title: Food web modeling of a river ecosystem for risk assessment of down-the-drain chemicals: a case study with AQUATOX.
abstract: Conventional approaches to estimating protective ecotoxicological thresholds of chemicals, i.e. predicted no-effect concentrations (PNEC), for an entire ecosystem are based on the use of assessment factors to extrapolate from single-species toxicity data derived in the laboratory to community-level effects on ecosystems. Aquatic food web models may be a useful tool to improve the ecological realism of chemical risk assessment because they enable a more insightful evaluation of the fate and effects of chemicals in dynamic trophic networks. A case study was developed in AQUATOX to simulate the effects of the anionic surfactant linear alkylbenzene sulfonate and the antimicrobial triclosan on a lowland riverine ecosystem. The model was built for a section of the River Thames (UK), for which detailed ecological surveys were available, allowing for a quantification of energy flows through the whole ecosystem. A control scenario was successfully calibrated for a simulation period of one year, and tested for stability over six years. Then, the model ecosystem was perturbed with varying inputs of the two chemicals. Simulations showed that both chemicals rapidly approach steady-state, with internal concentrations in line with the input bioconcentration factors throughout the year. At realistic environmental concentrations, both chemicals have insignificant effects on biomass trends. At hypothetical higher concentrations, direct and indirect effects of chemicals on the ecosystem dynamics emerged from the simulations. Indirect effects due to competition for food sources and predation can lead to responses in biomass density of the same magnitude as those caused by direct toxicity. Indirect effects can both exacerbate or compensate for direct toxicity. Uncertainties in key model assumptions are high as the validation of perturbed simulations remains extremely challenging. Nevertheless, the study is a step towards the development of realistic ecological scenarios and their potential use in prospective risk assessment of down-the-drain chemicals.
authors.affiliation: LASA - Environmental Systems Analysis Lab, Department of Industrial Engineering, University of Padova, via Marzolo 9, 35131 Padova, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Lombardo
authors.affiliation: Unilever Safety and Environmental Assurance Centre, Colworth Science Park, Sharnbrook MK441LQ, UK.
authors.forename: Antonio
authors.initials: A
authors.lastname: Franco
authors.affiliation: Environmental Group - Department of Industrial Engineering, University of Padova, via Marzolo 9, 35131 Padova, Italy.
authors.forename: Alberto
authors.initials: A
authors.lastname: Pivato
authors.affiliation: LASA - Environmental Systems Analysis Lab, Department of Industrial Engineering, University of Padova, via Marzolo 9, 35131 Padova, Italy. Electronic address: alberto.barausse@unipd.it.
authors.forename: Alberto
authors.initials: A
authors.lastname: Barausse
mesh_terms: D000818:Animals; D059001:Aquatic Organisms; D017753:Ecosystem; D020387:Food Chain; D018570:Risk Assessment / Q000379:methods; D045483:Rivers / Q000737:chemistry; D018675:Toxicity Tests / Q000379:methods*; D014865:Waste Disposal, Fluid; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical
keywords: Down-the-drain chemicals; Ecological risk assessment; Food web; Indirect ecological effects; River ecosystem; Trophic dynamics