Water‐extractability, free ion activity, and pH explain cadmium sorption and toxicity to Folsomia candida (Collembola) in seven soil‐pH combinations

Abstract

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 Cd2+ ion activities ([Cd2+]s). Two-species Langmuir isotherms that used total cadmium concentration ([Cd]) or [Cd2+] 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 [Cd2+], 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 [Cd2+], 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.

Impact of Soil Properties on Critical Concentrations of Cadmium, Lead, Copper, Zinc, and Mercury in Soil and Soil Solution in View of Ecotoxicological Effects

“…The evidence that soil properties such as soil organic matter content, clay content and specifically pH do affect the bioavailability and toxicity of metals in biota (e.g. Spurgeon and Hopkin 1996;Van Gestel and Koolhaas 2004), is hardly accounted for in the critical limits assessment.…”

“…The evidence that soil properties such as soil organic matter content, clay content and specifically pH do affect the bioavailability and toxicity of metals in biota (e.g. Spurgeon and Hopkin 1996;Van Gestel and Koolhaas 2004), is hardly accounted for in the critical limits assessment.Since effects on micro organisms, plants and, to a large extent, also to invertebrates occur through the soil solution, in particular by the free metal ions, an approach to set critical limits for FMI is in particularly appropriate to evaluate the risks of effects. …”

Ecological changes in historically polluted soils: Metal(loid) bioaccumulation in microarthropods and their impact on community structure

“…According to Van Gestel and Koolhaas (2004), the main route for metal(loid) uptake by microarthropods is the soil solution, which contains fungi and which is in contact with the soil organic matter. Soil solution is actually considered as a major exposure pathway for the majority of pedofauna.…”

Influence of Ca and pH on the uptake and effects of Cd in Folsomia candida exposed to simplified soil solutions

“…To our knowledge, only 1 study has investigated the applicability of BLMs for the springtail F. candida [17]. The authors showed that the free Cd ion is the most important Cd species for predicting uptake and toxicity in this organism and showed that Cd toxicity may be affected by pH and Ca content.…”