A reproducible approach to the reporting of organochlorine compounds in epidemiologic studies

A growing body of research indicates that the most biologically active PCB congeners and organochlorines are not the most abundant components in human and wildlife samples. As researchers attempt measurement on a wider pool o f less abundant compounds, they inevitably face quantification problems. To address this problem and enhance comparability across studies, we propose a standardized approach to report organochlorines that is based on a reprod ucible method to determine the limit of quantification (L-Q). Two statistic al methods are incorporated into our approach, one by Gibbons termed the Al ternative Minimum Level (AML), and one based on determining a region of sta ble relativestandard deviation in instrument response (RSD). We illustrate our approach using historical samples collected during the 1960s from a coh ort of pregnant women enrolled in the Child Health and Development Study. T he results are applicable to determining the L-Q of any method, and are of utmost importance to environmental scientists conducting trace organic anal yses of complex mixtures. Our results demonstrate that: (1) precision as me asured by RSD is the most important criterion in determining L-Q; (2) the A ML routinely isolates a region of constant RSD; and (3) the precision of th e instrument detector response as measured with pure standards locates the L-Q applicable for real samples - that is, the true limits of quantificatio n reside in the detector, not the matrix effects or analyte recoveries asso ciated with real samples. A corollary of these findings is that bias due to matrix effects and analyte recoveries can be assessed separately from prec ision and L(Q)determination. Previous approaches involved spiking matrix bl anks to determine L-Q, a problematic strategy for real world, complex matri ces. We have now validated the use of pure standards in L-Q determination, an approach that is practical and accessible to most analysts. (C) 2001 Els evier Science Ltd. All rights reserved.