John Wiley & Sons, Ltd.

The effect of pH on the toxicity of ZnO nanoparticles to Folsomia candida in amended field soil

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The effect of soil pH on the toxicity of 30 nm ZnO to Folsomia candida was assessed in Dorset field soils with pHCaCl2 adjusted to 4.31, 5.71 and 6.39. To unravel the contribution of particle size and dissolved Zn, 200 nm ZnO and ZnCl2 were tested. Zn sorption increased with increasing pH and Freundlich kf values ranged from 98.9 to 333 (L/kg)1/n for 30 nm ZnO and from 64.3 to 187 (L/kg)1/n for ZnCl2. No effect of particle size was found on sorption and little difference was found in toxicity between 30 and 200 nm ZnO. The effect on reproduction decreased with increasing pH for all Zn forms, with 28‐d EC50s of 553, 1481 and 3233 mg Zn/kg for 30 nm ZnO and 331, 732 and 1174 mg Zn/kg for ZnCl2, at pH 4.31, 5.71 and 6.39, respectively. EC50s based on porewater Zn concentrations increased with increasing pH for 30 nm ZnO from 4.77 to 18.5 mg Zn/L, while for ZnCl2 no consistent pH‐related trend in EC50s was found (21.0–63.3 mg Zn/L). Porewater calcium levels in ZnCl2‐spiked soils were ten times higher than in ZnO‐spiked soils. Our results suggest that the decreased toxicity of ZnCl2 compared to 30 nm ZnO based on porewater concentrations was due to a protective effect of calcium and not a particle effect. Environ Toxicol Chem © 2013 SETAC

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