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Dicamba
Published in Philip H. Howard, Edward M. Michalenko, William F. Jarvis, Dipak K. Basu, Gloria W. Sage, William M. Meylan, Julie A. Beauman, D. Anthony Gray, Handbook of Environmental FATE and EXPOSURE DATA, 2017
Philip H. Howard, Edward M. Michalenko, William F. Jarvis, Dipak K. Basu, Gloria W. Sage, William M. Meylan, Julie A. Beauman, D. Anthony Gray
Summary: Dicamba is released directly to the environment by its application as a herbicide for the control of annual broadleaf weeds. If released to soil, microbial degradation will probably be the major removal process under most conditions. The principal soil metabolite appears to be 3,6-dichlorosalicylic acid. Dicamba is very mobile in most soils and significant leaching is possible. Based on the results of one study, volatilization from soil surfaces may not be an important process, although some volatilization may occur from plant surfaces. The persistence half-life of dicamba in soil has been observed to vary from 4 to 555 days with the typical half-life being 1 to 4 weeks. Under conditions suitable to rapid metabolism, the half-life is less than two weeks. If released to water, microbial degradation appears to be the important dicamba removal process; photolysis may contribute to its removal from water. Aquatic hydrolysis, volatilization, adsorption to sediment, and bioconcentration are not expected to be significant. If released to the atmosphere, dicamba will probably exist in both the vapor-phase and adsorbed to particulate phase. The half-life for the vapor-phase reaction of dicamba with photochemically produced hydroxyl radicals has been estimated to be 6 days. Particulate phase dicamba will be subject to wet and dry deposition. General population exposure to dicamba may occur through oral consumption of contaminated drinking water. Occupational exposure via inhalation and dermal routes associated with application (spraying, loading and mixing) of dicamba as a herbicide may be significant.
Physical Properties of Agrochemicals
Published in John H. Montgomery, Thomas Roy Crompton, Environmental Chemicals Desk Reference, 2017
John H. Montgomery, Thomas Roy Crompton
The half-lives for dicamba in soil incubated in the laboratory under aerobic conditions ranged from 0 to 32 days (Altom and Stritzke, 1973; |Smith, 1973, 1974; Smith and Cullimore, 1975). In field soils, the half-lives for dicamba ranged from 6 to 10 days with an average half-life of 7 days (Scifres and Allen, 1973; Stewart and Gaul, 1977). The mineralization half-lives for dicamba in soil ranged from 147 to 309 days (Smith, 1974; Smith and Cullimore, 1975). In a Regina heavy clay, the loss of dicamba was rapid. Approximately 10% of the applied dosage was recovered after 5 weeks. At the end of 5 weeks, approximately 28% was transformed to 3,6-dichlorosalicylic acid and carbon dioxide (Smith, 1973a).
Drift
Published in James N. Seiber, Thomas M. Cahill, Pesticides, Organic Contaminants, and Pathogens in Air, 2022
James N. Seiber, Thomas M. Cahill
Dicamba (3,6-dichloro-2-methoxy benzoic acid) is a post-emergent, growth regulator herbicide used in agriculture for control of broad leaf weeds. The herbicide is volatile (4.5 mPa, 25°C). So, it must be applied as a salt, which, by definition, is normally nonvolatile. Drift to nontarget fields during application can be minimized by using ground rigs with height-adjusted (~24 in.) spray nozzles that produce aerosols of sufficient size that quickly deposit onto the target plants under optimum environmental conditions of temperature (<30°C) and wind speed (<10 mph). However, in practice, regardless of the dicamba formulation, damage to nearby, nontarget fields continues, implying that the herbicide volatilizes post application from treated fields, sometimes called “vapor drift.” This was observed early on for the dimethylamine salt and sodium salt formulations and continues to be observed for the newer diglycolamine formulations. A number of field studies have identified factors that contribute to post-application volatilization: (1) temperature (Behrens and Lueschen, 1979; Mueller and Steckel, 2019), (2) pH of the tank mix (Mueller and Steckel, 2019), (3) pH of the soil surface (Oseland et al., 2020), and (4) leaf surface in the area treated (Behrens and Lueschen, 1979). Only the factors that had a direct bearing on the stability of the dicamba salt are included here. Other factors that have been associated with volatilization and nontarget damage include the following (Behrens and Lueschen, 1979; Bish et al., 2019): (1) application rate; (2) application time of day; (3) effect of dicamba formulation; (4) rainfall and relative humidity; (5) time after application; and (6) wind speed and atmospheric stability.
Catalytic efficiency of laterite-based FeNPs for the mineralization of mixture of herbicides in water
Published in Environmental Technology, 2019
Sanjeev Sangami, Basavaraju Manu
The stock solutions (3 mmol L−1 of 2,4-D, dicamba and 0.4 mmol L−1 of ametryn) and standard solution (0.13–0.65 mmol L−1 of 2,4-D, dicamba and 0.02–0.1 mmol L−1 of ametryn) was prepared in HPLC grade water along with the calibration curves for all standards. The initial herbicide concentration was considered based on the actual values observed in the field (2,4-D = 25 mg L−1, ametryn = 3.5 mg L−1, dicamba = 94 mg L−1) [40]. Totally, 26 experiments were performed in a conical flask in triplicate (250 ml mixed herbicides prepared in deionized water) according to the central composite design (CCD) matrix (Tables 1 and 2) at room temperature (30–34°C) with shaking speed of 200 rpm and an average of three was finally used for the optimization process. After completion of each set of experiment, the sample was filtered (0.2 μm) and absorption intensity was measured with HPLC calibration curves (S1: Supplementary Material 1) and finally percent removal of each compound was calculated (Equation (1)). The mineralization of the all three compounds was measured as COD (Equation (2)) and interference due to H2O2 was corrected [41]. Finally, the catalyst reusability study was conducted in optimum conditions:where CODi is the initial COD (mg L−1) and CODf (mg L−1) is its final COD after designed reaction time.
Sediment-associated organopollutants, metals and nutrients in the Nechako River, British Columbia: a current study with a synthesis of historical data
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2019
Philip N. Owens, David J. Gateuille, Ellen L. Petticrew, Barry P. Booth, Todd D. French
Phenoxy acid herbicide (triclopyr, bromoxynil, clopyralid, 2,4-D, dicamba, 2,4-DB, 2,4-DP [dichlorprop], dinoseb, MCPA, MCPB, mecoprop, picloram, 2,4,5-T, and 2,4,5-TP) determinations in bottom sediment were done by ALS Environmental Ltd (Burnaby, BC) in collaboration with AXYS. Per ALS Method L1856769, 5-g samples were mixed with methanol, acidified and extracted with toluene; derivatized extracts were analyzed by capillary column GC-MS. Samples were run in batches of 20; each batch included a method blank based on Baked Ottawa Sand, a laboratory control and duplicate, phenoxy acid herbicide surrogates, a sample split duplicate, and a phenoxy acid herbicide matrix spike.