Periphyton growth reduces cadmium but enhances arsenic accumulation in rice (Oryza sativa) seedlings from contaminated soil

Periphyton is ubiquitous in paddy fields, but its role in arsenic (As) and cadmium (Cd) bioavailability to rice plants remains unknown. A paddy field was simulated under controlled conditions to investigate the influences of periphyton on As and Cd accumulation in rice seedlings grown in soil contaminated with both As and Cd. The presence of periphyton significantly enhanced the growth of rice seedlings in As and Cd contaminated soil. Periphyton had significant effects on soil pH and Eh, resulting in a substantial decrease in the Cd concentration, but in an increase in the total As and As (III) concentrations in soil solution. Corresponding with these changes, Cd concentrations in rice roots and shoots were significantly decreased in the presence of periphyton, while As concentrations increased. This study demonstrates that periphyton growth can significantly affect soil As, Cd bioavailability and soil As speciation by changing soil pH and Eh, which affect As and Cd accumulation in rice seedlings as a result. These results suggest that controlling native periphyton growth may be an effective strategy to regulate As and Cd translocation to the edible organs of food crops.