Toluene threshold value

Electrochemical redox studies of electroactive species solubilized in the water core of reverse microemulsions of water, toluene, cosurfactant, and AOT [28,29] have illustrated a percolation phenomenon in faradaic electron transfer. This phenomenon was observed when the cosurfactant used was acrylamide or other primary amide [28,30]. The oxidation or reduction chemistry appeared to switch on when cosurfactant chemical potential was raised above a certain threshold value. This switching phenomenon was later confirmed to coincide with percolation in electrical conductivity [31], as suggested by earlier work from the group of Francoise Candau [32]. The explanations for this amide-cosurfactant-induced percolation center around increases in interfacial flexibility [32] and increased disorder in surfactant chain packing [33]. These increases in flexibility and disorder appear to lead to increased interdroplet attraction, coalescence, and cluster formation. 

Changes in odour and taste are frequently more irksome than minor health disorders. Industrial odour immissions by toluene, xylenes and styrene have been referred to earlier [42]. Odours from combustion processes, such as for example from diesel fuels, are unpleasant. Comparative odour threshold values have been given for benzene of 4.7 ppm, for toluene of 2.1 ppm, for xylene of 0.5 ppm, for chlorobenzene of 0.2 ppm, for styrene of 0.05 ppm, and for nitrobenzene of 0.005 ppm [11]. Slightly lower odour thresholds are reported by other scientists 0.9-1.6 ppm for benzene, 0.03-0.5 ppm for toluene, and 0.15-0.18 ppm for xylene [12]. In water, quantities higher than 6.8 mg/m naphthalene, 37 mg/m styrene and 140 mg/m ethylbenzene cause unpleasant odours [13]. The following compounds may cause... 

The ACGIH threshold limit value-time-weighted average (TLV-TWA) for p-tert-hutyl toluene is Ippm (6.1mg/m ). 

Benzene has a low threshold limit value or TLV. The time weighted average TLV (TWA) is the allowable exposure for an average 8 hr day or a 40 hr week. The short-term exposure limit TLV (STEL) is the maximum allowable exposure for any 15-min period. For benzene the TWA = 0.5 ppm and the STEL is 2.5 ppm, as given by the American Conference of Governmental Industrial Hygienists (ACGIH). This allowable exposure is much lower than those for toluene and xylene, probably because these latter two compounds have benzyl ic positions that are easily oxidized in vivo to compounds that can be eliminated from the body. 

The American Conference of Governmental Industrial Hygienists (ACGIH) (1997) has recommended 188 mg/m as the 8-h time-weighted average threshold limit value, with a skin notation, for occupational exposures to toluene in workplace air. Values of 100— 380mg/m3 are used as standards or guidelines in other countries (International Labour Office, 1991). 

Another physiological toxicokinetic model (Tardif et al., 1993b, 1997) has been used to predict potential interactions between, e.g., toluene, ethylbenzene and we/tr-xylene the model and experimental data from exposed volunteers indicate that no biologically significant changes in their toxicokinetics will occur if these three solvents are present in the air as a mixture within the permissible concentrations for mixtures (Tardif et al., 1997). A model approach also predicted that interactions between dichloromethane and toluene at their current threshold limit values are not relevant for humans (Pclekis Krishnan, 1997). 

Toluene (methylbenzene) does not possess the myelotoxic properties of benzene, nor has it been associated with leukemia. It is, however, a central nervous system depressant. See Table 57-1 for the threshold limit values. Exposure to 800 ppm can lead to severe fatigue and ataxia 10,000 ppm can produce rapid loss of consciousness. Chronic effects of long-term toluene exposure are unclear because human studies indicating behavioral effects usually concern exposures to several solvents, not toluene alone. In limited occupational studies, however, metabolic interactions and modification of toluene s effects have not been observed in workers also exposed to other solvents. 

In another study Slobodian et al. (57) found that the percolation threshold for electrical conductivity of MWCNT-PMMA composites depends on the solvent used. The lowest percolation threshold was achieved for toluene where percolation was found to be at 4 wt% of MWCNT, for chloroform at 7 wt% and for acetone at 10 wt%. The highest conductivity was obtained at 20 wt% of MWCNT at values around 4x 10 5 Sc nr1 for composite prepared from toluene solution. They observed that the Hansen solubility parameters of individual solvent play an important role in the dispersion of MWCNT in PMMA. 

The American Conference of Governmental Industrial Hygienists threshold limit value for toluene diisocyanate is 0.005 ppm. The reference exposure level for toluene diisocyanate is 0.01 ppb. 

Estimate the dilution ventilation required in an indoor work area where a toluene-containing adhesive is used at a rate of 3 gal/8-h workday. Assume that the specific gravity of toluene (C7Hg) is 0.87, that the adhesive contains 40vol% toluene, and that 100% of the toluene is evaporated into the room air at 20°C. The plant manager has specified that the concentration of toluene must not exceed 80% of its threshold limit value (TLV) of 100 ppm. 

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... 

Most of the selected female reproductive toxicology studies examined explicitly stated chemical exposure levels either as parts per million, stratifying as to number of days of exposure, or as estimates of the percentage of the threshold limit values. Medline, Toxline, and Dissertation Abstracts databases were utilized to search for all research papers published in any language from 1966 to 1996. In total, 559 studies were obtained from the literature search. Of these, only 21 studies explicitly stated some sort of exposure level for the various chemicals. These chemical exposure levels in the literature and subsequent pregnancy outcomes were compared to lOL chemical exposure indices. The following is an example of one of the many chemical exposures encountered, namely exposure to toluene. For other compounds, Table 20.3.5 contrasts values in the literature with lOL indices of chemical exposure. 

Lindbohm et al., " for two of four air measurements, reported concentrations of white spirit exceeded the Finnish Threshold Limit Value (150 ppm) during flie cleaning of the printing machine. Industrial hygiene measurements were performed in three of the five work places of the shoe workers. The concentration of toluene in air varied from 1 ppm to 33 ppm. Other solvents detected were acetone and hexane. In two of the fluee shoe factories from which industrial hygiene measurements were available, relatively high levels of hexane (33-56 ppm) were noted. 

Hohnberg et al. and Tikkanen considered workers substantially exposed if their estimated continuous exposure had been at least one-third of the current TLV concentration or if the estimated peak exposure had reached the TLV concentration. Similarly, Ng described high concentrations of toluene (mean 88, range 50-150 ppm) exceeding current standards. All these exposure levels for toluene exceed the current threshold limit value. lOL toluene exposure levels are considerably lower than any value reported in the literafrue. 

Self-diffusion coefficients for all chemical components in microemulsions may be determined by NMR pulse gradient spin echo experiments as exemplified by Lindman and coworkers [55-57]. Self-diffusion coefficients for toluene, water, acrylamide, and AOT in this aqueous acrylamide-AOT-toluene system are illustrated in Fig. 12 as a function of (J [58]. The self-diffusion coefficients for water, acrylamide, and AOT exhibit breakpoints near, but below the percolation threshold, in the neighborhood of 1.2-1.3% acrylamide. This breakpoint corresponds to the onset of percolation in electrical conductivity illustrated in Fig. 6 at 0- The AOT diffusion coefficients run parallel to those for acrylamide, but are offset to lower values. 

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