The effects of a mixture of copper, nickel, and zinc on the structure and function of a freshwater planktonic community

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Abstract

It is generally assumed that as long as the majority of species experiences no direct adverse effects attributable to a single substance (i.e., potentially affected fraction [PAF] 0.05 (i.e., in the Cu-Ni-Zn mixture). However, consistent effects on the abundance of various phytoplankton species groups (structural traits) and on 2 measures of community respiration, overnight Δ dissolved oxygen (ΔDO) and ΔpH (functional traits), were already observed at msPAF values of ≤0.05 (i.e., in the Ni-Zn mixture). This indicates that the threshold msPAF value of 0.05 was not protective against metal mixture exposure for all community-level structural and functional endpoints in the present study. A possible explanation for this result is the mismatch between the species in the SSD and those in our microcosm community. Indeed, our data suggest that the presence of one single dominant and very Zn- and/or Ni-sensitive species in the investigated community (i.e., a cyanobacteria of the genus Oscillatoria), which is not represented in the SSD of these metals, was probably the driver of all observed effects at or below an msPAF of 0.05. Overall, the present results show that SSDs are not necessarily a good predictor of community-level effects for all types of communities and that the presence of dominant sensitive species may result in significant, consistent effects on certain structural and functional community-level endpoints at msPAF values ≤0.05, which is generally considered protective in many regulatory frameworks. Environ Toxicol Chem 2018;37:2380-2400. © 2018 SETAC.

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