Impact of sewage sludge-borne Ag and TiO2 nanoparticles on Eisenia fetida coelomocytes

Summary

The majority of nanomaterials (NMs) used in commercial applications are likely to enter the wastewater stream and reach wastewater treatment plants (WWTP). Studies have shown high association of NMs with sewage sludge therefore soils can be a sink for NM pollution making terrestrial organisms vulnerable. NMs undergo transformations in different environmental matrices leading to altered behaviour, bioavailability and subsequent toxicity that can differ from the pristinepristine material. The NM transformation and the potential hazard they pose in these compartments are poorly understood. The aim of the study was to elucidate (i) the behaviour of Ag and TiO2 NMs in sewage sludge and sludge amended-soil and (ii) the subsequent effects of transformed NMs on the coelomocytes of the earthworm E. fetida.Spherical polyvinylpyrrolidone (PVP)-coated Ag nanoparticles (Ag NPs, 25 nm) and uncoated TiO2 NPs (anatase, 5 nm primary size, NM-101,JRC) were used in this study. Two types of sludge were used for the exposures, one from a municipal WWTP (Oslo, Norway), and another from a lab-scale WWTP simulating biological wastewater treatment processes continuously dosed during 5 weeks with well-characterised Ag and TiO2 NPs. Earthworms (adults E. fetida) were exposed to LUFA 2.2 soil amended with sewage sludge at two application rates: 20 t ha-1 (maximum recommended application rate in Europe), and 3 times this application rate, i.e. 60 t ha-1 (worst-case scenario). After 12 and 39 days, coelomocytes were isolated from exposed earthworms, and effects on cell population, metabolic activity, lysosomal integrity and reactive oxygen species (ROS) formation were assessed. Characterization of NMs in the sludge amended-soil and soil elutriates, in whole earthworms and coelomocytes isolated from exposed earthworms, was carried out at the beginning (day 0), during (day 12) and the end (day 39) of the exposure period, using inductively coupled plasma-mass spectrometry (ICP-MS) and single-particle (sp)-ICP-MS. Dose and exposure time-dependent effects were observed, with an alteration in the cell composition of coelomocytes, increase in ROS formation and decrease in lysosomal membrane integrity being more pronounced at the highest exposure concentration. The importance of taking NM transformation into account and the sensitivity of the E. fetida coelomocytes as a model to study the effects of transformed NMs in vitro are discussed.