Effect of age on acute toxicity of cadmium, copper, nickel, and zinc in individual‐metal exposures to Daphnia magna neonates

Abstract

In previous studies, variability was high among replicate acute cadmium (Cd) Daphnia magna lethality tests (e.g., >10-fold range of median effect concentrations [EC50s]), less among zinc (Zn) tests, and relatively low for copper (Cu) and nickel (Ni) tests. Although the US Environmental Protection Agency’s (USEPA’s) protocol includes starting toxicity tests with neonates less than 24 h old, the authors hypothesized that age-related differences in sensitivity to metals might occur even within that relatively narrow age range. Daphnia magna neonates were collected during 3 age windows (0–4 h, 10–14 h, and 20–24 h old) and immediately exposed to each of the 4 metals for 48 h using the standard USEPA protocol. In repeated sets of tests during different weeks, the Cd EC50 of the youngest neonates was approximately 10-fold greater than the EC50 of the oldest neonates (i.e., Cd was less toxic to the youngest neonates) and the EC50 of neonates aged 10 h to 14 h was intermediate. Age-related differences were negligible in Cu, Ni, and Zn tests. Therefore, variability in toxicity of Cd may partly be caused by temporal variability in neonate age at the start of toxicity tests. Decreasing the age range of D. magna used in toxicity tests could help to improve the accuracy and precision of toxicity models, particularly for metal mixtures.

Effects of plant oligosaccharides derived from dragon fruit on growth, reproduction and survival of freshwater crustaceanDaphnia magna

“…We also found that very high concentration of DFO caused some mortality in the early stage of Daphnia culture. High excessive concentration of oligosaccharide would affect the osmoregulation of Daphnia at an early stage because the early‐life stages of aquatic animals are the most sensitive stage in their life cycles (Bianchini & Wood, ; Noonak & Peerakietkhajorn, ; Traudt, Ranville, & Meyer, ).…”

Reducing the number of fish in regulatory bioconcentration testing: Identifying and overcoming the barriers to using the 1‐concentration approach

“…Because organisms of different developmental stages may differ in their sensitivity to a chemical, many regulatory agencies (USEPA 2002;OECD 2004) specify that acute toxicity tests should be started with D. magna younger than 1 day old. However, we have observed relatively high variability in the toxicity of Cd and Zn to D. magna neonates Traudt et al 2015) and have demonstrated that this variablity is at least partly caused by major changes in sensitivity to the metals even within their first day postbirth (Traudt et al 2016). This methodologically induced variability can have important consequences, especially for predictions of metal-mixture toxicity when using results from individual-metal tests.…”

Acute Toxicity of Ternary Cd–Cu–Ni and Cd–Ni–Zn Mixtures to Daphnia magna: Dominant Metal Pairs Change along a Concentration Gradient

“…Those EC50 values, slopes, and their standard errors were calculated from results of the individual-metal toxicity tests conducted concurrently with each ternary-metal toxicity test. Due to high age-dependent variability of EC50 values for D. magna neonates exposed to some of these metals, 18 it was important to calculate the predicted toxicity based on the individual-metal tests that had been conducted on the same day as a given mixture test (instead of consolidating all of the individual-metal data to obtain a central-tendency concentration–response curve for each metal).…”