Perchlorate in human blood serum and plasma: Relationship to concentrations in saliva

The perchlorate anion (ClO4-,MW=99) is present in food, drinking water, groundwater, and surface waters. Exposure to perchlorate is of concern, due to the ability of the anion to disrupt the function of the thyroid gland, and affect the synthesis of thyroid hormones. In this study, liquid chromatography – tandem mass spectrometry (LC–MS/MS) method has been optimized to analyze for perchlorate in blood sera and plasma samples from 84 US donors. In addition, 15 volunteers provided saliva and serum samples concurrently, to enable assessment of the ratio of perchlorate in these two matrices. Recoveries of perchlorate from fortified blanks and from serum/plasma samples were between 92% and 97%. Replicate analysis of blood-matrix spikes had a relative standard deviation (RSD) of <3%, and the relative percent difference (RPD) of repeat analysis of samples was <4%. Perchlorate concentrations in serum and plasma ranged from below the limit of quantitation (0.05 ng mL−1) to a maximum of 7.7 ng mL−1. Perchlorate concentrations in serum and plasma were log-normally distributed. The mean and median concentrations of perchlorate in 84 serum and plasma samples were 0.32 and 0.17 ng mL−1, respectively. No significant difference existed in perchlorate concentrations between serum and plasma. Analysis of paired saliva and serum samples showed a significant positive correlation for log-normalized perchlorate concentrations (r2 = 0.60) and perchlorate concentrations themselves (r2 = 0.86). The mean saliva:serum concentration ratio of perchlorate was 14:1 (after exclusion of two pairs of outliers). This is the first report to provide measurement data for perchlorate in blood sera and plasma of populations in the US.