Environ. Sci. Technol. 2008, 42, 8452–8458
Chiral Current-Use Herbicides in Ontario Streams PERIHAN BINNUR KURT-KARAKUS,† T E R R Y F . B I D L E M A N , * ,† DEREK C. G. MUIR,‡ STEVE J. CAGAMPAN,‡ JOHN STRUGER,‡ ED SVERKO,‡ JEFF M. SMALL,‡ AND LIISA M. JANTUNEN† Center for Atmospheric Research Experiments, Environment Canada, 6248 Eighth Line, Egbert, L0L 1N0, Ontario, Canada, and Science and Technology Branch, Environment Canada, 867 Lakeshore Road, Burlington, L7R 4A6, Ontario, Canada
Received April 30, 2008. Revised manuscript received August 8, 2008. Accepted August 11, 2008.
Concentrations of mecoprop, dichlorprop, and metolachlor were investigated in 393 samples from Ontario streams in 2003-2004. Maximum concentrations of mecoprop, dichlorprop, and metolachlor were 1900, 6.62, and 1560 ng L-1, respectively in 2003, and 103,000, 110, and 5290 ng L-1, respectively, in 2004. Concentrations of metolachlor in agricultural watersheds were significantly (p < 0.0001) higher than those in urban watersheds, whereas concentrations of mecoprop did not differ (p > 0.1) between the two watershed types. Enantiomer fractions (EFs) of the acid herbicide mecoprop ranged from 0.236 to 0.928 and for dichlorprop EFs ranged from 0.152 to 0.549. EFs of mecoprop did not differ significantly (p > 0.1) between agricultural and urban land usage. Mecoprop EFs g0.5 were found in 54% of samples, a situation expected during the transition years when racemic mecoprop was replaced by mecoprop-P, consisting of only the R(+) enantiomer. However, EFs MQL. Table 1 summarizes the seasonal concentration patterns for each herbicide. Most of the positive samples occurred in the spring through summer (April-August). Lower concentrations were found in fall and winter (September-December). On the basis of the overall results, higher maximum concentrations for all compounds were observed in 2004 than in 2003. Higher median concentrations were also observed in 2004 for mecoprop, dichlorprop, and metoVOL. 42, NO. 22, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
8455
TABLE 2. Summary Statistics for Chiral Herbicides in Ontario Streams
range mean SD median n
EF, mecoprop
EF, dichlorprop
S/R, metolachlor
0.236-0.928 0.470 0.113 0.490 72
0.152-0.549 0.300 0.123 0.286 10
1.08-12.7 6.73 2.28 7.33 148
summary statistics (2-tailed t test) EF, mecoprop p N Mean EF ( s.d. agricultural vs urban agric. row crop vs agric. fruitland S/R, metolachlor agricultural vs urban agric. row crop vs agric. fruitland
0.24
39 vs 23
0.07
11 vs 28
0.0003
96 vs 49
0.036
48 vs 48
0.442 ( 0.122 vs 0.473 ( 0.084 0.490 ( 0.088 vs 0.423 ( 0.130 Mean S/R ( s.d. 7.26 ( 2.17 vs 5.80 ( 2.21 6.79 ( 2.49 vs 7.79 ( 1.70
summary statistics (SYSTAT 12) mecoprop dichlorprop
FIGURE 3. Log scale box-and-whiskers plots of acid herbicide concentrations in 2003 and 2004. In each case, the center box is bounded by the 25th and 75th percentiles; the cross depicts the median value whereas the vertical blue line represents the standard deviation. Lines A and B: log value of Water Quality Guidelines for metolachlor and mecoprop, respectively (CCME); there is no guideline for dichlorprop. Numbers beside the boxes represent the positive/total samples. lachlor. Twenty Mile Creek-Bailey (Station #1), 20 Mile CreekCherry (Station #2), Indian Creek (Station #3), and Vineland Creek (Station #4) were the sites where sampling was carried out both in 2003 and 2004 (Tables S1 and S2, Figure 2). In general, quantitation frequencies in these watersheds during 2003 and 2004 were similar. The highest concentrations for mecoprop, dichlorprop, and metolachlor in 2003 were 1900, 6.62, and 1560 ng L-1 from Station #14 (Vineland Creek, 2 July, mecoprop), Station #7 (Indian Creek, 3 July, dichlorprop), and Station #1 (20 Mile Creek-Bailey, 17 June, metolachlor) (Figure 2 and Table S1). In 2004, the highest concentrations were 103,000, 110, and 5290 ng L-1 from Station #14 (Vineland Creek, 26 August, mecoprop), Station #20 (Chatham, 29 June, dichlorprop), and Station #32 (Nissouri Creek, 14 June, metolachlor) (Figure 2 and Table S1). Plots of frequency vs concentration (C) and log C are shown in Supporting Information, Figure S3. Skewness and kurtosis, and their standard errors SES and SEK, for these distributions were calculated using Systat v. 12 (Systat Software Inc., Chicago, IL) (Table 2). Skewness is a measure of asymmetry of a distribution around its mean; kurtosis is a measure of flatness or peakedness compared to a normal distribution. Frequency vs C distributions have significant skewness and kurtosis, as shown by coefficients (skewness/ SES and kurtosis/SES) >2. Plots of frequency vs log C do not show significant kurtosis (Table 2). There is still significant skewness for dichlorprop and metolachlor (though far less than for frequency vs C distributions), but not for mecoprop. The Shapiro-Wilk test indicates non-normal distributions of log C for all compounds (p < 0.001). Land use data were available for 211, 115, and 201 samples in both years for mecoprop, dichlorprop, and metolachlor, respectively. A 2-tailed Student’s t test showed that land use has a significant effect on concentrations of metolachlor, with concentrations at agricultural sites (n ) 161) being higher 8456
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 22, 2008
C
Log C
C
Log C
metolachlor C
Log C
skewness 14.80 0.31 4.86 0.80 5.65 0.64 std error of 0.163 0.163 0.217 0.217 0.172 0.172 skewness (SES) kurtosis 220.40 -0.47 27.82 0.42 47.46 -0.45 std error of 0.32 0.32 0.43 0.43 0.34 0.34 kurtosis (SEK) p (shapiro-Wilk
