Phragmites australis shows potential for the phytoremediation of chlorinated chemicals. Also there has been some attempt to determine the phytotoxic effects of organochlorines (OC). This study reports for lindane (HCH), monochlorobenzene (MCB), 1,4-dichlorobenzene (DCB) and 1,2,4-trichlorobenzene (TCB), a no-observed-effect-concentration (NOEC(7d)) that was 1000-300,000 times higher than environmental concentrations. Nevertheless, the combined OC mixture (NOEC(7d) level of each congener) induced a synergistic toxic effect, causing a severe drop (70%) in chlorophyll concentration. The mixture 0.2 mg L(-1) MCB+0.2 mg L(-1) DCB+2.5 mg L(-1) TCB+0.175 mg L(-1) HCH, that was 15 times more concentrated than environmental OC mixture, did not cause phytotoxicity during 21 days. Antioxidant enzymes were affected immediately after the start of exposure (3 days), but the plants showed no signs of stress thereafter. These data suggest that environmental OC mixtures do not pose a significant risk to P. australis.