Environmental concentrations of agricultural herbicides: 2,4-d and triallate

Occurrence and transformation of phenoxy acids in aquatic environment and photochemical methods of their removal: a review

The article presents the behavior of phenoxy acids in water, the levels in aquatic ecosystems, and their transformations in the water environment. Phenoxy acids are highly soluble in water and weakly absorbed in soil. These highly mobile compounds are readily transported to surface and groundwater. Monitoring studies conducted in Europe and in other parts of the world indicate that the predominant phenoxy acids in the aquatic environment are mecoprop, 4-chloro-2-methylphenoxyacetic acid (MCPA), dichlorprop, 2,4-dichlorophenoxyacetic acid (2,4-D), and their metabolites which are chlorophenol derivatives. In water, the concentrations of phenoxy acids are effectively lowered by hydrolysis, biodegradation, and photodegradation, and a key role is played by microbial decomposition. This process is determined by the qualitative and quantitative composition of microorganisms, oxygen levels in water, and the properties and concentrations of phenoxy acids. In shallow and highly insolated waters, phenoxy acids can be decomposed mainly by photodegradation whose efficiency is determined by the form of the degraded compound. Numerous studies are underway on the use of advanced oxidation processes (AOPs) to remove phenoxy acids. The efficiency of phenoxy acid degradation using AOPs varies depending on the choice of oxidizing system and the conditions optimizing the oxidation process. Most often, methods combining UV radiation with other reagents are used to oxidize phenoxy acids. It has been found that this solution is more effective compared with the oxidation process carried out using only UV.

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.

Mutagenic assessment of Lithobates catesbeianus tadpoles exposed to the 2,4-D herbicide in a simulated realistic scenario

The aim of the current study is to assess possible erythrocyte mutagenic effects on Lithobates catesbeianus tadpoles exposed to water contaminated with 2,4-D. In order to do so, tadpoles were exposed to a predictive and environmentally relevant herbicide concentration (1.97 mg/L), which is likely to be found in lentic environments formed by superficial water runoffs in pasture areas where the herbicide was applied. The micronucleus test, as well as tests for other nuclear abnormalities, was conducted after 3, 5, and 9 days of exposure (d.e.). Changes in the biomass and mouth-cloaca length or interference in the larval development of the animals (in the three evaluated times) were not recorded. However, tadpoles exposed to 2,4-D showed the highest total number of nuclear abnormalities, as well as the highest frequency of binucleated erythrocytes and kidney-shaped nuclei (shortly after 3 d.e.). The micronucleus frequency was also higher in animals exposed to 2,4-D (in the 3rd, 5th, and 9th d.e.), as well as the frequency of binucleated cells (3rd, 5th, and 9th d.e.) presenting notched (9th d.e.) and blebbled (9th d.e.) nuclei in comparison to those of the control, after 5 and 9 days of exposure. Therefore, the current study is a pioneer in showing that 2,4-D has a mutagenic effect on L. catesbeianus tadpoles, even at low concentrations (environmentally relevant) and for a short period of time, a fact that may lead to direct losses in anuran populations living in areas adjacent to those subjected to 2,4-D herbicide application.

Critical and systematic evaluation of data for estimating human exposures to 2,4-dichlorophenoxyacetic acid (2,4-D) - quality and generalizability

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been commercially available since the 1940's. Despite decades of data on 2,4-D in food, air, soil, and water, as well as in humans, the quality the quality of these data has not been comprehensively evaluated. Using selected elements of the Biomonitoring, Environmental Epidemiology, and Short-lived Chemicals (BEES-C) instrument (temporal variability, avoidance of sample contamination, analyte stability, and urinary methods of matrix adjustment), the quality of 156 publications of environmental- and biomonitoring-based 2,4-D data was examined. Few publications documented steps were taken to avoid sample contamination. Similarly, most studies did not demonstrate the stability of the analyte from sample collection to analysis. Less than half of the biomonitoring publications reported both creatinine-adjusted and unadjusted urine concentrations. The scope and detail of data needed to assess temporal variability and sources of 2,4-D varied widely across the reviewed studies. Exposures to short-lived chemicals such as 2,4-D are impacted by numerous and changing external factors including application practices and formulations. At a minimum, greater transparency in reporting of quality control measures is needed. Perhaps the greatest challenge for the exposure community is the ability to reach consensus on how to address problems specific to short-lived chemical exposures in observational epidemiology investigations. More extensive conversations are needed to advance our understanding of human exposures and enable interpretation of these data to catch up to analytical capabilities. The problems defined in this review remain exquisitely difficult to address for chemicals like 2,4-D, with short and variable environmental and physiological half-lives and with exposures impacted by numerous and changing external factors.

