Environmental Engineering Reference
In-Depth Information
reported fullerene aggregates to elevate lipid oxidation levels in the brains of fish; she
observed extensive brain damage to fish exposed to fullerenes for a period of just 48
hours at a relatively moderate dose of 0.5 mg/L (commiserate with levels of other kinds
of pollution found in bays). The fish also exhibited changed gene markers in their livers,
indicating their entire physiology was affected. At modest concentrations in aquarium
water, NPs triggered damaging biochemical reactions in the brains of fish. They also
wiped out entire populations of "water fleas," tiny animals that fill an ecologically
crucial niche near the bottom of the aquatic food chain (Weiss, 2004). Kashiwada
(2006) explored the distribution of 4 types of water-suspended fluorescent NPs
throughout the eggs and adult bodies of a see-through medaka (Oryzias latipes). He
found that NPs were in fact taken up into the bloodstream and deposited throughout the
body. In the medaka eggs, there was a high accumulation of NPs in the yolk; most often
bioavailability was dependent on specific sizes of the particles. Adult samples of medaka
had accumulated NPs in the gills, intestine, brain, testis, liver, and bloodstream. One
major result from this study is the fact that salinity may have a large influence on the
bioavailability and toxicity of NPs to penetrate membranes and eventually kill the
15.4.2 Abiotic Transformation
Abiotic (nonbiological) transformation processes affect NMs fate and transport
by causing interactions between NMs and mobile materials in the aquatic environment
or stationary subsurface materials (e.g., sorption, ion exchange) or by changing the form
of the NMs (e.g., hydrolysis, redox reactions) which may subsequently interact with the
materials. The major abiotic transformation processes to be discussed in this section
include hydrolysis, oxidation/reduction, photocatalyzed reaction, ion exchange.
Additional abiotic processes could be identified, but are beyond the scope of this
Hydrolysis. Hydrolysis is the reaction of a compound with water. Hydrolysis of
organic compounds often results in the formation of alcohols and alkenes. Hydrolysis
reactions involve the cleavage of the molecules of NMs into smaller, more water-soluble
portions and in the formation of new C-OH or C-H bonds. They can generally be
categorized into acid-catalyzed, alkaline, and neutral (or pH independent) hydrolysis.
Several methods for preparation of NMs materials involve hydrolysis, such as
hydrodynamic cavitation micro emulsion, sonochemical processing techniques, and sol-
gel techniques (see Chapter 2). Sol-gel techniques involve four steps: hydrolysis,
condensation, growth and agglomeration of particles. During hydrolysis, addition of
water results in the replacement of the [OR] group with the [OH-] group. Hydrolysis
occurs by attack of oxygen on silicon atoms in silica gel. Hydrolysis can be accelerated
by adding a catalyst such as HC1 and NHj. Hydrolysis continues until all alkoxy groups
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