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Methyl bromide controls three major problems in crop production: weeds, nematodes and phytopathogenic fungi. An alternative system was investigated that used various colored plastic mulches with Telone C35 (63.4% 1,3-dichlropropene, 34.7% chloropicrin, 1.9% inert ingredients). This alternative to methyl bromide was to investigate: 1) control weeds through wavelength selective plastic mulches, 2) control fungi by chloropicrin, and 3) control weeds and nematodes by 1,3-dichloropropene. These mulches control weeds by a thickness that prevented weed penetration, especially nutsedges, by retaining phytotoxic fumigant longer, or by allowing infra-red and red light to penetrate through the film while restricting other photo synthetically active wavelengths. Infra-red and red light changed the morphology of nutsedges from a hard plastic-penetrating point to a soft leafy structure that cannot tear the film. The mulches tested were blue virtually impermeable film (VIF), black VIF, black polyethylene film (PE), as well as blue, green, olive, brown, and metalized PE. Conclusions after a two-year study were: 1) that there was no direct correlation between the amount of light transmitted through colored mulch with tomato yield per plant, 2) that the use of fumigation with plastic mulches led to an average increase of 40% in crop yield compared to non-fumigated beds, and 3) finally, that if the grower decided not to use any pesticide, fungicide, or herbicide, then metalized PE mulch would maximize weed control and crop yield.

The purpose of this study was to conduct a field study at a Florida field site on surface emissions and subsurface distribution of cis-and trans-1,3-dichloropropene (1,3-D) and chloropicrin (CP) in raised beds injected with Telone C35 with four replications. A total of 16 beds were applied with Telone C35 by chisel injection and covered with four different plastic films, 4 beds for each film. Each bed was installed with five 20-cm long soil pore air probes and a surface air collection pan at arbitrarily locations along the length of each bed for sampling soil pore air and surface air, respectively, for analysis of the three biologically active compounds, cis- and trans-1,3-D and CP. We found that average concentrations of the three compounds at 20-cm depth among the beds covered with four different plastic films generally were not statistically different. Among the four beds covered with the same plastic film, average concentrations of the three compounds were statistically different only in the four metallic PE covered beds at 5 and 24 hours after injection. Volatilization rates of the three compounds among the beds covered with four different plastic films, with the exception of CP at 48 hours after injection, were not statistically different. It appeared that initial upward diffusion and volatilization flux were influenced by solar radiation. Initial subsurface concentrations of the three compounds and volatilization flux, especially cis-1,3-D, were greater in the beds on the east side of the field than that in the beds on the west side of the field. Whether or not difference in initial subsurface concentrations of the compounds between east side beds and west side beds may influence fumigant efficacy remains to be determined.

The concentration and distribution of a soil fumigant in the subsurface of field plots are two key factors in the determination of the fumigant efficacy. Subsurface concentrations of the biologically active compounds cis- and trans-1,3-dichloropropene (1,3-D) and chloropicrin (CP) were determined in soil at two adjacent injection traces and midpoint between the two traces in plastic-covered field beds after injection of the fumigant Telone C35 by conventional chisels or by a coulter rig (Avenger coulters). Two of the four beds were covered with metallic polyethylene film (MPE) and the remaining two were covered with virtually impermeable film (VIF). Three hours after chisel injection, concentrations of the three compounds at the two adjacent injection traces in the two beds were highly variable. Large concentrations of the compounds were detected at the side traces, whereas the compounds were not detected at the middle traces (bed centers) in the two chisel-injected beds covered with MPE or VIF. Initial concentrations of the three compounds at the two adjacent injection traces in the two Avenger-coulter-injected beds were more uniform than in the chisel-injected beds but still variable. Also, the three compounds had diffused horizontally to midpoint between the two injection traces in all four beds, generally in smaller concentrations. Concentrations of the three compounds in the shallow subsurface soil layer (0.5-30 cm) in the beds became progressively more uniform and then declined slowly. Volatilization losses from the two Avenger-coulter-injected beds and the chisel-injected bed covered with VIF were low. Combination of Avenger coulter injection and VIF provided better retention of the compounds in this soil layer and, thus, likely would provide better fumigant efficacy and crop yield.

