[Psychomotor responses under standardized trichloroethylene load (author's transl)]

Psychomotor performance and subjective symptoms at low level toluene exposure

OBJECTIVES

Possible effects of long term occupational exposure to toluene below the level of 100 ppm on psychomotor performance and subjective symptoms were investigated in a cross sectional approach.

METHODS

From German rotogravure printing plants 278 male workers, mean age 39.8 years, mean duration of employment 14.9 years, were examined. A mean lifetime weighted average exposure (LWAE) of 45.1 ppm toluene in ambient air was found for 154 exposed workers (rotogravure printing area), with a mean current exposure of 24.7 ppm. The corresponding data for a second group of 124 workers with very low exposure (endprocessing area) had LWAE of 9.3 ppm and a current exposure of 3.3 ppm toluene. Psychomotor performance (steadiness, line tracing, aiming, tapping, and peg board) and subjective symptoms were examined.

RESULTS

No significant differences between the two exposure groups were found by analysis of variance (ANOVA). By stepwise linear regression analyses there were weak associations of LWAE with one performance variable and two symptoms scales, but the results were not significant after correction for the alpha error. Psychomotor performance was mostly affected by age (maximum explained variance up to 13%), and handedness (up to 9%), whereas subjective symptoms are mostly affected by anxiety (up to 38%).

CONCLUSIONS

The weak associations between long term exposure to toluene should be used to indicate further longitudinal investigations. The results of this cross sectional study show no obvious dose response relation for psychomotor functions and subjective symptoms among workers exposed to toluene at a current exposure level of 1-88 ppm.

Short duration exposures to organic solvents: the relationship between neurobehavioral test results and other indicators

Short duration exposure to solvents at even low concentrations can induce signs of mild toxicity such as mucous membrane irritation, tearing, nasal irritation, headache, and nausea. These irritant effects are often used as warning properties for potential solvent toxicities and have frequently been classified in the literature as pre-narcotic effects. With higher exposures the toxic effects are more pronounced and can include intoxication, incoordination, exhilaration, sleepiness, stupor, and the beginning stages of anesthesia. Collectively these effects are taken as indicators of narcosis. Offering recommendations for safe exposure limits for these shorter term exposures is made difficult because, (1) the mild toxic effects are often reported subjectively and tolerance usually develops, (2) the solvent concentration(s) cannot be documented in all cases, and (3) the effects are reversible when individuals are removed from exposure. Laboratory experiments involving controlled exposures to solvents using neurobehavioral performance tests represent one form of investigation that can provide meaningful information in this instance. The results can be viewed in two ways with reference to issues of safe exposure limits. One is to ensure that performance functions that can compromise safety are not affected by the exposure limits prescribed. The second is to consider performance changes due to short-term exposures as possible precursors of similar but more severe effects given longer term exposures. Thus, setting exposure limits to protect against these performance changes could possibly prevent the development of more serious cases of chronic solvent neurotoxicity. This paper compares solvent concentrations from short-duration exposure studies using neurobehavioral tests with the concentrations producing irritant and narcotic effects, as documented by the two main standards recommending bodies, the National Institute for Occupational Safety and Health and the American Conference of Governmental Industrial Hygienists. Comparisons are also made with the regulatory exposure limits established by the Occupational Safety and Health Administration. In general, the neurobehavioral changes which occur following short-duration exposures are reported at concentrations between those which produce irritant effects and narcosis. For the chemicals which have been tested, the performance changes measured by the present day neurobehavioral tests in use rarely occur at or below those limits recommended by the standards recommending bodies.

Pharmacokinetics, pharmacodynamics and aspects of neurotoxic effects of four inhaled aliphatic chlorohydrocarbon solvents as relevant in man

Intermittent inhalation exposure of adult male rats to dichloromethane, trichloroethylene, 1,1,1-trichloroethane, perchloroethylene or to a combination of trichloroethylene and 1,1,1-trichloroethane for 5 days, for 6 h daily, induced significantly different accumulations of solvent molecules in the body. Adipose tissue served as a storage site for these solvents. The fat-stored molecules were not totally mobilized during the intermissions in exposure. Co-exposure of trichloroethylene and 1,1,1-trichloroethane induced higher accumulations than those induced by exposure to a single solvent in both the body and the brain. This increase in the accumulation of trichloroethylene might be due to competition with 1,1,1-trichloroethane for a binding site in the oxidative enzyme complex. Behavioural and neurochemical effects on trichloroethylene and dichloromethane exposure may be due to the formation of reactive metabolites. Experiments with 1,1,1-trichloroethane singly or in combination with trichloroethylene showed no observable behavioural effects. Perchloroethylene-induced effects were similarly small although, it caused the highest body concentration detected in these experiments. The metabolic activation of solvent molecules appears to also be a significant factor in neurotoxicity. Therefore biochemical interactions of agents occurring simultaneously in the environment, merit further consideration.

