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Decontamination Process Validation

Ensuring Representative Water Test Results

Why is it important to refrigerate water samples on their way back to the laboratory?
Sample refrigeration during transportation is crucial to maintain the sample integrity and to ensure that the test results are representative (i.e. the results are the same as what they were when sampled). ISO 5667-3:2018 Water Quality Sampling, states that the laboratory receiving the samples for many of the tests "examine the chilled samples collected within four hours of collection if stored at room temperature, or within 24 hours if stored at 2– 5°C." It is therefore critical that your water samples are returned to the laboratory within the correct temperature band and timescale to ensure compliance with the guidelines, but why are these in place?

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The principle is quite straightforward – at between 2°C and 5°C, most bacteria go into stasis, and neither replicate or die off meaning that water kept at this temperature will maintain its integrity until testing begins. Although logic may say that bacteria will multiply at higher temperatures (as is the case with food hygiene), where water samples are concerned the bacteria is more likely to die off due to lack of any nutrients to support them, therefore potentially leading to a false negative result as the bacteria present at sampling has potentially died off by the time the sample reaches the laboratory.

Water sample diagram

Even at low temperatures this can still happen gradually, hence the 24 hour time limit. Similarly, although cold does not kill a lot of common bacteria on food or water, if a sample is frozen or kept at elevated temperatures (for a significant period), some bacteria can be killed as the act of freezing/heating breaks down the cell membranes, potentially leading to false negative results being produced from your water samples.Therefore maintaining the sample temperature between 2°C and 5°C during transportation is crucial to the samples integrity and ultimately the results produced.

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Given the quite tight restrictions on time and temperature it is clearly important to be aware of how samples are returned to the laboratory (assuming they are not handed off in person within the 4 hour ‘room temperature’ limit).

The efficacy of different shipping solutions was a key part of quality control considerations when the Isopharm Laboratory was set up. Although we had been shipping chilled test soil for many years, gradual warming to room temperature during shipment was not an issue as the intent was simply to preserve the raw egg/blood mix rather than limit bacterial growth.

Click here for more information on the vagaries of test soil manufacture >

When the temperature of a polystyrene box filled with water ice packs was measured over the course of 24 hours, it was quite clear that this is not a viable solution for keeping samples between 2 and 5°C. In fact although test soil and the ice were cold, the air temperature of the box never even reached 5°C and the sample rapidly warmed once the ice pack melted over the course of a few hours. Given that water samples are often taken warm and would melt the ice packs even more rapidly, this is a major issue for sample integrity.

For more information on how we look after your samples click here >

Orange-Box

The solution Isopharm devised to ensure representative water test results from an environmental perspective is the ‘Orange Box’ – which is exclusive to Isopharm and is an integral part of our accredited water testing service. Our Orange Box provides a combination of significantly improved insulation instead of simple polystyrene, and non-water ice packs which rapidly freeze and thaw at a considerably reduced rate in comparison to the more conventional polystyrene/ ice pack combination used by other laboratories. The Orange Box effectively acts as a fridge, maintaining sample integrity for up to 5 days between 2 and 5°C, and up to 9 days between 2 and 8°C. This not only allows us to ship soil and surrogates to engineers in a fully controlled environment, but also means they can retain the box to use in shipping water samples back to Isopharm without needing to refreeze ice packs. It is also worth noting that the temperature of a warm sample also drops much quicker in the Orange Box than in a pack with water ice (which never achieves the required temperature).

The like for like comparison of sample temperatures can be seen here:

Water test results New