Quantification of differentially expressed genes in Daphnia magna exposed to rubber wastewater

In this study, differentially expressed genes (DEGs) were investigated in Daphnia magna exposed to rubber wastewater using an annealing control primer (ACP)-based polymerase chain reaction (PCR) and real-time PCR. Among three identified DEGs, two genes (DEG1 and DEG2) were up-regulated, and DEG1 expression was well-correlated to a logarithm of rubber wastewater concentration (r² = 0.971, p < 0.0001). In addition, DEG1 expression in D. magna exposed to rubber wastewater was strongly correlated with that of D. magna exposed to Zn (r² = 0.9513, p < 0.05), suggesting that the induction of DEG1 was caused by Zn, which is the dominant toxicant in rubber wastewater. In addition, DEG1 expression was more sensitive to toxicants than immobility, which is the conventional endpoint in toxicity tests using D. magna. The lowest observed effect concentrations (LOEC) determined using immobility tests were 2.5% for rubber wastewater and 1.6 mg l^-1 for Zn. In contrast, a significant increase in DEG1 expression was observed at exposure concentrations of as low as 0.6% rubber wastewater and 0.2 mg l^-1 Zn. These results indicate that DEG1 is a sensitive and quantitative biomarker of water and wastewater containing Zn.