What aspect must be ensured for samples before transportation?

For samples being transported, it is crucial that they are appropriately preserved. Preservation prevents changes in the composition of the sample that can occur due to environmental factors, such as temperature fluctuations, exposure to light, or chemical interactions. By using suitable preservation methods—such as refrigeration, addition of preservatives, or maintaining pH levels—the integrity of the sample is maintained, ensuring that the analytical results are reliable and representative of the original conditions when the sample was collected.

While proper labeling is important for identification and tracking, and specific temperature requirements may apply to certain types of samples, preservation is the primary concern to maintain the sample's validity during transport. The option regarding bulk transportation does not contribute to the integrity of the samples and may complicate issues related to contamination or sample integrity. Therefore, appropriate preservation stands out as the most critical requirement before transporting samples for environmental compliance testing.