Subclinical neurotoxic lead effects: two-year follow-up studies with psychological test methods

Using a prospective, follow-up approach a group of storage battery plant workers was tested by means of a number of psychodiagnostic tests, as e.g., subtests of the WAIS and WMS, Bourdon-Wiersma test, Santa Ana test, before and two years after entering lead-works. Their performance was compared with that of an age-equivalent group of non-exposed controls. Blood lead levels of the lead group increased from an initial 15.3 +/- 6.7 micrograms/dl (Mean +/- SD) to a final 30.5 +/- 9.6 micrograms/dl after two years, whereas the corresponding PbB-value of the controls was 10.5 +/- 3.7 micrograms/dl and 10.3 +/- 4.0 micrograms/dl, respectively. In the primary psychological examination there were no detectable performance differences between the exposed and controls. Whereas the control group displayed pronounced performance improvement due to training for most of the tests over the two-year period, a sizeable portion of the exposed group exhibited even performance deterioration. Group-comparisons were tested by the non-parametric ch 2-test and two-sided Kolmogorov-Smirnov test. The most sensitive indicators of psychological impairment among the lead workers were Block Design test, Santa Ana coordination test and Digit Span test. It is concluded that the impairment of CNS function, as evidenced by differential test performance, was caused by lead exposure. No exact threshold for impaired performances could be estimated.