Chlorinated Phenoxy Acid Herbicides Research Articles

Real-Time Measurement of Herbicides in the Atmosphere: A Case Study of MCPA and 2,4-D during Field Application.

Atmospheric sources of herbicides enable short- and long-range transport of these compounds to off-target areas but the concentrations and mechanisms are poorly understood due, in part, to the challenge of detecting these compounds in the atmosphere. We present chemical ionization time-of-flight mass spectrometry as a sensitive, real-time technique to detect chlorinated phenoxy acid herbicides in the atmosphere, using measurements during and after application over a field at Colorado State University as a case study. Gas-phase 2,4-dichlorophenoxyacetic acid (2,4-D) mixing ratios were greatest during application (up to 20 pptv), consistent with rapid volatilization from spray droplets. In contrast, atmospheric concentrations of 2-methyl-4-chlorophenoxyacetic acid (MCPA) increased for several hours after the initial application, indicative of a slower source than 2,4-D. The maximum observed gas-phase MCPA was 60 pptv, consistent with a post-application volatilization source to the atmosphere. Exposure to applied pesticides in the gas-phase can thus occur both during and at least several hours after application. Spray droplet volatilization and direct volatilization from surfaces may both contribute pesticides to the atmosphere, enabling pesticide transport to off-target and remote regions.

Atmospheric OH Oxidation of Three Chlorinated Aromatic Herbicides.

Chlorinated phenoxy acids are a widely used class of herbicides and have been found in remote regions far from sources. However, the atmospheric chemistry of these compounds is poorly understood. We use an oxidative flow reactor coupled to chemical ionization mass spectrometry to investigate OH oxidation of two chlorinated phenoxyacid herbicides (2-methyl-4-chlorophenoxyacetic acid (MCPA) and mecoprop-p) and one chlorinated pyridine herbicide (triclopyr). OH radicals add to the aromatic rings of the three herbicides, produce peroxides via hydrogen abstraction, or fragment at the ether bond. OH oxidation of MCPA produced two potentially toxic compounds: chlorosalicylaldehyde and chlorosalicylic acid. We use standards to validate the detection of these oxidation products by acetate CIMS and quantify the reaction rate. Oxidation of triclopyr produced a known endocrine disruptor, 3,5,6-trichloro-2-pyridinol. Thus, while some OH oxidation products are less toxic than the parent molecules (e.g., C1-5 carboxylic acids), others may be as or more toxic than the parent herbicide. We determine effective rate coefficients for OH addition to the aromatic ring ( kOH) for mecoprop-p of 1.5 (±0.7) × 10-12 cm3 molecules-1 s-1 and for MCPA of 2.6 (±0.3) × 10-12 cm3 molecules-1 s-1. The atmospheric lifetimes with respect to OH are thus long enough that photochemistry may be relevant to the environmental fate of these pesticides.

Determination of Chlorinated Phenoxy Acid Herbicides in Tobacco by Modified QuEChERS Extraction and High-Performance Liquid Chromatography/Tandem Mass Spectrometry

A new method for determination of phenoxy acid herbicide residues in tobacco based on the use of liquid extraction/partition and dispersive SPE followed by HPLC/electrospray ionization-MS/MS is reported. Formic acid (2%, v/v) in acetonitrile as the extraction solvent and inclusion of citrate buffer helped partitioning of all analytes into the acetonitrile phase. Quantitative analysis was done in the multiple-reaction monitoring mode using two combinations of selected precursor ion and product ion transition for each compound. The recoveries obtained for each pesticide ranged between 85 and 110% at two spike concentration levels. Good linear relationships were observed, with the correlation coefficient (r2) >0.998 for all analytes. The method is simple, efficient, and sensitive, and each of its performance characteristics meets the requirements for determination of phenoxy acid herbicide residues in tobacco.

