The impact of the herbicide diuron on photosynthesis in three species of tropical seagrass

The impact and recovery from exposure to the herbicide diuron [DCMU; 3-(3',4'-dichlorophenyl)-1,1-dimethylurea] was assessed for three tropical seagrasses, maintained in outdoor aquaria over a 10-day period. Photosynthetic stress was detected using chlorophyll a fluorescence, measured with a Diving-PAM (pulse amplitude modulated fluorometer). Exposure to 10 and 100 μg l diuron resulted in a decline in effective quantum yield (F/F(m')) within 2 h of herbicide exposure in Cymodocea serrulata, Halophila ovalis and Zostera capricorni. Effective quantum yield also declined over the first 24 h of exposure in H. ovalis at even lower diuron concentrations (0.1 and 1.0 μg l). Effective quantum yield in H. ovalis and Z. capricorni was significantly depressed at all diuron concentrations (0.1-100 μg l) after 5 days exposure, whereas effective quantum yield in C. serrulata was only significantly lower in plants exposed to highest diuron concentrations (10 and 100 μg l). Effective quantum yield depression was present 5 days after plants exposed to 10 and 100 μg l diuron were returned to fresh seawater. These results indicate that exposure to herbicide concentrations present in nearshore Queensland sediments present a potential risk to seagrass functioning. (C) 2000 Elsevier Science Ltd