The Soil Environment

Plastic objects (such as hags, picnic cutlery, food packaging) are left or thrown on the ground. The fate of these objects is generally not to be buried. The typical environment is forests or terrain along motorways. 

Soil varies widely from place to place. As a matter of fact, soil scientists have set up classification systems in which soil is considered to be composed of a large number of individual soils. The term soil is a collective term for all the soils just as vegetation is used to designate all plants [11]. The soil environment is affected by several uncontrolled parameters. The temperature (which is dependent on the regional climate and the seasonal fluctuations), the soil water content [dependent on rainfall (a climatic factor) and irrigation 

The environmental factors active in soil can be divided into two main classes surface (ground) factors and underground factors. This classification is linked to two phases which typically characterise the life of a biodegradable item located in soil  

Usually the first phase is the functional phase the object must satisfy some functional requirement, for example, the mulch film must control growth of weeds. If degradation happens during this phase, it will be considered a negative factor. The second phase corresponds to the disposal phase, when the item must disappear and be recycled through natural processes. In this phase, fast and complete degradation is a positive factor. 

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Agronomic Properties and Nutrient Release Mechanisms. The mechanism of nutrient release from SCU is by water penetration through micropores and imperfections, ie, cracks or incomplete sulfur coverage, ia the coating. This is followed by a rapid release of the dissolved urea from the core of the particle. When wax sealants are used, a dual release mechanism is created. Microbes ia the soil environment must attack the sealant to reveal the imperfections ia the sulfur coating. Because microbial populations vary with temperature, the release properties of wax-sealed SCUs are also temperature dependent. 

Davies, W.J., Schurr, U., Taylor, G. Zhang, J. (1987). Hormones as chemical signals involved in root to shoot communication of effects of changes in the soil environment. In Hormone Action in Plant Development - A Critical Appraisal, ed. G.U. Hoad, M.B. Jackson, J.R. Lenton and R. Atkin, pp. 201-6. London Butterworths. 

The objectives of the soil persistence experiments were (1) to learn the effect of soil type and concentration on the TCDD degradation rate, (2) to isolate and characterize degradation products from DCDD and TCDD, and (3) to determine whether chlorodioxins could be formed from chlorophenol condensation in the soil environment. This last study was essential since quality control at the manufacturing level could reduce or eliminate the formed dioxin impurity. But the biosynthesis of chlorodioxins by chlorophenol condensation in the soil environment could not be controlled and would have connotations for all chlorophenol-de-rived pesticides if formation did occur. The same question needed to be answered for photochemical condensation reactions leading to chloro-... 

A survey of TCDD content in 2,4,5-T samples (I) revealed that levels of 30—40 ppm TCDD were not uncommon before 1969. Therefore, it is not unreasonable to expect residue in the soil environment within the surface 36 inches of soil at the two higher treatment rates. The fact... 

The application of various antibiotics such as rifampicin/tetracycline (63), cefatoxime/trimethoprim (64), or bacteriostatic compounds such as Micropur (Roth, Karlsruhe, Germany) (65) used for root pretreatment or added to collection media is another strategy to prevent biodegradation during root exudate collection. However, depending on dosage and plant species, also phytotoxic effects of antibiotics have been reported (Table 3). Antibiotics in the soil environment... 

H.H. Cheng, Pesticides in the Soil Environment Processes, Impacts and Modeling, Soil Science Society of America, Madison, WI (1990). 

Goring, C.A. and Hamaker, J.W., Organic Chemicals in the Soil Environment, Marcel-Dekker, New York, 1972. 

Methoxychlor. Methoxychlor is strongly adsorbed to the soil and does not leach, and volatilization is slow. There is no evidence for oxidation, and although photolysis is rapid in aquatic systems, it is assumed not to occur in the soil environment. The hydrolysis half-life is a year in aquatic systems (33) and probably longer in soil systems because of adsorption. Biodegradation does occur in soil systems, however, with a half-life of from 1 to 3 weeks (34). Methoxychlor would not persist in the soil environment. 

Malathion. Malathion is not strongly adsorbed and could leach deeply into the soil. It is not volatile and would volatilize from the soil only as rapidly as it was carried to the surface by evapotranspiration. Biotransformation is rapid (35), however, so it should not persist in the soil environment. 

Goring, C.A.I. "Agricultural Chemicals in the Environment A Quantitative Viewpoint." Chapter 13 in "Organic Chemicals in the Soil Environment" Marcel Dekker New York, 1972. 

Khan, S.V, "Pesticides in the Soil Environment", El Sevior Scientific Publishing Co., New York (1980), page 41. 

Smedley PL, Kinniburgh DG (2002) A review of the source, behaviour and distribution of arsenic in natural waters. Appl Geochem 17 517-568 Smith E, Naidu R, Alston AM (1998) Arsenic in the soil environment a review. Adv Agron 64 149-195... 

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