Enhanced degradation of carbofuran in Pacific Northwest soils.

Persistence of 14C-carbonyl carbofuran was measured in Pacific Northwest soils that had received 1-14 applications of the insecticide for root weevil control on perennial crops. Insecticide decay curves were obtained in nonautoclaved soil and several autoclaved soil samples from previously-treated fields and in nonautoclaved soils from paired control sites not previously treated with carbofuran. The insecticide usually degraded faster in soil from previously-treated fields than in soil from corresponding control fields. Among 26 previously-treated fields, the pseudo half-life (time for 50% loss) of carbofuran was less than one wk in 11 soils, 1-3 wks in 8 soils and greater than 4 wks in the remaining soils. Among the nontreated control fields the pseudo half-life was greater than 2 wks in all cases and greater than 15 wks in 5 of the soils. The carbofuran decay curve always possessed an initial lag phase where soil mixing enhanced insecticide decline. Carbofuran degraded very slowly in autoclaved soil samples. The half-life of carbofuran exceeded 16 wk in all autoclaved soils tested and in most instances 85-90% of the original dosage remained when the tests were terminated 112 days after treatment. These results provided evidence that many of the soils which received applications of carbofuran over the past several years have developed a capacity to degrade carbofuran very rapidly.

Simultaneous gas chromatographic determination of carbofuran, metalaxyl, and simazine in soils.

A method for extraction, cleanup, and simultaneous gas chromatographic detection of carbofuran, metalaxyl, and simazine in soils has been developed. Pesticide residues were extracted from soil with acetone containing 10% 0.2M HCl-KCl buffer (pH 2.0), cleaned up with methylene chloride-carbonate buffer (pH 10.7) solvent partitioning and solid-phase extraction on disposable silica gel columns, and quantitated with gas chromatography using a Supelcowax 10 megabore capillary column and a nitrogen-selective detector. Method limits of detection were 0.02 microgram/g for the 3 pesticides in surface soils (0-30 cm depths) and 0.02, 0.02, and 0.005 microgram/g in soils below 30 cm (subsoils) for carbofuran, metalaxyl, and simazine, respectively. Recoveries for carbofuran, metalaxyl, and simazine were 92.6 +/- 5.5, 93.6 +/- 5.0, and 88.4 +/- 6.7%, respectively, when soil samples were spiked with pesticide concentrations ranging from 0.02 to 2.0 micrograms/g.

Isolation of an enzyme from soil that degrades the organophosphorus insecticide, crotoxyphos.

An enzyme which catalyzed the hydrolysis of crotoxyphos ((E)-1-phenylethyl 3-[(dimethoxyphosphinyl)oxy]-2-butenoate) was isolated from nonsterile and radiation-sterilized Chehalis clay loam with 1.5M Tris (2-(hydroxymethyl)-2-nitro-1,3-propanediol) and partially purified with lead acetate treatment. Two soil-g equivalents of lead acetate purified enzyme in pH 8 buffer hydrolyzed 0.13 mumol of substrate to dimethyl phosphate and alpha-methylbenzyl 3-hydroxycrotonate in 16 hr at 37 degrees C. The enzyme exhibited maximal activity around pH 8.0 and was irreversibly inactivated below pH 5.0 or above pH 10.0. The Km value for crotoxyphos was calculated to be 4.63 x 10(-3) M. The enzyme was stable at 60 degrees C for 10 min, retained activity indefinitely at -10 degrees C, and was completely inactivated within a week at room temperature. When applied to autoclayed Chehalis clay loam, purified enzyme lost 75% of its activity after one week and the remainder within two weeks.

Persistence of methidathion in soils.

The organophosphorus insecticide, methidathion, degraded rapidly in a sandy loam, silt loam, clay loam and organic soil. Fifty percent of the initial applications decomposed in less than 2 weeks and more than 90% of the insecticide disappeared within 16 weeks. When soils were treated with methidathion containing(14)C in the ring or methyl side chain 40 to 66% of the radioactivity was expired as(14)CO2 after 16 weeks. Over half of the remaining radioactivity could not be extracted from the soils while lesser amounts were recovered as the parent compound or as water-soluble degradation products.In fumigated soils 50% of the initial insecticide applications still remained after 16 weeks and less than 3% of the radioactivity was expired as(14)CO2 which suggests that microorganisms are primarily responsible for the degradation of methidathion in soil.