Effects of a herbicide mixture on primary and bacterial productivity in four prairie wetlands with varying salinities: an enclosure approach

Wetlands in the Prairie pothole region of Saskatchewan and Manitoba serve an important role in providing wildlife habitat, water storage and water filtration. They display a wide range of water quality parameters such as salinity, nutrients and major ions with sulfate as the dominant ion for the most saline wetlands. The differences in these water quality parameters among wetlands are reflected in the composition of aquatic plant communities and their productivity. Interspersed within an intensely managed agricultural landscape where pesticides are commonly used, mixtures of herbicides are often detected in these wetlands as well as in rivers, and drinking water reservoirs. One freshwater and three wetlands of varying salinity in the St. Denis National Wildlife Area, Saskatchewan, Canada were selected to study the effects of a mixture of eight herbicides (2,4-D, MCPA, dicamba, clopyralid, bromoxynil, mecoprop, dichlorprop, and glyphosate) on wetland microbial communities using an outdoor enclosure approach. Six enclosures (three controls and three treatments) were installed in each wetland and the herbicide mixture added to the treatment enclosures. The concentration of each herbicide in the enclosure water was that which would have resulted from a direct overspray of a 0.5-m deep wetland at its recommended field application rate. After herbicide addition, primary and bacterial productivity, and algal biomass were measured in both planktonic and benthic communities over 28 days. The herbicide mixture had a stimulatory effect on primary productivity in the nutrient-sufficient freshwater wetland while no stimulatory effect was observed in the nutrient-deficient saline wetlands. The differences observed in the effects of the herbicide mixture appear to be related to the nutrient bioavailability in these wetlands.

Influence of usage and chemical-physical properties on the atmospheric transport and deposition of pesticides to agricultural regions of Manitoba, Canada

This study quantified the masses of 14 pesticides deposited as wet (precipitation) versus dry (gaseous and particle) atmospheric deposition at a research farm in southwestern Manitoba, Canada. The concentration in air of these pesticides was also measured. Total bulk deposition amounts (wet+dry) ranged from 0.009 to 2.3 μg m(-2) for the 12 pesticides detected, and for the six pesticides with both wet and dry deposition detections, dry deposition contributed 12-51% of the total deposition over the crop growing season. Although not applied at the site, eight herbicides registered for use in Canada, as well as lindane (γ-HCH), were all frequently detected (92-100%) in the 12 air samples analyzed during the crop growing season, with by-product isomer α-HCH (75%), clopyralid (50%) and atrazine (8%) detected to a lesser extent. The chemical's physicochemical properties and the relative mean mass of each agricultural pesticide applied in the province of Manitoba and in a 13 km radius were significant parameters in explaining the trends in the concentrations of pesticides detected in our samples. The important contribution of dry deposition to total pesticide deposition warrants greater attention in arid and semi-arid areas such as the Prairie Region of Canada, also because under a changing climate this region is estimated to experience more severe droughts while the more favorable conditions predicted for pest infestations could lead to increased pesticide applications in agricultural and urban areas.

A multimedia activity model for ionizable compounds: validation study with 2,4-dichlorophenoxyacetic acid, aniline, and trimethoprim

Fugacity models are widely adopted for the environmental exposure assessment of organic chemicals but are inconvenient for nonvolatile substances, such as ionizable chemicals. The activity approach is a robust alternative to the fugacity concept and provides the thermodynamically exact equations to describe the behavior of neutral and ionizable molecules in nonideal systems. A multimedia activity model applicable to neutral and ionizable molecules (MAMI) was developed and tested for 2,4-dichlorophenoxyacetic acid and the bases aniline and trimethoprim. The model features pH and ionic strength dependence and species-specific estimations of partition coefficients from physicochemical properties. Sorption estimates consider both lipophilic and electrical interactions. A realistic regional exposure scenario was simulated for the three test compounds, and model results were compared with results obtained with a conventional fugacity model and with monitoring data. The better performance of MAMI indicates that the activity approach can enlarge the applicability domain and improve model predictions of existing regional models. Model results, supported by experimental evidence, showed the importance of dissociation, electrical interactions in solids, humidity in air, and to a lesser extent salinity in seawater to describe the environmental fate of ionizable organic chemicals.

