Interactions of mixed organic contaminants in uptake by rice seedlings

Uptakes of o-chlorophenol (CP), 2,4-dichlorophenol (DCP), trichloroethylene (TCE), and atrazine (ATR), as single and mixed contaminants, by roots and shoots of rice seedlings (Oryza sativa L.) from hydroponic solutions were measured following a 48-h exposure of plant roots. As single contaminants, the concentrations of CP, DCP, and ATR in rice roots and shoots increased significantly with increasing concentrations in external solutions; however, TCE concentrations in rice roots and shoots decreased with increasing external TCE concentration or the exposure time. The observed bioconcentration factors (BCFs) of CP and DCP with roots and the BCF of ATR with shoots approximated the equilibrium values according to the partition-limited model. The BCF of DCP with shoots was about 30% of the partition limit, due to insufficient water transport into plants for DCP. In the ATR-CP-DCP mixed system, the BCFs of CP and DCP with both roots and shoots decreased significantly with increasing contaminant concentrations due to the enhanced mixed-contaminant phytotoxicity, as manifested by the greatly reduced plant transpiration rate. In the ATR-CP-DCP mixture system, the BCFs of ATR with roots at low concentrations were comparable with those for ATR alone, whereas the BCFs increased at high concentrations for an unknown reason. In the TCE-DCP system, TCE concentrations in roots increased with increasing TCE in external solutions, while TCE concentration in shoots stayed steady because of the strong TCE exchange at the air-leaf interface. The BCF of DCP with roots was comparable with that of DCP alone because there was no significant effect of added TCE on the plant transpiration rate.