Biological responses of maize (Zea mays) plants exposed to chlorobenzenes. Case study of monochloro-, 1,4-dichloro- and 1,2,4-trichloro-benzenes

A 7-day-exposure time experiment was designed to investigate the phytotoxicity of chlorobenzenes (CBs) on Zea mays seedlings, focusing on the growth and generation of oxidative stress. Significant growth inhibition (based on biomass gain) was observed for exposure to monochlorobenzene (MCB), dichlorobenzene (DCB) and trichlorobenzene (TCB) concentrations higher than 10 mg l−1. It would seem that CBs inhibit cell division, since the mitotic index decreased for roots exposed to DCB at 80 mg l−1 dose (8%) and to all the TCB concentrations tested (20% inhibition). CBs exposure resulting in an increase in the oxidative stress response in maize seedlings [reactive oxygen species like H2O2, antioxidant enzymes (POD, GR), lipid peroxidation] correlated to the compound’s degree of chlorination, where damage increasing with the number of chlorine atoms (MCB < DCB < TCB). This biological response was also dependent on the dose-exposure. Z. mays exposed to CBs at concentrations <10 mg l−1 did not induce sufficient oxidative damage to cause root cell death. Therefore, CBs at current environmental concentrations are unlikely to produce evident phytotoxic effects on Z. mays seedlings.