Comparative study of the sensitivity of Daphnia galeata and Daphnia magna to heavy metals.

Daphnia galeata and Daphnia magna belong to the family Daphniidae. Daphnia galeata has a smaller body size and longer helmet than D. magna. Although D. galeata is widely distributed in the northern hemisphere, it is not as commonly used in aquatic ecotoxicity tests as D. magna. There have been only few ecotoxicological studies on the toxicity of heavy metals, organic matter, and nanomaterials in D. galeata. Thus, there is a need to discover new test species and expand the number of currently known test species to elucidate species sensitivity to aquatic pollutants. We carried out a comparative study on the sensitivity of D. magna (which represents the test water flea species) and D. galeata to heavy metal toxicity. The acute toxicity values (EC50 and LC50) of 11 heavy metal species, including silver (Ag+), arsenite (As3+), cadmium (Cd2+), chromate (Cr6+), cupric (Cu2+), ferrous (Fe2+), mercury (Hg2+), manganese (Mn2+), nickel (Ni2+), lead (Pb2+), and zinc (Zn2+), in D. galeata and D. magna were compared by conducting acute toxicity assays and comparing the data with the available data. The age of the tested Daphnia individuals and the type of exposure medium were considered for more reliable comparison of species sensitivity. We observed that D. galeata was more sensitive to Ag+, As3+, Cr6+, Fe2+, Ni2+, and Pb2+ than D. magna. The sensitivity to Cu2+, Cd2+, and Zn2+ was similar for D. magna and D. galeata. This study presents important aquatic toxicity and sensitivity data on D. galeata, which is not a widely used species in aquatic ecotoxicology studies. Our results recommend D. galeata as a suitable species for aquatic ecotoxicity tests because of its higher sensitivity.