Table 1.
Toxic and nontoxic metals that may be detectable in yeast‐bioprocess feedstocks (see Table 4)
| Metal | Some possible valency states | Toxicity in the diet |
|---|---|---|
| Selenium | SeII/SeVI | Toxic at 500 μg day−1; essential at 50 μg day−1 so is a benemin metalloid (beneficial at minimal dose) |
| Iron | FeII/FeIII/FeV | Bioaccumulates |
| Copper | CuI/CuII | Bioaccumulates |
| Tin | SnII/SnIV | Limit of 5 ppm in canned foods |
| Barium | BaII | Very toxic |
| Aluminium | AlII | Accumulates in brain |
| Arsenic | AsIII/V | Biocumulative poison (AsIII) |
| Mercury | HgI/HgII | Destroys cysteine (thiol) enzymes |
| Cadmium | CdII | Destroys cysteine (thiol) enzymes |
| Antimony | SbIII/V/VI | Destroys cysteine (thiol) enzymes |
| Lead | PbII/IV | Enzyme inhibitor |
| Nickel | NiII/III/V | Skin irritant and nongenomic carcinogen |
| Silver | AgI/II | Mildly toxic |
| Beryllium | BeII | Toxic |
| Magnesium | MgII | Can compete with CaII |
| Strontium | SrII | Can compete with CaII |
| Lithium | LiI | Can antagonize Na+ |
| Plutonium | PuIV | Very toxic |
| Chromium | CrIII | All these metal ions are largely nontoxic in humans; but not necessarily so in bacteria of the nitrogen cycle (Butler 2002) |
| Zinc | ZnII | |
| Molybdenum | MoVI | |
| Cobalt | CoII | |
| Vanadium | VV | |
| Calcium | CaII | |
| Manganese | MnIV/MnVII |