Ecotoxicity modelling

Risk-Based Ecotoxicity model 5(e) order (Sept. 2004) 5 e Order Ecotoxicity... 

The development of models incorporating biomarker assays to predict the effects of chemicals upon parameters related to r has obvious attractions from a scientific point of view and is preferable, in theory, to the crude use of ecotoxicity data currently employed in procedures for environmental risk assessment. However, the development of this approach would involve considerable investment in research, and might prove too complex and costly to be widely employed in environmental risk assessment. 

Fourteen formulations of chemical alternatives were submitted to EPA under confidentiality and they were assessed based on numerous human health and ecotoxicity endpoints in addition to bioaccumulation potential and environmental persistence. They were also screened for potential exposure to workers, users and the aquatic environment. Where data gaps existed, EPA experts used models and chemical analogs to estimate the hazard for a particular endpoint. The literature and test data reviews were published in the final report, Environmentally Preferable Options for Furniture Fire Safety Low Density Furniture Foam . In addition, each hazard endpoint was ranked with a concern level (High, Moderate or Low) based on the criteria used by the EPA s New Chemicals Program to rate the concern level of new chemicals submitted under the Toxic Substance Control Act (TSCA). As seen in Figure 8.2, where the hazard endpoint rankings are bold, the value is based on experimental data. Where the hazard endpoints are presented in italic font, the value is estimated based on models or chemical analogs. In this way, detailed hazard information was summarized and presented in a clear and concise format. 

In a study by Andersson et al. [30], the possibilities to use quantitative structure-activity relationship (QSAR) models to predict physical chemical and ecotoxico-logical properties of approximately 200 different plastic additives have been assessed. Physical chemical properties were predicted with the U.S. Environmental Protection Agency Estimation Program Interface (EPI) Suite, Version 3.20. Aquatic ecotoxicity data were calculated by QSAR models in the Toxicity Estimation Software Tool (T.E.S.T.), version 3.3, from U.S. Environmental Protection Agency, as described by Rahmberg et al. [31]. To evaluate the applicability of the QSAR-based characterization factors, they were compared to experiment-based characterization factors for the same substances taken from the USEtox organics database [32], This was done for 39 plastic additives for which experiment-based characterization factors were already available. 

In a first attempt to derive characterization factors with QSARs, the entire dataset of plastics additives was included, and aquatic ecotoxicity was predicted for two different trophic levels. This generated characterization factors that did not correspond well with the ones derived from experimental data [30]. Hardly surprising, but a clear indication that two trophic levels are unsufficient. A second attempt to derive characterization factors with QSARs are currently being performed [31]. In this second attempt, substances that are difficult to model in QSAR models have been removed from the dataset and the ecotoxicity has been predicted for three different trophic levels instead of two. However, results have not yet been obtained from this second attempt. If the results show that it is possible to derive reliable characterization factors by the use of QSARs, the current data gap regarding characterization factors for human toxicity and ecotoxicity could be... 

USEtox calculates characterization factors for human toxicity and freshwater ecotoxicity. Assessing the toxicological effects of a chemical emitted into the environment implies a cause-effect chain that links emissions to impacts through three steps environmental fate, exposure, and effects. Linking these steps, a systematic framework for toxic impacts modeling based on matrix algebra was developed to some extent within the OMNIITOX project [10]. USEtox covers two spatial scales, the continental and the global scales. 

Impact 2002 This model provides close to 1,000 characterization factors for the midpoint categories human toxicity, aquatic ecotoxicity, and terrestrial ecotoxicity according to the LCIA methodology. The model is parameterized in a nonspatial and a spatial European model nested in a nonspatial world model, as well as a complete world model... 

The Danish (Q)SAR database is a repository of estimates from over 70 [28] (Q)SAR models for 166,072 chemicals. The (Q)SAR models encompass endpoints for physicochemical properties, fate, ecotoxicity, absorption, metabolism, and toxicity... 

Rosenbaum R, Bachmann TM, Gold LS, Huijbregts MAJ, Jolliet O, Juraske R, Koehler A, Larsen HF, MacLeod M, Margni M, McKone TE, Payet J, Schuhmacher M, van de Meent D, Hauschild MZ (2008) USEtox the UNEP-SETAC toxicity model recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment. Int J Life Cycle Assess 13 532-546... 

