Neuropsychological Effects from Solvent Exposure


Nancy A. Didriksen, Ph.D.
Richardson, TX

Organic solvents are one of the major classes of neurotoxic chemicals which adversely affect neuropsychological functioning. Personality and behavioral functioning is adversely affected as well, and may occur as a direct result of exposure, or secondary to the negative life changes resulting from exposure and subsequent illness. Deterioration may be gradual and often insidious.

Organic solvent exposure studies indicate various neuropsychological deficits, including reduced speed of thinking, impaired coordination, decreased concentration, memory, and vocabulary, in addition to psychiatric symptomology including anxiety, panic disorder, and psychosis. Organic solvents are suspected to be causative agents in senile dementia. The following classifications of solvent-exposed individuals were suggested at the World Health Organization (WHO) meeting on organic solvents in Copenhagen in 1985:

1. Affective Syndrome: neuropsychiatric symptoms reported, no objective findings, considered reversible.

2. Mild Chronic Toxic Encephalopathy: neuropsychiatric symptoms, impairments on objective assessment, uncertain reversibility.

3. Severe Chronic Toxic Encephalopathy: severe neuropsychiatric symptoms, impairments more pronounced on objective assessment, usually irreversible.

Examination of neuropsychological test results of 36 solvent-exposed patients referred for evaluation by physicians at the Environmental Health Center-Dallas indicated approximately 70 percent impairment in the higher-order or executive functions of new problem-solving, abstract-reasoning, concept formation, judgment, mental efficiency, and new learning ability as demonstrated by scores on the Halstead Category Test (average score, 62 errors), and on the Tactual Performance Test (average time, 16.04 minutes). Approximately 12 percent of patients tested scored within normal limits.

Impairment was not as severe on measures of visual tracking and scanning. Approximately 70 percent of patients scored within the normal or low-normal ranges on Trail Making Test Part A. Approximately 55 percent scored within the normal and low-normal ranges on Trail Making Test Part B, which requires greater mental flexibility.

The majority of patients (59 percent) scored in the mildly impaired range on the Halstead-Reitan Neuropsychological Test Battery and 15 percent in the moderately impaired range. Approximately 26 percent had General Neuropsychological Deficit Scale scores within normal limits and none scored in the severely impaired range.

Memory functioning was measured using the Wechsler Memory Scale-Revised. Mean scores on measures of memory functioning were below average for verbal memory, attention and concentration, and delayed memory for verbal and visual information. Greatest impairment was observed on measures of immediate verbal memory. The mean immediate visual memory score was slightly above average.

Three members of a family exposed to gasoline-contaminated well water containing primarily benzene, toluene, and xylene, were examined. The most significant negative effect of exposure appeared to occur in the 63-year-old male family member who demonstrated borderline performances in immediate and delayed verbal and visual memory, and severely impaired executive functioning. Overall, neurocognitive abilities appeared to fall in a moderately impaired range.

The 41-year-old male member of the family was evaluated in 1997 and reevaluated in 1998. He demonstrated significant improvement in general learning ability and range and richness of ideas and words and expression (WAIS-R Vocabulary) from initial evaluation, in addition to improved executive functioning from the low normal to the perfectly normal range on the Halstead Category Test. Memory functioning (verbal and visual, immediate and delayed) also improved from initial evaluation.

The 36-year-old female member of the family demonstrated generally low normal performances, overall. She appeared least impaired on measures of immediate visual memory, but demonstrated an inability to retrieve the information after a short delay.
All family members indicated higher levels of confusion, fatigue, anger, depression, and tension subsequent to toxic exposure, as measured by the Profile of Mood States. Reevaluation results of one family member indicated diminished levels of tension, depression, anger, fatigue, and confusion compared with initial evaluation results, but remaining greater than preexposure levels.

The neuropsychological effects of solvent exposure may be subtle or severe and appear to depend upon a variety of factors including frequency, intensity, and duration of exposure, age, educational level, and concomitant illnesses and/or neurotoxic exposures. Reevaluation of one member of the family approximately one year after initial evaluation clearly demonstrated improvement with avoidance of the contaminated well water. The possibility of permanent injury may be determined only by subsequent reevaluation. The positive effects of treatment, such as heat depuration therapy, and avoidance of toxic/neurotoxic substances may also be assessed by reevaluation after an appropriate period of time, usually 12 to 18 months.

Arlien-Soborg, P. (1992). Solvent neurotoxicity. Boca Raton: CRC Press.
Hartman, D. (1995). Neuropsychological toxicology. (2nd ed.) New York: Plenum.
Singer, R. (1990). Neurotoxicity guidebook. New York: Van Nostrand Reinhold.