average zT value of 1.05 for p-type and 0.84 for n-type bismuth telluride alloys. Lanthanum telluride can be potentially used in deep space as a thermoelectric generator due to the huge temperature difference in space. The zT value reaches to a maximum of ~1.0 for a La3-xTe4 system with x near 0.2. This composition also allows other chemical substitution which may enhance the TE performance. The addition of Yb, for example, may increase the zT value from 1.0 to 1.2 at 1275K, which is greater than the current SiGe power system. Biological role Tellurium has no known biological function, although fungi can incorporate it in place of sulfur and selenium into amino acids such as telluro-cysteine and telluro-methionine. Organisms have shown a highly variable tolerance to tellurium compounds. Many bacteria, such as Pseudomonas aeruginosa, take up tellurite and reduce it to elemental tellurium, which accumulates and causes a characteristic and often dramatic darkening of cells. In yeast, this reduction is mediated by the sulfate assimilation pathway. Tellurium accumulation seems to account for a major part of the toxicity effects. Many organisms also metabolize tellurium partly to form dimethyl telluride, although dimethyl ditelluride is also formed by some species. Dimethyl telluride has been observed in hot springs at very low concentrations. Tellurite agar is used to identify members of the corynebacterium genus, most typically Corynebacterium diphtheriae, the pathogen responsible for diphtheria. Precautions Tellurium and tellurium compounds are considered to be mildly toxic and need to be handled with care, although acute poisoning is rare. Tellurium poisoning is particularly difficult to treat as many chelation agents used in the treatment of metal poisoning will increase the toxicity of tellurium. Tellurium is not reported to be carcinogenic. Humans exposed to as little as 0.01 mg/m3 or less in air exude a foul garlic-like odor known as "tellurium breath". This is caused by the body converting tellurium from any oxidation state to dimethyl telluride, (CH3)2Te. This is a volatile compound with a pungent garlic-like smell. Even though the metabolic pathways of tellurium are not known, it is generally assumed that they resemble those of the more extensively studied selenium because the final methylated metabolic products of the two elements are similar. People can be exposed to tellurium in the workplace by inhalation, ingestion, skin contact, and eye contact. The Occupational Safety and Health Administration (OSHA) limits (permissible exposure limit) tellurium exposure in the workplace