Elevated pH As a Disinfection Tool Against Three Invasive Mollusks of Concern

Global commerce and transportation has increased the risk of transporting invasive organisms from one region to another. Organisms that are easily transported on aquatic gear, on boats and in ship ballast include mollusks, because they can often survive adverse conditions, and long periods out of water. We are evaluating inexpensive and safe disinfection tools such as hydrated lime (calcium hydroxide: Ca(OH)₂) or sodium hydroxide (NaOH) to raise treatment waters to a elevated pH (11- 12). These tools may have widespread application as the pH can be rapidly reversed with aeration. We conducted a series of laboratory based, static exposure tests with three invasive mollusk species known to be resistant to many disinfection procedures: New Zealand mud snail (Potamopyrgus antipodarum ) (NZMS), quagga mussel (Dreissena bugensis), and Asian clam (Corbicula fluminea). Temperature of test system, salinity, as well as the test chemical  affected the time to mortality. Test organisms exposed to solutions of NaOH and Ca(OH)₂ of equal pH responded differently.  Mollusks exposed to Ca(OH)₂ died faster. Adult sized Asian clams were the most difficult to kill. Quagga mussel veligers were sensitive to both compounds, and veligers tested with Ca(OH)₂ at 15°C and 20°C showed 100% mortality after 6 and 8 min respectively. Veligers were killed rapidly (within 0.5 h) in exposures to NaOH at temperatures from 15°C to 20°C. Quagga mussels exposed to brackish water conditions (15 ppt) in combination with elevated pH had more rapid mortality than organisms tested in freshwater at the same pH. However, brackish water did not affect the response measured in NZMS. We are replicating our tests to determine the range of safety and options for scaled up experiments. These disinfection tools hold promise for use on large and small vessels, or as a rapid response tool for eradicating small established populations.