Soil degradation temperature

Disulfoton was translocated from a sandy loam soil into asparagus tips. Disulfoton sulfoxide, disulfoton sulfone, disulfoton oxon sulfoxide, and disulfoton oxon sulfone were recovered as metabolites (Szeto and Brown, 1982 Szeto et al., 1983). Disulfoton sulfoxide and disulfoton sulfone were also identified in spinach plants 5.5 months after application (Menzer and Dittman, 1968). Menzer et al. (1970) reported that degradation of disulfoton in soil degraded at a higher rate in the winter months than in the summer months. They postulated that soil type, rather than temperature, had a greater influence on the rate of decomposition of disulfoton. Soils used in the winter and summer months were an Evesboro loamy sand and Chillum silt loam, respectively. The half-life in soil is approximately 5 d (Jury et al., 1987). 

Similarly, Aga (excerpt 13A) describes the types of columns that she will use to achieve enantiomeric separation (an essential feature of her proposed work), but she does not devote space to a description of GC/MS parameters (e.g., temperature program, carrier gas, flow rates). She describes the general approach that she will use to analyze soil samples in the soil degradation study but provides few details on how soil moisture will be controlled or how the soil samples will be extracted and analyzed (details we would expect to see in a journal article describing this work). 

Rate-limiting factors for bioremediation can include a lack of sufficient organisms with the metabolic pathways required for degradation. Temperature, oxygen supply, contaminant availability, chemical structure of the contaminant, and soil chemistry can all effect aerobic biodegradation rates. Nutrients such as nitrogen and phosphorous are necessary for biodegradation. 

The difficulty of elucidating mechanisms and pathways for the degradation of. v-triazine compounds is illustrated by the continuous effort over more than 40 years to define the respective roles of biotic versus abiotic degradation pathways. As early as the 1960s it was evident that the capacity of soil microbial populations to release C02 from. v-triazincs was variable. Degradation depended on the microbial composition of the soil (diversity and biomass) and on soil conditions (i.e., soil type, temperature, humidity, pH, additional energy sources, etc.) (Knusli et al., 1969 Walker, 1987). 

Soil degradation ty, = 3 d by microorganisms isolated from soil or waste water at 30°C (Kurane et al. 1977) degradation ty, = 11 to 53 d as affected by soil type, pH, temperature, aeration status and sterilization (Inman... 

A typical field site, varying in area from about 1 to 10 ha, may include several soil series. The model parameter values may be different not only for each of these soil series, but may also vary considerably within a single series. Such variability in a number of soil hydraulic properties (e.g., soil hydraulic conductivity, soil water flux, etc.) has been widely reported in the literature ( 5 - 1 ). The model parameter values for a given location in the field may also vary with profile depth depending upon soil horizonation as well as a function of the soil and environmental factors (e.g., soil aeration, temperature, etc.). Since soil and environmental factors undergo dynamic changes with time, model parameters are also expected to exhibit temporal variability. At present, only limited data are available to characterize such spatial and temporal variability in pesticide sorption and degradation parameters required in several simulation models. 

The variation in soil degradation rates depend on factors influencing biological activity including temperature, moisture, and oxygen tension along with those factors that control the availability of the substrate. 

Much of the data compiled for soil degradation rates under field conditions has been taken from studies in the temperate zone. A useful comparison of soil degradation rates in the tropics has been provided by a study in Brazil carried out in the central western region, latitude 15°53 S where the mean annual temperature is 23°C. The dissipation of 10 different pesticides was monitored for 80 days under field conditions. The data was found to fit a biexponential decay model (r > 0.97) ... 

Applehans (18) lists several factors that Increase the rate of organophosphate pesticide degradation temperature of 32 C or more, a basic pH, organic compounds In the soil, and activity of microorganisms. Laundering aids or practices that correspond with these factors can be established. 

Pol5mier samples were subjected to soil degradation in a laboratory at a temperature 22-25°C. Samples in the form of a film thickness of 50 pm was placed in the soil to a depth of 1.5-2 cm. Biodegradation rate was assessed by evaluating the mass loss of the samples. Mass loss was fixed by weighing the samples on an analytical balance. 

Urea and uracil herbicides tend to be persistent in soils and may carry over from one season to the next (299). However, there is significant variation between compounds. Bromacil is debrominated under anaerobic conditions but does not undergo further transformation (423), linuron is degraded in a field soil and does not accumulate or cause carryover problems (424), and terbacd [5902-51-2] is slowly degraded in a Russian soil by microbial means (425). The half-hves for this breakdown range from 76 to 2,475 days and are affected by several factors including moisture and temperature. Finally, tebuthiuron apphed to rangeland has been shown to be phytotoxic after 615 days, and the estimated time for total dissipation of the herbicide is from 2.9 to 7.2 years (426). 

CDU in pure form is a white powder. It is made slowly available to the soil solution by nature of its limited solubihty in water. Once in the soil solution, nitrogen from CDU is made available to the plant through a combination of hydrolysis and microbial decomposition. As with any CRE which is dependent on microbial action, the mineralization of CDU is temperature dependent. Product particle size has a significant effect on CDU nitrogen release rate. Smaller particles mineralize more rapidly because of the larger surface contact with the soil solution and the microbial environment. The rate of nitrogen release is also affected by pH because CDU degrades more rapidly in acidic soils. 

Pesticides vary widely in their chemical and physical characteristics and it is their solubility, mobility and rate of degradation which govern their potential to contaminate Controlled Waters. This, however, is not easy to predict under differing environmental conditions. Many modern pesticides are known to break down quickly in sunlight or in soil, but are more likely to persist if they reach groundwater because of reduced microbial activity, absence of light, and lower temperatures in the sub-surface zone. 

Some Physico-chemical Interactions of Paraquat with Soil Organic Materials and Model Compounds. I. Effects of Temperature, Time and Absorbate Degradation on Paraquat Adsorption, I. G. Bums, M. H. B. Hayes, and M. Stacey, Weed Res., 13 (1973) 67 -78. 

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