Pesticide Fate and Transport throughout Unsaturated Zones in Five Agricultural Settings, USA

Abstract

Pesticide transport through the unsaturated zone is a function of chemical and soil characteristics, application, and water recharge rate. The fate and transport of 82 pesticides and degradates were investigated at five different agricultural sites. Atrazine and metolachlor, as well as several of the degradates of atrazine, metolachlor, acetochlor, and alachlor, were frequently detected in soil water during the 2004 growing season, and degradates were generally more abundant than parent compounds. Metolachlor and atrazine were applied at a Nebraska site the same year as sampling, and focused recharge coupled with the short time since application resulted in their movement in the unsaturated zone 9 m below the surface. At other sites where the herbicides were applied 1 to 2 yr before sampling, only degradates were found in soil water. Transformations of herbicides were evident with depth and during the 4‐mo sampling time and reflected the faster degradation of metolachlor oxanilic acid and persistence of metolachor ethanesulfonic acid. The fraction of metolachlor ethanesulfonic acid relative to metolachlor and metolachlor oxanilic acid increased from 0.3 to >0.9 at a site in Maryland where the unsaturated zone was 5 m deep and from 0.3 to 0.5 at the shallowest depth. The flux of pesticide degradates from the deepest sites to the shallow ground water was greatest (3.0–4.9 μmol m−2 yr−1) where upland recharge or focused flow moved the most water through the unsaturated zone. Flux estimates based on estimated recharge rates and measured concentrations were in agreement with fluxes estimated using an unsaturated‐zone computer model (LEACHM).

Review of risk from potential emerging contaminants in UK groundwater

“…Compounds with the highest risk index were metabolites of cyanazine, followed by those of isoproturon, flufenacet, tebuconazole and dicamba. (Chang and Liao, 2002;Fava et al, 2005;Giacomazzi and Cochet, 2004;Hancock et al, 2008;Hildebrandt et al, 2007;Kolpin et al, 2004;Montana Dept of Agriculture, 2006). Worrall et al (2000) proposed using a probability index for predicting groundwater contamination risk using soil K oc and DT 50 where points along a diagonal line have a similar estimated leaching probability.…”

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

“…After application, metolachlor is readily transported into the soil where it is transformed into several compounds, the most abundant being, metolachlor ethane sulfonic acid (2-[(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl)amino]-2-oxoethanesulfonic acid, MESA) (Baran and Gourcy, 2013;Bayless et al, 2008;White et al, 2010). MESA can be found in groundwater wherever metolachlor has been used and it appears to be quite stable in groundwater (Baran et al, 2004;Barbash et al, 1999;Bayless et al, 2008;Denver et al, 2010;Domagalski et al, 2008;Huntscha et al, 2008;Kalkhoff et al, 2012;Krutz et al, 2006;Rebich et al, 2004;Hancock et al, 2008).…”

Emerging Organic Contaminants in Groundwater

“…In northern Europe as well as derivatives of atrazine, degradates from a range of herbicides including glyphosate, chloridazon, bentazone, diuron and metribuzin [39,[150][151][152][153][154]. In southern Europe and the USA the focus has been on the degradates of the acetanilide herbicides: acetochlor, alachlor and metolachlor [40,[155][156][157][158][159].…”