Case Studies Neurotoxic Chemical Mixtures

The case studies presented here are all from the published literature. In every study the neurotoxic effects found are related to exposures to chemical mixtures of lipophiles and hydrophiles that induced neurotoxic effects not anticipated from the individual chemicals. The Kovi/ values for each of the chemicals are given. If not listed in a column they follow the individual chemical names in parentheses. 

A 57-year-old man who had spent 41 years as a painter was disabled and forced to retire. He was diagnosed with chronic toxic encephalopathy. The man started work as a painter at the age of 16. He started experiencing impaired short-term memory function while in his forties. His condition progressed until he retired and his exposures to the paint solvents ceased. Following his retirement, his condition stabilized and even improved in some areas. Material safety data sheets provided by his employer indicated that this man had been exposed to lead, titanium dioxide, creosote, and the following volatile solvents  

As can be seen from the Kow values, this painter was exposed to mixtures of lipophiles and hydrophiles. His case history reveals that his exposures ranged from concentrations exceeding TLVs to very low levels of inhalation exposure. He was also dermally exposed, frequently having used naphtha to wash his hands after work. His exposures are typical of many painters and his neurotoxicological symptoms are consistent with those observed in other paintersJ87-89  

In a study of hospital histology technicians it was found that these workers had greater disturbances of memory, mood, equilibrium, and sleep and had greater frequencies of headaches than other unexposed clerical workers in the same hospitals. The chemicals they were exposed to included 

The histology technicians were regularly exposed to mixtures of formaldehyde toluene, and xylene and less frequently to ethanol, chloroform, and methyl methacrylate. All exposures were at levels below TLVs for the individual chemicals and below levels at which the neurotoxic effects that were observed are expected. All the mixtures to which the histology technicians were exposed contained at least one lipophile and one hydrophile. 

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Virtually aU human environmental exposures to toxic chemicals are to mixtures. This is particularly the case for exposures to pesticides, heavy metals, and organic solvents, known as neurotoxins. Despite this, relatively few studies have been carried out on the neurotoxic effects of chemical mixtures. This section addresses the results of these mixture studies. 

In this study, neurological symptoms, including memory loss and reduced olfaction in the printers were found to increase with increasing levels of exposure. It is interesting to note that all exposure levels were below TLVs. The neurotoxic effects are attributed to the mixture of lipophilic and hydrophilic chemicals. The results of this study concur with a neurotoxic exposure case involving a printer exposed to the same chemicals that I investigated, but have not to date been published. In that case, the exposure levels to which the printer was exposed were more than an order of magnitude below the TLVs of all the chemicals. 

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