posted on 2017-10-10, 00:00authored byJohn P. Stegemeier, Astrid Avellan, Gregory V. Lowry
Ag0- and CuO-engineered
nanomaterials (ENMs) or their
sulfidized forms are introduced into freshwater wetlands through wastewater
effluent and agricultural runoff. Knowledge about the rates of transformations
of these ENMs in realistic environments and the impact of the form
of the incoming ENM (i.e., sulfidized or pristine) on bioavailability
and fate is limited. Here, five freshwater wetland mesocosms were
exposed to 3 g of total metal as CuO, CuS, Ag0, or Ag2S ENMs or soluble CuNO3 added weekly for 1 month.
Total metal and metal speciation was measured in sediment and plant
samples collected 1, 3, 6, and 9 months after addition. The form of
the added ENM did not affect the metal distribution, and ENMs distributed
similarly to added ionic Cu or Ag. For the dosing condition used,
∼50% of the added Ag or Cu metal mass was found in Egeria densa plant tissue, with the remainder primarily
in the surficial sediment. Ag0 and CuO ENMs transformed
quickly in sediment, with no evidence of CuO and only ∼4% of
silver present as Ag0 ENM 1 week after the last ENM addition.
In contrast to sediment, Ag0 and CuO ENMs were persistent
in E. densa tissues for up to 9 and 6 months, respectively.
The persistence of ENMs in E. densa suggests that
chronic exposures, or food web transfers, for both the transformed
and the initially added ENMs are possible.