Leaching from soils

Other environmental properties of interest are those that govern movement of chemicals, for these properties can influence not only the possibility of human exposure but also the lifetime and fate of the chemical. Clearly, if a nitrosamine is formed in, or introduced into, the soil and stays there, it presents little threat to man, and its lifetime will depend on the chemical or microbiological properties of the soil. If it should move to the surface and volatilize into the atmosphere, on the other hand, there will exist the possibility of human exposure via inhalation and also the possibility of vapor-phase photodecomposition. If a nitrosamine were to leach from soil into water, it could perhaps be consumed in drinking water alternatively, exposure of the aqueous solution to sunlight could provide another opportunity for photodecomposition. 

By using this model, we find that roughly the same proportion of atmospheric Hg has been transported from the catchments to the various lakes in modern and preindustrial times (26% and 22%, respectively). The balance of the Hg is either volatilized back to the atmosphere or retained by soils in the catchment. Because Hg has a high affinity for soil organic matter, it is not appreciably leached from soils even under acidic conditions, in contrast to other metals (68, 69). However, volatilization to the atmosphere from soils can be significant. In one experiment with undisturbed soil profiles, none of the Hg applied at the surface moved deeper than 20 cm after 19 weeks of irrigation and incubation, although 7-31% of the applied Hg was... 

Sorption is the dominant process controlling partitioning in water and movement in soil. Silver may leach from soil into groundwater acidic conditions and good drainage increase the leaching rate. Silver is bioconcentrated to a moderate extent in fish and invertebrates. 

Grabek et al. [22] has reported a semi-automated isolation procedure and the detection of"strontium in soils. The strontium is leached from soil by employing a water suspension of Amberlite IR-120 and then separating strontium from other cations with Amberlite GC-400 or Dowex. 

Fischer, H., Meyer, A., Fischer, K., and Kuzyakov, Y. (2007). Carbohydrate and amino acid composition of dissolved organic matter leached from soil. Soil Biol. Biochem. 39, 2926-2935. 

The loss of nitrogen through leaching from soils... 

The metals of most concern are the heavy metals, especially cadmium, lead, and mercury. Although it is a metalloid with characteristics of both metals and nonmetals, arsenic is commonly classified as a heavy metal for a discussion of its toxicity. Though not particularly toxic, zinc is abundant and may reach toxic levels in some cases. For example, zinc accumulates in sewage sludge and crop productivity has been lowered on land fertilized with sludge because of zinc accumulation. Copper may be toxic to plants. Aluminum, a natural constituent of soil, may be leached from soil by polluted acidic rainwater and reach levels that are toxic to plants. Other metals that may be of concern because of their toxicides include chromium, cobalt, iron, nickel, and vanadium. Radium, a radioactive alpha particle-emitting metal, can be very toxic at even very low levels in water or food. 

Chemicals may enter groundwater as landfill leachates or from deep-well injection of hazardous wastes, leaching from soil and water, or septic tanks. Diffusion and advection are the typical mechanisms of chemical transport in groundwater. Groundwater may be taken up via human use or empty onto the surface waters via a natural spring. 

Table VIII. 4-Amino- 3,5,6 -trichloropicolinic Acid Leached from Soil...

A similar case is that of the Great Salt Lake, whose origin is Lake Bonneville (a remnant of a huge freshwater lake that lost its outlet to the sea), which receives inputs from several rivers and streams but with no outflow other than evaporation. It receives 2 million tons of dissolved salts each year, leached from soils and rocks, and its salinity fluctuates from 5% (similar to seawater) to 27% (near saturation) depending on the water inflow and rain input. 

Nitrate (NO3 ). This is a negatively charged ion (or auiou), and is highly soluble in water. Nitrate is the preferred form of nitrogen nutrition for most species of plants. If nitrate is not assimilated by plants or microorganisms, it is readily leached from soils. 

The mobility of dinitrophenols in soils decreases with increase in acidity, clay, and organic matter content, but the mobility in soil will increase as the basicity of soil-water increases because the ionized form is more water soluble and moves faster through soil (Kaufman 1976). 2,4-DNP has been measured in groundwater from waste disposal sites (ATSDR 1988 Plumb 1991), indicating the possibility that these compounds leach from soil. Depending on the nature of soil and climatic conditions, the residence time of 2,4-DNP in soil has been determined to be <8-120 days (Kincannon and Lin 1985 Loehr 1989 O Connor et al. 1990). 

A mean of approximately 9% of applied radioactivity was leached from soil columns treated with aged soils. Most of the radioactivity was retained in the aged soil sample layer applied to the soil column. The leachate radioactivity comprised MDB alcohol (4,7%), aldehyde (1.6%) and acid (1.4%), all of which arc more mobile than the parent compound. A comparison of the leaching pattern of nonaged and aged PBO in sandy loam soil is shown in Figure 7.8,... 

A third issue is that even though the soil is one source of stream humic substances, it is not necessary that soil and stream humic substances have the same composition. If they were of the same composition, then stream humic substances would be primarily humic acids, because the humic cidjo J fulvic acid ratio in soil is approximately 3 1. However, as previously dis- -cussed in this chapter, stream humic substances are approximately 90% fulvic acids. One may say that fulvic acids are leached from soils in preference to humic acids. This may be true, but no one has shown water leachates of soil to contain fulvic acid of the same composition as in the bulk soil. Beck et al. (1974) state that meteoric waters percolating through soil will selectively mobilize nonrepresentative fractions of the soil organic matter. It should be emphasized that even if stream humic substances are the same as soil humic substances, one can not infer that one is the source of the other, but that the same precursors and humification process are probably operable in both soil and stream environments. 

A third theory speculates that stream humic substances are soil fulvic acids leached from soil in the initial stages of humification and then modified, transformed, or aged by stream humification processes which result in humic substances unique to this aquatic environment. 

The transport of the two compounds from moist and dry soil to air via volatilization is negligible because of the low values for Henry s law constant and vapor pressure. The estimated values of 62 and 186 for 2-butoxyethanol and 2-butoxyethanol acetate, respectively (ASTER 1995a, 1995b), suggest that both compounds would be mobile in soils and would leach from soil to groundwater, although the leachability of 2-butoxyethanol is higher than that of 2-butoxyethanol acetate (Swann et al. 1983). 

It does not harm most beneficial insects, has a low toxicity to mammals and birds, does not bioaccumulate, breaks down quickly in sunlight, adsorbs to and does not leach from soils, but still has a broad spectrum of activity against Lepidoptera. Strains of B. thuringiensis that control Coleoptera (beetles) have also been found. Bacillus sphaer-icus works better on mosquitoes because it resists ultravio-... 

Stanforth, R. R., and Chowdhury, A. K. (1993). In Situ Method for Decreasing Heavy Metal Leaching from Soil or Waste, U.S. Patent No. 5,202,033. 

The phosphate content of soils tends to remain roughly constant during soil development. Phosphate is only slowly leached from soils, at about the same rate as silica loss, so the total phosphorus content of soils varies little with soil maturity. The form of phosphate, however, changes from predominantly apatite (Cas(OH,F)(P04)3) in igneous rocks to AI(III) and Fe(III) phosphates in moderately to strongly weathered soils. 

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