Metolachlor, concentrations

A vegetative filter strip reduced losses of metribuzin and metolachlor by more than 85% (Webster and Shaw, 1996). Grassed waterways reduced loads of 2,4-D by 69% and 71% under wet and dry conditions, respectively (Asmussen et al., 1977), while trifluralin retention dropped from 96% under dry conditions to 86% under wet conditions (Rhode et al., 1980). A 6-m vegetative buffer strip composed of trees, shrubs, and grass almost completely removed terbuthylazine from runoff (Vianello et al., 2005). Oats as a strip crop below corn reduced atrazine runoff losses by 91% and 65% after applications of 2.2 and 4.5kg/ha, respectively (Hall et al., 1983). Atrazine and metolachlor concentrations in runoff were reduced 83-94% and 82-96%, respectively, with 4.3- and 8.5-m vegetative filter strips (Barone et al., 1998). 

Figure 2. Flow rate and atrazine and metolachlor concentrations in the Susquehanna River in 1994 26).

Conservation tillage increased atra2ine and metolachlor surface mnoff by 42% and decreased tile discharge by 15% compared with conventional tillage, but total field mnoff was the same from all treatments (53). Runoff events shordy after herbicide appHcation produced the greatest herbicide concentrations and losses in both surface mnoff and subsurface drainage. 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

Acetochlor, alachlor, and metolachlor are determined in ground and surface water samples. Deuterated internal standards are added to each water sample, and analytes are extracted using an SPE column. After elution and concentration to an appropriate volume, the analytes are quantitated by GC/MS. 

Limits of detection for each of the three parent herbicides in surface and groundwater were determined using results obtained from control samples analyzed along with hundreds of surface and ground water sets during the years 1995-2001. In each of these years, the calculated LODs (minimum detectable true concentrations/detection) were below 0.03 pg for acetochlor and metolachlor and 0.05 pg for alachlor. A detection criterion is a measured concentration threshold that defines a likely upper bound for samples not containing the analyte. If the actual concentration of an analyte is at this detection limit or greater, there is at least a 95% chance of detection. 

LOQs for each of the three parent herbicides in surface water were determined using all the analytical results (not corrected for background) of samples fortified at the lowest fortification level, 0.05 pgL , during the analysis in years 1995-2001. The calculated LOQs were below 0.05 pgL for acetochlor and metolachlor and approximately 0.05 pgL for alachlor. If the true concentration of an analyte is at the LOQ or greater, the standard error of individual measured concentration values relative to the true concentration is at most 10%. 

Results of adsorption experiments for butylate, alachlor, and metolachlor in Keeton soil at 10, 19, and 30°C were plotted using the Freundlich equation. A summary of the coefficients obtained from the Freundlich equation for these experiments is presented in TABLE IV. Excellent correlation using the Freundlich equation over the concentration ranges studied (four orders of magnitude) is indicated by the r values of 0.99. The n exponent from the Freundlich equation indicates the extent of linearity of the adsorption isotherm in the concentration range studied. If n = 1 then adsorption is constant at all concentrations studied (the adsorption isotherm is linear) and K is equivalent to the distribution coefficient between the soil and water (Kd), which is the ratio of the soil concentration (mole/kg) to the solution concentration (mole/L). A value of n > 1 indicates that as the solution concentration increases the sorption sites become saturated, resulting in a disproportionate amount of chemical being dissolved. Since n is nearly equal to 1 in these studies, the adsorption isotherms are nearly linear and the values for Kd (shown in TABLE IV) correspond closely to K. These Kd values were used to calculate heats of adsorption (AH). 

The most ubiquitous pesticide was simazine, present in 80% of the samples, followed by atrazine, diuron, DEA and diazinon, present in more than 50% of the samples (64%, 56%, 56% and 50%, respectively). Cyanazine, molinate, fenitro-thion and mecoprop were detected in less than 5% of the samples. The maximum individual concentrations were observed for alachlor (9,950 ng/L in M33, 2008), dimethoate (2,277 ng/L in M35, 2010), DEA (1,370 ng/L in M48, 2007) and linuron (1,010 ng/L in M33, 2008), while many others, such as terbuthylazine, DIA, atrazine and metolachlor, presented levels also higher than 500 ng/L. Results are consistent when evaluated with the GUS index (see Table 2). Mots triazines and metolachlor, i.e., the compounds with GUS index > 3 and therefore with higher leaching potential, were among the most ubiquitous an abundant compounds. In contrast, fenitrothion, which according to its GUS index (0.64) is a nonlixiviable pesticide, was detected at low levels in less than 5% of the samples. 

