A test of the additivity of acute toxicity of binary‐metal mixtures of ni with Cd, Cu, and Zn to Daphnia magna, using the inflection point of the concentration–response curves

Abstract

Mixtures of metals are often present in surface waters, leading to toxicity that is difficult to predict. To provide data for development of multimetal toxicity models, Daphnia magna neonates were exposed to individual metals (Cd, Cu, Ni, Zn) and to binary combinations of those metals in standard 48-h lethality tests conducted in US Environmental Protection Agency moderately hard reconstituted water with 3 mg dissolved organic carbon (DOC)/L added as Suwannee River fulvic acid. Toxicity tests were performed with mixtures of Ni and 1) Cd, which is considerably more toxic than Ni; 2) Cu, which is less toxic than Cd but more toxic than Ni; and 3) Zn, which has a toxicity threshold similar to Ni. For each combination of metals in the binary mixtures, the concentration of 1 metal was held constant while the second metal was varied through a series that ranged from nonlethal to lethal concentrations; then the roles of the metals were reversed. Inflection points of the concentration–response curves were compared to test for additivity of toxicity. Sublethal concentrations of Ni caused less-than-additive toxicity with Cd, slightly less-than-additive toxicity with Zn, and greater-than-additive toxicity with Cu. One explanation of these results might be competition among the metals for binding to biological ligands and/or dissolved organic matter. Therefore, models might have to incorporate sometimes competing chemical interactions to accurately predict metal-mixture toxicity.

Toxicity of Zinc Dissolved In Saigon River to the Tropical Micro-Crustacean Daphnia Lumholtzi

“…The values of 48h-LC 50 of D. magna and Ceriodaphnia.dubia to Zn were 928 and 102 -130 µg/L, respectively (Naddy et al, 2015;Traudt et al, 2016) at moderately hard water (in the test with D. magna) and hard water (in the test with C. dubia) revealed that D. lumholtzi was more sensitive to Zn than D. magna but less sensitivity to Zn than C. dubia. This record is in line with previous investigation revealing the high sensitivity of D. lumholtzi to trace metals (Dao et al, 2016).…”

“…Vardia et al (1998) and Chishty et al (2012) reported the 48h-LC 50 values of D. lumholtzi tested with Zn dissolved in tap water were 2290 and 2300 µg/L, respectively. The median effective (immobilized) concentration (48h-EC 50 ) values of four different metals (Cd, Cu, Ni, Zn) to Daphnia magna were much different and the toxicity order of those metals to the tested species was Cd > Cu > Zn > Ni (Traudt et al, 2016). Besides, Cu was more toxic than some other metals such as Ni, Zn and chromium (Cr) to the two cladocerans, Moina macropora and D. magna (Biesinger and Christensen, 1972;Wong, 1992).…”

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.…”

“…We previously exposed D. magna to binary and ternary mixtures of Cd, Cu, Ni, and Zn in 48-h, static, nonrenewal lethality tests following USEPA-recommended procedures Traudt et al 2015). We observed high variability in mortality in the binary and ternary mixtures that contained either Cd or Zn but relatively lower variability in mixtures containing Cu or Ni.…”

Age‐related differences in sensitivity to metals can matter for Daphnia magna neonates

“…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 (Meyer et al 2015; 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.…”