Sessional Committee on Environment and Sustainable Development Written Submissions Received Volume 2 Issues associated with the progressive entry into the Northern Territory of Cane Toads October 2003
Tabled Paper 1123
Tabled Papers for 9th Assembly 2001 - 2005; Tabled papers for 9th Assembly 2001 - 2005; Tabled papers; ParliamentNT
Tabled by Delia Lawrie
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Written Submissions Power & Water Corporation Volume 2 Cane Toad Inquiry Report 129 RISK TO WATER QUALITY The presence of bufotoxin in water secreted by eggs, tadpoles and adult cone toads may pose a potential risk to water quality (Van Dam et al, 2002). However, only a limited amount of studies or research has been conducted in this field. Since the introduction of cane toads in Queensland, there have not been any water contamination or quality issues to drinking water supplies as a result of cane toad toxins till date (Clayton, Cairns Water, pers. comm., 2003). Most reports have been related to poisoning of poultry and pets as a result of drinking water from boreholes and water troughs contaminated by bufotoxin (Van Dam et al, 2002). This is because during breeding periods larval and adult toads die in these water bodies and release toxin upon death. Furthermore, rotting toad carcasses in water bodies contaminate the water with its subsequent release of cytolitic toxins (Freeland, 1984). The cause of death for most adult toads in boreholes, water troughs or irrigation canals is by drowning. Their limited capacity to jump or climb barriers and walls results in them being trapped and eventually drowning (Waiden, Environment Australia, pers. comm., 2003). Therefore it is unlikely for cane toads to be trapped and drowned in large dams and reservoirs where they have access to and from the water at all times. However, if they are trapped and drowned in large water bodies due to exceptional circumstances, toxin levels will be reduced considerably due to the large volume of water and sufficient mixing in the water source (Van Beurden, 1980). Therefore, smaller water holes and stagnant water are at potential risk from cone toad toxins compared to larger water bodies (Alford, James Cook University, pers. comm., 2003). In addition the threat cane toads pose to bore water supplies will depend on the maintenance and protection of the bore itself. If drinking water supply bores are well protected and managed, the effect cane toads will have on drinking water quality will be negligible (Clayton, Cairns Water, pers. comm., 2003). Toads and frogs have access to elevated tanks via pipes (Waiden, Environment Australia, pers. comm., 2003). However, water tanks can largely be protected from cane toads by maintaining frog flaps and ensuring that all hatches are sealed properly. Cane toads are known to be carriers of human strains of bacteria leg. salmonella as a result of consuming human faeces (Van Dam et al, 2002). Van Dam et al (2002) has identified this to be a potential health hazard especially in areas with poor sanitation and water services. However, only a limited amount of studies and research has been conducted to assess the health risks cane toads pose to humans through water consumption. Taylor et al (2000) indicated that salmonella identified in workers from a construction site in Central Queensland may have been a result of mice or toads in the water tank. However, this variety of salmonella could not be isolated in cane toads. Furthermore, the lack of protection of the tank resulted in this waterborne outbreak of salmonellae. O'Shea et al (1990) tested cane toads in Townsville region and found about 13% carrying salmonella species in their gut. If cane toads defecate in water sources there is a possibility for the water to be contaminated with salmonella (Speare, James Cook University, pers. comm., 2003). However there have been no record or studies showing the risk of Salmonella being present in water at a concentration sufficient to cause disease. Speare (2003) also indicates that this could be a significant risk to water supplies in remote Aboriginal outstations where there is inadequate maintenance and treatment of water before consumption. Barton (James Cook University, pers. comm, 2003) stated that there has been one record of cane toads acting as a carrier of nematode eggs through its faeces. However, the potential for nematode contamination in water through the environment (soil) is recorded to be much higher than through cane toads. Furthermore, most of the viruses carried by cane toads have been identified to be a risk to cold-blooded aquatic wildlife, such as the Bohle iridovirus which kills barramundi, and not to humans (Barton, James
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