticides, microcosm and mesocosm studies are the highest aquatic experimental tier to assess their environmental effects. Evaluations of microcosm/mesocosm studies rely heavily on no observed effect concentrations (NOECs) calculated for different population-level endpoints. Ideally, a power analysis should be reported for the concentration–response relationships underlying these NOECs, as well as for measurement endpoints for which significant effects cannot be demonstrated. An indication of this statistical power can be provided a posteriori by calculated minimum detectable differences (MDDs). The MDD defines the difference between the means of a treatment and the control that must exist to detect a statistically significant effect. The aim of this paper is to expand on the Aquatic Guidance Document recently published by the European Food Safety Authority (EFSA) and to propose a procedure to report and evaluate NOECs and related MDDs in a harmonised way. In addition, decision schemes are provided on how MDDs can be used to assess the reliability of microcosm/mesocosm studies and for the derivation of effect classes used to derive regulatory acceptable concentrations. Furthermore, examples are presented to show how MDDs can be reduced by optimising experimental design and sampling techniques.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-014-3398-2) contains supplementary material, which is available to authorized users.
Individual-based models (IBMs) predict how dynamics at higher levels of biological organization emerge from individual-level processes. This makes them a particularly useful tool for ecotoxicology, where the effects of toxicants are measured at the individual level but protection goals are often aimed at the population level or higher. However, one drawback of IBMs is that they require significant effort and data to design for each species. A solution would be to develop IBMs for chemical risk assessment that are based on generic individual-level models and theory. Here we show how one generic theory, Dynamic Energy Budget (DEB) theory, can be used to extrapolate the effect of toxicants measured at the individual level to effects on population dynamics. DEB is based on first principles in bioenergetics and uses a common model structure to model all species. Parameterization for a certain species is done at the individual level and allows to predict population-level effects of toxicants for a wide range of environmental conditions and toxicant concentrations. We present the general approach, which in principle can be used for all animal species, and give an example using Daphnia magna exposed to 3,4-dichloroaniline. We conclude that our generic approach holds great potential for standardized ecological risk assessment based on ecological models. Currently, available data from standard tests can directly be used for parameterization under certain circumstances, but with limited extra effort standard tests at the individual would deliver data that could considerably improve the applicability and precision of extrapolation to the population level. Specifically, the measurement of a toxicant's effect on growth in addition to reproduction, and presenting data over time as opposed to reporting a single EC50 or dose response curve at one time point.
Abstract-In the Daphnia reproduction test, the number of living offspring per living parent, mortality, and, occasionally, growth and time to first brood are used as endpoints for the determination of no-observed-effect concentration (NOEC)/lowest-observedeffect concentration (LOEC), or 50% effective concentration (EC50). It is known that chemicals can influence not only the number of neonates but also the offspring size (and, thus, possibly the neonate fitness) in daphnids. Changes in neonate size and fitness have not been routinely recorded in Daphnia reproduction tests, although they are an important factor in population growth. Some of our previous research with some dispersants showed clear effects on offspring quality (smaller neonates with enhanced mortality). We tested one of these dispersants in two different test designs: the reproduction test and a population growth experiment. The results from these two experimental designs differed completely: in the reproduction test, the living offspring number was increased (by up to 10.2 mg/L of the dispersant Dispersogen A) in comparison with the control, whereas in the population growth experiment, the population size was already reduced at concentrations of 1.64 mg/L. A F1-reproduction test, conducted in control medium with neonates born in the reproduction test, showed that neonate fitness was significantly reduced at concentrations of 1.64 mg/L and higher. Therefore, it appears absolutely necessary to take neonate fitness into account if we intend to assess population-level effects. This is easily considered in a population growth experiment but not in the Daphnia reproduction test. To evaluate the fitness of the neonates, an additional test with neonates (F1 test) or another test design (population growth experiment) is necessary.
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