Page 456 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

P. 456

VetBooks.ir Chapter 25

Chromium, Iodine, and Phosphorus

Larry J. Thompson

CHROMIUM However, using a safety factor of 10 for cross-species
extrapolation, a maximum tolerated dose of 10 ppm total
Chromium is a metallic element that can exist in six
chromium in dog and cat food products was determined by
valence states, with the trivalent chromium form most
the FDA-CVM in response to confusion concerning the
commonly found in nature as ferrochromite ores. Both tri-
misinterpretation of chromium analytical results in pet food
valent (13) and hexavalent (16) chromium are widely
products (FDA-CVM, 2011).
used in various industrial and manufacturing processes.
Chromium is an essential trace element, and functions in
a number of metabolic processes, including glucose, lipid,
IODINE
and amino acid metabolism (NRC, 2005a). Hexavalent
chromium is considered to be more toxic than the triva- Iodine is a non-metallic element of the halogen group that
lent form, which may be a direct result of its increased occurs as a purple-black crystalline solid, but has several
21
systemic availability. common other forms, including iodide (I )and iodate
23
While hexavalent chromium is considered to be a (IO ). Iodine is widely distributed in nature in both
human carcinogen, acute chromium toxicosis in animals is organic and inorganic forms, but only in low concentra-
probably of minimal concern in all but the most unusual tions, with rare exceptions. Iodine is essential for the nor-
circumstances. Both hexavalent chromium and dichromate mal synthesis of thyroid hormones and a deficiency of
are easily converted to trivalent chromium in mammalian iodine can result in thyroid enlargement or goiter.
systems, but the burning of chromium-treated lumber does Deficiencies may occur from eating feeds grown on iodine-
not produce enough heat to convert the dichromate to the deficient soils or from the presence of goitrogenic
trivalent chromium form. Oil field contamination with hex- substances (NRC, 2005b). High dietary iodine for a pro-
avalent chromium has been associated with cases of cattle longed period of time can reduce the iodine uptake by the
death (Thompson et al., 1991), and a solution of strong, thyroid, thus causing a clinical syndrome of iodine defi-
oxidizing chromium was responsible for dairy cattle deaths ciency, especially when normal levels are subsequently fed.
when the solution dripped on cattle and was absorbed der- Common dietary sources of iodine include iodized salt,
mally (Talcott et al., 2005). Acute chromium toxicosis is ethylenediamine dihydroiodide (EDDI), calcium iodate, as
associated with severe congestion and inflammation of the well as naturally high iodine sources such as kelp and cer-
digestive tract, kidney damage, and liver damage. tain seaweeds. Iodized salt can contain 0.01% iodine
Dogs were given potassium chromate in drinking water (100 ppm), and has not been associated with excess iodine
for 4 years with hexavalent chromium concentrations up to exposure. EDDI has been used to prevent and treat foot rot
11.2 ppm (Anwar et al.,1961). The calculated dose was up in cattle, although its efficacy is unclear (Morgan, 2004).
to 0.30 mg/kg BW/day of hexavalent chromium (Grevatt, Toxic effects of iodine excess have been reported in cattle
1998), with no significant adverse effects reported in the consuming iodine-containing feed additives (Thompson
dogs. No adverse effects were reported in cats fed diets et al., 1991). Clinical signs include decreased feed intake,
containing chromium oxycarbonate for 80 days, which decreased milk production, rapid breathing, nasal and ocu-
delivered up to approximately 100 mg/kg BW/day trivalent lar discharge, dry hair coat, and non-responsive hock
chromium (Akatsuka, 1934). Maximum tolerated levels of lesions. Affected cattle were on high intakes of iodine
trivalent chromium were set at 100 ppm for mammalian (68 600 mg/head/day and above) for several weeks before
species and 500 ppm for poultry, with allowances for insol- obvious clinical signs appeared. Young calves exhibited
uble chromic oxide up to 3000 ppm (NRC, 2005a). chronic coughing and profuse nasal discharge at

451 452 453 454 455 456 457 458 459 460 461