Page 160 - Design for Environment A Guide to Sustainable Product Development

Design Rules and Guidelines 139

oxygen depletion in water bodies; an extreme example is the dead
zone in the Gulf of Mexico. One way to combat this problem, accord-
ing to Professor William Mitsch at The Ohio State University, is to
build wetlands and riparian buffer zones that act as natural filters
along waterways.
There are several available strategies for achieving benign waste
disposition in the environment:
• Waste sequestration—It is possible to isolate wastes for vary-
ing lengths of time, so that they do not come in contact with
humans or sensitive ecosystems. Examples include:
Deposition of liquid wastes in settling ponds adjacent to
industrial facilities
Isolation of radioactive nuclear wastes for long periods of
time in sealed containers
Underground sequestration of carbon dioxide, currently
being explored by the electric power industry and the U.S.
Department of Energy (see Chapter 18).

However, all of the above solutions are reversible and poten-
tially vulnerable to unforeseen problems.
• Ecosystem adsorption—There exist a variety of ecosystem
processes that can reduce the concentrations or impacts of
wastes in an envi ronment over time. These include processes

that change wastes into less toxic forms, e.g., sorption to
sediments, as well as processes that disperse and transport
wastes in ways that dilute their impact. However, there is
also a possibility that ecosystems will concentrate wastes into
‘‘hot spots’’ of relatively high waste concentrations, in cluding
bioaccumulation through the food chain. The assimilative
capacity of an ecosystem to adsorb waste may be defined as
the amount and rate of a given waste that can be added to an
ecosystem before some specified level of detrimental effect is
reached [5]. Given the current rates of material throughput,
many terrestrial ecosystems are already stressed, and reliance
on ecosystem adsorption cannot be taken for granted.
• Biodegradation—Many consumer products are disposed of
rather than recycled, or may have unavoidable residuals
that enter municipal solid or liquid waste streams. Examples
include plastic bags, polystyrene pellets, batteries, deterg ent
residues, and pharmaceuticals. While the concentrations of
harmful substances in these wastes may be low, the cumu-
lative volume and potential exposures may cause concern.
A worthwhile approach toward risk reduction is to ensure
that such substances are biodegradable in the environment.