2 research outputs found
Fate of Zinc Oxide Nanoparticles during Anaerobic Digestion of Wastewater and Post-Treatment Processing of Sewage Sludge
The rapid development and commercialization of nanomaterials will
inevitably result in the release of nanoparticles (NPs) to the environment.
As NPs often exhibit physical and chemical properties significantly
different from those of their molecular or macrosize analogs, concern
has been growing regarding their fate and toxicity in environmental
compartments. The wastewater–sewage sludge pathway has been
identified as a key release pathway leading to environmental exposure
to NPs. In this study, we investigated the chemical transformation
of two ZnO-NPs and one hydrophobic ZnO-NP commercial formulation (used
in personal care products), during anaerobic digestion of wastewater.
Changes in Zn speciation as a result of postprocessing of the sewage
sludge, mimicking composting/stockpiling, were also assessed. The
results indicated that “native” Zn and Zn added either
as a soluble salt or as NPs was rapidly converted to sulfides in all
treatments. The hydrophobicity of the commercial formulation retarded
the conversion of ZnO-NP. However, at the end of the anaerobic digestion
process and after postprocessing of the sewage sludge (which caused
a significant change in Zn speciation), the speciation of Zn was similar
across all treatments. This indicates that, at least for the material
tested, the risk assessment of ZnO-NP through this exposure pathway
can rely on the significant knowledge already available in regard
to other “conventional” forms of Zn present in sewage
sludge
Independent Data Validation of an in Vitro Method for the Prediction of the Relative Bioavailability of Arsenic in Contaminated Soils
In
vitro bioaccessibility (IVBA) assays estimate arsenic (As) relative
bioavailability (RBA) in contaminated soils to improve accuracy in
human exposure assessments. Previous studies correlating soil As IVBA
with RBA have been limited by the use of few soil types and sources
of As, and the predictive value of As IVBA has not been validated
using an independent set of As-contaminated soils. In this study,
a robust linear model was developed to predict As RBA in mice using
IVBA, and the predictive capability of the model was independently
validated using a unique set of As-contaminated soils. Forty As-contaminated
soils varying in soil type and contaminant source were included in
this study, with 31 soils used for initial model development and nine
soils used for independent model validation. The initial model reliably
predicted As RBA values in the independent data set, with a mean As
RBA prediction error of 5.4%. Following validation, 40 soils were
used for final model development, resulting in a linear model with
the equation RBA = 0.65 × IVBA + 7.8 and an <i>R</i><sup>2</sup> of 0.81. The in vivo–in vitro correlation and
independent data validation presented provide critical verification
necessary for regulatory acceptance in human health risk assessment