A field experiment was conducted to compare two plastic mulches and two application rates on surface emissions and subsurface distribution of methyl bromide (MBr) in field beds in Florida. Within 30 minutes after injection of MBr to 30 cm depth, MBr had diffused upward to soil surface in all beds covered with polyethylene film (PE) or virtually impermeable film (VIF) and applied at a high rate (392 kg/ha) and a low rate (196 kg/ha). Due to the highly permeable nature of PE, within 30 minutes after injection, MBr volatilized from the bed surfaces of the two PE-covered beds into the atmosphere. The amount of volatilization was greater for the high rate-treatment bed. On the other hand, volatilization of MBr from the bed surfaces of the two VIF-covered beds were negligible. Volatilization losses occurred from the edges of all the beds covered with PE or VIF and were greater from the high rate-treatment beds. Initial vertical diffusion of MBr in the subsurface of the beds covered with PE or VIF was mainly upward, as large concentrations of MBr were detected from near bed surfaces to 20 cm depth in these beds 30 minutes after injection and little or no MBr was found at 40 cm depth. The two VIF-covered beds exhibited greater MBr concentrations and longer resident times in the root zone (0.5-40 cm depth) than corresponding PE-covered beds. Concentrations of MBr in the root zone of the high rate-treatment beds were 3.6-6.1 times larger than the low rate-treatment beds during the first days after application. In conclusion, VIF promoted retention of MBr in the root zone and, if volatilization loss from bed edges can be blocked, volatilization loss from VIF-covered beds should be negligible.

This study was conducted to examine the effects of three application methods of metam sodium (broadcast, single irrigation drip tape delivery, and double irrigation drip tape delivery) and two plastic covers (polyethylene film and virtually impermeable film) on volatilization and on horizontal and vertical distributions of the biologically active product of metam sodium, methyl isothiocyanate (MITC), in field plots in a Florida sandy soil. Volatilization of MITC from field beds lasted for about 20 hours after completion of metam sodium application regardless of application methods. Virtually impermeable film (VIF) was a better barrier to reduce volatilization loss than polyethylene film (PE). Since water was not applied during broadcast application, MITC was mainly retained in the shallow soil layer (0- to 20-cm depth) and downward movement of MITC was limited to about 30 cm. Large values of standard deviation indicated that initial spatial distribution of MITC in the root zone (10- and 20-cm depths) of the two broadcast applied beds covered with PE or VIF was variable. Twice more water was delivered through the single drip tape than through individual tapes of double drip tape treatments during drip application of metam sodium. More water from the single drip tape likely facilitated downward movement of MITC to at least 60-cm depth, but MITC did not penetrate to this depth in the double drip tape beds. On the other hand, horizontal distribution of MITC in the root zone (10- and 20-cm depths) in the double drip tape beds was more uniform than in the single drip tape beds. More MITC was retained in the subsurface of the VIF-covered beds regardless of application methods than in the PE-covered beds.

Methyl bromide, a pre-emergent soil fumigant, is scheduled to be phased out in the US by 2005, with exceptions for critical use. Comparison of some of the physical constants related to distribution and retention for methyl bromide (MBr) to other fumigants yields a useful quantification of possible alternatives. In this study, the atmospheric and subsurface dissipation of methyl bromide as well as (Z)- and (E)-1,3-dichloropropene (1,3-D) isomers in Telone II were examined. The Henry's law constants of the three chemicals at soil temperature and their mass transfer coefficients for movement through an agricultural mulch of UV-resistant, high-density polyethylene (PE) were evaluated using field data. At the soil temperature of 16.4 degrees C, calculated Henry's law constant gave a fumigant ranking of MBr (0.21)(Z)-1,3-D (0.041)(E)-1,3-D (0.027). Since rapid subsurface distribution of a fumigant is highly dependent on the amount in the gas phase, the greater value for Henry's law constant implies faster distribution throughout the soil. After distribution through the soil, retention of the fumigant becomes imperative. Calculation of the fumigant's mass transfer coefficients through PE from field data gave a ranking of the three chemicals: MBr (1.08 cm/h)(E)-1,3-D (3.25 cm/h)(Z)-1,3-D (4.13 cm/h). With mass transfer coefficients of this magnitude, it was concluded that PE film was an inadequate barrier for retaining these fumigants in an agricultural setting.

