Cadmium in wheat grain: Its nature and fate after ingestion

Abstract

Cadmium intake in humans derives primarily from vegetable foods, yet the extent to which the chemical form and dose of cadmium in such foods influences the fate and toxicity of this metal is poorly understood. We have compared the fate in mice of trace levels--approximating that in agriculturally produced grain--and high levels of cadmium supplied as wheat grain with that of cadmium supplied as CdCl2. The amounts and forms of the metal in kidney and liver, target organs in cadmium accumulation, were compared. Results indicate that, in mice, cadmium orally administered as grain and that as CdCl2 have a similar fate in terms of organ distribution and the nature of the Cd-forms in kidney and liver. A low dose of either form resulted in higher kidney versus liver cadmium. Preliminary characterization studies indicate that cadmium in wheat grain occurs primarily as an 11,000-dalton, aqueous-soluble complex, which is not inducible by cadmium.

Characterization of a Cadmium-Binding Complex of Cabbage Leaves

“…Cd,Zn-thionein may have a different fate in animals than in inorganic Cd and we do not know the relative fate of inducible, plant lOK,Cd-complex. Comparative feeding studies using CdC12 and a noninducible Cd-complex in wheat grain suggest that the fate in mice of these forms is similar (26).…”

“…In another case, the principal Cdbinding constituent of wheat grain is apparently not inducible by Cd and not highly enriched in cysteine, yet it binds about 60% of the Cd in grain (26; G. J. Wagner, unpublished data). Its fate in animals has recently been tested (26). Cu-binding complexes which have relatively high cysteine content but have amino acid compositions which differ somewhat from that of animal metallothionein have been isolated from animal liver (30), yeast (29), Scenedesmus (22), and from Agrostis roots (17).…”

“…Although 10K,Cdcomplex was found to be heat stable (see "Results"), we avoided heat denaturation of contaminants to prevent possible adverse effects on the secondary structure of the Cd-complex. Exchange binding of '"9Cd to complex (25,26) For electrophoretic-preparative purification of 10K-Cd-complex, system B (running gel only) was used. In a typical experiment, 65 g of frozen-lyophilized leaves harvested from 30 plants were used to prepare G-25 coarse desalted material (see above) which was dialyzed and lyophilized.…”

Accumulated forms of thallium and cadmium inLemna minor. II. Relationship between duration of exposure and metal-protein binding

“…However, it was not until 1980 that the existence of metal binding proteins was first reported in higher plants (Rauser and Curvetto, 1980). Subsequently, they have been found to occur in a number of plant species; for example, tomato (Lue-Kim and Rauser, 1986), soybean (Cataldo et al, 1981), wheat (Wagner and Nulty, 1984), tobacco and ~abbagc (Wagner and Trotter, 1982;Wagner and Yeargan, 1986). Grill et al (1985) isolated a group of Cd binding polypeptides from cell suspension cultures of more than a dozen different plant species and referred to these as phytochclatins.…”

Effects of Different Cations on the Toxicity and Absorption of Cd in Barley Root

“…Due to this, Cd is one of a very small group of metals for which the Food and Agriculture Organization and World Health Organization (1978) had set a limit for the provisional daily intake by humans (70μg Cd d -1 ). In the 1980s, the U.S. adult was reported to receive about 20% of the World Health Organization (WHO) allowable daily intake of Cd from the consumption of grain and cereal products [8] .Cadmium enters plants by the soil solution. In plants, Cd accumulation in the roots was increased with high rhizosphere Cd concentrations [9] .Cadmium could decrease the transfer and absorption of essential substances by plants, including wheat and barley.…”