Degradation rapid rate

Many acrylic acid copolymers are water-soluble but unlike poly(vinyl alcohol) they are not degraded by alkali. In fact they need alkali for effective desizing as they are more soluble at alkaline pH than in neutral solutions. They are sensitive to acidic media, which should not be used. Solubilisation occurs by the formation of sodium carboxylate groups from the anionic polyacid. The polyelectrolyte formed in this way is readily soluble and shows a rapid rate of dissolution. However, the presence of electrolytes such as magnesium or calcium salts from hard water can inhibit removal [191]. 

Diazinon degrades rapidly in plants, with half-time persistence usually less than 14 days. However, persistence increases as temperatures decrease, and is longer in crops with a high oil content (Table 16.1). In water, diazinon breaks down to comparatively nontoxic compounds with little known hazard potential to aquatic species (Meier et al. 1976 Jarvinen and Tanner 1982), although the degradation rate is highly dependent on pH (Table 16.1). The half-time persistence of... 

Spatial trends in LAS concentrations in marine and estuarine environments show clear relationships with the location of sampling points relative to point sources of wastewater discharges and a rapid rate of decrease is observed as one moves downstream from these. LAS tend to be degraded relatively rapidly in summer, whereas in winter a higher recalcitrance is observed. Sediments constitute the final sink of LAS that have not been degraded. 

In aerobic soils, aldicarb degraded rapidly (half-life = 7 d) releasing carbon dioxide. Mineralization half-lives for the incubation of aldicarb in aerobic and anaerobic soils were 20-361 and 223-1,130 d, respectively. At an application rate of 20 ppm, the half-lives for aldicarb in clay, silty clay loam, and fine sandy loam were 9, 7, and 12 d, respectively (Coppedge et al, 1967). Other soil metabolites may include acids, amides, and alcohols (Hartley and Kidd, 1987). 

Most often, the rates for feedstock destruction in anaerobic digestion systems are based upon biogas production or reduction of total solids (TS) or volatile solids (VS) added to the system. Available data for analyses conducted on the specific polymers in the anaerobic digester feed are summarized in Table II. The information indicates a rapid rate of hydrolysis for hemicellulose and lipids. The rates and extent of cellulose degradation vary dramatically and are different with respect to the MSW feedstock based on the source and processing of the paper and cardboard products (42). Rates for protein hydrolysis are particularly difficult to accurately determine due the biotransformation of feed protein into microbial biomass, which is representative of protein in the effluent of the anaerobic digestion system. 

Exposure. Exposure to 1,3-DNB is currently measured indirectly by determining levels of methemoglobin in the blood (Donovan 1990). However, increased methemoglobin formation is not a specific response to 1,3-DNB exposure and may occur after exposure to other nitrobenzene compounds such as the other two isomers of dinitrobenzene. Determination of methemoglobin levels is widely used and is a reliable detection method. Very few methods are available for direct evaluation of 1,3-DNB levels, and they are not extensively used, probably because of the relatively rapid rate of conversion of 1,3-DNB to its degradation products (Cossum and Rickert 1985). Preliminary data suggested that the formation of adducts of 1,3,5-TNB with tissue DNA and/or with blood proteins may be useful as markers for exposure to 1,3,5-TNB (Reddy et al. 1991). Further research with both 1,3-DNB and 1,3,5-TNB in the area of adduct formation could provide valuable additional information. 

Examination of the penetration and metabolism of 17 in the house fly and honey bee showed that it penetrated into the honey bee at a much slower rate than into the house fly (14). Further, owing to the combined action of slow conversion rate of 17 to propoxur and rapid rate of degradation of propoxur to nontoxic products, the amount of propoxur in the honey bee remained at a low, non-intoxicating, steady-state level. 

In spite of some claims to the contrary, venom exonuclease is capable of attacking double-stranded high molecular DNA. In fact, double-stranded DNA is a better substrate than denatured DNA. Bjork (1 ) studied the rates of degradation of native and heat-denatured DNA using a pH stat. Denatured DNA was degraded at a steady rate, which was dependent on the ionic strength of the medium. An increase in NaCl concentration from 1 to 100 mM decreased the rate of hydrolysis by a factor of two. With native DNA a two-phase reaction was observed. The initial, very rapid, rate was independent of NaCl concentration. After about one-third of the linkages had been hydrolyzed, the rate slowed down to that of denatured DNA and became salt dependent. Similar biphasic kinetics was observed previously with DNA that was denatured by an exhaustive dialysis (40). 

The level of a protein within a cell is determined by the balance between its rates of synthesis and degradation. As a consequence, changes in protein levels can be brought about by changes either in synthetic or degradative rates. Moreover, a rapid rate of degradation ensures that the concentration of a protein rises or falls rapidly when its synthetic rate changes. 

Sometimes, the experimental n = f(t) curve is not linear in its initial part for example, in the case of polycarbonate, where the rate of chain scission decreases rapidly in the early period of exposure and tends towards a constant value, r, so that n = nj + r t. In such cases, there is no other way to explain this behavior than to assume that the material contains very unstable groups (in a concentration close to n = n that degrade rapidly. When they are consumed, the system adopts a normal pseudo-zero-order behavior. 

Some oxidation of the cellulose chains also seems to take place, suggested by the rise in HAS matter during exposure and by the initially rapid rate of change that occurred upon subsequent thermal degradation of the exposed papers. This represents the "potentially harmful" effect of exposure, leading to loss in degree of polymerization through thermally-induced reactions. These concepts are not new but the authors trust that a clear demonstration of the effects has been useful. 

The two most common natural textile fibers encountered in modern fabrics have contrasting responses to soil burial. Under most soil burial conditions cellulose will degrade rapidly whereas wool will decay at a slower rate. These phenomena are demonstrated by the degradation of textile fibers from the Experimental Earthworks Project (Janaway 1996a). Figures 7.9 and 7.10 compare wool and linen buried in the chalk environments at Overton Down for 32 years. The linen is denatured to the point that there is little surviving morphology, whereas the wool retained some fiber structure. 

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