PESTICIDES AND INDUSTRIAL ORGANIC CHEMICALS - Marine Pollution: What Everyone Needs to Know - page 107

zooplankton, and reduced numbers of zooplankton means
less food for small fishes. Also affected are larger crustaceans
such as shrimps and crabs, particularly when they are in lar-
val stages and must molt frequently.
Bacteria that cause insect diseases can also be used as
pesticides. The principal one used on salt marshes is Bacillus
thuringiensis israelensis (Bti), which produces protein crystals
that are selectively toxic to mosquito larvae. After being eaten,
they rupture the digestive tract of the host, causing rapid death.
When specific diseases of insects are used as pesticides there is
less likelihood of harm to nontarget organisms, but honeybees,
butterflies, dragonflies, and other useful insects may also be at
risk.
How are pesticides regulated?
In the United States, FIFRA requires that the adverse ecologi-
cal outcomes of a pesticide be balanced against its beneficial
effects in controlling pest populations (e.g., increased agri-
cultural production). In registering pesticides for use, it has
always been easier to document its financial benefits than to
estimate ecological costs, and the toxicity testing is done by
the manufacturer of the pesticide, who has an interest in min-
imizing its adverse effects. Most of the toxicity testing under
FIFRA is based on lethal effects (LC 50 , or the concentration
that kills 50% of the exposed animals) rather than sublethal
effects. The LC 50 is not relevant to real-world effects of pes-
ticides, since it does not encompass species differences, sub-
lethal effects, or delayed effects. Most of the standard aquatic
test organisms are freshwater species—rainbow trout, blue-
gill, and daphnids. Individual chemicals are evaluated by
these standardized tests; in nature, however, animals are
exposed to a variety of chemicals, with new ones coming into
use every year, and the toxicity of complex mixtures is not
well understood at all.