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<p>Nanomaterials are being increasingly produced and used across a myriad of applications
while their novel properties are still in the midst of being designed and explored.
Thus the full implications of introducing these materials into the environment cannot
be understood, yet the need to assess potential risks is already upon us. This work
discusses a comprehensive view of environmental impact with respect to material flows
from across the value chain into all compartments of the environment, whereby interactions
and potential hazardous effects become possible. A subset of this broad system is
then chosen for evaluation; a model is derived to describe the fate of nanomaterials
released to wastewater. </p><p>This analysis considers the wastewater treatment plant
(WWTP) as a complete mixed reactor aerobic secondary clarifier, and predicts whether
nanomaterials will associate with effluent or sludge to project potential concentrations
in each. The concentration of nanomaterials reaching a WWTP is estimated based on
a linear weighting of total production, and the fate of nanomaterials within the WWTP
is based on a characteristic inherent to the material, partition coefficient, and
on design parameters of the WWTP, such as retention times and suspended solids concentration.
</p><p>Due to the uncertainty inherent to this problem, a probabilistic approach is
employed. Monte Carlo simulation is used, sampling from probability distributions
assigned to each of the input parameters to calculate a distribution for the predicted
concentrations in sludge and effluent. Input parameter distributions are estimated
from values reported in the literature where possible. Where data do not yet exist,
studies are carried out to enable parameter estimation. In particular, nanomaterial
production is investigated to provide a basis to estimate the magnitude of potential
exposure. Nanomaterial partitioning behavior is also studied in this work, through
laboratory experiments for several types of nano-silver. </p><p>The results presented
here illustrate the use of nanomaterial inventory data in predicting environmentally
relevant concentrations. Estimates of effluent and sludge concentrations for nano-silver
with four different types coatings suggest that these surface treatments affect the
removal efficiency; the same nanomaterial with different coatings may have different
environmental fates. Effluent concentration estimates for C60 and nano-TiO2 suggest
that these nanomaterials could already be present at problematic concentrations at
current levels of annual production.</p><p>Estimates of environmentally relevant concentrations
may aid in interpretation of nanotoxicology studies. These relative estimates are
also useful in that they may help inform future decisions regarding where to dedicate
resources for future research. Beyond attempting to estimate environmental concentrations
of nanomaterials, this type of streamlined model allows the consideration of scenarios,
focusing on what happens as various input parameters change. Production quantity and
the fraction of this quantity that is released to wastewater are found to greatly
influence the model estimates for wastewater effluent concentrations; in the case
of wastewater sludge concentrations, the model is sensitive to those parameters in
addition to solids retention time.</p>
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