Neurobehavioural evaluation and kinetics of inhalation of constant or fluctuating toluene concentrations in human volunteers

Application of physiologically-based pharmacokinetic modeled toluene blood concentration in the assessment of short term exposure limits

Toluene is a volatile hydrocarbon with solvent applications in several industries. Acute neurological effects in workers exposed to toluene have been reported in various publications. To inform the basis for a toluene Short Term Exposure Limit (STEL), studies of toluene-exposed workers were modeled using customized exposure scenarios within an existing physiologically-based pharmacokinetic (PBPK) model to simulate blood concentrations during individual studies. Maximum simulated blood concentration ranged from 0.3 to 1.7 (mean = 0.74 mg/L, median = 0.73, upper 95th percentile = 1.07) at the studies identified No Observed Adverse Effect Concentration (NOAEC). Maximum simulated blood concentration ranged from 0.7 to 4.1 mg/L (mean = 1.81, median = 1.63, lower 95th percentile = 0.92) at the studies identified Lowest Observed Adverse Effect Concentration (LOAEC). The maximum blood concentration for a 100 ppm STEL-like simulation was 0.4 mg/L, at the lower end of the NOAEC range and below the 95th percentile of the LOAEC. Therefore, it appears that a STEL <100 ppm would be unnecessary to protect workers due to peak occupational exposures to toluene.

N,N-dimethylglycine prevents toluene-induced impairment in recognition memory and synaptic plasticity in mice

Toluene intoxication produces deleterious effects on cognitive function, which has been associated with the inhibition of N-methyl-d-aspartate receptor (NMDAR). The present study determined whether N,N-dimethylglycine (DMG), a nutrient supplement and a partial agonist for NMDAR glycine binding site, could counteract recognition memory deficits and hippocampal synaptic dysfunction after acute toluene exposure. Male ICR mice were treated with toluene (250-750 mg/kg) for monitoring the sociability and social novelty in three-chamber test and long-term potentiation (LTP) of hippocampal synaptic transmission. Moreover, the combined effects of DMG (30-100 mg/kg) pretreatment with toluene (750 mg/kg) on three-chamber test, novel location and object recognition test and synaptic function were determined. Toluene decreased the sociability, preference for social novelty, hippocampal synaptic transmission and LTP in a dose-dependent manner. DMG pretreatment significantly reduced the toluene-induced memory impairment in social recognition, object location and object recognition and synaptic dysfunction. Furthermore, NMDAR glycine binding site antagonist, 7-chlorokynurenic acid, abolished the protective effects of DMG. These results indicate that DMG could prevent toluene-induced recognition memory deficits and synaptic dysfunction and its beneficial effects might be associated with modulation of NMDAR. These findings suggest that DMG supplementation might be an effective approach to prevent memory problems for the workers at risk of high-level toluene exposure or toluene abusers.

Neurobehavioral Effects of Acute Exposure to Aromatic Hydrocarbons

This article reports the results of neurobehavioral tests on representative aromatic constituents, specifically C9 to C11 species. The testing evaluated effects in several domains including clinical effects, motor activity, functional observations, and visual discrimination performance. Exposures ranging from 600 to 5000 mg/m3, depending on the molecular weights of the specific aromatic constituents, produced minor, reversible effects on the central nervous system (CNS), particularly in the domains of gait and visual discrimination. There was little evidence of effects at lower exposure levels. There was some evidence of respiratory effects at 5000 mg/m3 in 1 study, and there were also minor changes in body weight and temperature. The CNS effects became less pronounced with repeated exposures, corresponding to lower concentrations in the brain of 1 representative substance, 1,2,4-trimethyl benzene (TMB). At high exposure levels, the alkyl benzenes apparently induced their own metabolism, increasing elimination rates.