Page 597 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

562 SECTION | VII Herbicides and Fungicides

VetBooks.ir pigs. In rats, high doses of propachlor produce erosion, can occur with chronic dinitrophenol intoxication.
Exposure to these compounds may cause yellow staining
ulceration, and hyperplasia of the gastric mucosa; herni-
of skin, conjunctiva, or hair (Lorgue et al., 1996).
ated mucosal glands in the pyloric region of the stomach;
hypertrophy; and necrosis of the liver. In dogs, there is
poor diet palatability, which results in weight loss and
Triazolopyrimidine Herbicides
poor consumption of food. Propachlor may produce slight
developmental or adverse reproductive effects (Table 44.1). Triazolopyrimidine herbicides include cloransulam-
It is not genotoxic or clastogenic in mammals. However, methyl, diclosulam, florasulam, penoxsulam, flumetsu-
there is evidence that it produces benign hepatic tumors lam, metosulam, and pyroxsulam. The generic structure
in male mice (Heydens et al., 2010). The previously dis- of the triazolopyrimidine herbicides connected to a substi-
cussed data support grouping alachlor, acetochlor and tuted phenyl ring through a sulfonamide bridge is shown
butachlor based on a common mechanism of toxicity for in the second edition of this book.
evaluation of risk assessment to humans and animals The acute oral toxicity of triazolopyrimidine herbicides
(Heydens et al., 2010). is very low. On repeated exposure, the primary organs are
the kidney (rat and mouse), liver (rat, mouse, and dog) and
thyroid (rat) (Billington et al., 2010). In dogs, the target
Amides and Acetamides
organ is eye as compared to other species (Timchalk et al.,
The commonly used amides and acetamides include 1996). No adverse effects on neurotoxicity, reproductive
bensulide, dimethenamid-P and propanil and are slightly performance and mutagenic abnormalities have been
to moderately hazardous in normal use. Dimethenamid is observed. The compound has no carcinogenic potential in
a racemic mixture of the M and P stereoisomers, whereas humans (EPA, 1997a,b).
P isomer has useful herbicidal activity. Both substances
produce only mild reversible skin and eye irritation and Imidazolinones
skin sensitization in guinea pigs. Comparison of racemic
dimethenamid with dimethenamid-P indicates that there is Imidazolinone herbicides include imazapyr, imazametha-
little difference in their toxicological profiles. The signs benzmethyl, imazapic, imazethapyr, imazamox, and ima-
of toxicity in mice, rats and dogs are similar, with reduced zaquin. These are selective broad-spectrum herbicides
BW gain and liver enlargement with induction of liver discovered in the 1970s.
xenobiotics metabolizing enzyme. There is strong binding These herbicides are relatively nontoxic. Results from
to hemoglobin in rats, but this has no relevance to primary eye irritation studies range from no irritation
humans. Dimethenamid can reduce fetal BW but is not (imazaquin) to slightly irritating (imazamethabenzmethyl)
teratogenic. There is no compound-related mutagenic or and moderately irritating (imazapic and imazethapyr),
carcinogenic potential (JMPR, 2005). showing complete recovery within 7 days postdosing. The
rabbit primary irritation study with imazapyr showed irre-
versible irritation. Toxicological effects of imidazolinone
Dinitrophenol Compounds
herbicides are slight to moderate skeletal myopathy and/
Several substituted dinitrophenols alone or as salts, such or slight anemia in dogs occurring in the 1-year dietary
as DNP (2,4-dinitrophenol), DNOC (dinitro-o-cresol) and toxicity studies with three structurally similar imidazoli-
dinoseb (2-(1-methylpropyl)-4,6-dinitro), are used as her- nones (imazapic, imazaquin and imazethapyr). There is
bicides. The main source of poisoning in animals is no evidence of any adverse effect on reproductive perfor-
human negligence in removing the preparation if it spills, mance and on fetal abnormalities in the rat and the
in disposing of the containers and in preventing animals rabbit. Neither mutagenicity nor any carcinogenicity has
access to treated fields. been reported in either of these species (Hess et al.,
In general, the dinitro compounds are not very water- 2010).
soluble and are highly hazardous to animals. The oral
acute LD 50 of DNOC in mice, guinea pigs, rabbits, hens, Benzoic Acids
dogs, pigs and goats ranges from 25 to 100 mg/kg BW. In
sheep, a dosage of 25 mg/kg/day causes toxicosis in 2 5 The herbicides in this group include chloramben,
days. Clinical signs include fever, dyspnea, acidosis, oli- dicamba, and naptalam. These have a low order of
guria, muscular weakness, tachycardia and convulsions toxicity.
followed by coma and death with a rapid onset of rigor In practice, dicamba is often combined with other
mortis. Abortions have been reported in sows. In cattle herbicides and is used to control a wide spectrum of
and ruminants, methemoglobinemia, intravascular hemo- weeds. The signs and lesions are similar to those
lysis and hemoproteinemia have been observed. Cataract described for the chlorophenoxy acids. Poisoning after