Pesticides are also taken up by roots and may be metabolized in plants. In addition, vegetation at the soil surface adsorbs pesticides during runoff events. Few studies have investigated pesticide trapping by constructed wetlands. Some pesticides are relatively short-lived in water. Thus degradation occurring while runoff or tile effluent is sequestered in wetlands reduces contaminants reaching streams.
Wetlands can also serve to ameliorate pulses of concentrated runoff before it enters streams.
Some pesticides are relatively persistent once they reach water. However, the high organic matter content of wetlands sediments binds these pesticides, removing them from water. Considering buffer research to date, under controlled conditions, buffers have been effective in trapping both highly adsorbed and moderately adsorbed pesticides. Table 1 is a summary of buffer studies showing trapping efficiency for specific pesticides and pesticide Koc values. Lowest percent pesticide retention by buffers occurred when buffer soil was saturated due to previous rains.