Biomedical Engineering Reference
In-Depth Information
n a no -TiO
2
but not with bulk TiO
2
. These results suggest a “carrier” effect of the
NMs, in that the combination of the NM-xenobiotic can facilitate adsorption or
absorption into the cells [148]. Similarly, in the carp, a 132% increase in arsenic
accumulation was found following coexposure to 0.2 mg L
-1
As and 10 mg L
-1
TiO
2
for 25 days [149]. On the other hand, it is possible that water-soluble toxi-
cants become greatly adsorbed onto an NM, causing a decrease in the bioavail-
able fraction of the toxicant to organisms and subsequently less toxicity; this was
evidenced by the formation of newly formed complexes, for example, pentachlo-
rophenol and C
60
, or diuron and carbon black [147]. The detailed mechanism(s)
by which the bioavailability of xenobiotics can be modified when adsorbed onto
NMs are not well known and further studies are warranted.
10.4.3 Bioaccumulation and Trophic Transfer
Many authors have discussed the mechanisms underlying the trophic transfer
and biomagnification of NMs. For instance, Baun and colleagues [1] suggested
that a possible route for nano-TiO
2
biomagnification is the ingestion of NP-coated
alga by planktonic species, such as
D. magna
. The inefficient elimination of TiO
2
by
D. magna
resulted in significant bioaccumulation (72 h or longer exposure)
that may lead to a direct effect on the organism following food intake [104].
Transfer of quantum dots 545 ITK carbonyl to
Daphnia
fed by exposed alga was
detected by fluorescence microscopy, and quantified by means of an increase in
light (pixel) intensity [75]. A food web based on bacteria, ciliates, and rotifers was
used by Holbrook et al. [150]. This food web was not optimal, as bacteria could
not absorb the test NPs (e.g., carboxylated quantum dots). It was noted, however,
that the quantum dots adhered to ciliates and resulted in significant bioconcen-
tration with bioconcentration factor (BCF) values in the range of 1000 to 1400
(kg
-1
wet weight), depending on the coating of the quantum dots. Surprisingly,
further ingestion of ciliates by rotifers did not lead to biomagnification.
In a bioaccumulation study of TiO
2
in carp, Zhang et al. [151] reported a
BCF value around 600 kg
-1
wet weight (whole body, accumulation mainly in
viscera and gill; 25-day exposure to 3 or 10 mg
-1
). The transfer of gold nano-
rods was demonstrated by Ferry et al. [152] using a mesocosm that contained
seawater, sediment, sea grass, microbes, biofilms, snails, clams, shrimp, and
fish. After a 12-day exposure period, clams and bacterial biofilms accumu-
lated the highest amounts of gold NP, suggesting that NPs can readily pass
from the water column to the food web.
10.5 Concluding Remarks
There is no doubt that some NMs have the ability to adversely affect differ-
ent environmental receptors (at least in conditions of high bioavailability);