In the Ebro river zone (NE Spain), pesticide concentrations in groundwater were much higher than in the Llobregar river area. Hildebrandt et al. [18, 19] found in groundwater samples collected in 2000-2001 very high levels of metolachlor (10-2000 ng/L) and triazines (2460, 1980, 1270, 790 and 540 ng/L for atrazine, DEA, terbuthylazine, DIA and simazine, respectively). However, 3 years later (2004), triazines concentrations decreased dramatically, whereas metolachlor presented levels even higher (from 2,000 to 5,370 ng/L). 

Another example of the potential pernicious effects of pesticides upon human health is the study conducted at the University of Colorado where researchers have found that higher concentrations of four pesticides - atrazine, simazine, alachlor and metolachlor - in groundwater are significantly associated with higher levels of Parkinson disease. For every 10 pg/L increase of pesticide levels in the drinking water, they found that the risk for Parkinson disease increased by 3% and their water samples had pesticide concentrations ranging from 0.0005 to 20 pg/L [38]. 

Extracts of samples from the Agronomy pit were also analyzed for chlorambem, glyphosate, malathion, metolachlor and perflura-lin. They were either not detected or, if detected, concentrations were <1 ppm. Plots are not included for several pesticides where only results from 1979 were available. These pesticides, with their average ppm concentrations in parentheses, were bentazon (150), 2,4-D (30), dicamba (10), paraquat (20) and 2,4,5-T (40). 

This study will provide fundamental information on the effect of stereoisomerism on the environmental fate of a widely used chloroacetanilide herbicide, metolachlor. Metolachlor is classified as a potential carcinogen and is the second most extensively used herbicide in the United States (7). Biological dechlorination of metolachlor leads to the formation of more polar metabolites (8), metolachlor oxanilic acid (OXA), and metolachlor ethanesulfonic acid (ESA) (Figure 3). Metolachlor OXA and metolachlor ESA are found at higher concentrations and are more frequently detected in surface and ground water than their parent compound (9). 

After elution from the SPE cartridges, the eluents will be evaporated slowly under nitrogen gas. The concentrated samples containing metolachlor will be analyzed by GC/MS while the fractions containing the polar metabolites will be analyzed by HPLC. Both the GC and HPLC will be equipped with chiral columns. For GC/MS, a fused silica column coated with tert-butyldimethylsilyl-P-cyclodextrin will be used. This column has been shown to partially separate metolachlor isomers (13). 

Both atrazine and metolachlor are classified as potential human carcinogens by the USEPA, which has established a maximum contaminant level in drinking water of 3000 ng/L [78]. The maximum concentrations of atrazine and metolachlor measured in the 1994-2000 Great Lakes survey were 1039 ng/L and 736 ng/L, respectively. The effects of long-term, low-level concentrations of atrazine and metolachlor on aquatic ecosystems are largely unknown [79]. The Canadian guidelines for the protection of aquatic fife and drinking water (Table 8) were not exceeded for either of these herbicides [80-83]. 

Metolachlor. Both state reports of metolachlor are new. It was found in 4 out of 82 wells sampled in the USGS central Pennsylvania study (57). Metolachlor was also found in a well in an incipient karst area and two springs draining a solution limestone aquifer in northern Iowa (48, 49). Concentrations typically range between 0.1 and 0.5 ppb. 

So far only certain details of the biochemical mode of action of metolachlor are known. Pillai and Davis (1975) found that in 2 hours metolachlor at a concentration of 110 mole/dm reduced the photosynthesis of Chlorella pyrenoidosa by 33%. It is remarkable that the other structural analogue investigated CGA 17020, 2-chloro-N-(2-methoxyethyl)-2,6-dimethylacetanilide, does not inhibit photosynthesis at this concentration. 

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