Soil microbial biomass carbon and fatty acid composition of earthworm Lumbricus rubellus after exposure to engineered nanoparticles

The aim of this work was to investigate the effect of engineered nanoparticles (NPs) on soil microbial biomass C (MBC) and on earthworm Lumbricus rubellus. An artificial soil was incubated for 4 weeks with earthworms fed with vegetable residues contaminated by NPs, consisting of Ag, Co, Ni and TiO2. After the treatments, soils were analysed for MBC and total and water soluble metal-NPs, whereas earthworms were purged for 28 days and then analysed for fatty acids (FAs) and total metal-NPs. Longitudinal sections of earthworms were investigated by environmental scanning electron microscopy (ESEM), equipped with energy-dispersive X-ray spectroscopy (EDS), to provide insights about the retention and localization of NPs within earthworms. The nanoparticles reduced the MBC content in the following order Ag>Co>Ni, whereas TiO2 did not affect it. The ESEM-EDS analysis confirmed NP retention in earthworm guts and tissues. The solid/water coefficient of partition suggested that NPs interfered with living organisms due to their presence in suspension. Among the 27 FAs identified in earthworm tissues, the eicosapentaenoic acid (20:5ω3) was the most abundant. The degree of unsaturation of FAs was reduced by supplying NP-contaminated food.