With the phase-out of methyl bromide scheduled for 2005, alternative fumigants are being sought. This study of Telone C35, a mixture of (Z)- and (E)-1,3-dichloropropene (1,3-D) with chloropicirin (CP), focuses on its emissions, distribution, and persistence in Florida sandy soil in microplots with different soil-water and organic matter carbon (C) content with and without two different plastic film mulches. The addition of CP did not affect the physical behavior of the isomers of 1,3-D. Slower subsurface dispersion and longer residence time of the mixed fumigant occurred at higher water content. An increase in the percent organic carbon in the soil led to a more rapid decrease for chloropicirin than for 1,3-dichloropene isomers. The use of a virtually impermeable film (VIF) for soil cover provided a more even distribution and longer persistence under all the conditions studied in comparison to polyethylene (PE) film cover or no cover. The conditions of near field capacity water content, low organic matter, and a virtually impermeable film cover yielded optimum conditions for the distribution, emission control, and persistence of Telone C35 in a Florida sandy soil.

The fumigant 1,3-dichloropropene (1,3-D) is considered to be a potential replacement for methyl bromide when methyl bromide is phased out in 2005. This study on surface emissions and subsurface diffusion of 1,3-D in a Florida sandy soil was conducted in field beds with or without plastic covers. After injection of the commercial fumigant Telone II by conventional chisels to field beds at 30cm depth which were covered with polyethylene film (PE), virtually impermeable film, or no cover (bare), (Z)- and (E)-1,3-D rapidly diffused upward. Twenty hours after injection, majority of (Z)- and (E)-1,3-D had moved upward from 30 cm depth to the layer of 5-20 cm depth. Downward movement of the two isomers in the beds with or without a plastic cover was not significant. (Z)-1,3-D diffused more rapidly than (E)-1,3-D. Virtually impermeable films (VIF) had a good capacity to retain (Z)- and (E)-1,3-D in soil pore air space. Vapor concentrations of the two isomers in the shallow subsurface of the field bed covered with VIF were greater than that in the two beds covered with polyethylene film (PE) or no cover (bare). In addition, VIF cover provided more uniform distribution of (Z)- and (E)-1,3-D in shallow subsurface than PE cover or no cover. Virtually impermeable film also had a better capability to retard surface emissions of the two isomers from soil in field beds than PE cover or no cover.

The main objective of this study was to determine the influence of soil moisture, organic matter amendment and plastic cover (a virtually impermeable film, VIF) on diffusion and emissions of (Z)- and (E)-1,3-dichloropropene (1,3-D) in microplots of Florida sandy soil (Arredondo fine sand). Upward diffusion of the two isomers in the Arredondo soil without a plastic cover was greatly influenced by soil-water content and (Z)-1,3-D diffused faster than (E)-1,3-D. In less than 5 h after 1,3-D injection to 30 cm depth, (Z)- and (E)-1,3-D in air dry soil had diffused to a 10 cm depth, whereas diffusion for the two isomers was negligible in near-water-saturated soil, even 101 h after injection. The diffusion rate of (Z)- and (E)-1,3-D in near-field-capacity soil was between the rates in the two water regimes. Yard waste compost (YWC) amendment greatly reduced diffusion of (Z)- and (E)-1,3-D, even in air-dry soil. Although upward diffusion of (Z)- and (E)-1,3-D in soil with VIF cover was slightly less than in the corresponding bare soil; the cover promoted retention of vapors of the two isomers in soil pore air in the shallow subsurface. More (Z)-1,3-D vapor was found initially in soil pore air than (E)-1,3-D although the difference declined thereafter. As a result of rapid upward movement in air-dry bare soil, (Z)- and (E)-1,3-D were rapidly volatilized into the atmosphere, but emissions from the near-water-saturated soil were minimal. Virtually impermeable film and YWC amendment retarded emissions. This study indicated that adequate soil water in this sandy soil is needed to prevent rapid emissions, but excess soil water slows diffusion of (Z)- and (E)-1,3-D. Thus, management for optimum water in soil is critical for pesticidal efficacy and the environment. Copyright © 2004 Society of Chemical Industry