The evaluation for aquatic toxicity on daphnids and fish is reported in Tables 12 and 13. Bold values indicate that compounds are out of the model applicability domain (ECOSAR) or that the prediction is not reliable. ECOSAR and ToxSuite are able to predict all the selected compounds while T.E.S.T. fails in prediction for the daphnia toxicity of perfluorinated compounds (PFOS and PFOA). Tables 12 and 13 include also a limited number of experimental results provided by the model training dataset (some data are extracted from USEPA Ecotox database). Predicted results are in agreement for five compounds only (2, 3, 5, 13 and 14) for both endpoints while the predictions for the other compounds are highly variable. 

Rippen, G., Ilgenstein, M., Klopffer, W., Poreniski, H.J. (1982) Screening of the adsorption behavior of new chemicals natural soils and model adsorbents. Ecotox. Environ. Saf. 6, 236-245. 

A ruling has been passed by the European Commission s scientific committee on toxicity, ecotoxicity and the environment, (the CSTEE), that the use of acetyl tributyl citrate as a plasticiser in children s toys is safe. It has also ruled that the current risk assessment models are reliable. Brief details are given in this little article. 

Environment Canada recently developed an evaluation system based on effluent toxicity testing, capable of ranking the environmental hazards of industrial effluents [185]. This so-called Potential Ecotoxic Effects Probe (PEEP) incorporates the results of a variety of small-scale toxicity tests into one relative toxicity index to prioritize effluents for sanitation. In the index no allowance has been made for in-stream dilution, therefore the acmal risk for environmental effects is not modeled. The tests performed on each effluent are the following bacterial assay [V.fisheri (P. phosphoreum), Microtox], microalgal assay S. capricornutum) crustacean assay (C. dubiay, and bacterial genotoxicity test E. coli, SOS-test). 

Frank, R. and W. Klopffer. 1989. A convenient model and program for the assessment of abiotic degradation of chemicals in natural water. Ecotox. Environ. Safety 17 323-332. 

Yoshida, K., Shigeoka, T., Yamauchi, F. (1983b) Non-steady state equilibrium model for the preliminary prediction of the fate of chemicals in the environment. Ecotox. Environ. Safety 7, 179-190. 

Nendza, M. (1991) Predictive QSAR models estimating ecotoxic hazard of phenylureas Aquatic toxicity. Chemosphere 23, 497-506. 

The DEMETRA project [20, 26] represents the first important case of a European project to develop QSAR models for regulatory purposes. DEMETRA developed five free models to determine the ecotoxicity of pesticides using endpoints that include trout, daphnia, bees, and quails (oral and dietary exposure). Since the target was to develop models for the user, these five endpoints were decided by them, not by the developers. 

The USEPA Office of Pollution Prevention and Toxics (OPPT) (Q)SAR Analysis Methods Branch assesses the model domain for ecotoxicity (Q)SAR determined by structural attributes used to predict toxicity. For example, the domain for molecular... 

Besides meeting its assumptions, other problems in the application of SSD in risk assessment to extrapolate from the population level to the community level also exist. First, when use is made of databases (such as ECOTOX USEPA 2001) from which it is difficult to check the validity of the data, one does not know what is modeled. In practice, a combination of differences between laboratories, between endpoints, between test durations, between test conditions, between genotypes, between phenotypes, and eventually between species is modeled. Another issue is the ambiguous integration of SSD with exposure distribution to calculate risk (Verdonck et al. 2003). They showed that, in order to be able to set threshold levels using probabilistic risk assessment and interpret the risk associated with a given exposure concentration distribution and SSD, the spatial and temporal interpretations of the exposure concentration distribution must be known. 

Mesman M, Posthuma L. 2003. Ecotoxicity of toxicant mixtures in soils recommendations for application in the Dutch regulatory context, as derived from a scientific review on approaches, models and data. No. 711701035. Bilthoven (The Netherlands) National Institute of Public Health and the Environment (RIVM), 70 p. 

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