REGULATING AND REDUCING POLLUTION - Marine Pollution: What Everyone Needs to Know - page 223

Even offshore aquaculture methods can be modified to
reduce pollution. Mobile fish pens that move around over
different areas are one new approach. Methods are being
developed to recycle fish sewage, and new feed formula-
tions are being developed that use smaller amounts of wild
fish and replace it with vegetable protein—for example,
from soy. Multitrophic aquaculture, or integrated farms, put
salmon pens near farmed plants and animals that consume
the salmon wastes, species that can later be marketed them-
selves. Seaweeds are efficient waste recyclers that can extract
about 40% of the dissolved nutrients available. Seaweed can
be grown on ropes dangling from rafts downstream from
salmon pens and grow in the wastewater, primarily ammonia
(excreted by salmon) and decaying food. Filter-feeding mus-
sels can also be cultured nearby to grow on particles of excre-
ment and food scraps.
What is “Green Chemistry?”
Plastics can be manufactured that are degradable. Microbes
have been genetically engineered to produce biodegradable
plastics, which could benefit the oceans. Standards for measur-
ing how plastics break down in particular environments have
emerged recently and are still in development. Comparisons
among plastics are complicated by the fact that no one entity
is recognized as setting those standards. Nevertheless, there is
consensus on distinctions among the key terms “degradable,”
“biodegradable,” and “compostable.” Degradable means that
chemical changes take place, maybe due to sunlight or heat,
that alter a plastic's structure and properties, like clouding
or fragmenting. Biodegradable more narrowly indicates that
degradation results from naturally occurring microorgan-
isms (bacteria, fungi, or algae), but makes no guarantee that
the degradation products are nontoxic or make good compost.
Compostable goes a step further: the microorganisms' break-
down products must yield CO 2 , water, inorganic compounds,