Time-dependent aggregation,
sedimentation, dissolution, and transformation
of three copper-based engineered nanomaterials (ENMs) of varied properties
were measured in eight natural and artificial waters. Nano-Cu and
Cu(OH)<sub>2</sub> aggregated rapidly to >10<sup>3</sup> nm while
the aggregate size of nano-CuO averaged between 250 and 400 nm. Aggregate
size for both nano-Cu and nano-CuO showed a positive correlation with
ionic strength with a few exceptions. Aggregate size did not correlate
well with sedimentation rate, suggesting sedimentation was influenced
by other factors. Controlling factors in sedimentation rates varied
by particle: Cu(OH)<sub>2</sub> particles remained stable in all waters
but groundwater, nano-Cu was generally unstable except in waters with
high organic content, and nano-CuO was stabilized by the presence
of phosphate, which reversed surface charge polarity at concentrations
as low as 0.1 mg PO<sub>4</sub><sup>3–</sup> L<sup>–1</sup>. Dissolution generally correlated with pH, although in saline waters,
dissolved copper formed insoluble complexes. Nano-Cu was rapidly oxidized,
resulting in dissolution immediately followed by the formation of
precipitates. These results suggest factors including phosphate, carbonate,
and ENM oxidation state may be key in determining Cu ENM behavior
in natural waters
