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Toxicity to other aquatic organisms

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The toxicity of different phosphates to the freshwater gastropod, Helisoma duryi, was studied by Bernhardt et al. (1985). The mortality of neonates and sublethal effects were reported for 3 nominal concentrations of phosphates (15, 150 and 1500 mg/l) and an exposure period of 4 weeks. 100% mortality of the neonates was obtained with 1500 mg/l after 7 days of exposure to pentasodium tripolyphosphate and tetrasodium pyrophosphate, and after 21 days of exposure to sodium orthophosphate.

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The increased neonatal mortality seen in Helisoma at all concentrations tested, as  well as the significant reduction in shell growth seen at 15 and 150 ppm would suggest that STPP can produce significant sub-lethal and lethal effects on mollusc populations. The result from this test is questionable as mollusc shells are made of calcium carbonate. STPP complexes calcium, and will thus reduce calcium availability in water. It is therefore to be expected that molluscs, in significant concentrations of STPP cannot manufacture shells, and consequently development is impacted. The observed effects may therefore not be due to STPP toxicity but to non availability of calcium, particularly as the mortality and shell growth experiments were carried out without the addition of extra calcium to the medium. This is not an effect which is expected to occur in the real environment, where STPP will already be complexed (e.g. to dirt in washing machine, minerals in sewage, minerals in surface waters) and is in any case unlikely to remove all available calcium from a natural environment. The results from this test should not therefore be used for assessment of aquatic toxicity

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