The frequency of zinc deficiency, copper toxicity and low zinc/copper in children with autism spectrum disorders (ASDs) may indicate decrement in metallothionein system functioning. A retrospective review of plasma zinc, serum copper and zinc/copper was performed on data from 230 children with autistic disorder, pervasive developmental disorder-NOS and Asperger's syndrome. The entire cohort's mean zinc level was 77.2 microg dl(-1), mean copper level was 131.5 microg dl(-1), and mean Zn/Cu was 0.608, which was below the 0.7 cut-off of the lowest 2.5% of healthy children. The plasma zinc/serum copper ratio may be a biomarker of heavy metal, particularly mercury, toxicity in children with ASDs.

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The financial assistance of the Analytical Division of the American Chemical Society through an award of a 1976-77 full year fellowship to L.M.U. is gratefully acknowledged. Research support provided by the State of New Jersey under provisions of the Independent Colleges and Universities Utilization Act is also gratefully acknowledged.

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EPA Methods 3060A (alkaline extraction) and 7196A (colorimetric measurement) currently constitute a pair of protocols for the measurement of Cr(VI) in environmental soil samples in EPA RCRA SW-846 Update III. To identify the sources of possible biases, we applied the newly developed Speciated Isotope Dilution Mass Spectrometry (SIDMS) as an alternative detection method to Method 7196A. SIDMS is capable of correcting for species transformation, while Method 7196A is not. In Method 3060A, soluble Cr(III) could be oxidized during extraction, resulting in positive errors of Cr(VI); Cr(VI) could be lost or reduced during neutralization, leading to negative errors of Cr(VI). When sand and soil extracts were analyzed, low recoveries were obtained with Method 7196A. However, SIDMS achieved approximately 100% recoveries. The influence of some soil matrix components on the detection of Cr(VI) using Method 7196A has been evaluated. As expected, reducing agents could cause low recoveries of Cr(VI). Surprisingly, we found that strong oxidizing agents could also result in low recoveries. We identify these method biases and discuss the mechanisms in this paper.