Threshold Limit Values derivation

A commercially interesting low calorie fat has been produced from sucrose. Proctor Gamble has patented a mixture of penta- to octafatty acid ester derivatives of sucrose under the brand name Olestra. It was approved by the FDA in January 1996 for use as up to 100% replacement for the oil used in preparing savory snacks and biscuits. Olestra, a viscous, bland-tasting Hquid insoluble in water, has an appearance and color similar to refined edible vegetable oils. It is basically inert from a toxicity point of view as it is not metabolized or absorbed. It absorbs cholesterol (low density Hpoprotein) and removes certain fat-soluble vitamins (A, D, E, and K). Hence, Olestra has to be supplemented with these vitamins. No standard LD q tests have been performed on Olestra however, several chronic and subchronic studies were performed at levels of 15% in the diet, and no evidence of toxicity was found. No threshold limit value (TLV), expressed as a maximum exposure per m of air, has been estabhshed, but it is estimated to be similar to that of an inert hpid material at 5 mg/m. ... 

TLV-TWA is the Threshold Limit Value—time weighted average concentration for a conventional 8-hour workday and a 40-hour workweek, to which it is believed that nearly all workers may be repeatedly exposed, day after day, without adverse effect (ACGIH 2001). In general, TLV-TWA values are used to derive BEIs (Biological Exposure Indices). 

An example of a nonoccupational exposure is methanol, which is formed endogenously, probably as the result of the activities of intestinal flora or enzymatic processes. It is present in a number of consumer products. Methanol may be present in low concentrations in some foods, juices, and alcoholic beverages. Methanol can also be derived from the intestinal enzymatic hydrolysis of the artificial sweetener aspartame, which results in methanol absorption from the intestine (Butchko et al. 2002). It is estimated that a 355-mL serving of aspartame-sweetened beverages and of various fruit and tomato juices may contribute about 20-100 mg of dietary methanol (Butchko et al. 2002). For comparison purposes, exposure at the current Threshold Limit Value time-weighted average of methanol (262 mg/m3) would result in a daily dose of about 1,500 mg, assuming an 8-hour inhaled volume of 10 m3 of air and absorption of 57%. 

For occupational exposures, Permissible Exposure Levels (PELs), Threshold Limit, Values (TLVs), and NIOSH Recommended Exposure Levels (RELs) are developed. They represent dose levels that will not produce adverse health effects from repeated daily exposures in the workplace. The method used to derive them is conceptually the same. Safety factors are used to derive the PELs, TLVs, and RELs. 

Leung, H. W., and Paustenbach, D. J. (1988). Application of pharmacokinetics to derive biological exposure indexes from threshold limit values. Am Ind Hyg Assoc J 49, 445-450. 

The toxic threshold limit value as reported by Sax (Ref 3) ia ( pm in air or 750mg/m of air, and by Plunkett (Ref 8) is lOOppm and 375mg/m. Acute poisoning from the use of toluene is the result of a small amount of benz in commercial (coal-tar) derived toluene. Table 1 presents the effects of toluene vapor (Ref 4). Plunkett (Ref 8) reports that prolonged exposure to toluene vapor can result in permanent central nervous system changes such as cerebellar degeneration, tremulousness, ataxia, emotional lability and EEC changes... 

Generic Exposure Values (GEVs) are generic threshold values for occupational exposure (and derived dermal values) derived from OELs (Occupational Exposure Limits). The effects used to estimate GEVs are acute and repeated dose toxicity for a total of 63 organic and nonorganic substances, both volatile and nonvolatile. 

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