Cadmium soil solution

D. Hirsch and A. Banin, Cadmium speciation in. soil solutions. J. Environm. Qual. 19 366 (1990). 

Organic complexed Cd is not important in arid soil solution. Hirsh and Banin (1990) observed 5-10% of Cd bound to organic ligands in Israeli arid soil solution. Emmerich et al. (1982) found that organic-Cd complexes constituted 1-4% of Cd in California arid soil solution. However, Villarroel et al. (1993) reported that in a California sludge-treated soil, Cd was mainly present in both free ion and organic complex forms (each accounted for 32-40% and 30-45% of total Cd in soil solution, respectively), followed by the chloride complexes (8-20%), S04-complex (3-10%), and P04-Cd complex (1.5-7.7%). The nitrate Cd complexes were the lowest. Cadmium activities and speciation is not significantly affected by P and N treatments. 

In addition to soil solution, speciation of trace elements in water of the Nahr-Ibrahim river valley of Lebanon was studied with the AQUACHEM model. The results indicate that a high percentage of Pb and Zn is present as carbonate species, but in low percentages in free hydrated ion species. Cadmium exhibits as a high percentage of a free hydrated Cd2+. 

Trace elements can be precipitated as carbonates, sulfates, phosphates and hydroxides in arid and semi-arid environments. But most carbonates are more stable in arid and semi-arid soils than other solid phases. Cadmium hydroxide (Cd(OH)2), sulfate (CdS04) and phosphates (Cd3(P04)2) are more soluble than carbonate (CdC03, octavite), therefore the former minerals are not stable in arid soils. In calcareous soils, CdC03 (octavite) is the main Cd mineral to control Cd2+ activity in soil solution. At high C02... 

Candelaria L.M., Chang A.C. Cadmium activities, solution speciation, and solid phase distribution of Cd in cadmium nitrate and sewage sludge-treated soil systems. Soil Sci 1997 162 (10) 722-732. 

Hirsh D., Banin A. Cadmium speciation in soil solutions. J Environ Qual 1990 19 366-372. 

Mitchell L.G., Grant C.A., Racz G.J. Effect of nitrogen application on concentration of cadmium and nutrient ions in soil solution and in durum wheat. Can J Soil Sci 2000 80 107-115. 

Smolders E., McLaughlin M.J. Effect of soil solution chloride on cadmium availability to Swiss chard. Soil Sci Soc Am J 1996 60 1443-1447. 

Berggren, D. (1989) Speciation of aluminium, cadmium, copper, and lead in humic soil solutions - a comparison of the ion exchange column procedure and equilibrium dialysis. Int.J. Environ. Anal. Chem., 35, 1-15. 

Andersen, M. K., Raulund-Rasmussen, K., Strobel, B. W., and Hansen, H. C. B. (2002). Adsorption of cadmium, copper, nickel, and zinc to a poly(tetrafluorethene) porous soil solution sampler. 

Figure 7.5. Cadmium and zinc concentration in soil solution from the bulk soil and the rhizosphere of radish ( Raphanus sativus). (Modihed from Lorenz et al., 1997.)...

Knight, B., Zhao, F. J., McGrath, S. P., and Shen, Z. G. (1997). Zinc and cadmium uptake by the hyperaccumulator Thlaspi caerulescens in contaminated soils and its effects on the concentrations and chemical speciation of metals in soil solution. Plant Soil 197, 71-78. 

T. H., and McGrath, S. P. (1997). Cadmium and zinc in plants and soil solutions from contaminated soils. Plant Soil 189, 21-31. 

Hirsch, D., and Banin, A. J. (1990). Cadmium speciation in soil solutions the residual effect of sewage sludge on heavy metal content of tobacco and peanut. J. Environ. Qual. 19, 366-372. 

We have considered only two biogeochemical metal fluxes (accumulation in wood biomass and leaching) that exist in the forest ecosystems. Both of these fluxes contribute to the removal of heavy metals from soil solution and, consequently, to the ecosystem depletion in HM. The calculated values of critical loads of lead ranged from < 50g/ha/yr. to > 250g/ha/yr. Cadmium critical loads are within the limits < 5 and > 25 g/ha/yr. 

From this result, the surface-applied Ca(N03)2 solution must leach to a 10-meter depth to force the Cd " ions down 1 meter (on average). Because the soil s porosity is 0.42, a 10-meter depth of solution in the soil matrix is equivalent to a 4.2-meter depth of applied water. It would take a number of years of rainfall in a temperate humid climate to provide this extent of leaching, and since the concentration of exchanging cations in soil solutions (Ca, Mg, etc.) is typically well below the 0.01 M concentration used in this calculation, cadmium movement out of the surface horizon of soils is likely to take several decades even if no chemisorption of the... 

Salam, A.K., Helmke, P.A., 1998. The pH dependence of free ionic activities and total dissolved concentrations of copper and cadmium in soil solution. Geoderma 83, 281-291. 

Cadmium speciation in the soil solution may well play a role in its bioavailability. An element s bioavailability is reported to be a function of at least three parameters (Brummer, 1986) ... 

Alloway, B.J., 1986. Cadmium and lead in soils and vegetables investigation of the factors controlling concentrations in soil solutions and the tissues of crop plants. DOE Project PECD 7/8/05. 

Sauve, S., Norvell, W.A., McBride, M.B., Hendershot, W, 2000. Speciation and complexation of cadmium in extracted soil solutions. Environ. Sci. Technol. 34, 291-296. 

Based on the results of zinc and cadmium uptake by the T. caerulescens in contaminated soils, Knight et al. (1997) observed the mobilization of metals along with a significant increase in pH in the rhizosphere, which facilitated the dissolution of humic substances in the soil matrix. They also suggested that acidification of the soil solution was not the reason for the increase in zinc availability (Knight et al., 1997). A similar conclusion was also reached in a study performed by McGrath et al. (1997). 

Cadmium is of particular note partly because there is more understanding regarding its mobilisation mechanism/ but also because of its toxicity and ability to accumulate up the food chain The mobilisation of cadmium is dependent upon the pH of the soil solution/ and unlike other heavy metals/ cadmium does not become fixed within the soil structure. Research has shown that the divalent cadmium ion will be displaced by hydrogen ions when the pH is lowered by one unit from pH 5 to 4. Concentrations of up to 1-2 g/1 have been obtained. 

The effects of soil contamination with potentially toxic trace elements on plant composition has attracted a great deal of attention from research workers in recent years and there has also been an increase in interest in the relationship between plant uptake and the concentration of particularly toxic elements, such as cadmium, in soil solutions. For example, Lagerwerff [297] has reported work on the uptake of cadmium, lead and zinc by radishes from the soil and... 

In the atmosphere, cadmium is present as a result of both namral and man-made activities, mainly in finer particles. It mainly occurs in various inorganic forms, though organic complexation may play important roles in some cases. In the natural waters, cadmium is mainly present as chloride and/or carbonate species, though the presence of organic ligands may influence its speciation. In soils and sediments, including soil solutions, cadmium speciation is deeply affected by the characteristic of the matrix. 

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