Which statement correctly characterizes the relationship between a QA/QC plan and chain-of-custody in environmental sampling?

• A. QA/QC and chain-of-custody are the same thing.
• B. QA/QC focuses on data quality and integrity; chain-of-custody tracks sample custody to support defensible results.
• C. Chain-of-custody replaces the need for QA/QC.
• D. QA/QC deals only with equipment maintenance.

Answer: (B)

The main idea here is that QA/QC and chain-of-custody serve different, complementary roles in making environmental data trustworthy. A QA/QC plan governs how data are generated and evaluated for quality—ensuring accuracy, precision, completeness, representativeness, and proper validation of methods. It covers practices like calibration, method blanks, performance checks, replicate analyses, and data review to confirm the results are reliable.

Chain-of-custody, on the other hand, tracks who handles each sample and when, from collection through transport, storage, analysis, and disposal. This creates a documented, unbroken record of sample possession and integrity, which is essential for defensible results and for preventing mislabeling, contamination, or tampering.

These functions are distinct yet work together: QA/QC makes the data trustworthy, while chain-of-custody ensures the samples analyzed are the ones collected and that their provenance is demonstrable. They are not the same thing, one does not replace the other, and QA/QC covers more than just equipment maintenance.