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Evaluation and improvements of a mayfly, Neocloeon (Centroptilum) triangulifer ?(Ephemeroptera: Baetidae) toxicity test method
Citation:
Lazorchak, Jim, H. Haring, K. Wyatt, W. Thoeny, S. DeCelles, J. Miller, A. Dickinson, T. Schmidt, D. Soucek, D. Walters, M. Raby, AND T. Watson-Leung. Evaluation and improvements of a mayfly, Neocloeon (Centroptilum) triangulifer ?(Ephemeroptera: Baetidae) toxicity test method. Ontario MOECC Webinar, Webinar, ON, CANADA, May 16 - 23, 2016.
Impact/Purpose:
This is an invited presentation for a Webinar Sponsored by the Ontario Ministry of the Environment and Climate Change as well as a Poster for SETAC Europe on the further development of a Mayfly toxicity test method that improves repeatability
Description:
A recently published test method for Neocloeon triangulifer assessed the sensitivities of larval mayflies to several reference toxicants (NaCl, KCl, and CuSO4). Subsequent exposures have shown discrepancies from those results previously reported. To identify potential sources of variability, the authors measured 7-day growth and survivorship in NaCl, using: (a) 1- vs. 3- vs. 5-day-old larvae, (b) 1-day-old larvae hatched from freshly collected eggs vs. eggs held in long-term storage at 4°C, and (c) 1-day-old larvae from four different laboratory cultures (two U.S. EPA, one USGS and one University of Illinois). Fifty percent lethal concentration (LC50, mg/L) and 25% inhibition concentration (IC25, µm) point estimates were used to quantify survival and growth, respectively. Statistically significant differences in survival were found amongst all cohorts via sensitivity of mayflies at differing test initiation ages (LC50=616.56, 989.43, 1667.24), with survivorship positively correlating to age. No significant differences in growth could be elucidated between different aged treatments. Survival and growth of fresh eggs (LC50=701.27, IC25=626.56) differed significantly from eggs stored at 4°C for either three (LC50=394.13, IC25=424.47) or five (LC50=424.18, IC25=361.28) months, though no significant differences were observed between stored cohorts. A comparison of fresh eggs from four different laboratory cultures showed no significant differences in survival or growth. Additional results will also be presented on KCl & CuSO4 using fresh eggs and 1 day old larvae as well as results of comparing fresh eggs vs 2 month old stored eggs at 10°C. To ensure consistent and sensitive test results we recommend continuing the use of 1-day-old larvae and freshly hatched eggs when using this species.