Acute toxicity and antioxidant responses in the water flea Daphnia magna to xenobiotics (cadmium, lead, mercury, bisphenol A, and 4-nonylphenol)

Heavy metals have adverse effects to aquatic organisms, and endocrine-disrupting chemicals (EDCs) alter the normal functioning of hormones in living organisms. In the present study, an acute toxicity test was performed to determine the EC50 values in the water flea Daphnia magna exposed to Cd, Pb, Hg, 4-nonylphenol (NP) and bisphenol A (BPA) for 48 h, according to the OECD test guideline 202. The mRNA expression of Cu/Zn-SOD, Mn-SOD, and catalase (CAT) was analyzed using real time RT-PCR. The results indicate that all chemicals tested showed a negative effect on the mobility of D. magna. The 48-h EC50 values were 21.0 μg/L for Cd, 694.6 μg/L for Pb, 3.8 μg/L for Hg, 18.9 μg/L for 4-NP and 8.3 mg/L for BPA. The order of toxicity based on the EC50 values was as follows: Hg>4-NP>Cd>Pb>BPA. Gene expression patterns indicated that Cd and Pb increased the mRNA levels of the genes encoding three antioxidant enzymes upon exposure for 48 h. Mn-SOD and CAT mRNAs were sensitively modulated in response to Pb. In contrast, the expression of these genes was up-regulated at 24 h and then reduced at 48 h after exposure to Hg. These findings suggest that the heavy metals (Cd, Pb, and Hg) can induce oxidative stress in D. magna and that the antioxidant enzymes were sensitive to 24h-Hg and 48h-Pb exposure. A significant increase in the mRNA expression of three antioxidant enzymes was observed after exposure to 4-NP, whereas a slight modulation of Mn-SOD and CAT mRNA levels was detected in response to BPA, indicating that these genes are involved in a cellular defense system against EDCs-mediated oxidative stress. © 2017, Korean Society of Environmental Risk Assessment and Health Science and Springer Science+Business Media Dordrecht.