Pesticide Excretion - Pesticide Biotransformation and Disposition - page 183

Milk
Because milk is an emulsion of lipids in an aqueous protein solution, it may contain
xenobiotics of many different physicochemical properties, ranging from polar com-
pounds such as alcohol and caffeine, to less polar clinical drugs and to highly lipophilic
chemicals such as DDT and DDE. Elimination of toxicants in milk is highly depen-
dent on the biological half-life of the toxicant. Milk normally plays a minor role in the
excretion of chemicals with short half-lives but may be important for some chemicals
with long half-lives. In experimental studies with chlorinated insecticides, up to 25%
of the dose administered to cows was eliminated in the milk. In some South American
countries, the DDT content of human mothers' milk is close to the acceptable daily
intake recommended by the World Health Organization. Although adverse effects on
infants were not seen in these cases, when nursing mothers were accidentally exposed
to hexachlorophene (Turkey) or polychlorinated biphenyls (PCBs) (Japan), signs of
intoxication were seen in a number of infants.
Eggs
Polar toxicants and metabolites may be eliminated in egg white and lipophilic com-
pounds in the yolk. The effects of this on developing birds are controversial but may
be significant, particularly if bioconcentration has occurred in the food chain. Effects
of toxicants excreted into avian eggs should not be mistaken for the well-documented
eggshell thinning, which is an effect on the female reproductive system.
Fetus
The elimination of maternally derived toxicants in the fetus is of little or no benefit to
the mother and, because of the generally small amounts involved, is usually of little or
no harm to the fetus. However, as shown by the toxic effects of mercury, thalidomide,
and diethylstilbestrol, this is not always the case.
Alimentary Elimination
Passive elimination of lipophilic toxicants directly through the wall of the alimentary
canal is probably, in most cases, unimportant, at least from a quantitative viewpoint.
However, although slow, it may be an important route for excretion of chlordecone,
particularly if reabsorption is prevented by administration of cholestyramine.
Obscure Routes of Excretion
Because passive diffusion of lipophilic toxicants may occur across any cell membrane,
it might be expected that such chemicals will appear in many body secretions, such as
sweat, or in growth products, such as hair, nails, and skin. The sebaceous glands secrete
an oily secretion and, probably for this reason, insecticides and PCBs have been found
in human hair. Arsenic, mercury, and selenium have also been associated with hair.