Perturbation of lipids and glucose metabolism associated with previous 2,4-D exposure: a cross-sectional study of NHANES III data, 1988-1994

BACKGROUND

Results from previous population studies showed that mortality rates from acute myocardial infarction and type-2 diabetes during the 1980s and 1990s in rural, agricultural counties of Minnesota, Montana, North and South Dakota, were higher in counties with a higher level of spring wheat farming than in counties with lower levels of this crop. Spring wheat, one of the major field crops in these four states, was treated for 85% or more of its acreage with chlorophenoxy herbicides. In the current study NHANES III data were reviewed for associations of 2,4-dichlorophenoxy acetic acid (2,4-D) exposure, one of the most frequently used chlorophenoxy herbicides, with risk factors that are linked to the pathogenesis of acute myocardial infarction and type-2 diabetes, such as dyslipidemia and impaired glucose metabolism.

METHODS

To investigate the toxicity pattern of chlorophenoxy herbicides, effects of a previous 2,4-D exposure were assessed by comparing levels of lipids, glucose metabolism, and thyroid stimulating hormone in healthy adult NHANES III subjects with urinary 2,4-D above and below the level of detection, using linear regression analysis. The analyses were conducted for all available subjects and for two susceptible subpopulations characterized by high glycosylated hemoglobin (upper 50th percentile) and low thyroxine (lower 50th percentile).

RESULTS

Presence of urinary 2,4-D was associated with a decrease of HDL levels: 8.6% in the unadjusted data (p-value = 0.006), 4.8% in the adjusted data (p-value = 0.08), and 9% in the adjusted data for the susceptible subpopulation with low thyroxine (p-value = 0.02). An effect modification of the inverse triglycerides-HDL relation was observed in association with 2,4-D. Among subjects with low HDL, urinary 2,4-D was associated with increased levels of triglycerides, insulin, C-peptide, and thyroid stimulating hormone, especially in the susceptible subpopulations. In contrast, subjects with high HDL did not experience adverse 2,4-D associated effects.

CONCLUSIONS

The results indicate that exposure to 2,4-D was associated with changes in biomarkers that, based on the published literature, have been linked to risk factors for acute myocardial infarction and type-2 diabetes.

Liquid chromatography with post-column reagent addition of ammonia in methanol coupled to negative ion electrospray ionization tandem mass spectrometry for determination of phenoxyacid herbicides and their degradation products in surface water

A new liquid chromatography (LC)-negative ion electrospray ionization (ESI(-))-tandem mass spectrometry (MS/MS) method with post-column addition of ammonia in methanol has been developed for the analysis of acid herbicides: 2,4-dichlorophenoxy acetic acid, 4-chloro-o-tolyloxyacetic acid, 2-(2-methyl-4-chlorophenoxy)butyric acid, mecoprop, dichlorprop, 4-(2,4-dichlorophenoxy) butyric acid, 2,4,5-trichlorophenoxy propionic acid, dicamba and bromoxynil, along with their degradation products: 4-chloro-2-methylphenol, 2,4-dichlorophenol, 2,4,5-trichlorophenol and 3,5-dibromo-4-hydroxybenzoic acid. The samples were extracted from the surface water matrix using solid-phase extraction (SPE) with a polymeric sorbent and analyzed with LC ESI(-) with selected reaction monitoring (SRM) using a three-point confirmation approach. Chromatography was performed on a Zorbax Eclipse XDB-C18 (50 x 4.6 mm i.d., 1.8 mum) with a gradient elution using water-methanol with 2 mM ammonium acetate mobile phase at a flow rate of 0.15 mL/min. Ammonia in methanol (0.8 M) was added post-column at a flow rate of 0.05 mL/min to enhance ionization of the degradation products in the MS source. One SRM transition was used for quantitative analysis while the second SRM along with the ratio of SRM1/SRM2 within the relative standard deviation determined by standards for each individual pesticide and retention time match were used for confirmation. The standard deviation of ratio of SRM1/SRM2 obtained from standards run on the day of analysis for different phenoxyacid herbicides ranged from 3.9 to 18.5%. Limits of detection (LOD) were between 1 and 15 ng L(-1) and method detection limits (MDL) with strict criteria requiring <25% deviation of peak area from best-fit line for both SRM1 and SRM2 ranged from 5 to 10 ng L(-1) for acid ingredients (except dicamba at 30 ng L(-1)) and from 2 to 30 ng L(-1) for degradation products. The SPE-LC-ESI(-) MS/MS method permitted low nanogram-per-liter determination of pesticides and degradation products for surface water samples.

