**Table 1.**

**209**

samples.

**3.1 Planning**

*Considerations for Stability of Environmental Samples in Storage for Long-Term Studies*

The change in concentration over time that indicates significant degradation is often set to 5 or 10 percent, particularly for biological samples. This level is likely too stringent for environmental samples where, for instance, sample processing may itself introduce a reduction of 5 to 10 percent and, therefore, a decision crite-

environmental sample storage, we found very little documentation to support preservation of analytes during long-term storage. The findings of the literature review were disappointing in that many questions went mostly unanswered for

*• What are acceptable long term storage times for various sample types?*  Storage times in the identified studies varied from a few days up to five years. One study extended the storage study to 12 years for air samples [82]. For water, only a few published reports were found on storage stability over 6months, mostly on pesticide stability. These studies do not fully address the

*• What are acceptable long term storage conditions for various samples* 

*types?* Storage conditions in the identified studies included ambient or room temperature (generally around 20°C), refrigerator (4°C), freezer (−20°C), and/or cryogenic temperatures (−60–80°C). Environmental specimen banks store samples for 50–100 years in cryogenic conditions [79, 80, 87], but do not document the rationale for sample stability under these conditions and time periods. For longer-term storage, some researchers have extracted water contaminants through solid phase extraction (SPE) cartridges and stored frozen for up to a year. Interestingly, colder storage does not always equate to

We also reviewed standard analysis methods for the samples and analytes of interest in the NCS. We found that standard methods are generally focused on regulatory compliance and do not consider long term storage. For example, for ambient vapor and gas sampling, updated storage studies of SUMMA and whole air canisters

The overall objective of the planned NCS storage studies was to determine the stability of target analytes in NCS environmental samples stored in collection containers at specific storage conditions, including reconstitution after thawing and re-freezing of samples, as applicable. For instance, the objective of the tap water study was to evaluate the effect of prolonged storage at −20°C on the stability of the pesticide and pharmaceutical target analytes spiked in analyte-free water. The results of this study were to be used to extrapolate the observed changes in the target analyte concentrations to the stability of those compounds in the NCS study

The stability study plans included stability samples similar to environmental field samples, sample processing, analytes or classes of analytes of interest, and analysis methods. The in-depth literature review addressed the prevalence of

many sample matrices and analytes of interest, in particular:

compounds or tap water matrix [4, 7, 28, 73, 83–86].

less analyte degradation, as commonly assumed [74].

are needed (US EPA method allows storage of only 30days).

**3. NCS stability study experience**

Despite the widespread practice and numerous and strong benefits of long-term

*DOI: http://dx.doi.org/10.5772/intechopen.97445*

rion of 20 percent change is most often used.

*monitorin.*

*Summary of environmental sample stability studies identified in the literature by matrix and analytes.*

*Considerations for Stability of Environmental Samples in Storage for Long-Term Studies DOI: http://dx.doi.org/10.5772/intechopen.97445*

The change in concentration over time that indicates significant degradation is often set to 5 or 10 percent, particularly for biological samples. This level is likely too stringent for environmental samples where, for instance, sample processing may itself introduce a reduction of 5 to 10 percent and, therefore, a decision criterion of 20 percent change is most often used.

Despite the widespread practice and numerous and strong benefits of long-term environmental sample storage, we found very little documentation to support preservation of analytes during long-term storage. The findings of the literature review were disappointing in that many questions went mostly unanswered for many sample matrices and analytes of interest, in particular:


We also reviewed standard analysis methods for the samples and analytes of interest in the NCS. We found that standard methods are generally focused on regulatory compliance and do not consider long term storage. For example, for ambient vapor and gas sampling, updated storage studies of SUMMA and whole air canisters are needed (US EPA method allows storage of only 30days).
