Soil, metabolism mobility

Soil. Metabolized oxidatively under paddy soil conditions C02 was the major metabolite. The calculated half-lives ranged from several weeks to several months, resp. Low mobility... 

Plants. In apples, grapes, rice, and sugar beet, the major component is unchanged tebufenozide. Small amounts of metabolites result from oxidation of the alkyl substituents of the aromatic ring, primarily at the benzylic positions Soil. Metabolic DTJ0 in soil 7-66 days DT50 for field dissipation 4—53 days. No mobility below 30 cm... 

Animals. The major metabolic path is ring hydroxylation to form ethyl [2- p-(p-hydroxyphenoxy)phenoxy]ethyl]carbamate Plants. Rapidly degraded in plants Soil. Low mobility in soil, no bioaccumulation. Relatively fast degradation. DT50 1.7-2.5 months (lab.), few to 31 days (field)... 

An environmental protocol has been developed to assess the significance of newly discovered hazardous substances that might enter soil, water, and the food chain. Using established laboratory procedures and C-labeled 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), gas chromatography, and mass spectrometry, we determined mobility of TCDD by soil TLC in five soils, rate and amount of plant uptake in oats and soybeans, photodecomposition rate and nature of the products, persistence in two soils at 1,10, and 100 ppm, and metabolism rate in soils. We found that TCDD is immobile in soils, not readily taken up by plants, subject to photodecomposition, persistent in soils, and slowly degraded in soils to polar metabolites. Subsequent studies revealed that the environmental contamination by TCDD is extremely small and not detectable in biological samples. 

The Critical concentrations with respect to the soil organisms should be related to a low effect level on the most sensitive species. The effects on the process of metabolism and other processes within the organisms should be considered and also the diversity of the species, which is most sensitive to the heavy metals, has to be accounted. Critical limits must refer to the chronic or accumulated effects. For assessment of the critical concentrations in crops and in drinking water, human-toxicological information is required. In general, for establishing critical loads we should also account the additive effects of the different metals and combination effect between the acidification and biogeochemical mobilization of the heavy metals in soils and bottom sediments. 

Soil Gas The minmum 02 concentration that can support aerobic metabolism in unsaturated soil is approximately 1%. 02 diffuses into soil because of pressure gradients, and CO 2 moves out of soil because of diffusivity gradients. Excess water restricts the movement of 02 into and through the soil. A minimum air-filled pore volume of 10% is considered adequate for aeration. Soil gas surveys using a mobile geoprobe unit have become a valuable tool to demonstrate a zone of enhanced microbial metabolism in the subsurface. 

Although O2 leakage compromises the root s internal aeration, some leakage is desirable for a number of purposes. These include oxidation of toxic products of anaerobic metabolism in submerged soil such as ferrous iron (van Raalte, 1944 Bouldin, 1966 van Mensvoort et al., 1985) nitrification of ammonium to nitrate, there being benefits in mixed nitrate-ammonium nutrition (Kronzucker et al., 1999, 2000) and mobilization of sparingly soluble nutrients such as P (Saleque and Kirk, 1995) and Zn (Kirk and Bajita, 1995) as a result of acidification due to iron oxidation and cation-anion intake imbalance. 

Aluminum levels in soil also vary with different vegetation types. For example, aluminum levels in the soils of coniferous forests are often higher than in soils of beech forests since coniferous forests tend to have more acid soils (Brusewitz 1984). Alternate views of the data are that the acidic soil produced by conifers can preferentially mobilize aluminum from deeper layers toward surface soil, or that conifers over beech preferentially grow in soils rich in aluminum and it is their metabolic processes which produce more acidic soil. An analysis of aluminum in soils by depth could improve the understanding of this process. 

Metal bioavailability is the fraction of the total metal occurring in the soil matrix, which can be taken up by an organism and can react with its metabolic system (Campbell, 1995). Metals can be plant-bioavailable, if they come in contact with plants (physical accessibility) and have a form which can be uptaken by plant roots (chemical accessibility). Soil metals become accessible for humans by ingestion, inhalation and dermal contact. Available forms of PTMs are not necessarily associated with one particular chemical species or a specific soil component. Main soil PTMs pools of different mobility, target organisms and routes of transfer are sketched in Fig. 9.2. The most labile fraction, corresponding to the soluble metal pool, occurs as either free ions or soluble complexed ions and is considered the... 

DT50 30-70 days (corrected for metabolism) The apparent transformation DT50 in aerobic soils 9-13 days (est.). May be mobile... 

Animals. Partially absorbed and rapidly eliminated 20-44% of the dose was eliminated in urine and 49-79% in feces. Total radioactive residues in tissues <3% of the administered dose. Eliminated primarily as unchanged parent compound Soil. Average DTJ0 in field soil 4.5 days. Very mobile Metabolities also very mobile. However, based upon proposed use, US EPA does not expect diflufenzopyr to reach drinking water... 

Plants. Very rapidly metabolized The metabolism is the same as in animals Soil. Very rapidly degraded. The metabolism is similar to that in animals and plants. It exhibits medium to low mobility in soil... 

Because of their large surface-to-volume ratio and high metabolic activity, microorganisms are important vectors in the introduction of heavy metal and radionuclide pollutants into food webs. As discussed in Chapter 5, heavy metals in soils and sediments tend to be immobilized by precipitation at neutral to alkaline pH and/or adsorption to cation exchange sites of clay minerals. Microbial production of acid and chelating agents can reverse this adsorption and mobilize toxic metals. Microbial metabolism products that can chelate metals include... 

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