Correlated Ni, Cu, and Zn Sensitivities of 8 Freshwater Algal Species and Consequences for Low-Level Metal Mixture Effects

Metal Mixture Effects of Ni, Cu, and Zn in a Multispecies, Two-Trophic-Level Algal-Daphnid Microcosm Can Be Predicted From Single-Trophic-Level Effects: The Role of Indirect Toxicity

Effect assessments of metals are mostly based on single-metal, single-species tests, thereby ignoring metal-mixture effects and indirect effects through species interactions. We tested the combined effects of metal and species interactions in two-trophic algal-daphnid microcosms. Metal-mixture effects on daphnid communities may propagate from effects on the generally more sensitive algal communities. Four different algal communities (three species each), with and without addition of the same daphnid community (three species) were exposed to single metals and one metal mixture (17:17:51 µg/L Ni:Cu:Zn). Daphnid densities were negatively affected by metals in the two-trophic test, the magnitude of which depended on the algal community composition. Algal densities were overall positively affected by the metals in the two-trophic test but negatively in the single-trophic test, illustrating an indirect positive effect in the two-trophic system due to a reduced grazing pressure. Metal effects on daphnid communities in the two-trophic test (day 21) were correlated with metal effects on the single-trophic-level algal communities during exponential growth (R2 = 0.55, p = 0.0011). This finding suggests that metal effects propagate across trophic levels due to a reduced food quantity. However, the indirect positive effects on algal densities, resulting in abundant food quantity, suggests that metal effects can also propagate to daphnids due to a reduced food quality (not measured directly). Metal-mixture interactions on daphnid densities varied during exposure, but were additive or antagonistic relative to independent action when final daphnid densities were considered (day 56). This suggests stronger indirect effects of the mixture compared with the single metals. Overall, our study highlights the dynamic aspect of community-level effects, which empirical reference models such as independent action or concentration addition cannot predict. Environ Toxicol Chem 2024;43:2350-2364. © 2024 SETAC.

Extrapolating Metal (Cu, Ni, Zn) Toxicity from Individuals to Populations Across Daphnia Species Using Mechanistic Models: The Roles of Uncertainty Propagation and Combined Physiological Modes of Action

Mechanistic effect modeling is a promising tool to improve the ecological realism of environmental risk assessment. An open question for the mechanistic modeling of metal toxicity is whether the same physiological mode of action (PMoA) could be assumed for closely related species. The implications of various modeling choices, such as the use of parameter point estimates and assumption of simplistic toxicodynamic models, are largely unexplored. We conducted life-table experiments with Daphnia longispina, Daphnia magna, and Daphnia pulex exposed to the single metals Cu, Ni, and Zn, and calibrated toxicokinetic-toxicodynamic (TKTD) models based on dynamic energy budget theory. We developed TKTD models with single and combined PMoAs to compare their goodness-of-fit and predicted population-level sensitivity. We identified the PMoA reproduction efficiency as most probable in all species for Ni and Zn, but not for Cu, and found that combined-PMoA models predicted higher population-level sensitivity than single-PMoA models, which was related to the predicted individual-level sensitivity, rather than to mechanistic differences between models. Using point estimates of parameters, instead of sampling from the probability distributions of parameters, could also lead to differences in the predicted population-level sensitivity. According to model predictions, apical chronic endpoints (cumulative reproduction, survival) are conservative for single-metal population effects across metals and species. We conclude that the assumption of an identical PMoA for different species of Daphnia could be justified for Ni and Zn, but not for Cu. Single-PMoA models are more appropriate than combined-PMoA models from a model selection perspective, but propagation of the associated uncertainty should be considered. More accurate predictions of effects at low concentrations may nevertheless motivate the use of combined-PMoA models. Environ Toxicol Chem 2024;43:338-358. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Investigation of heavy metals in tissues and habitats of three edible frogs from Türkiye

