Assessing effects of dissolved organic carbon and water hardness on metal toxicity to Ceriodaphnia dubia using diffusive gradients in thin films (DGT)

• Published in: The Science of the total environment Vol. 697; no. C; p. 134107
• Main Authors: Paller, Michael H., Harmon, S. Michele, Knox, Anna Sophia, Kuhne, Wendy W., Halverson, Nancy V.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.12.2019; Elsevier
• Subjects: Animals; Cladocera - physiology; Copper; Diffusive gradients in thin films (DGT); Dissolved organic carbon; Metals - chemistry; Metals - toxicity; Speciation; Toxicity; Toxicity Tests; Water - chemistry; Water Pollutants, Chemical - chemistry; Water Pollutants, Chemical - toxicity; Zinc; Dissolved organic carbon; Copper; Toxicity; Zinc; Speciation; Diffusive gradients in thin films (DGT)
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.134107

We evaluated the ability of diffusive gradients in thin films (DGT) to assess the effects of water hardness and dissolved organic carbon (DOC consisting of humic acids) on Cu and Zn toxicity (i.e., 48 h LC50s) to Ceriodaphnia dubia. When DOC was high, Cu concentrations measured by DGT (DGT Cu) were significantly lower than Cu concentrations in water (dissolved Cu), and DGT LC50s were significantly lower than LC50s based on dissolved concentrations. When DOC was low, differences between dissolved Cu and DGT Cu were small, as were differences between dissolved LC50s and DGT LC50s. Differences between DGT and dissolved measurements of Zn were small compared with the differences observed for Cu, and DGT Zn LC50s were relatively similar to dissolved Zn LC50s. Humic acids formed strong organic-Cu complexes that were both inaccessible for biological uptake and excluded by DGT, which selected for free or weakly bound Cu. In contrast, Zn did not form strong complexes with DOC that greatly affected either toxicity or the measurement of Zn by DGT. The effects of hardness on DGT measurements of Cu and Zn were smaller and more complex than the effects of DOC. Large, statistically significant differences between DGT measurements of Cu in low and high DOC water accurately reflected the strong effects of DOC on Cu toxicity. However, the effects of DOC were inconsistent for Zn, and DGT provided less information about the toxic fraction of this metal. Dissolved organic carbon (DOC) had large effects on DGT measurements of Cu, but small effects on DGT measurements of Zn. This paralleled the large effects of DOC on Cu toxicity and small effects of DOC on Zn toxicity to Ceriodaphnia dubia. [Display omitted] •Humic acids formed complexes with Cu that were nontoxic and unmeasured by DGT.•Zn did not form organic complexes that greatly affected toxicity or DGT measurements.•DGT measurements did not fully reflect the effects of hardness on metal toxicity.•DGT can predict the toxic metal fraction when organics bind strongly with metals.