Solar Radiation, Relative Humidity, and Soil Water Effects on Metolachlor Volatilization

Abstract

Pesticide volatilization is a significant loss pathway that may have unintended consequences in nontarget environments. Field-scale pesticide volatilization involves the interaction of a number of complex variables. There is a need to acquire pesticide volatilization fluxes from a location where several of these variables can be held constant. Accordingly, soil properties, tillage practices, surface residue management, and pesticide formulations were held constant while fundamental information regarding metolachlor volatilization (a pre-emergent pesticide) was monitored over a five-year period as influenced by meteorological variables and soil water content. Metolachlor vapor concentrations were measured continuously for 120 h after each application using polyurethane foam plugs in a logarithmic profile above the soil surface. A flux gradient technique was used to compute volatilization fluxes from metolachlor concentration profiles and turbulent fluxes of heat and water vapor (as determined from eddy covariance measurements). Differences in meteorological conditions and surface soil water contents resulted in variability of the volatilization losses over the years studied. The peak volatilization losses for each year occurred during the first 24 h after application with a maximum flux rate in 2001 (1500 ng m(-2) s(-1)) associated with wet surface soil conditions combined with warm temperatures. The cumulative volatilization losses for the 120-hour period following metolachlor application varied over the years from 5 to 25% of the applied active ingredient, with approximately 87% of the losses occurring during the first 72 h. In all of the years studied, volatilization occurred diurnally and accounted for between 43 and 86% during the day and 14 and 57% during the night of the total measured loss. The results suggest that metolachlor volatilization is influenced by multiple factors involving meteorological, surface soil, and chemical factors.

Environmental fate of S-Metolachlor: a review

“…Interacting with moisture content, soil and air temperatures variations also affect metolachlor losses by volatilization (Jury et al, 1987). In four of the five years evaluated, the total daytime volatilization was greater (60-86%) than the nighttime period (14-57%) and largest losses of metolachlor occurred under warm and wet soil conditions while minimal losses were observed under cool and dry soil (Prueger et al, 2005).…”

“…(Table 1), volatilization losses are considered minimal but they still occur under certain environmental conditions. These losses appear to be highly variable occurring during the day and night periods in response to varying and complicated interactions involving meteorological, soil and chemical factors (Prueger et al, 2005). Among these factors, soil moisture content plays a major role on S-metolachlor volatilization.…”

Opinion of the Scientific Panel PPR on the Final Report of the FOCUS Air Working Group on Pesticides in Air: Consideration for exposure assessment. (SANCO/10553/2006 draft 1 (13 July 2006))

“…Majewski (1999) details this level of uncertainty of direct measurements. o on emission by volatilization from paddy fields: (Ferrari et al, 2005) o Prueger et al, (2005) also support the effect of atmospheric humidity and soil moisture on volatilization from soils.…”

Analysis of metolachlor ethane sulfonic acid (MESA) chirality in groundwater: A tool for dating groundwater movement in agricultural settings

“…The cropped area was continuously maintained in maize production and was treated with a mixture of metolachlor and atrazine each year (Prueger et al, 2005). Herbicides were applied via spray broadcast onto a bare soil surface shortly after the corn was planted.…”