Group-specific fragmentation of pesticides and related compounds in liquid chromatography–tandem mass spectrometry

Current strategies in the LC–MS analysis of pesticides and related compounds in environmental samples, fruits and vegetables, and biological samples mostly rely on the selection of appropriate precursor/product-ion combinations (transitions) for selected reaction monitoring (SRM), often based on automated parameter optimization and selection of the transition. Such a procedure does not require any information on the type of fragmentation reaction involved in the generation of the product ion from the selected precursor ion. However, such information does become important in untargeted screening for unknown contaminants in environmental and food samples, which are generally based on a combination of high-resolution mass spectrometry and (multistage) tandem mass spectrometry. With this in mind, the group-specific fragmentation behaviour has been studied for six classes of pesticides and herbicides, i.e., triazines, organophosphorous pesticides, phenylurea herbicides, carbamates, sulfonylurea herbicides, and chlorinated phenoxy acid herbicides. When relevant, some comparison was made between fragmentation of protonated molecules in MS–MS and of molecular ions generated by electron ionization in GC–MS.

Automated on-line in-tube solid-phase microextraction followed by liquid chromatography/electrospray ionization-mass spectrometry for the determination of chlorinated phenoxy acid herbicides in environmental waters.

A method for the determination of six chlorinated phenoxy acid herbicides in river water was developed using in-tube solid-phase microextraction (SPME) followed by liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS). In-tube SPME is an extraction technique for organic compounds in aqueous samples, in which analytes are extracted from a sample directly into an open tubular capillary by repeated draw/eject cycles of the sample solution. Simple mass spectra with strong signals corresponding to [M-H]- and [M-RCOOH]- were observed for all herbicides tested in this study. The best separation of these compounds was obtained with a C18 column using linear gradient elution with a mobile phase of acetonitrile-water containing 5 mmol l-1 dibutylamine acetate (DBA). To optimize the extraction of herbicides, several in-tube SPME parameters were examined. The optimum extraction conditions were 25 draw/eject cycles of 30 microliters of sample in 0.2% formic acid (pH 2) at a flow rate of 200 microliters min-1 using a DB-WAX capillary. The herbicides extracted by the capillary were easily desorbed by 10 microliters acetonitrile. Using in-tube SPME-LC/ESI-MS with time-scheduled selected ion monitoring, the calibration curves of herbicides were linear in the range 0.05-50 ng ml-1 with correlation coefficients above 0.999. This method was successfully applied to the analysis of river water samples without interference peaks. The limit of quantification was in the range 0.02-0.06 ng ml-1 and the limit of detection (S/N = 3) was in the range 0.005-0.03 ng ml-1. The repeatability and reproducibility were in the range 2.5-4.1% and 6.2-9.1%, respectively.

Application of the Base-Promoted Esterification Procedure to the Chlorophenoxy Acid Herbicides of U.S. EPA Method 515.3

Determination of chlorinated phenoxyacid herbicides by gas chromatography is complicated by the fact that these compounds exhibit low volatilities due to the hydrogen bonding of their carboxylic acid and phenol functionalities. Furthermore, these functional groups can cause the parent molecule to adsorb on the stationary phase of the column, thus producing asymmetric peaks. Masking of these polar groups can significantly increase the volatility and reduce the adsorption effects of these compounds, yielding products that can undergo analysis by gas chromatography. A variety of reactions have been employed in the preparation of less polar derivatives. Two categories are examined in this work: silylation and alkylation. Within the category of alkylation, derivatization techniques examined include acid-catalyzed esterification, extractive alkylation, and base-promoted esterification. Of all the investigated techniques, base-promoted esterification is determined to be the most effective. This paper reports the application of this procedure in the development of a sensitive method for the determination of a variety of phenoxyacid herbicides at concentrations below the microgram-per-liter level in water.

Rapid Extraction of Chlorinated Phenoxyacid Herbicides from Drinking Water Using Octadecylsilane Extraction Disks

A series of chlorinated phenoxyacid herbicides is extracted from 1 L of drinking water in approximately 10 min using 47-mm diameter polymer disks impregnated with octadecylsilane adsorbent. The herbicides are subsequently eluted with ethyl acetate and derivatized prior to analysis by gas chromatography-mass spectrometry. Overall average percent recoveries for the herbicides studied range from 71 to 91% for concentrations of 10, 1, and 0.1 μg/L of reagent water. Similar recoveries are observed for well water samples, which are fortified with known concentrations of each herbicide.

