The Carbon Quandary: Essential and Detrimental - Sustainable Design: The Science of Sustainability and Green Engineering - page 257

the movement and fate of nanoparticles in the environment, possible hazards
and risks to users of nanomaterials in products, and health and safety issues in
the lab. *
* D. A. Vallero, “Beyond responsible conduct in research: new pedagogies to address macroethics
of nanobiotechnologies,” Journal of Long-Term Effects of Medical Implants , 2007 (in press).
In teaching green engineering and sustainable design, especially to first-year
engineering students, open-ended questions can be quite revealing. Here is one:
“Is carbon good or bad?” Most students who take our courses have learned that
the best answer is almost always, “It depends.” This leads to a follow-up question:
“Okay, on what does it depend?” This usually leads to tortuous discussion of
what (e.g., the chemical species), when (e.g., at the beginning of photosynthesis
or at the end of respiration), where (e.g., in the soil versus the atmosphere), and
how (e.g., the processes by which carbon cycles through the environment). This
also gives the instructor an opportunity to discuss why carbon is important for
good or ill.
Carbon is at the center of every environmental discussion. Most recently, this
is in large part because the two most prominent greenhouse gases, carbon dioxide
and methane, are carbon-based compounds. However, these are just two of the
carbon compounds that are cycled continuously through the environment (see
Fig. 7.1).
Figure 7.1 demonstrates the importance of carbon sinks and sources. For
example, if carbon can remain sequestered in the soil, roots, sediment, and other
compartments, it is not released to the atmosphere. Thus, it cannot have an
impact on the greenhouse effect. Even relatively small amounts of methane and
carbon dioxide can profoundly increase the atmosphere's greenhouse potential.
Suffice it to say that carbon is an amazing element. It can bond to itself and
to other elements in a myriad of ways. In fact, it can form single, double, and
triple bonds with itself. This makes possible millions of organic compounds. An
organic compound is a compound that includes at least one carbon-to-carbon or
carbon-to-hydrogen bond.
By far most pesticides and toxic substances include carbon. However, all liv-
ing tissues so consist of organic compounds. All life on Earth is carbon-based.
Biochemistry is known as the chemistry of life, or at least the chemistry of what
takes place in living systems. Biochemistry is a subdiscipline of organic chemistry.
Slight changes to an organic molecule can profoundly affect its behavior in
the environment. For example, there are large ranges of solubility for organic
compounds, depending on the presence of polar groups in their structure. The
addition of an alcohol group to n -butane to produce 1-butanol, for example,
increases the solubility several orders of magnitude. This means that an engineer
deciding to use an alcohol-based compound in a manufacturing step is making