A bacterial consortium capable of degrading the fumigant 1,3-D ((Z)- and (E)-1,3-dichloropropene) was enriched from an enhanced soil. This mixedculture degraded (Z)- and (E)-1,3-D only in the presence of a suitable biodegradable organic substrate, such as tryptone, tryptophan, or alanine. After 8 months of subculturing at 2- to 3-week intervals, a strain of Rhodococcus sp. (AS2C) that was capable of degrading 1,3-D cometabolically in the presenceof a suitable second substrate was isolated. (Z)-3-chloroallyl alcohol (3-CAA) and (Z)-3-chloroacrylic acid (3-CAAC), and (E)-3-CAA and (E)-3-CAAC were the metabolites of (Z)- and (E)-1,3-D, respectively. (E)-1,3-D was degraded faster than (Z)-1,3-D by the strain AS2C and the consortium. AS2C also degraded (E)-3-CAA faster than (Z)-3-CAA. Isomerization of (E)-1,3-D to (Z)-1,3-D orthe (Z) form to the (E) form did not occur.

The influence of repeated annual field applications of the insecticide‐nematicide carbofuran on carbofuran-degrading microbial communities was studied at a site in Florida that exhibited enhanced degradation toward the chemical. Three successive annual applications of carbofuran at 4.5 kg ha 21 y 21 did not result in an increase in the size of the microbial community capable of mineralizing uniformly ringlabeled 14 C-carbofuran (carbofuran-ring degraders) in surface soil (0‐15 cm depth). After the second annual application, however, the community capable of mineralizing carbonyl-labeled 14 C-carbofuran (carbofuran hydrolyzers) in the treated surface soil was significantly larger than that after the first annual application. Communities of methylamine utilizers in treated and untreated soils were much larger than the communities of carbofuran phenol degraders, but not statistically different from the sizes of carbofuran hydrolyzers. In addition to no increase in the number of carbofuran ring degraders in the treated site during three consecutive annual applications of carbofuran, laboratory addition of 10 mg carbofuran g 21 to treated and untreated soils collected in 1995 did not result in an increase in the number of carbofuran ring degraders. This suggests that degradation of the ring structure of carbofuran in soil is a cometabolic process. q 2001 Elsevier Science Ltd. All rights reserved.

Sphingomonas sp. CFO6 (a member of the alpha group of Proteobacteria) was isolated from a Washington soil by enrichment on the insecticide carbofuran as a sole source of carbon and energy. This strain has been shown to harbor five plasmids, at least some of which are required for catabolism of carbofuran. Rearrangements, deletions, and loss of individual plasmids resulting in the loss of the carbofuran-degrading phenotype were observed following treatment with heat or introduction of Tn5. Several putative insertion sequence elements of different sizes were cloned from these plasmids by trapping in pUCD800, a positive selection vector for isolation of transposable elements. Three of the most common putative IS elements (designated IS1412, IS1487, and IS1488) in the clone library were of different sizes and cross-hybridize with each other. An element hybridizing with IS1412, IS1487, and IS1488 was mobilized during growth of CFO6 at 42 degrees C and inserted into one of CFO6's plasmids (pCFO4), corresponding to a deletion in the plasmid and a loss of catabolic function. IS1412 was completely sequenced and its sequence analyzed. IS1412 is 1656 bp in length and possesses terminal partially matched inverted repeats of unequal length (17 and 18 bp). In addition, IS1412 contains an open reading frame which encodes a putative transposase with significant homology to the putative transposases of IS1380 from Acetobacter pasteurianus, HRS1 from Bradyrhizobium japonicum, and IS1247 from Xanthobacter autotrophicus. These related IS elements form part of a family of common IS elements distributed among members of the alpha group of the Proteobacteria.

A bacterial strain (CF06) that mineralized both the carbonyl group and the aromatic ring of the insecticide carbofuran and that is capable of using carbofuran as a sole source of carbon and nitrogen was isolated from a soil in Washington state. Phospholipid fatty acid and 16S rRNA sequencing analysis indicate that CF06 is a Sphingomonas sp. CF06 contains five plasmids, at least some of which are required for metabolism of carbofuran. Loss of the plasmids induced by growth at 42 degrees C resulted in the inability of the cured strain to grow on carbofuran as a sole source of carbon. Introduction of the plasmids confers on Pseudomonas fluorescens M480R the ability to use carbofuran as a sole source of carbon for growth and energy. Of the five plasmids, four are rich in insertion sequence elements and contain large regions of overlap. Rearrangements, deletions, and loss of individual plasmids that resulted in the loss of the carbofuran-degrading phenotype were observed following introduction of Tn5.

