Environmental Engineering Reference
In-Depth Information
be produced by any one ingredient, or interactive effects among several active
ingredients, or other components of a formulation to which exposure occurs.
During the course of 7- and 14-day treatments, the toxic effects in mice of
mixtures of parathion (5 mg/kg), toxaphene (50 mg/kg), and/or dichlorophe-
noxyacetic acid (2,4-D; 50 mg/kg) were observed to emulate the effects exhib-
ited by the individual components (Kuntz et al. 1990 ). Metabolic aspects of these
three chemicals suggest that the toxicity of the parathion plus toxaphene mixture
would be lower than that of parathion, as toxaphene has the ability to increase
aliesterases and the biotransformation of parathion to paraoxon, thereby provid-
ing a pool of noncritical enzymes for the binding of paraoxon (Chaturvedi et al.
1991 ). Because of these properties of toxaphene, it is anticipated that the toxicity
of a mixture of parathion plus toxaphene plus 2,4-D would also be lower than
that of parathion alone (Chaturvedi et al. 1991 ). Chronic studies in mice on the
mixtures of three commonly used herbicides - alachlor, atrazine, and/or picloram -
suggest that the mixtures may cause hepatotoxicity and stimulate the liver xeno-
biotic-metabolizing enzymes (Chaturvedi 1993a ). A chronic toxicological
evaluation of mixtures of ten widely used pesticides - alachlor, aldrin, atra-
zine, 2,4-D, DDT, dieldrin, endosulfan, lindane, parathion, and toxaphene - in
mice revealed that these mixtures induce the xenobiotic-metabolizing enzymes
in liver. Therefore, exposures to such pesticidal mixtures may cause deleterious
effects in other species, including humans, by enhancing the metabolism of xen-
obiotics (Chaturvedi 1993b ).
In multichemical exposures, interactive effects among chemicals to which
exposure occurs may play a contributory role toward the associated poisonings.
This type of poisoning could be exempliied by citing two actual examples: irst,
a multichemical death that involved caffeine, nicotine, and malathion (Chaturvedi
et al. 1983 ), and another death attributed to ingestion of malathion insect spray
(Chaturvedi et al. 1989 ). In the later case, in vitro inhibition of cholinesterases
and the presence of xylenes and other volatiles, in certain postmortem samples,
were demonstrated (Chaturvedi et al. 1989 ). Therefore, these organic solvents
may not only interact with other mixture-chemicals, but may also exhibit their
own toxic effects.
Ethylbenzene, a major component of mixed xylenes, is used as solvents in
agriculture insecticide sprays and has been found to increase the incidences of renal
tubule, alveolar/bronchiolar, and hepatocellular neoplasms, and of testicular and
renal tubule adenomas, in rats (US National Toxicology Program 1999 ). Increased
incidences of renal tubule hyperplasia of alveolar epithelial metaplasia, and of
severe nephropathy have been reported in rats exposed to ethylbenzene. The herbi-
cide glyphosate, though it does not bioaccumulate, biomagnify, or persist in a
biologically available form in the environment, and is nontoxic to animals, is formu-
lated with surfactants (Solomon and Thompson 2003 ). Such formulations increase
the eficacy of the herbicide but, in some cases, are more toxic to aquatic organisms
than is the parent material. Some risks were observed for measured concentrations
of glyphosate in surface waters that resulted from aerial application to forests of a
formulation equivalent to Roundup ® in Canada.
Search WWH ::




Custom Search