Removal herbicides

Rugglerl, T. J., 1981, Determination of the ability of a flocculatlon/sedlmentatlon/actlvated carbon treatment plant to remove herbicides from application equipment wash water, and examination of the feasibility of bloassays for determination of activated carbon exhaustion. MSAE Thesis, Purdue Unlveslty, West Lafayette, Indiana. 

MAJOR USES Used in the production of resins, varnishes, perfumes, inks, paint removers, herbicides, whitening agents, artificial sweeteners solvent. 

The masses of vegetation produced by weed species such as elodea (Elodea canadensis Michx.), coontail (Ceratophyllum demersum L.), and Eurasian watermilfoil Myriophyllum spicatum L.) remove herbicide residues from water (14). Najas sp. and Potamogeton sp. in plastic pools... 

This chapter reports on the application of the electrokinetic process to remove herbicides such as atrazine, molinate, and bentazone from soils. The discussion is focused on (a) the assessment of the behavior of atrazine, molinate, and bentazone in soils when submitted to an electric field, and (b) the evaluation of the applicability of the technique to remove atrazine, molinate, and bentazone from soils. 

Figure 12.2 illustrates the cumulative mass of herbicide removed in some experiments (a) atrazine in experiment C (b) moUnate in experiment E and (c) ben-tazone in experiment I. Figure 12.3 presents the quantities of herbicide remaining at the end of all the experiments in the passive membranes, nearer the cathode (CAT membrane) and nearer the anode (AN membrane) in the soil, in the soil slice near to the cathode (CAT soil slice), in the central soil slide and in the soil slice nearer to the anode (AN soil slice) as well as an estimate of the removed herbicide percentages obtained. 

Other methods of determining adsorption involve flowing systems similar to that used to measure mobility these have been reviewed recently by Hance. Wahid and Sethunathan proposed a method for determination of rapidly adsorbed compounds for which the inclusion of a centrifugation stage precludes measurement of the kinetics of adsorption. Their method involved the use of a hypodermic syringe, with a filter to remove herbicide in solution. 

The FDA has pubhshed methods for the deterrnination of residual solvents in spice extracts such as oleoresins and has limited the concentrations of those specific solvents that are permitted. Chlorinated hydrocarbons and benzene have been almost completely removed from use as extracting solvents in the United States their use continues overseas where toxicity regulations are less stringent. The presence of pesticides or herbicides in spices is rigidly controHed by the FDA. 

Nonchemical or traditional practices, such as weed seed removal, optimal crop seeding rates, crop selection, enhanced crop competitiveness, crop rotation, and mechanical weed control are all important components of an effective weed management program (458,459). In the context of modern intensive chemical herbicide appHcation, nonchemical practices may even represent an innovative approach to weed management and should receive careful consideration. 

Sulfamic acid has a unique combination of properties that makes it particularly well suited for scale removal and chemical cleaning operations, the main commercial appHcations. Sulfamic acid is also used in sulfation reactions, pH adjustment, preparation of synthetic sweeteners (qv), and a variety of chemical processing appHcations. Salts of sulfamic acid are used in electroplating (qv) and electroforrning operations as well as for manufacturing flame retardants (qv) and weed and hnish killers (see Herbicides). 

Supercritical CO2 has also beea tested as a solveat for the removal of organic contaminants from sod. At 60°C and 41.4 MPa (6,000 psi), more than 95% of contaminants, such as diesel fuel and polychlotinated biphenyls (PCBs), may be removed from sod samples (77). Supercritical CO2 can also extract from sod the foUowiag hydrocarbons, polyaromatic hydrocarbons, chlotinated hydrocarbons, phenols, chlotinated phenols, and many pesticides (qv) and herbicides (qv). Sometimes a cosolvent is required for extracting the more polar contaminants (78). 

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. 

Herbicides. An array of herbicides are registered for use in aquatic sites, but copper sulfate and diquat dibromide are of additional interest because they also have therapeutic properties (9,10). Copper sulfate has been used to control bacteria, fungi, and certain parasites, including Jchthjophthirius (ich). Diquat dibromide can control columnaris disease, but it also exhibits fungicidal properties (9,10). EPA recentiy proposed to limit the amount of diquat dibromide, endothaH, glyphosate, and simazine that can be present in drinking water therefore, the use of these compounds may be reduced if they cannot be removed from the effluent. 

The second most important (3%) use of sodium chlorate in 1990 was as an intermediate in the production of other chlorates and of perchlorates. The use of sodium chlorate as in agricultural appHcation amounted to about 7000 metric tons in 1990. The agricultural use of sodium chlorate is as a herbicide, as a defoHant for cotton (qv). Magnesium chlorate is used as a desiccant for soybeans to remove the leaves prior to mechanical picking (see Desiccants). 

E. A. Hogendoorn, E. Dijkman, B. Baumann, C. Hidalgo, J. V. Sancho and E. Hernandez, Strategies in using analytical restricted access media columns for the removal of humic acid interferences in the trace analysis of acidic herbicides in water... 

The following brief account identifies only major groups of herbicides not mentioned elsewhere in the text, and is far from comprehensive. Their mode of action is only dealt with in a superficial way. From an ecotoxicological point of view, there has not been as much concern about their sublethal effects upon plants as there has been in the case of mammals, and there has not been a strong interest in the development of biomarker assays to establish their effects. The major concern has been whether weeds, or nontarget plants, have been removed following herbicide application—a rather easy matter to establish as plants are fairly sedentary. For a more detailed account of herbicide chemistry and biochemistry, see Hassall (1990). 

A very useful, but difficult, case has been reported by Smith and Barclay (1992) for the recovery of Monsanto s highly successful herbicide, glyphosphate (N-phosphonomethyl-glycine, tradename Roundup), from an aqueous waste stream. This stream contains a lot of unwanted products like HCHO, HCOOH, aminomethylphosphoric acid, and N-phosphonomethyl iminodiacetic acid (PMIDA). The removal of PMIDA and HCOOH from glyphosphate is essential as HCOOH can react to give the formyl derivative. Amberlite IRA-93 and Amberlite IRA-68 (anionic resins) were chosen to separate glyphosphate from PMIDA and HCOOH, respectively (HCHO does not get adsorbed). 1500 recovery cycles were tried, and the resin has two years plant life scale-up with a factor of 90,000 was very successful. 

The hydrilla 2-node explants were also sensitive to the herbicides chlorsulfuron. One part per billion chlorsulfuron (ca. 3 X 10 M reduced growth of new shoots by almost 80% but had no effect on new shoot initiation (Table XI). when the herbicide was removed after 14 days, new shoots began to elongate. 

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