Meanwhile, the combination of 1.0 mg/L 2,4-DCP and 5 mg/L Na2SeO3 or 5 mg/L Na2SeO3 alone caused a reduction of the global DNA methylation levels by 2.3% and 8.3% compared with control (Fig. 4), and the combination of 1.0 mg/L 2,4-DCP and 5 mg/L Na2SeO3 significantly decreased the SAM contents and the global DNA methylation levels by 31.56% and 19.18% compared to the 1.0 mg/L 2,4-DCP exposure group (P < 0.05).