Environmental Engineering Reference
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Pesticide concentration trends that commonly occur in streams and rivers of the
corn belt of the U.S were assessed Sullivan et al. (
2009
) and the relative applicability
and performance several statistical methods for trend analysis were evaluated.
Temporal trends in concentrations of 11 pesticides (including CPY) with sufficient
data were assessed at as many as 31 stream sites for two time periods: 1996-2002
and 2000-2006. Most sites had too few concentrations that were greater than the
MDLs to determine meaningful trends in CPY concentrations. All the 11 sites for
which flow-adjusted trends could be analyzed during 1996-2002 exhibited down-
ward trends in concentrations of CPY, including significant downward trends at two
sites and highly significant downward trends at five sites. Only three sites could be
analyzed during 2000-2006. One site had a statistically significant downward trend,
the second site had a non-significant upward trend, and the third site had a highly
significant upward trend. Overall, the results indicate downward trends in concentra-
tions of pesticides in general. This included decreasing CYP concentrations in Corn
Belt streams and rivers during 1996-2006, which were explained largely by the cor-
responding decreases in annual use due to regulatory actions or market forces.
The second USGS study (Ryberg et al.
2010
) used the Martin and Eberle (2009)
dataset to assess trends of pesticide concentrations in 27 urban streams in the
Northeastern, Southern, Midwestern and Western regions of the U.S. Three par-
tially-overlapping 9-yr periods (1992-2000, 1996-2004, and 2000-2008) were
examined for eight herbicides, five insecticides, and three degradation products.
The data were analyzed for trends in concentrations by use of a parametric regres-
sion model. Due to small and declining frequencies detection, trends in concentra-
tion of CPY were not assessable at most sites, particularly during 2000-2008. Most
of the streams for which adequate data were available exhibited significant down-
ward trends in concentrations (i.e., 10 of 11 sites during 1996-2004 and two of five
sites during 2000-2008). Between 2000 and 2008, most measured concentrations of
CPY were less than the MDLs and only five sites had more than 10 detections.
Concentrations of CPY at two of those sites continued to decline significantly, but
there were no significant downward trends at the remaining three sites during the
latter period. The downward trends of CPY concentrations in urban streams were
consistent with the regulatory phase-out of residential uses of CPY between 1997
and 2001.
The most recent USGS study to use the Martin and Eberle (2009) dataset assessed
trends in concentrations of two insecticides and five herbicides in 15 streams in
California, Oregon, Washington, and Idaho from 1993 to 2005 (Johnson et al.
2011
). Because of changes in amounts applied and methods of application in their
associated catchments, pesticide concentration trends were estimated by using a
parametric regression model to account for flow, seasonality, and antecedent hydro-
logic conditions. Short-term models of trends were developed for all sites for the
period 2000-2005, while long-term models of trends were developed at 10 of the 15
study sites: two small urban sites (1996-2005), three small agricultural sites (1993-
2005), and five large mixed land-use sites (1993-2005). Of the seven sites that had
a sufficient number of uncensored (>MDL) concentrations of CPY for short-term
trend analysis of flow-adjusted concentrations (2000-2005), only one site (Yakima
River, WA; a large mixed land-use site) had a significant upward trend. For the
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