Unexplained effects of mixtures

As noted in the introduction, exposure to chemical mixtures can produce enhanced effects, low level reactions, and unpredicted points of attack. The toxicological literature has reported these but until recently was at a loss to offer an explanation. The following published studies are illustrative of how toxicologists viewed the unexpected effects of exposures to mixtures prior to 2003. 

Alessio reviewed the literature and reported on the exposure of workers to multiple solvents in the workplace. His study showed that exposures to some solvent mixtures resulted in the inhibition of the metabolism of the solvents, whereas exposures to other solvent mixtures enhanced the metabolism of the solvents. 17] No explanations of the effects noted were offered. 

Feron et al., studied the effects of mixtures administered at the no observed adverse effect level (NOAEL) and the minimum observed adverse effect level (MOAEL). Evidence of an increased hazard was found when combinations of chemicals were administered at the NOAEL of each of the components, despite the fact that exposures to the individual chemicals had no adverse effects. When mixtures were administered at the MOAEL levels of the individual components, some severe adverse effects were noted. 18  

Alexandersson et al. studied the effects of exposure of carpenters to formaldehyde, terpenes, and dust particles. The mean formaldehyde levels were far below the threshold value. The terpenes levels were very low and 

Formaldehyde exposure is not known to cause neurobehavioral symptoms or disturbed mental of neurologic function. Kilburn et al., however, found that exposure by hospital histology technicians to formaldehyde, xylene, and toluene produced such effectsJ2°l No attempt was made to explain these results. 

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