Can Rice Paddies Mitigate Pesticides in Agricultural Runoff?.

Pesticides are responsible for over 1,800 water quality impairments in the United States. Management strategies such as constructed wetlands, grass buffers, and vegetated ditches are tools used to reduce pesticide runoff effects on aquatic receiving systems. The increased need for food and fiber production to supply a growing world population, combined with less available agricultural land and changing climate patterns, forces science to continually design alternative methods for mitigation of pesticide runoff. One proposed method is the use of rice paddies for phytoremediation of pesticide-contaminated water. Rice (Oryza sativa) is cultivated on every continent except Antarctica and is the staple food crop of 20% of the world’s population. Four, 0.01 ha paddies (two planted with rice, two left bare) were amended with a mixture of atrazine, diazinon, and permethrin during a one-time storm event, and pesticide concentrations and loads were monitored in water, sediment, and plant samples. The experiment was repeated the following year. Due to variability among years and individual paddies, there were no significant differences between rice and bare systems. However, overall atrazine loads in the water of rice systems decreased 85±5.8% from inflow to outflow, while atrazine loads in the water of bare systems decreased 58±4.5%. Similar patterns were seen for diazinon (88±3.4% versus 64±5.1%), cis-permethrin (95±1.5% versus 69±9.4%), and trans-permethrin (97±1.7% versus 72±11%). Only a few samples of sediment were above detection limits for atrazine during the two year study. During the first year, all three pesticides were found repeatedly sorbed to plant material in the inflow and outflow areas, 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.