The effect of trichloroethylene on some serum-enzymes, on the cytoenzymological activity in leucocytes, and on the acid-base equilibrium

Twenty male volunteers were exposed to 95 ppm trichloroethylene for 4 h. Immediately before and aftere xposure and 4 h and 20 h after cessation, some serum-enzymes, the cytoenzymological activity of the alkaline and acid phosphatases and the naphthol-AS-D-esterase in neutrophil granulocytes and the acid-base equilibrium were investigated. Compared with the control experiment, the activities of the three neutrophil enzymes increased during trichloroethylene exposure with high significance. No significant changes of the serum-enzymes and the acid-base equilibrium could be found.

Biochemical and toxicological effects of combined exposure to 1,1,1-trichloroethane and trichloroethylene on rat liver and brain

1. Inhalation exposure of adult male rats to a mixture of 1,1,1-trichloroethane (500 p.p.m.) and trichloroethylene (200 p.p.m.) for four days 6 h daily resulted in an accumulation of 1,1,1-trichloroethane in perirenal fat. Further exposure on the fifth day caused a rapid increase in various organ contents of both solvents with secondary depression of brain RNA. 2. The four-day exposure doubled the RNA content of liver and caused a slight decline in the concentrations of glutathione in liver. 3. The amount of cytochrome P-450 in liver was increased, as well as the overall mono-oxygenase activity, measured with styrene as substrate. During continuing treatment on the fifth day, styrene mono-oxygenase activity decreased, the activity after 6 h being only about 50% of that at the beginning of the fifth day of exposure. 4. UDP-glucuronosyl transferase activity (measured in digitonin-activated microsomes) was doubled by the four-day combined exposure to 1,1,1-trichloroethane and trichloroethylene. 5. The changes during the fifth day of exposure, e.g. rapid increase in the concentrations of solvents in organs, the detection of trichloroethylene in tissues and depression of mono-oxygenase activity, obviously also occurred during the exposures on days 1 to 4 and reverted during each post-exposure period.

Trichloroethylene and 1,1,1-trichloroethane: effects on brain and liver after five days intermittent inhalation

The inhalation exposure of adult male rats to 7.9 mumol/l (200 ppm) of trichloroethylene for 4 days 6 h each day led to an accumulation of the solvent in the perirenal fat 17 h after the last exposure. Exposures to 20 mumol/l (500 ppm) of 1,1,1-trichloroethane caused similar accumulation. The latter rats presented no changes in their behaviour in an open-field test whereas the motor behaviour of the animals exposed to trichloroethylene was more active in comparison to controls 1 h after the exposure on the 4th day. Trace effects of trichloroethylene on emotional behaviour of the same rats could be seen 17 h after the last exposure. Further exposures on the 5th day increased brain, liver, lung and blood contents of trichlorethylene and 1,1,1-trichloroethane. A slight decrease in brain RNA content was found in the 1,1,1-trichloroethane exposed rats while RNA decreased significantly after the fifth day of trichloroethylene inhalation. The exposure to 1,1,1-trichloroethane on the 5th day depressed also the microsomal cytochrome P-450 content in liver of rats whereas trichloroethylene increased the hemochrome content slightly at the same time.

Some aspects of the mechanisms by which industrial solvents produce neurotoxic effects

A Short Review is given of the biochemical neurotoxic mechanisms of common industrial solvents of various structures. The acute effects of organic solvents may be caused by their direct action on the nerve cell membrane and energy metabolism, whereas chronic neurotoxic effects may be explained by the formation of chemically and biologically reactive intermediates. The stability of the toxic metabolites appears to correlate with the development of neuropathy although this is structuredependent. The role of reactive intermediates is also emphasized by the potentiating effect of the induction of the cytochrome P-450 complex.