The objective of this study was to determine the disappearance of the leaded gasoline enhancer tetraethyllead (TEL), formation of degradation products, and mass balance in nonsterile and autoclaved Leon and Madison soils. Ethyl-1-14C-labeled TEL was used so that mineralization rates of TEL and mass balance could be determined.14C-TEL in nonsterile and autoclaved surface and subsurface samples of the two soils disappeared rapidly, and ionic ethyllead products, water soluble nonlead organic products and bound residues were rapidly formed. A small fraction (≤7.74%) of14C-TEL in nonsterile soil samples was mineralized to14CO2 in 28 days. Triethyllead (TREL) was the major ionic ethyllead product detected in both nonsterile and autoclaved soils; diethyllead (DEL) was occasionally detected. Recovery of14C from mass balance studies for all nonsterile and autoclaved soil samples after 28 days of incubation was poor, less than 50% of the14C applied. It appears that unknown volatile and/or gaseous organic products were the major degradation products of TEL in soils. Based on the observations of more rapid initial disappearance of14C-TEL, more rapid formation and more rapid disappearance of14C-DEL, and occurrence of14CO2 production in nonsterile soils, it was concluded that both biological and chemical degradation contributed to the degradation of TEL in soils, with chemical degradation being the major factor.

DDT and its metabolites, DDD and DDE, have been shown to be recalcitrant to degradation. The parent compound, DDT, was used extensively worldwide starting in 1939 and was banned in the United States in 1973. The daughter compound, DDE, may result from aerobic degradation, abiotic dehydrochlorination, or photochemical decomposition. DDE has also occurred as a contaminant in commercial-grade DDT. The p,p'-DDE isomer is more biologically active than the o,p-DDE, with a reported half-life of -5.7 years. However, when DDT was repeatedly applied to the soil, the DDE concentration may remain unchanged for more than 20 yr. Remediation of DDE-contaminated soil and water may be done by several techniques. Phytoremediation involves translocating DDT, DDD, and DDE from the soil into the plant, although some aquatic species (duckweedelodeaparrot feather) can transform DDT into predominantly DDD with some DDE being formed. Of all the plants that can uptake DDE, Cucurbita pepo has been the most extensively studied, with translocation values approaching "hyperaccumulation" levels. Soil moisture, temperature, and plant density have all been documented as important factors in the uptake of DDE by Cucurbita pepo. Uptake may also be influenced positively by amendments such as biosurfactants, mycorrhizal inoculants, and low molecular weight organic acids (e.g., citric and oxalic acids). DDE microbial degradation by dehalogenases, dioxygenases, and hydrolases occurs under the proper conditions. Although several aerobic degradation pathways have been proposed, none has been fully verified. Very few aerobic pure cultures are capable of fully degrading DDE to CO2. Cometabolism of DDE by Pseudomonas sp., Alicaligens sp., and Terrabacter sp. grown on biphenyl has been reported; however, not all bacterial species that produce biphenyl dioxygenase degraded DDE. Arsenic and copper inhibit DDE degradation by aerobic microorganisms. Similarly, metal chelates such as EDTA inhibit the breakdown of DDE by the extracellular lignolytic enzymes produced by white rot fungi. The addition of adjutants such as sodium ion, surfactants, and cellulose increased the rate of DDT aerobic or anaerobic degradation but did little to enhance the rate of DDE disappearance under anaerobic conditions. Only in the past decade has it been demonstrated that DDE can undergo reductive dechlorination under methanogenic and sulfidogenic conditions to form the degradation product DDMU, 1-chloro-2,2'-bis-(4'-chlorophenyl)ethane. The only pure culture reported to degrade DDE under anaerobic conditions was the denitrifier Alcaligens denitrificans. The degradation of DDE by this bacterium was enhanced by glucose, whereas biphenyl fumes had no effect. Abiotic remediation by DDE volatilization was enhanced by flooding and irrigation and deepplowing inhibited the volatilization. The use of zero-valent iron and surfactants in flooded soils enhanced DDT degradation but did not significantly alter the rate of DDE removal. Other catalysts (palladized magnesium, palladium on carbon, and nickel/aluminum alloys) degraded DDT and its metabolites, including DDE. However, these systems are often biphasic or involve explosive gases or both. Safer abiotic alternatives use UV light with titanium oxide or visible light with methylene green to degrade DDT, DDD, and DDE in aqueous or mixed solvent systems. Remediation and degradation of DDE in soil and water by phytoextraction, aerobic and anaerobic microorganisms, or abiotic methods can be accomplished. However, success has been limited, and great care must be taken that the method does not transfer the contaminants to another locale (by volatilization, deep plowing, erosion, or runoff) or to another species (by ingestion of accumulating plants or contaminated water). Although the remediation of DDT-, DDD-, and DDE-contaminated soil and water is beset with myriad problems, there remain many open avenues of research.

