Coupling mixture reference models with DGT-perceived metal flux for deciphering the nonadditive effects of rare earth mixtures to wheat in soils

Bing Gong, Erkai He, Willie J.G.M. Peijnenburg, Yuichi Iwasaki, Cornelis A.M. Van Gestel, Xinde Cao, Ling Zhao, Xiaoyun Xu, Hao Qiu*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The risk assessment of mixtures of rare earth elements (REEs) is hampered by a lack of fundamental understanding of their interactions in different soil types. Here, we assessed mixture interactions and toxicity to Triticum aestivum of Y and Ce in four different soils in relation to their bioavailability. Mixture toxicity was modelled by concentration addition (CA) and independent action (IA), in combination with different expressions of exposure: three equilibrium-based doses (total soil concentrations [M]tot, free ion activity in soil solution {M3+}, and the fraction (f) of metal ions bound to the biotic ligands (BLs)) and one kinetically controlled dose ([M]flux) metrics. Upon single exposure, REE toxicity was increasingly better described when using exposure expressions based on deepened understanding of their bioavailability: [M]flux > f > {M3+} > [M]tot. The mixture analyses based on [M]tot and {M3+} displayed deviations from additivity depending on the soil type. With the parameters derived from single exposures, the BLM approach gave better predictions of mixture toxicity (R2 ~ 0.70) than when using CA and IA based on either [M]tot or {M3+} (R2 < 0.64). About 30% of the variance in toxicity remained unexplained, challenging the view that the free metal ion is the main bioavailable form under the BLM framework based on thermodynamic equilibrium. Toxicity was best described when accounting for changes in the size of the labile metal pool by using a kinetically controlled dose metric (R2 ~ 0.80). This suggests that dynamic bioavailability analysis could provide a robust basis for modeling and reconciling the interplays and toxicity of metal mixtures in different soils.

Original languageEnglish
Article number109736
Pages (from-to)1-9
Number of pages9
JournalEnvironmental Research
Volume188
Early online date2 Jun 2020
DOIs
Publication statusE-pub ahead of print - 2 Jun 2020

Keywords

  • Bioavailability
  • Mixture
  • Rare earth
  • Toxicity
  • Triticum aestivum

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