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Donald Smith,¹ Mauricio Hernandez-Avila,² Martha Maria Téllez-Rojo,² Adriana Mercado,² and Howard Hu^3,4

¹Environmental Toxicology, University of California, Santa Cruz, California, USA; ²Centro de Investigaciones en Salud Poblacional, Instituto Nacional de Salud Pública, Cuernavaca, Morelos, Mexico; ³Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA; ⁴Occupational Health Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA

Abstract

Studies have suggested that plasma lead levels may better reflect the toxicologically labile fraction of circulatory Pb that is more freely available for exchange with target tissues than do Pb levels in whole blood. Studies have also reported an apparent severalfold variation in the relative partitioning of Pb between whole blood and plasma (or serum) for a given whole-blood Pb level. This may reflect inherent differences in the plasma Pb/whole blood Pb partitioning among individuals and/or methodologic challenges associated with the collection and analyses of samples that generally contain < 1-2 ng total Pb. Here, we conducted a longitudinal assessment of the relationship between Pb in whole blood and plasma in environmentally exposed reproductive-age women (n = 63) living in Mexico City, Mexico. We collected whole blood and plasma samples using trace metal clean techniques and analyzed them for Pb using high-resolution inductively coupled plasma mass spectrometry. A subset of subjects provided repeated blood samples weekly for 4 consecutive weeks (n = 17 subjects) or every 1-2 months over a 9-month period (n = 14 subjects) . Plasma Pb concentration was significantly positively associated with whole-blood Pb in a curvilinear fashion over the range of blood Pb values observed here (2.13-39.7 µg/dL) . This relationship was best described by the function Plasma Pb = e^{(-2.392 + 0.0898 blood Pb)} , where SE_coefficient = 0.0054, SE_constant = 0.063 (n = 63 subjects, n = 141 observations) . Results from the short- and long-term repeated collection subjects indicated that the within- and between-subject variance components were not significantly different between the two subsets of subjects. The between-subjects component accounts for 78% of the variance in plasma Pb levels, while the residual variance (22%) may be attributed to other unmeasured factors. Collectively, this study demonstrates that plasma Pb measurements may be applied to general clinical settings, provided that established trace metal clean techniques are adopted. This study also shows that the relative (%) partitioning of whole-blood Pb in plasma naturally varies by a factor of about 2-4-fold among subjects at a given blood Pb level. Because Pb in the plasma is considered to more closely represent the fraction of Pb in the circulation that is readily exchanged with peripheral target tissues (e.g., brain, kidney, skeleton) , the routine assessment of plasma Pb may provide a more meaningful measure of toxicologically available Pb. Key words: blood, human, ICP-MS, lead, plasma. Environ Health Perspect 110:263-268 (2002) . [Online 12 February 2002]

http://ehpnet1.niehs.nih.gov/docs/2002/110p263-268smith/ abstract.html

Address correspondence to D. Smith, Environmental Toxicology, University of California, Santa Cruz, California 95064, USA. Telephone: (831) 459-5041. Fax: (831) 459-3524. E-mail: smith@etox.ucsc.edu

We thank C. Seaton, D. Woolard, and S. Wallace for their expert analytical assistance and M.J.R. Perez, M.G.S. Gomez, M.L.S. Aguirre, P.R. Lopez, Z.L.F. Velazquez, and E. Alquicira for the collection of samples. We also thank all of the study participants for their involvement in this research.

Support for this study was provided by the March of Dimes ; the National Institute of Environmental Health Sciences [grants R01ES07821, P42 ES-05947 Project 1 (with funding from the U.S. Environmental Protection Agency) , and NIEHS center grant 2 P30 ES 00002] ; Consejo National de Ciencia y Tecnologia (CONACyT) grant 4150 M9405, and CONSERVA, Department of Federal District, Mexico.

Received 12 April 2001 ; accepted 7 September 2001.