Impact of toxicants on species composition of aquatic communities : concordance of predictions and field
Year: 2005
Type: other
Abstract: Cover design: 3D graphic "liquid-color filled spheres", Wietse de Zwart These studies were largely conducted within the strategic research project S860703 (QERAS) on "Quantitative Risk Assessment", financed by the Directorate of the Netherlands National Institute for Public Health and the Environment (RIVM), and supported by the RIVM Scientific Advisory Committee.variety of species from different trophic levels.For aquatic toxicity evaluation, OECD directs testing with at least one species each of the algae, crustaceans (Daphnia) and fish, to include the autotrophs, herbivores and carnivores.Selected chemicals have been tested with a (much) larger array of species.This is in part due to the wish of ecotoxicologists to identify and protect the "most sensitive species", which is a myth, as well as the wish to test and protect species of local or regional importance. Species sensitivity distributionsAnalyzing the results of the world's resources on laboratory derived toxicity observations learnt that species differ in their sensitivity towards a single chemical (Hoekstra et al. 1992, Hoekstra et al. 1994, Notenboom et al. 1995, Vaal et al. 1997a, Vaal et al. 1997b, Vaal et al. 2000).This may be due to differences in life history, physiology, morphology and behavior.Without attempting to explain the cause of variability in species sensitivity, this recognition led to attempts to describe the variation with statistical distribution functions, thereby putting the concept of species sensitivity distribution (SSD) into existence (Stephan et al. 1985, Van Straalen and Denneman 1989, Posthuma et al. 2002a).The basic assumption of the SSD concept is that the sensitivities of a set of species can be described by some kind of statistical distribution.Usually a parametric distribution function is applied, such as the triangular (e.g.Stephan 1985), normal (e.g.Wagner and Løkke 1991) or logistic distribution (e.g.Van Straalen and Denneman 1989).Non-parametric methods are used as well (e.g.Jagoe and Newman 1997).The available ecotoxicological data are seen as a sample from this distribution and are used to estimate the moment parameters of the SSD.The moments of the statistical distribution are used to calculate a concentration that is expected to be safe for most species of interest, which can be used to set an EQC.A more recent application is the use of SSDs in ERA of contaminated ecosystems.Since their introduction, the importance of SSDs in ecotoxicity evaluations has steadily grown until they are now used world wide.Intensive discussions have taken place on principles, statistics, assumptions, data limitations, and applications (e.g.Forbes and Forbes 1993, Hopkin 1993, Smith and Cairns 1993, Chapman et al. 1998, Posthuma et al. 2002a).So far, the SSD method is the only significant basis to predict toxic effects on natural ecosystems with multiple species.This thesis follows this prognostic approach, but also seeks verification from field observed effects that are attributable to toxicity.These effects are still hardly reported in literature. Bioavailability of toxicantsUnlike the concentrations of toxicants that are applied in more or less standardized and controlled toxicity tests, matrix interactions in natural ecosystems may interfere with bioavailability.Generally speaking, physico-chemical processes (ionization, dissolution, precipitation, complexation, sorption and partitioning) reduce the concentration of toxicants that is actually experienced by the biota.These processes are depending on individual properties of the toxicants and on abiotic characteristics of the ecosystem exposed.Uptake, body burden and reallocation to target sites of action in specific tissues are also depending on properties of the organism exposed.Monitoring of chemicals in the environment mostly reports total concentrations, irrespective of the form, binding and availability of the toxicants.Model calculations can be applied to estimate the bioavailable fraction from measured total concentrations in combination with ecosystem qualifier data and physico-chemical toxicant properties.A wide variety of speciation models with different levels of complexity is available that are either mechanistic or empirical in nature (Kenaga and Goring 1980, Van der Kooij et al. 1991, Van Leeuwen et al. 1991, Tessier and Turner 1995, DiToro et al. 2001, Specific aims are:1. to elaborate a calculation of risk to communities that covers different patterns of species sensitivity and incorporates the effects of a variable bioavailability and the simultaneous action of many toxicants, 2. to develop an eco-epidemiological approach to analyze monitoring data of water quality parameters and species composition in aquatic communities that allows for a validation of the risk-based predictions, and 3. to provide proof of concept in field studies and to carry out the first attempts to discriminate the role of toxicants from other potential stressors.Key parameters are summarized graphically to support communication and application in management. Outline of the thesisChapter 2 of this thesis introduces the concept and construction of species sensitivity distributions (SSD).Regularities are analyzed that can be observed in SSD curves constructed from a large set of aquatic toxicity data.The regularities observed relate to the slope of the SSD as a function of toxic mode of action, and to the differences between SSD curves based on acute and chronic toxicity data.Chapter 3 provides a review of methods and models that may be used to evaluate ecotoxicity risk in relation to matrix interactions, speciation and bioavailability of organic and inorganic chemicals in a contaminated environment.This paper is written as a manual to guide the selection of appropriate methods.No efforts have been undertaken to restrict the contents to the aquatic environment.Chapter 4 gives a detailed overview of methods and models for evaluating mixture toxicity.Existing models are proposed to be extended and combined.The proposed model extensions allow the evaluation of single and multiple species effects as a consequence of exposure to a complex mixture of toxicants.Complex mixtures of toxicants are characterized by many different constituents with a low individual concentration and a variety of toxic modes of action.In Chapter 5, an elaborate assessment model is used to generate maps of the ecological risk to macrofauna and macrophytes in field ditches that is associated with the application of all pesticides used in the Netherlands.Chapter 6 presents a novel method to attribute likely causation to observed effects in local fish communities in rivers.Fish abundance and abiotic monitoring data on total toxicant concentrations, physical habitat degradation and classical water chemistry are analyzed by applying a sequence of prediction models.The applied models are individually well established, but the most innovative aspect of this study involves linking the different types of models and applying them in concert.In Chapter 7 the dataset on fish and local conditions and the results of the previous chapter are further analyzed to reveal the meaning of ecological risk (msPAF) as a predictor of community impact that actually can be observed in field exposed biota.Chapter 8 provides a conceptual and technical outlook for the prediction models applied.Since the quantification of ecological risk for biota exposed to an environmental cocktail of 2 Observed regularities in species sensitivity distributions for aquatic biota De Zwart, D. 2002.Observed regularities in SSDs for aquatic species.In Species sensitivity distributions in ecotoxicology.
Author: Dick de Zwart
Language: English
Subfield: Health, Toxicology and Mutagenesis
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2107368069