Mobility , field soil studies

Acid amide herbicides are nonionic and moderately retained by soils. The sorption of several acid amide herbicides has been investigated (369). Acetochlor [34256-82-1] is sorbed more than either alachlor or metolachlor, which are similarly sorbed by a variety of soils. Sorption of all the herbicides is well correlated to soil organic matter content. In a field lysimeter study, metolachlor has been found to be more mobile and persistent than alachlor (370) diphenamid [957-51-7] and napropamide [15299-99-2] have been found to be more readily leached (356). 

Urea is expected to have very high mobility in soil. Urea is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Various field and laboratory studies have demonstrated that urea degrades rapidly in most soils. Urea is rapidly hydrolyzed to ammonium ions through soil urease activity, which produces volatile gases, that is, ammonia and carbon dioxide. However, the rate of hydrolysis can be much slower depending upon the soil type, moisture content, and urea formulation. 

However, the limited test of the screening model mobility prediction is more encouraging. Given that a certain amount of variability will occur under field conditions, the laboratory R values did present a picture of the relative order of leaching of the four chemicals in the two plot experiments. If this result is obtained when the field experiment is repeated on large numbers of chemicals in different soils, it may eventuality allow future comprehensive field research studies to focus on representatives of different mobility categories rather than requiring prohibitive numbers of experiments to be conducted on each chemcial. 

Conf.-Weeds 1982, 25 K. Hedlund, L. Andersson, Weeds Weed Control 28, I (1987). Activity of component isomers D. L- Shaner et al, Proc. Brit. Crop Prot, Conf.-Weeds 1982, 333. Mechanism of action J. B, Pill moor, J. C. Caseley, Peslic- Biockem, Physiol 27, 340 (1987). Persistence and mobility in soil R. Allen, J. C. Caseley, Ptuc. Brit. Crop Prot. Conf.-Weeds 1987, 569- Field studies K. Kirkland, N. E. Shafer, ibid. 1982, 33 A. A. Hudson, S. C. E. Townsend, ibid. 1985, 923 in food cropa S. D. Miller, H. P. Al -ley. Weed Technol. 1, 29 (1987). 

A two-step field test was used to examine the mobility of 4-nitroluene. A solution containing both 4-nitrotoluene and KCl was injected into a sandy aquifer and monitored at an exffaction well. A solution containing CaCl2 was subsequently injected into the aquifer, and mobiUty of the NAC was found to increase. In the presence of KCl, NAC mobility was attenuated by K-exchanged minerals present. Upon introduction of CaCb, ion exchange of K ions by Ca ions was proposed to account for the increased mobility of the NAC. This study provided field-scale evidence that exchangeable cations play a definite role in NAC mobility in soils and subsurface environments. 

Bewick DW, Hill IR, Pluckrose J, Stevens JEB, Weissler MS (1986) The role of laboratory and field studies, using radiolabelled materials, in the investigation of the degradation and mobility of tefluthrin in soil. Proceedings, BCPC Conference - Pest and Diseases, British Crop Protection Council, Brighton, 4B-2, pp 459-468... 

Typically, only 0.01-10% of the mass of pesticide compounds applied to fields is detected in streams [91]. The remaining 90-99% of pesticides adsorb to soil, percolate into groundwater, or volatilize [79]. The major degradates of the most heavily used herbicides found in surface water have not been studied widely. Many chemical properties of pesticides affect the amounts transported to streams. In general, acetanilide herbicides are more soluble in water, and thus more mobile than are the triazines [92], The solubilities of sulfonated degradates of acetanilides (ethane sulfonic acid, or ESA), can be 10 times the solubility of the parent compound [93]. The greater mobilities of the degradates of the acetanilides (amide family) can explain these com-... 

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