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Clay-organic complexes of urea-d₄, methylurea-d₃, and I,I-dimethylurea-d₂ with montmorillonite were examined by infrared spectroscopy in an effort to add to our understanding of the mechanism of adsorption of the substituted urea herbicides in soils. The complexes were examined in the infrared as dried thin self-supporting films. Deteration techniques were used to correlate infrared spectra with molecular structure. Urea-d₄ was found to be adsorbed in the interlayer space by montmorillonite through coordination of the carbonyl with the exchange cations. The degree of coordination with the exchangeable cation was least for Ca, intermediate for Ni (II), and largest for Al, representing alkaline earth cation-clay, transition metal cation-clay, and acid clay, respectively. Methylurea-d₃ and I,1-dimethylurea-d₂ reacted with montmorillonite through the carbonyl in a manner similar to urea. The reaction of dimethylurea with montmorillonite was limited by the presence of the methyl groups to the extent that its reaction was the same with Al or Ni as the exchange cation. The amino groups of urea, methylurea, and I,I-dimethylurea appear relatively inactive as bonding sites.

The effect of two nonionic surfactants on the adsorption and mobility of lindane, diuron, and atrazine in soil columns was studied. A wide range of surfactant concentrations was used in this study. Adsorption of the pesticides by soil from a surfactant solution was inversely related to the leaching of the pesticides through the soil in presence of the surfactants. Low concentrations of both surfactants did not influence adsorption and mobility of the pesticides. A marked increase in the adsorption and reduction in the mobility of the pesticides was observed with 500 ppm Aqua Gro and 2,000 ppm Soil Penetrant. At concentrations of 5,000 ppm and 10,000 ppm, both surfactants decreased the adsorption and increased the mobility of lindane and diuron, but did not influence the adsorption and mobility of atrazine. An attempt was made to explain the mechanisms by which the two surfactants influence adsorption and mobility of the pesticides using the concept of micelle formation and critical micelle concentration.

Equations are developed to describe the combined vapor and “nonvapor” phase diffusion of a volatile insecticide in soils and compared with the diffusion of lindane in a Gila silt loam in a transient state system. The quantity of diffused lindane appears to increase linearly with increased lindane concentration in the treated soil up to about 20 ppm but deviates from linearity at higher concentrations. The diffusion coefficient of lindane is independent of time until 22 ppm of the initial 80 ppm lindane concentration in the treated soil have diffused into the formerly untreated soil. The diffusion rate then decreases rapidly. The dependency of the diffusion coefficient on concentration and time may be explained by the fact that lindane will reach maximal vapor density in the range of 20 to 30 ppm. After these concentrations are built up in the initially untreated half-cells by diffusion, vapor diffusion approaches zero and all the diffusion is in the “nonvapor” phase. At a 10% soil water content, 50% of the lindane diffuses in the vapor phase and 50% in the “nonvapor” phase. At near saturation, total diffusion is in the “nonvapor” phase. Lindane diffusion in soils can easily change from “nonvapor” to vapor phase and back to “nonvapor” phase.

The volatilization of dieldrin from Gila silt loam as influenced by soil pesticide concentration was determined in the laboratory at two air flow rates at 20 and 30C. The influence of pesticide vapor pressure on volatilization was measured by comparing the volatilization from Gila silt loam of dieldrin with that of lindane and DDT. No net water movement to or from the soil occurred during any of the volatilization processes. The vapor density of the soil-applied pesticide was the main factor controlling volatilization. The rate of volatilization of dieldrin from Gila silt loam increased with increasing soil pesticide concentration until the soil dieldrin concentration reached approximately 25 µg/g. This is the soil dieldrin concentration required to give a maximum saturation vapor density equivalent to that of the pure compound. An increase in temperature of 10C increased the rate of volatilization approximately fourfold. Increasing the rate of air movement over the soil surface from 0.005 to 0.018 mile/hour increased the rate of volatilization twofold. The order of rate of volatilization of three insecticides was: lindane > dieldrin > DDT. This is the same order for increasing vapor pressures of the three insecticides. The increase in rate of volatilization of the three insecticides was less than the increase in saturation vapor density of the pure compounds. This resulted because the concentrations of lindane and dieldrin in the soil rapidly decreased below that required to give a maximum vapor density of the pesticides. The maximum volatilization rates obtained represent potential losses of lindane, dieldrin, and DDT from soils of 202, 22, and 5 kg/ha/year, respectively. The volatilization rates decreased rapidly as soil pesticide concentration decreased. Extrapolation of the laboratory data to field situations suggests that the rate of volatilization could account for a significant proportion of these applied pesticides lost under normal field conditions.

Until recently, microbial decomposition was considered the main pathway for detoxication of the s-triazine herbicides in soils. Organisms have been isolated which can detoxify these herbicides (Kaufman et al. 1965). Factors such as temperature and soil organic matter which influence soil microbial activity have been shown to correlate with the rate of s-triazine loss from the soil (Burnside et al. 1961, Talbert and Fletchall 1964). More recent studies, however, indicate that microbial decomposition may play a less significant role in the detoxication process and various nonbiological pathways may be more important than previously thought.

Dissolved organic matter (DOM) can affect the distribution of solutes between solution and sorbed phases and the availability and environmental fate of the solutes. Batch sorption isotherm techniques were used to evaluate solute-solute and solute-sorbent interactions that control the effects of DOM on the sorption of a nonionic, moderately polar organic solute by solid sorbents. The sorption of napropamide (2-(α-naphthoxy-N,N-diethyl propionamide) by Na⁺-, Cu²⁺-, and Al³⁺-montmorillonite decreased when dissolved humic acid derived from peat (peat-DHA) was present in the slurry. For Na-montmorillonite, the effect of DOM on sorption was reduced when a dialysis membrane prevented contact between the DOM and the clay. This suggests that competition for sorption sites on the clay between DOM and the pesticide contributed to decreased napropamide sorption. The extent of the DOM effect was also dependent on the concentration and the source of DOM added. In contrast to the montmorillonite system, the effect of DOM on napropamide sorption by soil was observed only when the dialysis membrane was present or when the dissolution of native organic matter from the sorbate surface itself was enhanced by increasing the pH of the slurry system. These results demonstrate that the effect of DOM on the sorption of nonionic pesticides by soils and sediments can be a function of the association of DOM with pesticides in the solution phase, interactive forces of both DOM and the pesticide with the sorbent surface and the nature of the sorbent surface. Contribution from the Dep. of Soil and Environ. Sci., Univ. of California, Riverside.