A variety of different methods are currently in use for preservation of dreissenid mussel detection field samples. Previous research has demonstrated that proper preservation of these samples is critical for subsequent detection of both veliger shells by microscopy and mussel-specific DNA by polymerase chain reaction (PCR). The USBR mussel detection laboratory in Denver, CO recommends the usage of isopropyl alcohol (isopropanol/rubbing alcohol) and baking soda (sodium bicarbonate) for preservation of field collected water samples. Isopropyl alcohol provides preservation of tissues and DNA, allowing for detection by PCR. Baking soda buffers against acidification of the sample, thereby preserving the calcareous shells of veligers and allowing detection by cross polarized light microscopy (CPLM). Isopropyl alcohol and baking soda where selected as the preservatives of choice because they are inexpensive and readily obtained even in remote sampling locations. A study by the Western Regional Panel subcommittee on mussel field sampling methods has evidenced that other laboratories vary in the preservation methods they request for field samples. For alcohol preservation, some laboratories request the use of absolute or reagent grade ethyl alcohol (ethanol). This choice is based on the general belief that ethyl alcohol is a superior preservative of DNA integrity, as compared to isopropyl alcohol. However, research on this topic is scant and studies of other tissue types have suggested that isopropyl alcohol and ethyl alcohol may be equally effective for short term preservation. There is also concern that rubbing alcohol obtained from retail stores may contain additives which could inhibit extraction and recovery of DNA from samples. With regards to practicality for field sampling, while absolute or reagent grade ethyl alcohol is frequently used for sample preservation in research laboratories, it is significantly more expensive.