Assessment of potential aquatic herbicide impacts to California aquatic ecosystems

A series of legal decisions culminated in 2002 with the California State Water Resources Control Board funding the San Francisco Estuary Institute to develop and implement a 3-year monitoring program to determine the potential environmental impacts of aquatic herbicide applications. The monitoring program was intended to investigate the behavior of all aquatic pesticides in use in California, to determine potential impacts in a wide range of water-body types receiving applications, and to help regulators determine where to direct future resources. A tiered monitoring approach was developed to achieve a balance between program goals and what was practically achievable within the project time and budget constraints. Water, sediment, and biota were collected under "worst-case" scenarios in close association with herbicide applications. Applications of acrolein, copper sulfate, chelated copper, diquat dibromide, glyphosate, fluridone, triclopyr, and 2,4-D were monitored. A range of chemical analyses, toxicity tests, and bioassessments were conducted. At each site, risk quotients were calculated to determine potential impacts. For sediment-partitioning herbicides, sediment quality triad analysis was performed. Worst-case scenario monitoring and special studies showed limited short-term and no long-term toxicity directly attributable to aquatic herbicide applications. Risk quotient calculations called for additional risk characterizations; these included limited assessments for glyphosate and fluridone and more extensive risk assessments for diquat dibromide, chelated copper products, and copper sulfate. Use of surfactants in conjunction with aquatic herbicides was positively associated with greater ecosystem impacts. Results therefore warrant full risk characterization for all adjuvant compounds.

Effects of prevalent freshwater chemical contaminants on in vitro growth of Escherichia coli and Klebsiella pneumoniae

Many surface and ground waters in the continental US are contaminated with a variety of chemical pollutants, which are usually present in concentrations in the ppm and ppb range. The effects of these pollutants on coliform bacteria, which are prominent members of the aquatic flora, are poorly understood. Using a microtiter plate assay, isolates of Escherichia coli (from chicken intestine and fresh water), and an isolate of Klebsiella pneumoniae (from bovine milk) were exposed to varying concentrations of common pollutants over a 24 h period. The herbicides/pesticides simazine, atrazine, and diazinon; the VOCs trichloroethene and MTBE; the estrogens estradiol and estrone; and caffeine, all failed to inhibit bacterial growth at ppm levels. Only ethylene glycol, and the herbicide 2,4-D, significantly inhibited bacterial growth compared to controls. These results suggest that the replication of coliform bacteria in fresh waters is not adversely impacted by many common pollutants.

Mortality from ischemic heart disease and diabetes mellitus (type 2) in four U.S. wheat-producing states: a hypothesis-generating study

In this ecologic study I examined ischemic heart disease (IHD) and diabetes mortality in rural agricultural counties of Minnesota, Montana, North Dakota, and South Dakota, in association with environmental exposure to chlorophenoxy herbicides, using wheat acreage as a surrogate exposure. I collected data on agricultural land use and 1979-1998 mortality from the U.S. Department of Agriculture and the Centers for Disease Control and Prevention websites, respectively. Counties were grouped based on percentage of land area dedicated to wheat farming. Poisson relative risks (RR) and 95% confidence intervals (CIs), comparing high- and medium- with low-wheat counties, were obtained for IHD, the subcategories acute myocardial infarction (AMI) and coronary atherosclerosis (CAS), and diabetes, adjusting for sex, age, mortality cohort, and poverty index. Mortality from IHD was modestly increased (RR = 1.08; 95% CI, 1.04-1.12). Analyses of its two major forms were more revealing. Compared with low-wheat counties, mortality in high-wheat counties from AMI increased (RR = 1.20; 95% CI, 1.14-1.26), and mortality from CAS decreased (RR = 0.89; 95% CI, 0.83-0.96). Mortality from AMI was more pronounced for those < 65 years of age (RR = 1.31; 95% CI 1.22-1.39). Mortality from type 2 diabetes increased (RR = 1.16; 95% CI, 1.08-1.24). These results suggest that the underlying cause of mortality from AMI and type 2 diabetes increased and the underlying cause of mortality from CAS decreased in counties where a large proportion of the land area is dedicated to spring and durum wheat farming. Firm conclusions on causal inference cannot be reached until more definitive studies have been conducted.