Persistence studies with [¹⁴C] 2,4‐D in soils previously treated with herbicides and pesticides

Abstract

Summary: The persistence of [14C] 2,4‐D at a rate equivalent to 1 kg/ha was compared under laboratory conditions in samples of heavy clay, sandy loam, and clay loam at 85% of field capacity moisture and 20 ± 1°C which had either received no pre‐treatment, or had been pre‐treated for 7 days at the 2 μg/g level with the herbicides benzoylprop‐ethyl, diclofop‐methyl, dinitramine, flamprop‐methyl, nitrofen, picloram, tri‐allate, trifluralin, and a combination of tri‐allate and trifluralin. The breakdown of [14C] 2,4‐D was also studied in the same soils that had similarly received pre‐treatments of 2 μg/g of the cereal seed dressing Vitaflo‐DB, the insecticide, malathion, and a combination of Vitaflo‐DB and malathion. In each soil type, the half‐life of the 2,4‐D was similar regardless of whether the soil had, or had not, received any pre‐treatment, indicating that none of the chemicals investigated adversely affected the soil degradation of 2,4‐D.

The Microbial Degradation of 2,4-Dichlorophenoxyacetic Acid in Soil

“…In the field study of Plumb et al (1977), the moderately coarse soils low in organic matter (1 to 5% in the upper 10 cm) did not favor a large microbial population; nevertheless, 2,4-0 disappeared rapidly from these soils, with a 40% reduction of the initial amount of 1.16 !lg 2,4-0/g soil after 29 d. Thompson et al (1984), in agreement with the results of Smith (1980), found that 2,4-0 was degraded more rapidly in a sandy clay loam than in a fine sand. The latter had a lower pH (5.2) and a higher organic content (28 g/kg), both of which could have caused a longer persistence and a greater adsorption of2,4-0 when compared to those of the sandy clay loam (Thompson et al 1984).…”

“…Of the 10 investigations involved with measuring extractable 14C, six indicated that extracts were analyzed for intact [I4C]-2,4-D or 2,4-D metabolites. Smith (1980) assumed that all the radioactivity extracted from the soil was due to [14C]-2,4-D. Smith and Muir (1980) and McCall et al (1981) followed the distribution of nonextractable 14C from [I4C]-2,4-D in three fractions, namely, humin, humic acid, and fulvic acid. Both groups found that nonextractable radioactivity reached a maximum in the soils after 1 wk to several wk of incubation following the application ofthe [I4C]-2,4-D, and then either remained constant or declined slowly thereafter.…”

Soil persistence studies with [14C]MCPA in combination with other herbicides and pesticides

“…Duplicate samples were extracted and analysed for MCPA remaining after 7,14 and either 21 or 28 days. The details of the fortification and incubation procedures are identical to those described for similar studies with [i''C]2,4-D (Smith, 1980). Solutions ofthe herbicides (20 lA, 100 /ig) that are normally applied in combination with MCPA as tank-mixes or split mixes (see Table 1) were added together with the ['"CJMCPA solution (20 til, 100 ng) to soils (50 g) that had been incubated for 7 days at 20±l°C and 85% of their field capacity moisture contents.…”

“…The effects of additional herbicides and pesticides on the breakdown of a particular herbicide are important, and a recent review (Hurle & Walker, 1980) has summarized evidence to show that the soil persistence of a number of herbicides may be changed when used in combination with other pesticides. Laboratory studies with ["•C]2,4-D have indicated that the breakdown rates of the herbicide in Saskatchewan soils were not affected by 12 different herbicides applied in combination with the 2,4-D (Smith, 1979;, nor was the persistence of the phenoxy herbicide affected by soil applications of the insecticide malathion, the commonly used seed dressing Vitaflow DB, or a combination of malathion and Vitaflow DB (Smith, 1980). The present work was undertaken to investigate the effects of selected herbicides and pesticides on the degradation rates of MCPA in three Saskatchewan soils.…”

Soil persistence studies with bromoxynil, propanil and [14C]dicamba in herbicidal mixtures

“…Field studies conducted in the province have confirmed that the persistence of tri-allate and trifluralin was not altered by being applied in combination with each other or with chloramben (Smith, 1979;Smith & Hayden, 1982a). In the cases of 2,4-D and MCPA, whose persistence in the soil is of short duration, controlled laboratory studies with three prairie soils have indicated that the breakdown rates of neither compound was affected by being applied in combination with herbicides normally recommended for use with the phenoxyalkanoic acids as tank-mix or splitmix components (Smith, 1979(Smith, , 1980a(Smith, , 1982. Similar results were noted from laboratory studies conducted in Saskatchewan soils with bromoxynil, since the degradation was unaffected by being applied in combination with herbicides commonly used with bromoxynil as tank-mix treatments (Smith, 1980b).…”