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Increasing uranium exposure durations to the aquatic snail, Amerianna cumingi, does not result in lower toxicity estimates

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Reproductive inhibition (egg production) of the aquatic snail, Amerianna cumingi, over 4 d has been used to derive toxicity estimates for toxicants of concern in tropical Australia. Toxicity estimates from this test have been used as chronic data points in Species Sensitivity Distributions (SSD) for deriving site‐specific guideline values (GVs). However, revised guidance for the Australian and New Zealand Water Quality Guidelines advises that test durations for adult macro‐invertebrates should be ≥14 d to be considered chronic. Hence, to strengthen the dataset underpinning the site‐specific GV for uranium (U) in Magela Creek, which receives water from Ranger U mine in northern Australia, the toxicity of U to A. cumingi was compared after 4 d, 9 d and 14 d. Daily U concentrations were measured due to expected U loss during testing, providing extensive chemical analyses of the U exposure during the toxicity tests. Comparison of the U concentrations causing 50% reproductive inhibition (IC50) after 4 d, 9 d and 14 d, showed no difference in toxicity (4 d IC50 = 161 (confidence limits of 133–195) µg L‐1 U, 9 d IC50 = 151 (127–180) µg L‐1 U and 14 d IC50 = 153 (129–180) µg L‐1 U). This study provides evidence that test durations of <14 d are suitable for assessing chronic toxicity to U for this species, and also supports the use of the 4 d toxicity estimate in the SSD for U. This article is protected by copyright. All rights reserved

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