The fumigant 1,3-dichloropropene (1,3-D) is considered to be a potential replacement for methyl bromide when methyl bromide is phased out in 2005. This study on surface emissions and subsurface diffusion of 1,3-D in a Florida sandy soil was conducted in field beds with or without plastic covers. After injection of the commercial fumigant Telone II by conventional chisels to field beds at 30cm depth which were covered with polyethylene film (PE), virtually impermeable film, or no cover (bare), (Z)- and (E)-1,3-D rapidly diffused upward. Twenty hours after injection, majority of (Z)- and (E)-1,3-D had moved upward from 30 cm depth to the layer of 5-20 cm depth. Downward movement of the two isomers in the beds with or without a plastic cover was not significant. (Z)-1,3-D diffused more rapidly than (E)-1,3-D. Virtually impermeable films (VIF) had a good capacity to retain (Z)- and (E)-1,3-D in soil pore air space. Vapor concentrations of the two isomers in the shallow subsurface of the field bed covered with VIF were greater than that in the two beds covered with polyethylene film (PE) or no cover (bare). In addition, VIF cover provided more uniform distribution of (Z)- and (E)-1,3-D in shallow subsurface than PE cover or no cover. Virtually impermeable film also had a better capability to retard surface emissions of the two isomers from soil in field beds than PE cover or no cover.

The main objective of this study was to determine the influence of soil moisture, organic matter amendment and plastic cover (a virtually impermeable film, VIF) on diffusion and emissions of (Z)- and (E)-1,3-dichloropropene (1,3-D) in microplots of Florida sandy soil (Arredondo fine sand). Upward diffusion of the two isomers in the Arredondo soil without a plastic cover was greatly influenced by soil-water content and (Z)-1,3-D diffused faster than (E)-1,3-D. In less than 5 h after 1,3-D injection to 30 cm depth, (Z)- and (E)-1,3-D in air dry soil had diffused to a 10 cm depth, whereas diffusion for the two isomers was negligible in near-water-saturated soil, even 101 h after injection. The diffusion rate of (Z)- and (E)-1,3-D in near-field-capacity soil was between the rates in the two water regimes. Yard waste compost (YWC) amendment greatly reduced diffusion of (Z)- and (E)-1,3-D, even in air-dry soil. Although upward diffusion of (Z)- and (E)-1,3-D in soil with VIF cover was slightly less than in the corresponding bare soil; the cover promoted retention of vapors of the two isomers in soil pore air in the shallow subsurface. More (Z)-1,3-D vapor was found initially in soil pore air than (E)-1,3-D although the difference declined thereafter. As a result of rapid upward movement in air-dry bare soil, (Z)- and (E)-1,3-D were rapidly volatilized into the atmosphere, but emissions from the near-water-saturated soil were minimal. Virtually impermeable film and YWC amendment retarded emissions. This study indicated that adequate soil water in this sandy soil is needed to prevent rapid emissions, but excess soil water slows diffusion of (Z)- and (E)-1,3-D. Thus, management for optimum water in soil is critical for pesticidal efficacy and the environment.

Mineralization rates of fenamiphos sulfoxide (FSO), total-toxic-residue [TTR, FSO + fenamiphos sulfone (FSO2)] disappearance rates for FSO, disappearance rates of FSO2, and metabolites in surface and subsurface soil samples collected from a turfgrass site (fairway) were determined. This site had been treated with fenamiphos annually or biannually for 20 years, and enhanced degradation of fenamiphos TTR was observed. Both the mineralization of FSO and the disappearance of FSO TTR, as well as the disappearance of FSO2 in soil samples collected from the fairway were much more rapid than in soil samples collected from a nearby site (rough) that had no previous history of fenamiphos application. Both FSO and FSO2 were degraded more rapidly in surface soil samples than in subsurface samples. The degradation pathway of FSO in the fairway soil samples was different from the rough samples. Hydrolysis to FSO phenol (FSO-OH) was the initial route of degradation of FSO in the fairway samples, whereas hydrolysis to FSO-OH and oxidation to FSO2 were the initial routes of degradation in the rough samples.

