Degradation environmental influences

Sugai SF, JE Limndstrom, JF Braddock (1997) Environmental influences on the microbial degradation of Exxon Valdez oil on the shorelines of Prince William Sound, Alaska. Environ Sci Technol 31 1564-1572. 

Also relevant is ISO 11403-3 [5], Acquisition and presentation of comparable multipoint data Environmental influences on properties. This selects properties and exposure conditions to enable environmental degradation data to be generated and presented in a standardised way. It includes the use of ISO 2578 [3] for studying resistance to prolonged exposure to heat. 

Step 2. The environmental fate and means of transport are substantiated, including movement of contaminants through different environmental media and change in their characteristics, such as degradation as a function of environmental influences. 

Adaptation has also been observed in anaerobic systems. Linkfield et al. (9) reported acclimation periods of 20 to more than 170 days for a variety of halogenated benzoates in anaerobic lake sediments. The periods required for adaptation (acclimation) were characteristically associated with chemical structure, and not with environmentally influenced variables such as population or nutrient status. It was concluded that the acclimation periods preceeding degradation of these compounds was due to induction of necessary enzymes. These results illustrate the fact that enyme induction and regulation remains a potential cause of adaptive responses in microorganisms. 

Creep is the measurement of the increase of strain with time under a constant applied stress stress relaxation is the measurement of change of stress with time under constant strain and set is a measure of the recovery after the removal of an applied stress or strain. For all of these properties there are two distinct causes, one physical and one chemical. The physical effect is due to the viscoelastic nature of polymers, which means that the response to an applied stress or strain is not instantaneous but develops with time. The chemical effect is due to the aging of the material under environmental influences. The tw o causes cannot be totally separated as both will always occur. However, at short times, normal ambient temperatures and in the absence of other environmental effects the ph -sical effects will dominate, but at longer times, higher temperatures and the introduction of other degrading agents the chemical effects will increase. 

The important matter in repair is to establish the nature and severity of the service environment, to properly assess how much degradation has occurred, and to reasonably estimate the intended service life. From these and known relationships of environmental influences on building materials, techniques can be developed to give a repair that will have a reasonable probability of success. 

The rate of degradation is influenced by a number of structural features, environmental variables and testing conditions. Chu has discussed the influences of Browning et al have considered... 

The rate at which the catalyst is lost or degrades has a major influence on the design. If degradation is rapid, the catalyst needs to be regenerated or replaced on a continuous basis. In addition to the cost implications, there are also environmental implications, since the lost or degraded catalyst represents waste. While it is often possible to recover useful materials from degraded catalyst and to recycle those materials in the manufacture of new catalyst, this still inevitably creates waste, since the recovery of material can never be complete. 

Degradation or Transformation. Degradation or transformation of a herbicide by soil microbes or by abiotic means has a significant influence not only on the herbicide s fate in the environment but also on the compound s efficacy. Herbicides that are readily degraded by soil microbes or other means may have a reduced environmental impact but may not be efficacious. Consider the phenomenon of herbicide-resistant soils. In these cases, repeated application of a given herbicide has led to a microbial population with an enhanced ability to degrade that herbicide (252,253). This results in a decrease or total loss of the ability of the herbicide to control the weed species in question in a cost-effective manner. 

Possible exposure to pesticide-derived N,-nitroso compounds depends on environmental processes that influence formation, movement, and degradation of the compounds. Although laboratory studies have shown the feasibility of environmental nitrosamine formation, there has been little evidence that it is an important process. Nitrosamines vary greatly in their environmental stabilities, but all seem to be susceptible to one or more modes of decomposition including photolysis, microbiological degradation, and plant metabolism. 

Chemical characteristics and environmental conditions will influence the design of fleld studies to assess distributions of occurrence and exposure." Important chemical characteristics of the test substance include water solubility. Aloe, vapor pressure, degradation rate and potentially labile functional groups. These characteristics also need to be known for toxicologically important fiansformation products. One shortcoming in many fleld studies is a failure to address adequately exposure to toxic transformation products. 

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