Page 471 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

448 Potential Impacts of Nanomaterials

the structure of a chemical and its likelihood to increase the toxicity of
a compound. Each chemical component is given a numerical value, and
the sum of its components determines its toxicity. One can also use sim-
ilar calculations to extrapolate the toxicity of a chemical to an organism
based on its toxicity to an unrelated organism [20].

Methods to Assess Ecotoxicity
As yet, a comprehensive ecotoxicity study of any nanomaterial has not
been performed. Most studies have analyzed nanomaterial impacts on
a type of organism in isolation. The methods for looking at ecosystems
impact as a whole are established and are reviewed in several texts
[20–22], so this review is by no means exhaustive.
There are many levels at which one can analyze the impact of a chem-
ical, from a single biochemical reaction up to an entire ecosystem with
all of its complexity. Most ecotoxicity tests relate to survival, mutation,
and reproduction. The majority of the current research on nanomateri-
als has examined their impact on biochemical reactions in a cell up to
the survivability of whole multicellular organisms. In order to make com-
parisons between chemicals and organisms for risk analysis, several
benchmark measurements have been established. The most common is
, or lethal concentration of chemical that kills 50 percent of an
the LC 50
exposed population as compared to a control. Another common meas-
urement is the EC , or effective concentration of a chemical that elic-
50
its some response in 50 percent of the population. The response
examined can be reproductive capacity, growth, respiration, or any
number of endpoints. Tests of both the LC and EC must be carefully
50
50
controlled and performed in a standardized manner to ensure compa-
rability between experiments and laboratories.
There are numerous methods and organisms at various trophic levels
to examine LC or EC . Part of the challenge in ecotoxicology is to find
50
50
appropriate biomarkers, or physiological processes that respond in a sen-
sitive manner to chemical exposure, and bioindicators, or organisms in
an ecosystem that reflect the health of that environment. Most of the
studies in nanomaterial toxicology have only looked at biomarkers and
not bioindicators of any specific ecosystem. Many pollutants have a spe-
cific biomarker, since the chemicals elicit a specific response from organ-
isms [22]. There are also some established organisms that can be
relatively easily cultured and used to assess toxicity. Table 12.1 lists
some of the commonly used organisms, their common name, and
common endpoints.
Bacteria are among the easiest and least expensive organisms to cul-
ture, and they are relatively sensitive to many of the same compounds