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

Abstract

Predicting metal sensitivities and metal mixture interactions for species within each trophic level is essential to understand the effects of metals at the ecosystem level. The present study was set up to explore the correlations of metal sensitivities among species and if these sensitivities or metal mixture interactions are related to growth or morphological traits. The toxicity of Ni, Cu, and Zn on algal growth was tested for 8 freshwater algal species when dosed singly and in combinations in phosphorus-limiting static systems. The metal sensitivities on specific growth rate (10% effect concentrations expressed as free ion activities) varied 2 to 3 orders of magnitude among species depending on metal. These sensitivities were unrelated (p > 0.05) to their specific growth rate (0.7-1.8 d -1 ) or cell volume (10 0 -10 3 m 3 cell -1 ). Species-specific differences in one or more toxicokinetic and/or toxicodynamic (TKTD) processes are likely at the basis of this variation. The logtransformed metal sensitivities positively correlated (p < 0.1) among the species in all 3 binary combinations (Ni-Cu, Ni-Zn, and Cu-Zn), suggesting that species have correlated TKTD rates for these metals. Furthermore, they would also predict stronger effects of metal mixtures on algal community biodiversity than what would be expected without a positive correlation. Low-level metal mixture effects varied similarly, largely among species and mixture interactions that were highly variable: ranging from synergistic to antagonistic relative to independent action during exponential growth, whereas mixture interactions at 10% effect shifted toward additivity/synergism relative to concentration addition at carrying capacity. Some evidence was found for stronger synergistic mixture effects in smaller species. Overall, the present study highlights the importance of incorporating more species in sensitivity distributions and accounting for mixture toxicity in risk assessment.

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

“…Thus, these community-level synergisms must be a result of species interactions. The mean correlation of single-species sensitivities among the single metals, a community property put forward in Fettweis et al (2021), did not explain the extent of mixture interactions during exponential growth (day 3; Figure 7). This is plausible because the compensatory dynamics related to the functional redundancy of a community only set in when a growth-limiting factor is present, which is not the case at day 3 when P is not yet limiting for the algal communities.…”

“…In that regard, it might be useful to consider community properties derived from single-species data to predict the mixture effects and interactions at the community level. The mean correlation of single-species sensitivities among single metals for all species in a community, as described in Fettweis et al (2021), is such an example (Figure 1). The hypothesis in that study stated that structural endpoints are relatively more sensitive compared to functional endpoints (e.g., total biomass) for algal communities with positively correlated single-metal sensitivities for all the species in the community when subjected to mixture toxicity.…”

“…Based on current understandings, metal‐mixture interactions at the species level are rarely synergistic (<10% of reviewed cases) and more often noninteractive or antagonistic (Cedergreen, 2014; Nys et al, 2018). The mechanisms leading to synergistic or antagonistic mixture effects at the species level are difficult to identify but most probably related to one or more toxicokinetic and/or toxicodynamic processes (Cedergreen, 2014; Fettweis et al, 2021). For example, Fettweis et al (2021) found that smaller algal species experience stronger synergisms when exposed to Cu–Ni–Zn mixtures.…”

“…The mechanisms leading to synergistic or antagonistic mixture effects at the species level are difficult to identify but most probably related to one or more toxicokinetic and/or toxicodynamic processes (Cedergreen, 2014; Fettweis et al, 2021). For example, Fettweis et al (2021) found that smaller algal species experience stronger synergisms when exposed to Cu–Ni–Zn mixtures. At the community level, it is still unknown how both mixture models perform in predicting mixture effects, what the frequency of synergisms and antagonisms is, and if it follows a similar pattern as observed on the single‐species level.…”

Trace element bioaccumulation and health risk assessment derived from leg consumption of the marsh frog, Pelophylax ridibundus (Pallas, 1771)

“…Therefore, it is crucial to figure out how trace elements interact with one another in tissues because trace elements have increased concentrations in the environment (Briffa et al, 2020). Contaminated water contains many metal mixtures rather than a single metal, and aquatic organisms are influenced by mixed metals (Zeng et al, 2019;Fettweis et al, 2021). Heavy metal concentrations are toxic to mg L -1 levels for most organisms due to heavy metal ions irreversible suppression of particular enzymes (Henczova et al, 2008).…”