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Water‐extractability, free ion activity, and pH explain cadmium sorption and toxicity to Folsomia candida (Collembola) in seven soil‐pH combinations
Author(s) -
van Gestel Cornelis A. M.,
Koolhaas Josée E.
Publication year - 2004
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/03-393
Subject(s) - cadmium , sorption , soil water , chemistry , environmental chemistry , langmuir , langmuir adsorption model , adsorption , ecology , biology , organic chemistry
Toxicity of cadmium to Folsomia candida was determined in soils at different pHs (3.5, 5.0, and 6.5). The Langmuir sorption constant ( K L ), based on pore‐water or water‐extractable concentrations, showed a pH‐related increase of cadmium sorption that was most pronounced when using free Cd 2+ ion activities ({Cd 2+ }s). Two‐species Langmuir isotherms that used total cadmium concentration ([Cd]) or {Cd 2+ } and pH in the water‐extractable fractions gave the best description of cadmium sorption on all soils together. Cadmium concentrations causing 50% reduction of growth and reproduction (median effective concentrations [EC50s]) differed by a factor of 4.5 to 20 when based on total soil concentrations and increased with increasing pH. However, when based on water‐extractable or pore‐water [Cd] or {Cd 2+ }, EC50s decreased with increasing pH, but differences between soils were still a factor of 4.5 to 32. The EC50s differed by less than a factor of 2.2 when based on body [Cd] in the surviving animals. Two‐species Langmuir isotherms were used to relate body [Cd] in survivors to {Cd 2+ }, corrected for pH in water‐extractable or pore‐water fractions. An excellent description of effects on growth and reproduction was found when related to the body concentrations predicted in this way; the difference in EC50s between soils was reduced to a factor <2. This demonstrates that F. candida is mainly exposed to cadmium through the soil solution, and suggests that principles of a biotic ligand model approach may be applicable for this soil organism.