Biotransformation and antioxidant response in Ceratophyllum demersum experimentally exposed to 1,2- and 1,4-dichlorobenzene

We report the effects of 1,2- and 1,4-dichlorobenzene (1,2-DCB and 1,4-DCB) on the aquatic macrophyte Ceratophyllum demersum. We evaluated the response of the antioxidant system through the assay of glutathione reductase (GR), guaiacol peroxidase (POD) and glutathione peroxidase (GPx). Additionally, the effect of DCBs on the detoxication system by measuring the activity of glutathione-S-transferase (GST) was evaluated.

C. demersum showed elevated GST activities when exposed to 10 and 20 mg l⁻¹ 1,2-DCB, and at 10 mg l⁻¹ for 1,4-DCB. These results show that glutathione conjugation take place at relatively high concentrations of both isomers. Significantly increased activities of POD were also detected in C. demersum exposed to concentrations above 5 mg l⁻¹ of the corresponding isomer.

The GR activity was enhanced in plants exposed to 1,2-DCB (5 mg l⁻¹) and 1,4-DCB (10 mg l⁻¹). GPx was also significantly increased in exposures to the corresponding isomer, each at a concentration of 10 mg l⁻¹. However, plants exposed to low doses of 1,4-DCB (1 mg l⁻¹) showed significantly decreased activities of both enzymes GR and GPx.

Consequently, it is clear that the exposure of the aquatic macrophyte C. demersum to DCBs is able to cause an activation of the antioxidant system, showing an isomer specific pattern, which suggests that the defence system of this plant is playing an important role in scavenging ROS, helping to protect the organism against adverse oxidative effects generated by the prooxidant action of the tested xenobiotics. Furthermore, increased GST activities give indirect evidence on the conjugation of either DCBs or the corresponding metabolites during phase II of detoxication, which supports the elimination process of toxic metabolites from cells of C. demersum.