Moist soils

Because many pesticides are appHed to the soil surface, the transport of pesticide during water infiltration is important. Water infiltration is characterized by high initial infiltration rates which decrease rapidly to a nearly constant rate. Dry soils have greater rates of infiltration than wet soils during the initial appHcation of water. Thus, perfluridone movement after appHcation of 3.8 cm of water was considerably greater in soil at a water content of <1% of field capacity than at 50% of field capacity (62). Fluometuron moved deeper into the soil in response to greater rainfall intensity or after rainfall onto a dry rather than a moist soil (63). 

The filariform larva found in moist soils may be either ingested or penetrate the skin of its host. It is then carried through the circulatory system to the lungs and migrates up the respiratory tree into the digestive tract. The worms feed on intestinal tissue and blood. Some worms may persist in humans as long as nine years. Infestations cause cutaneous reactions, pulmonary lesions, intestinal ulcerations, and anemia. 

Calcium cyanamide (lime nitrogen) has been used as a fertiliser (6). It hydrolyses ia moist soil to produce ammonia ... 

The occurrence of graphitic corrosion is not location specific, other than that it may occur wherever gray or nodular cast iron is exposed to sufficiently aggressive aqueous environments. This includes, and is common to, subterranean cast iron pipe, especially in moist soil (Case History 17.1). Cast iron pump impellers and casings are also frequent targets of graphitic corrosion (Case Histories 17.2 through 17.5). 

Deep roots, permitting water extraction from moist soil at depth. Passioura, 1983... 

Volatilization of NDPA, NDEA, NDMA and Ji-nitrosopendime-thalin were examined in a model system. The nitrosamines were either mixed into predetermined depths of the soil or applied to the soil surface (the conditions were chosen to represent those that would be encountered by nitrosamines coapplied with dini-troaniline herbicides). Volatilization of nitrosopendimethalin was extremely slow regardless of application. The volatile nitrosamines, NDPA, NDEA, and NDMA, in contrast, volatilized so rapidly after application to the surface of moist soil that we predicted that a substantial proportion of the nitrosamine thus applied would enter the atmosphere within a few hours. Incorporation of the nitrosamine in the top 7.5 cm of soil (as might be the case when the herbicide was applied and incorporated in a single operation) decreased total volatilization by at least an order of magnitude. 

Since hydrogen sulfide exists as a gas at atmospheric pressure, partitioning to the air is likely to occur after environmental releases. However, the compound is also soluble in oil and water, and therefore, may partition to surface waters, groundwaters, or moist soils, and subsequently travel great distances. In addition, sorption of hydrogen sulfide from air onto soils (Cihacek and Bremner 1993) and plant foliage (DeKoketal. 1983, 1988, 1991) may occur. 

Transport of the herbicides by vapor diffusion on moist soil was shown to be directly related to vapor pressure and inversely related to water solubility. Transport of the herbicides by leaching was shown to be inversely related to the Freundlich adsorption coefficient which in turn was directly related to the octanol/water partition coefficient and inversely related to water solubility (16). 

The effects of soil depth and moisture on pesticide photolysis were studied. Moist soil at depth of 3, 2.5, 2, 1.5, 1, and 0.5 mm were each dosed at 2.5 pg/g with 14C-niclosamide and photolyzed under a xenon lamp at constant temperature. Samples were removed after 20, 40, 110, and 153 h of continuous irradiation. The decrease in percent of niclosamide and the appearance of degradates were followed by analyzing the soil extracts by HPLC [76],... 

Acrylonitrile is both readily volatile in air (0.13 atm at 23° C) (Mabey et al. 1982) and highly soluble in water (79,000 mg/L) (Klein et al. 1957). These characteristics dominate the behavior of acrylonitrile in the environment. While present in air, acrylonitrile has little tendency to adsorb to particulate matter (Cupitt 1980), so air transport of volatilized material is determined mainly by wind speed and direction. Similarly, acrylonitrile dissolved in water has only a low tendency to adsorb to suspended soils or sediments (Roy and Griffin 1985), so surface transport is determined by water flow parameters. Based on its relatively high water solubility, acrylonitrile is expected to be higly mobile in moist soils. In addition, acrylonitrile may penetrate into groundwater from surface spills or from contaminated surface water. The high vapor pressure indicates that evaporation from dry soil samples is expected to occur rapidly (EPA 1987). 

No studies were located regarding the biodegradation of acrylonitrile in soil. However, it seems likely that acrylonitrile in moist soil would be subject to biodegradation similar to that observed in aerobic water, although degradation rates might differ. 

Potentially mineralizable C and N are often measured by incubating a sample of field-moist soil at a known temperature in a sealed chamber containing an alkali trap. The C02-C accumulated in the trap is measured by acid titration and this represents the quantity of C mineralized. Alternatively, C02 in the headspace of the incubation chamber can be measured using a C02 analyser. The amount of N mineralized during incubation is calculated as the difference in extractable NH4+ - andNCV-N measured in the soil before and after incubation. Mineralizable N can also be measured in an open incubation system where the soil is leached periodically and NH4+- andNCV-N in leachates is measured (Stanford 1982). 

In soils, PCP persisted for 15 to more than 60 days, depending on soil conditions and application rate. At initial concentrations of 100 mg PCP/kg soil, the Tb 1/2 was 10 to 40 days at 30°C under flooded conditions. However, in aerobic soils there was virtually no degradation after 2 months (Kaufman 1978). In rice paddy soils, initial concentrations of 4 mg PCP/kg fell to 2 mg/kg in 7 days (Bevenue and Beckman 1967). Pentachlorophenol was still measurable after 12 months in warm, moist soils (Cote 1972 USEPA 1980). In estuarine sediments, degradation was most rapid under conditions of increased oxygen and a pH of 8.0 (DeLaune et al. 1983). 

Persistency Not very stable (but can last for months in moist soil or other media). 

One easily demonstrated electrical characteristic of moist soil is seen in the production of electricity when two different metals, namely, copper and zinc, are inserted into it. This is not unexpected because any salt-containing solution adsorbed in media, such as paper or cloth, and placed between these same two electrodes will cause a spontaneous reaction that produces electricity. The source of this flow of electrons is an oxidation-reduction reaction, represented as two half-reactions as shown in Figure 9.1 for copper and zinc. 

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