Biology Reference
In-Depth Information
Comparative Aspects
Limitations of time and space militate against a comparative approach to pesticide
metabolism and this chapter is devoted, with only a few exceptions, to this subject as it
applies to humans and to surrogate mammals used in research and risk analysis.
However, pesticide metabolism in fish liver is of increasing importance to
environmental toxicologists and has been the subject of many recent reports. The
diversity of these reports is illustrated by the following examples:
Carassius auratus
and
alachlor (
Yi et al., 2007
),
Gasterosteus aculeatus
and prochloraz (
Sanchez et al., 2008
),
Ictalurus punctatus
and methoxychlor (
James et al., 2008
),
Micropterus salmoides
and
p,p-DDE (
Barberm et al., 2007
),
Oncorhynchus mykiss
and dieldrin (
Barnhill et al.,
2003
),
Oreochromis mossambicus
and monocrotophos (
Rao, 2006
),
Oreochromis niloticus
and paraquat (
Figueiredo-Fernandes et al., 2006
), Rhamdia quelen and glyphosate
(
Glusczak et al., 2007
), and
Salmo salar
and p,p-DDE (
Mortensen and Arukwe, 2006
).
There is a much smaller body of literature on birds (e.g.,
Cortright and Craigmill,
2006
), reptiles (e.g.,
Gunderson et al., 2006
), and various food and feral mammals (e.g.,
Dupuy et al., 2001
).
Biotransformation in Extrahepatic Tissues
The liver is generally more important than other organs in the biotransformation of
xenobiotics, including pesticides. However, other organs and tissues may be active to
some degree. For example, it was shown early that DDT is degraded by rat diaphragm,
kidney, and brain in vitro (
Judah, 1949
). Later study showed that these changes pro-
ceeded at a very slow rate in vivo
.
However, as shown in the following sections, not all
extrahepatic metabolism is inefficient.
Some enzymes outside the liver may be induced, but the matter has received little
attention.
Wattenberg (1971)
demonstrated that the small intestines of rats fed a bal-
anced purified diet or starved for 1 day possess virtually no benzo[
a
]pyrene hydroxylase
activity, whereas the intestines of rats fed the same diet plus turnip greens, broccoli,
cabbage, or brussels sprouts have marked activity of this enzyme. The same activity in
human skin is induced by polycyclic hydrocarbons (
Alvares et al., 1973
).
Neal (1972)
showed that monooxygenases of the lung active in the metabolism of parathion can be
induced by phenobarbital. Induction of enzymes that metabolize pesticides is consid-
ered in detail in Chapter 7.
Lung
The lung is a primary site of exposure to airborne as well as blood-borne environ-
mental pollutants, such as pesticides, and for this reason it is a target organ for many
chemically induced toxicities (
Bond, 1983, 1993; Dahl and Lewis, 1993; Ding and
Kamienski, 2003
). Because the lung has a full complement of metabolic enzymes, it has
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