Effect of different spiking procedures on the distribution and toxicity of ZnO nanoparticles in soil

Due to the difficulty in dispersing some engineered
nanomaterials in exposure media, realizing homogeneous
distributions of nanoparticles (NP) in soil may
pose major challenges. The present study investigated the
distribution of zinc oxide (ZnO) NP (30 nm) and non-nano
ZnO (200 nm) in natural soil using two different spiking
procedures, i.e. as dry powder and as suspension in soil
extract. Both spiking procedures showed a good recovery
([85 %) of zinc and based on total zinc concentrations no
difference was found between the two spiking methods.
Both spiking procedures resulted in a fairly homogeneous
distribution of the ZnO particles in soil, as evidenced
by the low variation in total zinc concentration between
replicate samples (\12 % in most cases). Survival of
Folsomia candida in soil spiked at concentrations up to
6,400 mg Zn kg-1 d.w. was not affected for both compounds.
Reproduction was reduced in a concentrationdependent
manner with EC50 values of 3,159 and
2,914 mg Zn kg-1 d.w. for 30 and 200 nm ZnO spiked as
dry powder and 3,593 and 5,633 mg Zn kg-1 d.w. introduced
as suspension. Toxicity of ZnO at 30 and 200 nm did
not differ. We conclude that the ZnO particle toxicity is not
size related and that the spiking of the soil with ZnO as dry
powder or as a suspension in soil extract does not affect its
toxicity to F. candida