The soil, water, and organisms have been contaminated by heavy metals due to human activities and industrialization, which has produced a major environmental problem that has a deleterious effect on human health and food quality. Frogs, one of the good bioindicators for environmental pollution, are also among the alternative essential protein sources for humans. In Türkiye, three of these frogs are edible: Pelophylax ridibundus, Pelophylax bedriagae, and Pelophylax caralitanus, also known as Anatolian water frogs. Hence, to assess the possible health risks that might result from consuming frog legs in addition aquatic habitat of Anatolian water frogs, the water, sediment, and frog tissue samples (muscle and liver) were obtained from 11 different provinces covering all regions of Türkiye and analyzed to determine Cd, Cu, Cr, Zn, Pb, and As concentrations. The results revealed considerable variations in heavy metal concentrations among frog tissues, influenced by the sampling sites and species (ANOVA: p < 0.05). The Estimated Daily Intake (EDI) values, calculated based on the average serving size, were also lower than the Provisional Tolerable Daily Intake (PTDI) levels for adult consumers. Furthermore, the study computed the Target Hazard Quotient (THQ) values for heavy metals, all of which were below the critical value of 1, indicating that consuming the hind leg muscles from these frog species would not pose an adverse health risk for humans.

Metal Mixture Toxicity of Ni, Cu, and Zn in Freshwater Algal Communities and the Correlation of Single-Species Sensitivities Among Single Metals: A Comparative Analysis

The effects assessment of metals is mainly based on data of single metals on single species, thereby not accounting for effects of metal mixtures or effects of species interactions. Both of these effects were tested in combination, thereby hypothesizing that the sensitivity of a community to synergistic mixture toxicity depends on the correlation of single-species sensitivities among the single metals. Single-metal and metal-mixture effects were tested in full concentration-response experiments (fixed ray of 1:1:3 and 5:1:13 mass ratio Ni:Cu:Zn) on eight single freshwater algal species and 14 algal communities of four species each. The mean correlation of single-species median effect concentrations among the single metals (Ni-Cu, Cu-Zn, and Zn-Ni) for all species in a community (r ̅ ) ranged from -0.4 to 0.9 among the communities; most of these (12/14) were positive. Functional endpoints (total biomass) were overall less sensitive than structural endpoints (Bray-Curtis similarity index) for communities with positively correlated single-species sensitivities among the single metals (r ̅ > 0.33 ), suggesting that such correlations indicate functional redundancy under metal-mixture stress. Antagonistic metal-mixture interactions were predominantly found in single species, whereas metal-mixture interactions were antagonistic and surprisingly synergistic for the communities, irrespective of the reference mixture model used (concentration addition or independent action). The mixture interactions close to the carrying capacity (day 7) of communities gradually shifted from antagonism to more noninteractions with increasing correlation of single-species sensitivities among the single metals. Overall, this suggests that functional redundancy under mixed-metal stress comes at the cost of reduced biodiversity and that synergisms can emerge at the community level without any synergisms on the single-species level. Environ Toxicol Chem 2023;42:2666-2683. © 2023 SETAC.

WHAM-FTOXβ - An aquatic toxicity model based on intrinsic metal toxic potency and intrinsic species sensitivity

We developed a model that quantifies aquatic cationic toxicity by a combination of the intrinsic toxicities of metals and protons and the intrinsic sensitivities of the test species. It is based on the WHAM-F_TOX model, which combines the calculated binding of cations by the organism with toxicity coefficients (α_H, α_M) to estimate the variable F_TOX, a measure of toxic effect; the key parameter α_M,max (applying at infinite time) depends upon both the metal and the test species. In our new model, WHAM-F_TOXβ, values of α_M,max are given by the product α_M* × β, where α_M* has a single value for each metal, and β a single value for each species. To parameterise WHAM-F_TOXβ, we assembled a set of 2182 estimates of α_M,max obtained by applying the basic model to laboratory toxicity data for 76 different test species, covering 15 different metals, and including results for metal mixtures. Then we fitted the log₁₀α_M,max values with α_M* and β values (a total of 91 parameters). The resulting model accounted for 72% of the variance in log₁₀α_M,max. The values of α_M* increased markedly as the chemical character of the metal changed from hard (average α_M* = 4.4) to intermediate (average α_M* = 25) to soft (average α_M* = 560). The values of log₁₀β were normally distributed, with a 5-95 percentile range of -0.73 to +0.56, corresponding to β values of 0.18 to 3.62. The WHAM-F_TOXβ model entails the assumption that test species exhibit common relative sensitivity, i.e. the ratio α_M,max / α_M* is constant across all metals. This was tested with data from studies in which the toxic responses of a single organism towards two or more metals had been measured (179 examples for the most-tested metals Ni, Cu, Zn, Ag, Cd, Pb), and statistically-significant (p < 0.003) results were obtained.

