Making Sense of Ecotoxicological Test Results: Towards Application of Process-based Models

Abstract

The environmental risk of chemicals is routinely assessed by comparing predicted exposure levels to predicted no-effect levels for ecosystems. Although process-based models are commonly used in exposure assessment, the assessment of effects usually comprises purely descriptive models and rules-of-thumb. The problems with this approach start with the analysis of laboratory ecotoxicity tests, because only a limited amount of information is extracted. Standard summary statistics (NOEC, ECx, LC50) are of limited use in part because they change with exposure duration in a manner that varies with the tested species and the toxicant. As an alternative, process-based models are available. These models allow for toxicity measures that are independent of exposure time, make efficient use of the available data from routine toxicity tests, and are better suited for educated extrapolations (e.g., from individual to population, and from continuous to pulse exposure). These capabilities can be used to improve regulatory decisions and allow for a more efficient assessment of effects, which ultimately will reduce the need for animal testing. Process-based modeling also can help to achieve the goals laid out in REACH, the new strategy of the European Commission in dealing with chemicals. This discussion is illustrated with effects data for Daphnia magna, analyzed by the DEBtox model.

A biology-based approach for quantitative structure-activity relationships (QSARs) in ecotoxicity

“…Although we only focussed on lethal effects, a similar approach can be followed for sub-lethal endpoints such as growth and reproduction (which would be far more relevant for regulatory purposes). For such endpoints, an incipient NOEC or ECx does not exist, leaving even more room for bias in QSARs due to the time-dependence of the effects (Alda Á lvarez et al 2006;Jager et al 2006). However, for biology-based methods to be applied, the original raw data from the experiments are required, which are hardly ever reported or stored in (publicly available) databases.…”

“…However, this information is not used to derive LC50s or in QSAR development but does contain valuable information on the kinetic and dynamic processes that govern toxicity. To extract all relevant information from toxicity test results requires biology-based methods (OECD 2006), such as DEBtox (Bedaux and Kooijman 1994;Jager et al 2006). These methods make use of all of the observations over the entire exposure time to extract parameter values that are independent of test duration.…”

Effects of repeated pulsed herbicide exposures on the growth of aquatic macrophytes

“…Toxicokinetic-toxicodynamic models for aquatic macroinvertebrates and survival may serve as inspiration for the development of such mechanistic effects models for Lemna in future work, taking into consideration the different physiology and endpoints. Alternatively, the modeling of energy budgets might provide a good description of growth in Lemna, also under chemical stress [52].…”

A probabilistic method for species sensitivity distributions taking into account the inherent uncertainty and variability of effects to estimate environmental risk

“…Numerous critical reviews have evaluated strengths and limitations of different methodologies (Power and McCarty 1997;Aldenberg and Jaworska 2000;Forbes and Calow 2002;Verdonck et al 2003;van der Hoeven 2004;Jager et al 2006).…”