American researchers have revealed that pesticide losses to the atmosphere, through volatilisation, increase when soil moisture levels are high. A long-term U.S. Department of Agriculture (USDA) study found that herbicide volatilisation regularly exceeded herbicide losses arising through field runoff.
Scientists from the USDA Agricultural Research Service studied the field dynamics of atrazine and metolachlor, two herbicides commonly used in maize production. Both herbicides are known to contaminate surface and ground water, which was primarily thought to occur through surface runoff.
The team found that when air temperatures increased, so too did soil moisture’s role in influencing atmospheric losses – volatilisation – of these two chemicals, something that had not been considered or observed in earlier experiments. When soils were dry and air temperatures increased, there was no increase in herbicide volatilization, but herbicide volatilization increased significantly when temperatures rose and soils were wet.
According to the report, most surprising was that throughout the study, herbicide volatilization losses were significantly larger than surface runoff. When averaged over the two herbicides, loss by volatilization was about 25 times larger than losses from surface runoff. Read more here.