The practical application of hot water to reduce the introduction and spread of aquatic invasive alien species

Methods to reduce the introduction and spread of Invasive Alien Species (IAS) are key to reducing the economic, environmental and social impacts of IAS. IAS propagules can be moved around accidentally on clothing and equipment used in agriculture, transport, trade and recreation. Campaigns to slow the spread of aquatic IAS encourage water users to check, clean and dry their equipment and clothes, using hot water during the cleaning process where feasible. The UK Check Clean Dry biosecurity campaign recommends immersion in hot water (45 °C) for 15 minutes, however, implementation time may be a barrier to adoption of biosecurity practices. Here we aim to refine the advice given and test the efficacy of hot water treatment in actual conditions, with a view to reduce the recommended time to clean equipment while still preventing spread. The effectiveness was tested for a range of temperature (40, 45, 50, 55 and 60 °C) and time (10 seconds, 1, 5, 10, 15 minutes) treatments in killing IAS propagules of two invasive aquatic animal species (Dreissena polymorpha, Dikerogammarus villosus) and two invasive aquatic plant species (Myriophyllum aquaticum, Crassula helmsii), which are of global/national importance. For both invasive animal species, 100% mortality was achieved at all temperature and time treatments. However, plant mortality was affected by both temperature and time, with higher mortality resulting from higher temperatures and exposure times. Immersion for the recommended 15 mins at 45 °C caused complete mortality of C. helmsii, but only 40% mortality of M. aquaticum. Immersion in water at 50 °C or higher led to 100% mortality for C. helmsii and 90% mortality for M. aquatium at shorter treatment durations of 5 or 10 mins. In addition, immersion in water at 60 °C caused 100% mortality after only 1 minute exposure. To ensure adoption and application of biosecurity practices, guidance should be simple, consistent and safe. For practical application in field we recommend, where feasible, immersion of equipment in water at 50 °C for a minimum of 5 minutes to achieve high mortality of IAS propagules.