RESUMEN
The increased export of terrestrial dissolved organic matter (terrDOM) to coastal marine ecosystems may affect local filter feeders and the local food web via the altered uptake of organic material and associated contaminants. To compare terrDOM to marine DOM (marDOM) as contaminant vectors to coastal biota, we exposed blue mussels (Mytilus sp.) to the different DOM types in combination with teflubenzuron, a widely applied lipophilic aquaculture medicine targeting salmon lice (Lepeophtheirus salmonis). A 16-day exposure of the blue mussels to DOM and teflubenzuron was followed by a depuration phase of 20 days without teflubenzuron. We calculated teflubenzuron adsorption rates and bioaccumulation factors (BAF) using a Bayesian model, expecting teflubenzuron uptake to be greater with terrDOM than marDOM due to the higher prevalence of large amphipathic humic acids in terrDOM. Humic acids have strong absorption properties and are able to envelope lipophilic molecules. Thus, humic acids can function as an efficient contaminant vector when taken up by filter feeders. Although there were varying degrees of overlap, the mussels tended to accumulate higher amounts of teflubenzuron in the DOM treatments than in the seawater control (bioaccumulation factor [BAF] in seawater: median 106 L/kg; 2.5 %-97.5 % percentile: 69-160 L/kg). Contrary to expectations, mussels exposed to marDOM showed a trend toward more bioaccumulation of teflubenzuron than those exposed to terrDOM (BAF marine 144 L/kg; 102-221 L/kg versus BAF terrestrial: 121 L/kg; 82-186 L/kg). The highest teflubenzuron accumulation was observed with the 50:50 mixture of marDOM and terrDOM (BAF mix: 165 L/kg; 117-244 L/kg). The slight difference in DOM-type accumulation rates observed in this experiment-especially the accumulation rate of terrDOM compared to that of the seawater-only treatment type-was not considered environmentally relevant. Further studies are necessary to see if the observed trends transfer to complex environmental systems.
RESUMEN
The standard Daphnia sp. acute toxicity test for assessing the adverse effects of chemicals on aquatic invertebrates stipulates the use of neonates that are ≤24 h old (hours post release [hpr]) at the start of the exposure. However, when one is assessing acute effects of chemicals interfering with endocrine relevant-processes such as molting, both age synchronization and absolute age can influence the test outcome, because the occurrence of molting and associated mortality is highly time specific. Hence, a 24-h age synchronization window may mask the real effects of these compounds. To explore the influence of age synchronization and absolute age in standard acute toxicity tests, we exposed D. magna from different synchronization windows and absolute ages (≤4, 4-8, 8-12, ≤12, and ≤24 hpr at the beginning of the exposure) to 0.5-12 µg/L of the chitin synthesis inhibitor (CSI) teflubenzuron (TEF) using the Organisation for Economic Co-operation and Development test guideline 202 (Daphnia sp. 48 h immobilization test). Our results show significant differences in 48-h median lethal concentrations between animals with a synchronization window of ≤4 hpr (2.9 µg/L) and longer synchronization windows such as ≤12 hpr (5.1 µg/L) and ≤24 hpr (16.8 µg/L). A concurrent decreasing trend in molting median effect concentrations was observed for the same synchronization windows: ≤4 hpr (4.0 µg/L), ≤12 hpr (5.9 µg/L), and ≤24 hpr (30.0 µg/L). Together, our results show that both synchronization and absolute age are determinant factors for the sensitivity of D. magna to TEF. A narrow synchronization window (e.g., ≤4 hpr) may provide a more conservative estimate of TEF toxicity and should be considered when one is performing standardized toxicity tests for molting-disrupting compounds such as TEF. Environ Toxicol Chem 2023;42:1806-1815. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
