Fate and Transport of Nanomaterials in Aquatic Environments - Nanotechnologies for Water Environment Applications - page 510

f-rr) = k 1 C w -apC f -k 2 C b -k e C b -k m C b - Rk r C b - GC b = -R a /M Tissu e (Eq. 15.48)

where (dC b /dt) a = bioaccumulation rate in biota, M of NMs/M of tissue-T; a = absorption
efficiency of a NM from food, 0 < a < 1; (3 = food consumption rate, M of food/M of
tissue-T; Cf = NM concentration in food, M/M of food; k e = rate constant for elimination
in feces, 1/T; k m = biotransformation rate constant, 1/T; k r = reproduction rate, 1/T; R =
a trigger value (= 0 without reproduction and = 1 with reproduction); G = the growth
dilution rate (factor), 1/T; and R a = NM decrease rate in water due to bioaccumulation,
M/L 3 -T. Analogous to BCF, the bioaccumulation factor, BAF, is expressed as:

BAF = C b /C w = (kj + <xpC f /C w )/(k 2 + k e + k m + Rk r + G)

(Eq. 15.49)

Table 15.9 NMs' Characteristics affecting NM's BA by ac uatic biota.

Examples/
References*
1. NP (39.4 nm) shifted into
the yolk and gallbladder;
474 nm NPs has the
highest bioavailability to
Medaka eggs
(Kashiwada, 2006).
2. The toxicity of NMs is
affected by multiple
physicochemical and
environmental factors
(Colvin, 2003; Sayes et
al., 2004; Hardman,
2006; Neletal., 2006).
3. The NP size affects the
rate for them to enter the
epithelium (Churg et al.,
1998).
4. CNT length affects
asbestos-like toxicity
(Poland etal., 2008;
Kostarelos, 2008).
5. Toxicity of SWNTs to
human cells varies with
functionalization of
SWNTs and the solution
(Kang et al., 2007; Lee et
al., 2004).
a Numbers in this column do not correspond the bullets in the other two columns.

Observation/Effects on BA of
NMs/Contaminants
• The transfer of NMs across a
membrane is influenced by its size,
shape, and structure.
• Polarity, presence of functional
groups, and degree of ionization affect
biosorption and BA.

• Unique Shape,

• Formation of aggregate will allow the
occurrence of NMs sedimentation and
the retaining of NMs by porous media,
which affects the extent of exposure of
biota to the NMs.
• The water solubility of a NM controls
its extent of sorption. BA increases
with increasing lipophilicity (a high
K ow ).
• Slow salvation of large hydrophobic
NMs may limit the transfer of NMs
across organism' membranes.

• Solubility/Lipo

• Bioaccumulative chemicals tend to be
resistant to both abiotic and biotic
degradation. Sorption, volatilization,
and degradation reactions (e.g.,
hydrolysis, oxidation, and photolysis)
are competing fate processes to BA.