Evidence for thermal decomposition contributions to the mass spectra of chlorinated phenoxyacid herbicides obtained by particle beam liquid chromatography mass spectrometry

The spectral quality of a group of chlorinated phenoxyacid herbicides has been shown to degrade under certain conditions upon introduction into the mass spectrometer by a particle beam interface. Experiments were performed to investigate these changes in spectra. Normalized ion chromatograms were generated for the herbicides, and the results showed a broadening of the profiles of some ions, indicating a longer residence time in the ion source. These ions were postulated as coming from the ionization of thermal degradation products from the herbicides. The generation of these ions was dependent on ion source temperature, analyte concentration, and, by implication, ion source cleanliness. Tandem mass spectrometry experiments were performed on these ions from the herbicides and ions from the corresonding phenols. The tandem mass spectra of the ions from the herbicides were similar to the tandem mass spectra of the ions from the phenols. Therefore, it appears that the particle beam mass spectra of the chlorinated phenoxyacid herbicides are composite spectra with contributions from the gas phase ionization of the parent herbidides and thermal decomposition products.

Phenoxy herbicides and chlorophenols: a case control study on soft tissue sarcoma and malignant lymphoma.

A case control study on patients with soft tissue sarcoma and malignant lymphoma was undertaken to test whether there was any association between these diseases and past exposure to chlorinated phenoxy acid herbicides or chlorophenols. It was carried out over the period 1982-1988 in Victoria, Australia. Thirty males with soft tissue sarcoma and 52 males with malignant lymphoma were matched by age, place of residence and sex with one population control and one cancer control each. Exposure was assessed by personal interviews conducted by an occupational hygienist. Exposures within 5 years prior to diagnosis of each matched case were ignored, both for the cases and their matched controls. The estimated relative risks for definite or probable exposure to chlorinated phenoxy compounds or chlorophenols for at least 1 day were 1.0 (95% confidence interval (CI): 0.3-3.1) for soft tissue sarcoma and 1.5 (95% CI: 0.6-3.7) for malignant lymphoma. When the criterion for exposure was raised to more than 30 days, the estimated relative risks were 2.0 (95% CI: 0.5-8.0) for soft tissue sarcoma and 2.7 (95% CI: 0.7-9.6) for malignant lymphoma. Additional analyses were carried out for exposure of at least 1 day to phenoxy herbicides alone or chlorophenols alone. None of the estimated relative risks was significantly greater than unity.

Liquid chromatography—mass spectrometry — a new window for environmental analysis

A series of liquid chromatography methods using particle beam mass spectrometry has been developed to determine a broader range of organic pollutants. Results are presented on the determination of aromatic sulfonic acids in aqueous leachates; chlorinated phenoxy acid herbicides in soil and water; and of polyaromatic hydrocarbons from various matrices.

Interlaboratory comparison of thermospray and particle beam liquid chromatography/mass spectrometry interfaces: evaluation of a chlorinated phenoxy acid herbicide liquid chromatography/mass spectrometry analysis method

Seven laboratories participated in an interlaboratory evaluation of a liquid chromatography/mass spectrometry (LC/MS) method for the analysis of 10 chlorinated phenoxy acid herbicides. The focus of this evaluation was to test the intercomparability of LC/MS data obtained from too types of LC/MS interfaces [i.e., thermospray (TS) and particle beam (PB)]

The cytochrome P450 IV family: constitutive and inducible haemoproteins

The cytochrome P450 IV family: constitutive and inducible haemoproteins

Mortality of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid herbicide applicators in Finland: first report of an ongoing prospective cohort study.

Some recent epidemiologic studies have suggested that chlorinated phenoxy acid herbicides are human carcinogens. The mortality experience in a cohort of 1,926 men who had sprayed 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) during 1955-1971 has been followed prospectively from 1972 to 1980. The total phenoxy acid exposure was generally rather low because the duration of work had mostly been less than two months. In 1972-1976 mortality from all natural causes in the cohort was only 54% of the expected value (based on age-specific rates for the general population), and in the succeeding 4-a period 81% of the expected value. In the assessment of cancer, mortality allowance was made for 10- and 15-a periods of latency between the first exposure and the start of the recording of vital status during the follow-up. No increase in cancer mortality was detected, and the distribution of cancer types was unremarkable. No cases of death from lymphomas or soft tissue sarcomas were found. The study results must, however, be viewed with great caution owing to the small size of the cohort, the low past exposure, and the brief follow-up period.