Expanding Wetland Mitigation: Can Rice Fields Remediate Pesticides in Agricultural Runoff?

Pesticides are responsible for nearly 1900 water quality impairments in the United States. Impacts of pesticide runoff on aquatic ecosystems can be mitigated by implementing management practices such as constructed wetlands, grass buffers, and vegetated ditches. A new practice currently being examined is the use of rice ( L.) fields for phytoremediation of pesticide-contaminated water. Rice is cultivated on every continent except Antarctica and is the staple food crop of 20% of the world's population. Four flooded 244-m fields (two planted with rice, two left bare) were amended with a mixture of atrazine (CHClN), diazinon (CHNOPS), and permethrin (CHClO) during a one-time simulated storm event, and pesticide concentrations and loads were monitored in water, sediment, and plant samples. The experiment was repeated the following year. Significant differences were noted for mitigation of atrazine and diazinon loads in rice versus bare systems. Overall, atrazine loads in the water of rice systems decreased 85 ± 8% from inflow to outflow, while atrazine loads in the water of bare systems decreased 58 ± 7%. Similar patterns were seen for diazinon (86 ± 4% versus 62 ± 7%), cis-permethrin (94 ± 2% versus 64 ± 12%), and trans-permethrin (97 ± 2% versus 67 ± 14%). All three pesticides were found repeatedly sorbed to plant material in the inflow and outflow areas during the first year, while the second year resulted in much less plant-pesticide contribution to overall mitigation. Further investigation is needed to compare rice's mitigation capacity of different pesticide classes, as well as potential transfer of pesticides to edible seeds.