Single and combined effects of Zn and Al on photosystem II of the green microalgae Raphidocelis subcapitata assessed by pulse-amplitude modulated (PAM) fluorometry

Increasing metal concentrations in aquatic environments are mainly due to anthropogenic actions, which is a matter of concern for the biodiversity of aquatic biota. It is known that metals coexist in environments, however environmental risk assessments do not usually take into account the effects of these mixtures. We aimed to test Zn and Al mixtures on the photosynthetic apparatus of a green microalga, for the first time, using PAM fluorometry. After 72 h exposure, single concentrations from 0.08 to 0.46 µM Zn and 22.24 to 37.06 µM Al affected the photosynthetic parameters of Raphidocelis subcapitata. Metals affected the efficiency of the oxygen-evolving complex - OEC (F₀/F_v), increasing it by 25% at 0.46 µM Zn and by 82% at 37.06 µM Al - concentrations where, 57% and 78% of growth inhibition occurred, respectively. We observed that the algal growth was more sensitive to infer Zn toxicity, while F₀/F_v was more affected by Al. Regarding quenching, there was an increase in passive energy dissipation ((Y(NO)) at 0.46 µM Zn, and we observed an increase in both regulated ((NPQ and Y(NPQ)) and non-regulated energy dissipation ((qN and (Y(NO)) at 37.06 µM Al. Our results showed synergism and antagonism at different concentrations in mixtures, the antagonism prevailing at higher metal concentrations and, in some cases, synergism at lower concentrations of Zn and Al. Since we observe more than additive and less than additive effects, it is of the utmost importance to take mixture toxicity tests into account when performing risk assessments on green algae.

Cu, Ni, and Zn effects on basic physiological and stress parameters of Raphidocelis subcapitata algae

The submitted work observed Cu, Ni, and Zn effects on selected physiological and stress parameters of the alga Raphidocelis (Pseudokirchneriella) subcapitata. In 96-h experiments, EC50 values for algal specific growth rates (SGR) inhibition in Cu, Ni, and Zn presence were estimated as 0.15, 0.50, and 0.20 mg l^-1. In addition to growth inhibition, the effect of metals at various concentrations on algal SGR was also monitored. While these experiments confirmed approximately the same toxicity of Zn and Cu on SGR, Ni toxicity on this parameter was observed as the lowest. In terms of the effect of metals on the level of selected photosynthetic pigments, chlorophyll a, chlorophyll b, and carotenoids, the following inhibition orders can be established: Zn > Cu > Ni, Ni > Cu > Zn, and Ni > Cu ≥ Zn, respectively. As a novelty of our research, we included monitoring and evaluation of the intensity of stress, which was the response of algal cells to the presence of Cu, Ni, and Zn, and its correlation with respect to production factors and metal accumulation in algal cells. As stress factors, thiol (-SH) group and TBARS (thiobarbituric acid reactive substances) as significant indicators of lipid level peroxidation were determined. The content of -SH groups depended on the concentration of metal, and its level was the most stimulated by Zn, less by Cu and Ni. The TBARS content was 2 to 5 times higher in Cu than in Zn or Ni presence. In the presence of Zn and Ni, TBARS content reached approximately the same levels. For this parameter, the following rank order can be arranged: Cu >> Ni ≥ Zn. While Cu and Ni accumulation in R. subcapitata was confirmed, Zn accumulation was not determined or was below the detectable limit. Regression analyses revealed significant positive correlation between Cu accumulation and TBARS while carotenoids as possible antioxidants confirmed with TBARS mostly negative correlations.