GM-troph: A Low Data Demand Ecotoxicity Effect Indicator for Use in LCIA (13+3 pp)
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- Hauschild, M. Int J Life Cycle Assessment (2007) 12: 79. doi:10.1065/lca2006.12.288
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Goal, Scope and Background
The development of ecotoxicity effect indicators (EEIs) for use in life cycle impact assessment (LCIA) has only been going on for about two decades. Traditionally, no-effect indicators have been applied. In this paper we focus on the development of an effect-based (i.e. EC50-based) average indicator, the GM-troph. The indicator is estimated by use of the hazardous concentration for 50% of the covered species (HC50EC50) and is designed to work on a low substance data availability of only three acute data values, which is often required in LCIA.
The study includes a theoretical description and a test on real data of three different effect-based average approaches (arithmetic mean, geometric mean and median) focusing on their statistical robustness. The data set used for the testing is composed of real ecotoxicity effect data for eleven different substances representing seven different toxic modes of action (TMoA).
Results and Discussion
The theoretical considerations and the test on real data show that the geometric mean is the most robust average estimator for HC50EC50, especially in the frequent situation where data availability is limited to a few data points. Test results indicate that in some cases of unequal representation of the different taxa (or trophic levels) in the underlying data set, estimations of average toxicity (i.e. HC50EC50) may be biased if each single test data (at a species level) is used as data points instead of averages at trophic levels.
and Recommendations. Based on these results, the following recommendations are given for the choice of estimation principle for the EEI: The indicator shall be based on HC50EC50 estimated as the geometric mean of three (average) EC50 values, covering the three main taxa, plants, invertebrates and vertebrates, which represent the three trophic levels of the ecosystem, primary producers, primary consumers and secondary consumers. In practice, the EEI shall be based on data from laboratory tests with algae, invertebrates (crustaceans) and fish. Instead of using the often wide 95% confidence limits, it is recommended to use the range given by the observed maximum and minimum values as limits around the HC50EC50. Further, it is recommended to use EC50(chronic) values when possible. Often, only acute data will be available, and here the use of best estimate assessment factors is recommended to extrapolate from acute to chronic values. As a starting point, an acute to chronic ratio of 2 between HC50EC50(acute) and HC50EC50(chronic) is recommended, but more research is certainly needed in this area. Due to the comparative framework of LCIA it is recommended only to use test results from laboratory tests, fulfilling certain standard conditions, i.e. applying standard organisms, and measuring well defined endpoints over restricted test durations.
The ability of a geometric, mean-based HC50EC50 to represent the toxicity of very toxic substances and toxicity towards very sensitive species has not been dealt with here, and further research is needed. However, on the basis of the results from the tests on real data, it may be anticipated that the GM-troph with its max-min limits to some degree accounts for the toxicity even to the most sensitive species among standard organisms, if representative toxicity data are available.