Food-web models

Here we will describe the methods that are used to derive critical limits for soil, based on direct ecotoxicological effects on microorganisms and plants. The indirect approaches (food web models) to derive critical limits for soil based on critical limits for terrestrial fauna such as MPC values for target organisms will be also considered. 

Biomagnification, which is the phenomenon that a chemical accumulates in species through different trophic levels in a food web, may cause toxic effects on mammals and birds as a secondary poisoning. Next to direct effects on soil organisms (see above), these indirect effects cam be considered in deriving critical limits for soil, by the use of simple food web models. 

There have been a few large-scale field studies of PCBs in the food webs of the lakes. These include two EPA mass balance studies, the Green Bay Mass Balance Study and the Lake Michigan Mass Balance Study. The field data collected for these studies was used to calibrate the complex contaminant models, which were developed as the primary goal of the studies. The ultimate objective of these mass balance studies was to predict concentrations of PBTs in top predator fish from only knowing the external loadings of the PBTs. Thus the models linked food web models to fate and transport, hydro-logic, and nutrient models. To calibrate the food web models, an extensive collection of all major trophic levels over both space and time was done and analyzed for PCBs and other selected analytes. 

Food-web modeling holds great promise in analyzing and predicting effects of chemical stressors (Baird et al. 2001) and has been developed for both terrestrial... 

A recently developed metapopulation model to extrapolate responses of aquatic invertebrates as observed in mesocosms to assess their recovery potential in the field is provided by Van den Brink et al. (2007). When the primary interest is in the recovery of processes and functional groups, food-web models are the required mathematical tools (for an example, see Traas et al. 2004). Two drawbacks of these models are that they require detailed information on the species and functional groups of concern and that they are very specific to the species and functional groups and sites for which they are developed. 

Computer models that simulate the dynamics of food webs might be used to extrapolate results of model ecosystem experiments to systems differing in size and ecological complexity. In principle, food-web models such as IFEM (Bartell et al. 1988), AQUATOX (Park 1999), and C-COSM (Traas 2004) can be adapted to do this, at least when detailed information on the ecology and ecotoxicology of the species and functional groups of concern is available. 

Prediction of responses Community to ecosystem Food-web models, metapopulation 4.5.4... 

Complex models (life stage, IBM, and energetic models) Food-web models, metapopulation models Food-web models... 

Extrapolation by Spatial variation in community Comparing model ecosystem Food-web models, IFEM,... 

Traas TP. 2004. Food web models in ecotoxicological risk assessment [PhD thesis]. Utrecht (The Netherlands) University of Utrecht, 231 p. 

Traas TP, Janse JH, Aldenberg T, Brock TCM. 1998. A food web model for fate and direct and indirect effects of Dursban 4E (active ingredient chlorpyrifos) in freshwater microcosms. Aquat Ecol 179-190. 

Traas TP, Janse JH, van den Brink PJ, Brock TCM, Aldenberg T. 2004. A freshwater food web model for the combined effects of nutrients and insecticide stress and subsequent recovery. Environ Toxicol Chem 23 521-529. 

The ability of chirality to assess biotransformation could lead to more accurate assessments of POP food web modeling and permit more precise determination of the extent of degradation and virmal elimination of POPs to support Stockholm Convention goals. 

Gandhi, N., Bhavsar, S. P, et al (2006) Development of a multichemical food web model application to PBDEs in Lake Ellasjoen, Bear Island, Norway. Environmental Science and Technology, 40(15) 4714-A721. 

One of the first models that included an expHcit representation of viruses in order to explore their role in nutrient cycHng was a steady-state food web model by... 

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