Root Elongation Method for the Quality Assessment of Metal-Polluted Soils: Whole Soil or Soil-Water Extract?
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Root Elongation Method for the Quality Assessment of Metal-Polluted Soils: Whole Soil or Soil-Water Extract? Eva V. Prudnikova 1 & Alexander Neaman 2 & Vera A. Terekhova 1,3 & Mikhail M. Karpukhin 1 & Evgenii L. Vorobeichik 4 & Ivan A. Smorkalov 4 & Elvira A. Dovletyarova 5 & Claudia Navarro-Villarroel 6 & Rosanna Ginocchio 7,8 & Patricia Peñaloza 9 Received: 5 December 2019 / Accepted: 6 July 2020 # Sociedad Chilena de la Ciencia del Suelo 2020
Abstract Root elongation method may be implemented using two internationally accepted protocols: exposing plants to either soil-water extract or whole soil. But which of the two protocols is more suitable for root elongation analysis undertaken for the quality assessment of metal-polluted soils? Soils were sampled at various distances from the site of the Middle Urals Copper Smelter located in Russia. White mustard was used as a bioindicator. We observed considerable differences in root elongation under the two protocols. In plants grown in whole soil, root length inversely correlated with pollution index, but in soil-water extract, metal concentrations had no effect on root length. Nutrient and metal concentrations in the soil-water extract were not buffered, due to the absence of the solid soil phase. It is for this reason that in highly polluted soils, root growth was greater in soil-water extracts rather than in whole soils, whereas in background soils (in the absence of toxicity), root growth was greater in whole soils compared with soil-water extracts. The quantity, intensity, and capacity factors are a plausible explanation for the differences in root length between the two protocols. The soil-water extract does not represent actual soil with respect to the desorptiondissolution reactions that take place between the soil solid phase and the soil solution. For this reason, whole soil protocol should be used for measuring root elongation given that only under this protocol, direct contact between metal-polluted soil and test organisms correctly replicates the risks inherent in the actual soil habitat. Keywords Aqueous extracts . Inhibition . Phytotoxicity . Toxicity . Ecotoxicity . Middle Urals
1 Introduction The ecotoxicity methods considered in published guidelines for the quality assessment of metal-polluted soils are based on
responses (growth, reproduction, mortality, etc.) of various organisms (plants, earthworms, microorganisms, etc.) (ISO 17402 2008; ISO 17616 2008). Among these, the root elongation method (ISO 11269-1 2012; US EPA 1996) is widely
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42729-020-00295-x) contains supplementary material, which is available to authorized users. * Alexander Neaman [email protected] 1
Faculty of Soil Science, Lomonosov Moscow State University, Moscow, Russia
2
Instituto de Ingeniería Agraria y Suelos, Facultad de Ciencias Agrarias y Alimentarias, Universidad Austral de Chile, Valdivia, Chile
3
Institute of Ecology and Evolution, Russian Aca
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