Effects of Cadmium and Nickel Mixtures on Multiple Endpoints of the Microalga Raphidocelis subcapitata.

This article focuses on the combined toxic effects of cadmium (Cd) and nickel (Ni) on the freshwater green microalga Raphidocelis subcapitata, evaluating multiple physiological and morphological endpoints. The study found that Cd inhibited algal growth, increased reactive oxygen species (ROS) production, chlorophyll a (Chl a) fluorescence, cell size, and cellular complexity, while Ni decreased ROS production and Chl a fluorescence but affected cell density only at the highest concentration tested. Mixture toxicity analysis using concentration addition (CA) and independent action (IA) models showed that the IA model with dose-level–dependent deviation best fit the data, indicating antagonism at low doses and synergism at high doses above median inhibitory concentrations. The Cd–Ni mixtures increased cell size and complexity and altered ROS and Chl a fluorescence without significantly affecting photosynthetic parameters such as maximum quantum yield (ΦM) and oxygen-evolving complex efficiency (F0/Fv). These findings highlight the importance of assessing metal mixtures in ecotoxicology, given their potential to produce different or enhanced effects compared to individual metals, with implications for aquatic ecosystem health and risk assessment.