Decomposers in the soil

Forensic taphonomy is an applied discipline that is coming of age. To date, however, the major advances in the field have been captured in publications that deal primarily with the cadaver and associated items rather than the grave itself. This book provides, for the first time, a collection of chapters from leading scientists in their fields that deal primarily with the burial environment. Our focus is on the processes of decomposition in soils, the decomposers in the soil, and the basic physiochemical composition of the soil as it relates to forensic science and taphonomy. 

To a large degree, decomposers in the soil and litter beneath a community are affected by the species of plants shedding the litter and penetrating the soil with roots. As Eyre (4) has pointed out, soils beneath northern conifer forests are acidic because conifer litter is acidic and its decomposition influences soil pH. Fungi, as a result, dominate the soil microflora while bacteria dominate more neutral soil beneath deciduous forests. There are also differences even within one conifer forest pine needles are much more acidic than spruce, and the soil beneath most pine species has less decomposer activity and is almost devoid of earthworms, in comparison with soil beneath spruce species. 

If a good deal of the organic protein (ossein) has been left in the bone, as is the case when the fat has been extracted by solvents, and not by steaming, the resulting bone-meal quickly decomposes in the soil, the phosphoric acid being made partly soluble by the decomposition products of the proteins. Such a bone-meal will contain (approximately) 45 per cent, of calcium phosphate, 1-5 per cent, of magnesium phosphate and over 30 per cent, of organic matter. 

It has been shown by tracer techniques that, when labeled glucose, hemi-cellulose, or cellulose is allow ed to decompose in the soil, the activity is rapidly distributed in all soil organic fractions examined. If the experiments were to be repeated on better defined fractions, the role of carbohydrates in humic-substance formation could be considerably clarified. 

Hydroprene is metabolised in insects by both microsomal oxidase and esterase, while methoprene is metabolised by microsomal oxidase only (Terriere and Yu, 1973 1977 Yu and Terriere, 1975). Methoprene is readily decomposed in the soil (Schooley et al., 1975). 

It is used mainly for seed treatment against smut and diseases of vegetable seeds (Schoene et al., 1949). Its use as a foliage fungicide is limited because it decomposes partly by hydrolysis and partly photochemically (Burchfield and McNew, 1950), and sublimates in hot weather. Neither can it be used efficiently as a soil fungicide, because it also rapidly decomposes in the soil (Domsch, 1958). One of its degradation products is chloroanilic acid (21), 2,5-dichloro-3,6-dihydroxy-l,4-benzoquinone, which is also biologically inactive. The acute oral lDj chloranil for rats is 4000 mg/kg. 

A possible degradation product of MBC is 2-aminobenzimidazole (42), which has been detected in the soil in very small quantities (Baude et al. 1974). Benomyl is also decomposed in the soil into MBC. Thiophanates decompose rapidly into MBC in the soil as well (Fleeker et al., 1974), this conversion is dependent on the pH value. At pH 7.4 cyclisation proceeds four times as rapidly than at pH 6.5. Benomyl does not affect the bacterial population of the soil (Siegel, 1975) it does, however, reduce the action of phytopathogenic nematodes (Xiphinema americanum, Tylenchorhynchus dubius) and increases the efficiency of certain nematicides (dazomet) (Romanenko, 1974). 

TCA is decomposed in the soil mainly by the microbial pathway (Gemmel and Jensen, 1964). Its persistence is 1-3 months (Jensen, 1960). 

It is rapidly decomposed in the soil by hydrolysis and microbial degradation. Its half-life is 7-10 days. 

Metribuzin is adsorbed strongly in the soil, mainly by the humic acids (Schmidt and Hoyer, 197S). It decomposes in the soil mainly via microbial degradation. The primer metabolite is deaminated diketo derivative (2), the final product is carbon-dioxide (Schumacher, 1974). Metribuzin is nonpersistent. Its half-life depends much on the climatic condition, optimally it is 14-28 days (Hyzak and Zimdahl, 1974). 

Glyphosate is a popular herbicide commercially called Round-Up. It kills plants by translocation to roots, where it has lethal effects. Glyphosate is then harmlessly decomposed in the soil. GMO crops incorporate a gene that allows than to produce a modified enzyme that makes them tolerant of glyphosate. Thus, fields can be sprayed with this habicide, and the only plants to die are the weeds. 

Urea, HgNCONHg, decomposes in the soil to form ammonia, NH. ... 

Top Urea is used as a plant fertilizer because it slowly decomposes in the soil to provide ammonia. Boffom A molecular model of urea. 

Another important environmental issue is the fate of cyanide. Hydrogen cyanide, if spilled, evaporates quite readily. That which does not evaporate is soon decomposed or rendered nonha2ardous by complexing with iron in the soil, biological oxidation, or polymeri2ation. 

It IS the stantng material for the preparation of nearly all manganese chemicals and is used m tenilizers tn arca.s of the world where there is a deficiency of Mn in the soil, since Mn is an essential irace element in plani growth. The anhydrous salt has a surprising Ihermal siabiliiy it remains unchanged even at red heal, whereas the solfates of Fe , Co" and Ni" all decompose under these conditions. 

Dead vegetation also afreets the global carbon cycle. Dead organic matter decomposes, releasing carbon dioxide to the atmosphere. Rates of decomposition vary with material, location, and climate. Non-woody organic matter decomposes rapidly woody organic matter slowly. Decomposition tends to occur faster at the soil surface than below. Decomposition is relatively fast in warm moist climates. In cold climates and in wetlands, decomposition is so slow that there is a net increase of stored carbon in the soil and organic soils called, "histosols, are formed. 

The TCDD is decomposed on or in the soil either photochem-ically or biologically. 

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