Chromium toxicity to planktonic organisms: comparison between different routes of exposure to the metal

Abstract Given the importance of metals in the contamination of aquatic ecosystems, studies are needed to assess the effects of these contaminants on aquatic organisms through different contamination pathways. Chromium (Cr) is a metal widely used in various industrial processes, considered a priority pollutant in several countries. In the present study, ecotoxicological tests were carried out with the microalga Chlorella vulgaris, evaluating the effects of Cr on cell density, pigment concentration, and biochemical composition. Additionally, the effects of chromium exposure on cladocerans (Ceriodaphnia dubia and Ceriodaphnia silvestrii) were investigated through three contamination routes: contaminated medium, contaminated food (C. vulgaris), and the combination of both situations (contaminated medium and food). The toxicity tests with cladocerans evaluated the metal effects on survival, number of newborn produced by female, and feeding activity. The results obtained demonstrated that 48 µg L-1 total dissolved Cr reduced cell density and increased protein, carbohydrate, and lipid content in C. vulgaris. The increase in the biochemical composition of microalgae upon exposure to Cr may have contributed to the non-observation of chronic toxic effects on daphnids in the treatment with contaminated food. A decrease of 31% and 26% in the number of C. silvestrii offspring was observed for the treatment with contaminated medium (35 µg L-1 total dissolved Cr) and associated treatment (35 µg L-1 total dissolved Cr and 3 × 10-14 g Cr cells-1), respectively. The importance of the Cr poisoning pathways and the difference in cladoceran species’ sensitivity to the metal were addressed.