Soil organic matter half-life

In the field, atrazlne has been found to have a half-life of <1 month, but the half-life is affected by the tillage system (44-46), the agricultural soil ammendments and soil pH (45-48), and soil organic matter (49). In another study, atrazine and hydroxyatrazlne have been found to persist into the following growing season (50). 

It has been reported that low concentrations of tributyltin fluoride were readily transformed to tributyltin chloride in sea water (Strand 1983). Tributyltin has been shown to undergo slow photolysis (Maguire et al. 1983). The half-life of the photolysis reaction was estimated to be greater than 89 days. The direct photolysis of tributyltin in water initiates a sequential removal of the butyl groups, leading to inorganic tin as a residual. The reaction was much faster in the presence of fulvic acid (a major component of soil organic matter). 

DDT is highly environmentally stable with a reported half-life of between 2 and 15 years. The insecticide is immobile in most soils and loss is the result of runoff, volatilization, photolysis, and biodegradation. Due to its extremely low solubility in water, DDT will be retained to a greater degree by soils and soil fractions. However, due to its persistence, DDT may be able to eventually leach into groundwater, especially in soils with little soil organic matter. 

Fenvalerate has low water solubility (<300(igH ). Its solubility in surface waters is increased with organic matter. Fenvalerate is moderately persistent in soil, with a half-life of 0.5-3 months. Fenvalerate and its degradation products are relatively immobile and not expected to pose leaching problems. Because of this and low water solubility, it has not been found in groundwater sampling. Fenvalerate undergoes photodegradation in water. 

Pendimethalin is moderately persistent, with a field half-life of 40 days. It does not undergo rapid microbial degradation. Pendimethalin is strongly adsorbed by most soils. Increasing soil organic matter and clay is associated with increased soil binding capacity. 

Table X, Effects of Varying Soil Organic Matter (SOM) and the Half-Life of Aldicarb on the Output of the PRZM Model, within Ranges in the Fields Studied...

A major problem concerns extraction techniques. Humic substances are extremely complex polymers, but they are also relatively inert. They are a major fraction of the soil organic matter but they are retained vdth a half-life of at least 1000 years Hov/ever treatment v ith even mild extract-... 

CASRN 52645-53-1 molecular formula C21H20CI2O3 FW 391.29 Soil. Permethrin biodegraded rapidly via hydrolysis yielding 3-(2,2-dichloroethenyl)-2,2-di-methylcyclopropanecarboxylic acid and 3-phenoxybenzyl alcohol (Kaufman et al., 1981). The reported half-life in soil containing 1.3-51.3% organic matter and pH 4.2-7.7 is <38 d (Worthing and Hance, 1991). 

Once in the soil, deactivation is related to kind and quantity of clay and to organic matter content (Upchurch and Mason 1962 Day et al, 1968 Weber et al, 1969). Burnside et al. (1961) reported that simazine remains in the upper few centimeters of soil and breaks down readily at high temperatures and low pH. Holly and Roberts (1963) emphasized the variability in the breakdown of simazine. In one study, simazine residue in soil was evaluated 1 year after treatment, where the half-life was 59 days. However, after 12 years of treatment, the half-life was 46 days, a slight but significant enhanced degradation rate (Rouchard et al, 2000). 

Dioxins (PCDDs) and furans (PCDFs) are polyhalogenated aromatic hydrocarbons of high toxicity. There are a total of 210 different congeners 75 dioxin congeners and 135 furan congeners, of which 17 are potentially toxic. Dioxins and furans are now found prevalent in air, water, and soil in almost all natural environments. PCDD/Fs are strongly bound to organic matter, where half-life in soil has been estimated at 10-20 years (Ryan et al., 1987). PCDD/Fs enter the environment primarily as unintentional byproducts of combustion and chemical processes. 

If released to soil, chlorobenzilate is expected to have low mobility, and therefore unlikely to leach into groundwater. Volatilization from soils is not expected to be a significant fate process. The half-life of chlorobenzilate in fine sandy soils was estimated to be 10-35 days, and degradation was primarily microbial. In silty clay loam and clay soils, the half-life of chlorobenzilate was estimated to be 10.8-15.1 and 29.5-169.1 days, respectively. If released into water, chlorobenzilate is expected to adsorb to particulate matter and sediment. Bioconcentration factors in carp were 224-709, indicating the potential for moderate to high accumulation in aquatic organisms. If released into air, chlorobenzilate will exist in both vapor and particulate phases. The half-life of... 

Aquatic fate If released to water, 2-heptanone is expected to rapidly volatalize to the atmosphere. The half-life for volatilization from a model river Im deep, flowing at Ims with a wind speed of 3ms is 8.4 h. The calculated bioconcentration factors ranging from 5.5 to 19 indicate that 2-heptanone is not expected to bioconcentrate in fish and aquatic organisms. The calculated soil adsorption coefficients ranging from 44 to 285 indicate that adsorption to sediment and suspended organic matter is not an environmentally important process. Screening... 

If released to soil, hexachlorocyclopentadiene will get adsorbed to organic matter and degrades via photolysis on soil surfaces. Volatilization from soil surfaces is expected to be of minor importance. In moist soil, this compound would be subject to chemical hydrolysis (half-life of hours to weeks) and biodegradation under aerobic and anaerobic conditions. A study indicates that loss of hexachlorocyclopentadiene from soil is the result of abiotic and biotic degradation as well as partitioning within the media. 

Lindane has been shown to have a low soil binding affinity. Therefore, it may be mobile in soils with especially low organic matter content or subject to high rainfall and pose a risk of groundwater contamination. Lindane is highly persistent in most soils, with a field half-life of 15 months. 

Permethrin is of low to moderate persistence in the soil (half-life of 30-38 days). Permethrin is readily degraded in most soils except those rich in organic matter, with microbial degradation predominant. Permethrin is tightly adsorbed to soil with little leaching and low mobility. Permethrin degrades rapidly... 

Prometryn binds readily to organic matter in soil and tends to remain in the top 12 in. of soil after application. Degradation by soil microorganisms occurs in 1-3 months the soil half-life is 60 days. In water, no hydrolysis occurred over a 28 day period. 

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