Effects of Dissolved Organic Carbon on Copper Toxicity to Embryos of Mytilus galloprovincialis as Measured by Diffusive Gradient in Thin Films

Abstract

Diffusive gradient in thin films (DGT) potentially better quantifies bioavailable copper (Cu) in seawater. Laboratory exposure of DGTs and Mytilus galloprovincialis embryos at varying concentrations of dissolved organic carbon and Cu were performed to resolve the degree to which mimicry of toxicity buffering occurs in passive sampler quantification. The results provide preliminary median effect concentrations (EC50s) ranging from 4.8 to 11.5 µg/L as CDGT Cu over the span of 0.896 to 8.36 mg/L DOC. Environ Toxicol Chem 2019;00:1‐6. Published 2019 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Toward Validation of Toxicological Interpretation of Diffusive Gradients in Thin Films in Marine Waters Impacted by Copper

“…Next, the percentage of normally developed larvae from the multiconcentration tests were used to calculate the EC50s of measured Cu DISS and C DGT Cu with the toxicity statistics program CETIS™ (Tidepool Scientific). The C DGT Cu EC50s were then assessed for agreement with the Strivens et al (2019b) model and integrated into the previous data set after acceptability, the null hypothesis being no significant difference between slopes or intercepts (α = 0.05). Regression analysis was used to model Cu EC50s, on the basis of DOC concentration, for site‐specific applications.…”

“…The need for a reliable passive sampling approach to Cu‐impacted waters, capable of mimicking bioavailability to the most sensitive saltwater organisms, is highlighted by recent efforts toward a biotic ligand model (Chadwick et al 2008; US Environmental Protection Agency 2016) and results from the understanding that ligand competition in marine waters modulates biotic uptake by encompassing >99% of dissolved Cu (Cu DISS ; Arnold et al 2005, 2006, 2010). The primary diffusive gradients in thin films (DGTs) passive sampling approach, which operationally measures trace concentrations integrated over time by chelation of free and weakly complexed transition metals (essentially measuring the free ion activity [Davison 2016]), has been demonstrated to more accurately represent the potential for biological effects resulting from Cu exposure (Strivens et al 2019b) and is therefore an enhanced option for assessment of protection goals.…”

“…The agarose crosslinked polyacrylamide (APA)/Chelex DGT configuration (Zhang and Davison 1995) functions in a manner that generally mimics larval‐stage uptake of bioavailable metals (Strivens et al 2019b), which are the basis for aquatic life criteria development (Stephan et al 1985; US Environmental Protection Agency 2016). Based on size discrimination, diffusion rates, and complexing ability (equilibrium constants and free energy–based dissociation rates), DGT retention of Cu will largely follow the order cupric ion > chlorides ~ fluorides > sulfates > carbonates > polysaccharides > amino acids > humic substances.…”

“…In addition, field trials have previously reported high precision, reproducibility, and reliability of DGT measurements in natural waters, over windows of 24 h to 14 d (Strivens et al 2019c). With this understanding, Strivens et al (2019b) modeled Mytilus galloprovincialis median effective concentrations (EC50s) as the concentration of Cu in solution (Sequim Bay seawater), as measured by DGT (C DGT Cu), versus dissolved organic carbon (DOC) concentrations.…”

“…The dose responses in Strivens et al (2019b) were reflective of the protective effects of allochthonous DOC derived from Suwannee River natural organic matter (SRNOM; International Humic Substances Society). The summary proposed a conservatively protective criterion maximum concentration (CMC), against which to interpret C DGT Cu, of 2.4 µg/L.…”