In laboratory studies on Cecil loamy sand and Webster sandy clay loam, I examined the influence of soil-water tension and soil temperature on 14C-2,4-D degradation and the formation of nonextractable 14C-residues, and I correlated the degradation rate with the growth rate of 2,4-D degrading microorganisms. 14C-2,4-D rapidly mineralized in the two soils maintained at 0.1 and 0.33 bar of soil-water tension. Because the total amounts of metabolites in the solvent extracts never exceeded 5% of the total 14C activity, the disappearance rate of extractable 14C essentially represented the disappearance rate of extractable 14C-2,4-D. Extractable 14C in the 14C-2,4-D treated soils maintained at 1 bar and below disappeared rapidly, and at the same time nonextractable 14C rapidly formed, whereas extractable 14C in soils maintained at 15 bars disappeared at much slower rates, and the formation of nonextractable 14C was also slower. After 14 d of slow disappearance, however, extractable 14C in the Cecil soil held at 15 bars started disappearing at a constant rate of 3.6% of applied 14C per day. The disappearance rates in soils incubated at 35°C were generally smaller than those incubated at 25°C. Even though the initial most probable number (MPN) of 2,4-D degrading microorganisms in the Cecil soil was one fourth of that in the Webster soil, the organisms propagated more rapidly in the moist Cecil soil (0.33 bar) than in the moist Webster soil in response to the application of 10 μg 2,4-D/g of soil. As a result, 2,4-D in the Cecil soil degraded at a faster rate. The growth rates of 2,4-D degrading organisms in dry soils (15 bars) were small, in spite of the rapid degradation occurring in the Cecil soil after 14 d of incubation. In addition to forming nonextractable 14C residues in humus components, as much as 4.2% of applied 14C could be associated with microbial mass.

114, 25 (1977). Fest, C., Schmidt, K. J., Ed., “The Chemistry of Organophosphorus Pesticides”, Springer, New York, 1973, pp 228-230. Gibson, D. T., in “Methods in Microbiology”, Vol6A, Norris, J. R., Ribbons, D. W., Ed., Academic Press, New York, 1970, pp 463-478. Hegeman, G. D., J . Bacteriol. 91, 1140 (1966). Kojima, N., Itada, Y., Hayaishi, O., J. Biol. Chem. 236,2223 (1961). Lowry, 0. H., Rosebrough, N. J., Farr, A. L., Randall, R. L., J. Biol. Chem. 193, 265 (1951).

Aerobic and anaerobic degradation rates for aldicarb were measured in soil samples collected at different depths from a citrus grove near Davenport, Florida, together with the changes in concentration of its two toxic oxidation products, aldicarb sulfoxide and aldicarb sulfone. These data were used to estimate the first-order rate-constants for concurrent oxidation and hydrolysis of aldicarb, aldicarb sulfoxide, and aldicarb sulfone, and for the loss of total carbamate residues (TCR = aldicarb + aldicarb sulfoxide + aldicarb sulfone). Both oxidation and hydrolysis rate-constants for aldicarb in surface samples (0-30 cm) were larger than those in sub-surface samples (30-300 cm). Under aerobic conditions, microbial oxidation appeared to be the major route for aldicarb degradation in surface and shallow sub-surface samples (30-150 cm), whereas chemical hydrolysis appeared to be the dominant pathway in deep sub-surface samples (150-300 cm). Aldicarb in deep sub-surface samples under anaerobic conditions was primarily degraded through hydrolysis and only trace amounts of aldicarb sulfoxide were detected. Time to 50% disappearance (DT50) values for TCR loss were generally invariant with depth. In sub-surface samples, DT50 values under aerobic and anaerobic conditions were similar.

