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Toxicity of proton-metal mixtures in the field: Linking stream macroinvertebrate species diversity to chemical speciation and bioavailability

Stockdale, Anthony, Tipping, Edward, Lofts, Stephen, Ormerod, Stephen James, Clements, William and Blust, Ronny 2010. Toxicity of proton-metal mixtures in the field: Linking stream macroinvertebrate species diversity to chemical speciation and bioavailability. Aquatic Toxicology 100 (1) , pp. 112-119. 10.1016/j.aquatox.2010.07.018

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Abstract

Understanding metal and proton toxicity under field conditions requires consideration of the complex nature of chemicals in mixtures. Here, we demonstrate a novel method that relates streamwater concentrations of cationic metallic species and protons to a field ecological index of biodiversity. The model WHAM-FTOX postulates that cation binding sites of aquatic macroinvertebrates can be represented by the functional groups of natural organic matter (humic acid), as described by the Windermere Humic Aqueous Model (WHAM6), and supporting field evidence is presented. We define a toxicity function (FTOX) by summing the products: (amount of invertebrate-bound cation) × (cation-specific toxicity coefficient, αi). Species richness data for Ephemeroptera, Plecoptera and Trichoptera (EPT), are then described with a lower threshold of FTOX, below which all organisms are present and toxic effects are absent, and an upper threshold above which organisms are absent. Between the thresholds the number of species declines linearly with FTOX. We parameterised the model with chemistry and EPT data for low-order streamwaters affected by acid deposition and/or abandoned mines, representing a total of 412 sites across three continents. The fitting made use of quantile regression, to take into account reduced species richness caused by (unknown) factors other than cation toxicity. Parameters were derived for the four most common or abundant cations, with values of αi following the sequence (increasing toxicity) H+ < Al < Zn < Cu. For waters affected mainly by H+ and Al, FTOX shows a steady decline with increasing pH, crossing the lower threshold near to pH 7. Competition effects among cations mean that toxicity due to Cu and Zn is rare at lower pH values, and occurs mostly between pH 6 and 8.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Biosciences
Subjects: Q Science > Q Science (General)
Uncontrolled Keywords: acidification; bioavailability; macroinvertebrates; metals; modelling; quantile regression; streamwaters; toxicity
Publisher: Elsevier
ISSN: 0166-445X
Last Modified: 04 Jun 2017 03:15
URI: http://orca.cf.ac.uk/id/eprint/18916

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