Care should be taken in choosing preservatives. For example, Method 5035 notes that, “Soil samples that contain carbonate minerals (either from natural sources or applied as an amendment) may effervesce upon contact with the acidic preservative solution in the low concentration sample vial.” Therefore, calcareous soils that effervesce on contact with the preservative solution, which is intended for low-level samples, should be preserved using an alternative technique. As an alternative to chemical preservatives, several studies have shown that freezing of unpreserved soils, at -7 o C or less, is an effective means of slowing the biodegradation process. .