A laboratory experiment was conducted to determine the degradation of high concentrations of 2,4-D (2,4-dichlorophenoxyacetic acid) and CO₂ evolution in three soils. Two forms of 2,4-D, technical grade and formulated, were added to each soil at rates of 50, 500, 5,000 and 20,000 µg/g of soil (ppm). Degradation of the 2,4-D was measured by ¹⁴CO₂ evolution resulting from the oxidation of uniformly ringlabeled carbon. At an application rate of 500 ppm, all three soils degraded 2,4-D. At 5,000 and 20,000 ppm, degradation occurred in the Webster silty clay loam and Terra Ceia organic soil, but not in the Cecil sandy loam during 80 days of incubation. The degradation rate was generally higher for the formulated 2,4-D than the technical grade material. For the higher 2,4-D concentrations, 5,000 or 20,000 ppm, when extensive degradation occurred, total CO₂ evolution was also greatly stimulated, and the pattern of total CO₂ evolution rate exhibited a two-peak response. Carbon dioxide-carbon (CO₂-C) from the first peak appeared to be mainly from the formulation materials or from the impurities and CO₂-C from the second peak was mainly from 2,4-D-C.

Cell walls isolated from a teichoic acid deficient mutant (52A5) of Staphylococcus aureus strain H were found to have lower capacities to bind cations than did walls of the parent strain. Both types of walls had higher binding affinities for Mg2+ and Ca2+ than for K+ and Na+. The reduced number of phosphate groups in 52A5 walls was reflected in a higher apparent pKa of 4.3 for displacement of Mg2+ (or Ca2+) during acid titration with HCl. The comparable pKa value for displacement of bound Mg2+ from parent-strain walls was 3.7. The reduced capacity of 52A5 walls to bind cations was not reflected in any significant increase in sensitivity to the growth inhibitory actions of ethylenediaminetetraacetate, low pH, or high NaCl concentrations. However, the 52A5 strain was somewhat more sensitive to the inhibitory effects of high pH. Also, mutant walls were found to be structurally more compact than walls of the parent strain, presumably because of less extensive electrostatic repulsion within the wall matrix.

Isolated cell walls of Staphylococcus aureus and Micrococcus lysodeikticus were found to expand and contract in response to changes in environmental p H and ionic strength. These volume changes, which could amount to as much as a doubling of wall dextran-impermeable volume, were related to changes in electrostatic interactions among fixed, ionized groups in wall polymers, including peptidoglycans. S. aureus walls were structurally more compact in the hydrated state and had a higher maximum charge density than M. lysodeikticus walls. However, they were less responsive to changes in electrostatic interactions, apparently because of less mechanical compliance. In media of nearly neutral p H, S. aureus walls had a net positive charge whereas M. lysodeikticus walls had a net negative charge. These charge differences were reflected in Donnan distributions of mobile ions between wall phases and bulk medium phases. Cell walls of unfractionated cocci also could be made to swell and contract, and wall tonus in intact cells appeared to be set partly by electrostatic interactions and partly by mechanical tension in the elastic structures due to cell turgor pressure. The experimental results led to the conclusions that bacterial cell walls have many of the properties of polyelectrolyte gels and that peptidoglycans are flexible polymers. A reasonable mechanical model for peptidoglycan structure might be a sort of three-dimensional rope ladder with relatively rigid, polysaccharide rungs and relatively flexible polypeptide ropes. Thus, the peptidoglycan network surrounding cocci appeared to be predominantly an elastic restraining structure rather than a rigid shell.

Isolated cell walls of Micrococcus lysodeikticus and Staphylococcus aureus were found to have relatively low densities in both the dried and hydrated states. Thus, it appears that the component polymers of these structures do not form crystallites or other highly condensed assemblies, but rather, that their distribution within the wall matrix is similar to that of the polymer chains in low-density, ion-exchange resins. Micrococcus lysodeikticus walls, which are composed mainly of peptidoglycan, swelled significantly when they were heated or transferred to 8 M urea solution. This finding suggests that the compactness of walls and their component peptidoglycans is determined in part by weak interactions that can be disrupted by urea or by heat.

Cells of Bacillus megaterium growing in the presence of glass microbeads with average diameters of 29 and 53 μm were frequently filamentous and sometimes reached lengths of 600 μm. Some of the filaments were nonseptate. The formation of filaments was prevented by magnesium but not by several other cations. In media with supplemental magnesium, the time required before active proliferation commenced was inversely related to the diameter of the particles. B. megaterium growing in media with the smaller size beads consumed oxygen and utilized glucose at greater rates than bacteria in media with the larger spheres or in bead-free solutions, and the uptake of oxygen was maintained for a longer period.