**4. Conclusions**

Collection and analysis of environmental samples for various analytes in largescale or longitudinal cohort studies is useful to investigate the contribution of the environment on health outcomes. Storing samples for long periods of time is necessary but expensive in these kinds of studies. Information about preserving sample quality and analyte stability in stored environmental samples is limited. Design and implementation of sample stability studies like those described here are recommended to ensure that samples are stored properly and generate reliable analytical results when required. Publication of environmental sample stability study results will likely provide valuable information to investigators who design and implement large-scale longitudinal environmental health studies.
