Development of a Sublethal Chronic Toxicity Test for the Northern Trout Gudgeon, Mogurnda mogurnda, and Application to Uranium, Magnesium, and Manganese.

Many international guidance documents for deriving water quality guideline values recommend the use of chronic toxicity data. For the tropical fish northern trout gudgeon, Mogurnda mogurnda, 96-h acute and 28-d chronic toxicity tests have been developed, but both tests have drawbacks. The 96-h toxicity test is acute and has a lethal endpoint; hence it is not a preferred method for guideline value derivation. The 28-d method has a sublethal (growth) endpoint, but is highly resource intensive and is high risk in terms of not meeting quality control criteria. The present study aimed to determine the feasibility of a 7-d larval growth toxicity test as an alternative to the 96-h survival and 28-d growth tests. Once the method was successfully developed, derived toxicity estimates for uranium, magnesium, and manganese were compared with those for other endpoints and tests lengths within the literature. As a final validation of the 7-d method, the sensitivity of the 7-d growth endpoint was compared with those of 14-, 21-, and 28-d exposures. Fish growth rate, based on length, over 7 d was significantly more sensitive compared with existing acute toxicity endpoints for magnesium and manganese, and was similarly sensitive to existing chronic toxicity endpoints for uranium. For uranium, the sensitivity of the growth endpoint over the 4 exposure periods was similar, suggesting that 7 d as an exposure duration is sufficient to provide an indication of longer term chronic growth effects. The sensitivity of the 7-d method, across the 3 metals tested, highlights the benefit of utilizing the highly reliable short-term 7-d chronic toxicity test method in future toxicity testing using M. mogurnda. Environ Toxicol Chem 2021;40:1596-1605. © 2021 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2021 SETAC.

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

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 (SSDs) for deriving site-specific guideline values. However, revised guidance for the Australian and New Zealand Water Quality Guidelines advises that test durations for adult macroinvertebrates should be ≥14 d to be considered chronic. Hence, to strengthen the data set underpinning the site-specific guideline value for uranium (U) in Magela Creek, which receives water from the Ranger Uranium 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 because of 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 µg L-1 , confidence interval = 133-195; 9-d IC50 = 151 µg L-1 , confidence interval = 127-180; 14-d IC50 = 153 µg L-1 , confidence interval = 29-180). The present study provides evidence that test durations of <14 d are suitable for assessing chronic toxicity to U for this species and supports the use of the 4-d toxicity estimate in the SSD for U. Environ Toxicol Chem 2016;35:2851-2858. © 2016 Commonwealth of Australia.