Occurrence and Fate of Pesticides in Four Contrasting Agricultural Settings in the United States

Abstract

Occurrence and fate of 45 pesticides and 40 pesticide degradates were investigated in four contrasting agricultural settings—in Maryland, Nebraska, California, and Washington. Primary crops included corn at all sites, soybeans in Maryland, orchards in California and Washington, and vineyards in Washington. Pesticides and pesticide degradates detected in water samples from all four areas were predominantly from two classes of herbicides—triazines and chloroacetanilides; insecticides and fungicides were not present in the shallow ground water. In most samples, pesticide degradates greatly exceeded the concentrations of parent pesticide. In samples from Nebraska, the parent pesticide atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] was about the same concentration as the degradate, but in samples from Maryland and California atrazine concentrations were substantially smaller than its degradate. Simazine [6‐chloro‐N,N′‐diethyl‐1,3,5‐triazine‐2,4‐diamine], the second most detected triazine, was detected in ground water from Maryland, California, and Washington. Metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide] rarely was detected without its degradates, and when they were detected in the same sample metolachlor always had smaller concentrations. The Root‐Zone Water‐Quality Model was used to examine the occurrence and fate of metolachlor at the Maryland site. Simulations accurately predicted which metolachlor degradate would be predominant in the unsaturated zone. In analyses of relations among redox indicators and pesticide variance, apparent age, concentrations of dissolved oxygen, and excess nitrogen gas (from denitrification) were important indicators of the presence and concentration of pesticides in these ground water systems.

Metolachlor metabolite (MESA) reveals agricultural nitrate-N fate and transport in Choptank River watershed

“…In addition, the resulting stream water attenuated nitrate-N concentration relative to the groundwater without evidence for MESA diminishment (data not shown). These observations in conjunction with previous studies (Denver et al, 2010;Phillips et al, 1999;Steele et al, 2008;McConnell et al, 2007) indicate that 1) MESA is stable even in anaerobic …”

“…As shown above and elsewhere (Denver et al, 2010;McConnell et al, 2007;Phillips et al, 1999;Steele et al, 2008), MESA is a stable, soluble indicator for agricultural waters and has a long half-life in surface waters (Huntscha et al, 2008). The residence time of waters in the Choptank River estuary has been estimated to be 19 days (Bricker et al, 2007).…”

“…Previous studies have shown that no relationship exists between ground water age and MESA concentration, i.e., the MESA is stable in ground water (Steele et al, 2008). We have also examined the fate of MESA relative to nitrate-N as part of a larger study to assess the effectiveness of riparian areas in mitigating agricultural nitrate-N.…”

“…In contrast to nitrate-N, once MESA enters ground water, it is very stable (Phillips Table 1 Conceptual model of landscape characteristics that influence transport, processing, and delivery of nitrate-N and MESA to headwater streams of the Choptank River (Ator et al, 2005;Bachman and Phillips, 1996;Denver et al, 2010, in press;Phillips and Bachman, 1996;Phillips et al, 1993 Steele et al, 2008); MESA persists over decadal time scales (Denver et al, 2010). In surface water, the modeled half-life for all MESA processing (phototransformation, transport, etc.)…”

Statistical screening for descriptive parameters for pesticide occurrence in a shallow groundwater catchment

“…Boesten and van der Pas, 2000;Funari et al, 1998) and regional and national monitoring programmes comparing the degree and character of contamination between different types of catchments (e.g. Gaw et al, 2008;Steele et al, 2008;Worrall and Kolpin, 2004). Meanwhile and as a result, a range of pesticide environmental fate models (e.g.…”