Soil, lead speciation

Preventive Measures. The intake uptake biokinetic model (lUBK) projects the impact of lead in the environment on blood lead. This model assumes conservatively high levels of intake and cannot account for chemical speciation, thus over-predictions of blood lead levels often occur. Nonetheless, because of the allegations of the impact of blood lead and neurobehavioral development, blood lead levels in children are being reduced adrninistratively to below 10 //g/dL. In order to do so, soil leads are being reduced to a level of between 500—1000 ppm where remediation is required. 

Chaney RL, Mielke HW, Sterret SB. 1989. Speciation, mobility and bioavailability of soil lead. Environ Geochem Health 9 105-129. 

Manceau A, Boisset M-C, Sarret G, et al. 1996. Direct determination of lead speciation in contaminated soils by EXAFS spectroscopy. Environ Science Technology 30(5) 1540-1552. 

Manceau A (1995) The mechanism of anion adsorption on iron oxides evidence for the bonding of arsenate tetrahedra on free Fe(0,OH)6 edges. Geochim Cosmocliim Acta 59 3647-3653 Manceau A, Boisset MC, Sarret G, Hazemann J-L, Mench M, Cambier P, Prost R (1996) Direct determination of lead speciation in contaminated soils by EXAFS spectroscopy. Environ Sci Technol 30 1540-1552... 

There are a variety of field and laboratory analytical methods for soil lead measurement, depending on the type of analysis and its purposes in a given evaluation. Bulk soil lead measurement refers to measurement of the total lead content of the soil sample. Chemical speciation and micromineralogical studies in the context of human lead exposure variability refer to amounts of specific chemical forms of lead and their geochemical states. These studies are sometimes done in tandem with relative bioavailability testings, i.e., amounts of lead being absorbed under in vivo or in vitro simulation of in vivo conditions (Casteel et al., 2006) with respect to Pb source attribution. Stable isotopic analysis studies deal with the quantitative stratification of lead s stable isotopic composition into the four main stable isotopes lead-204, lead-206, lead-207, and lead-208 (Gulson et al., 1995, 1997). 

Ho M.D., Evans G.J. Operational speciation of cadmium, copper, lead and zinc in the NIST standard reference materials 2710 and 2711 (Montana soil) by the BCR sequential extraction procedure and flame atomic absorption spectrometry. Anal Commun 1997 34 353-364. 

Ma L.Q., Choate A.L., Rao G.N. Effects of incubation and phosphate rock on lead extractabihty and speciation in contaminated soils. J Environ Qual 1997a 26 801-807. 

Arai, Y., Lanzirotti, A., Sutton, S.R. et al. (2006) Spatial and temporal variability of arsenic solid-state speciation in historically lead arsenate contaminated soils. Environmental Science and Technology, 40(3), 673-79. 

Carlosena et al. [60] and Hirsch and Banin [61] have conducted studies on the speciation of cadmium in soil. Feng and Barrett [62] showed that microwave dissolution of soil and dust samples with nitric-hydrofluoric acid gave recoveries of cadmium (and lead) of over 90% for a 30-minute digestion. Various other workers [65-68] have reviewed methods for the determination of cadmium in soils. 

Tills and Alloway [113] investigated the speciation of lead in soil solution using a fractionation scheme, ion exchange chromatography and graphite furnace atomic absorption spectrophotometry. Soils from four sites were selected (Snertingdal in Norway, Pen Craig-ddu in Dyfed, Wales, Velvet Bottom... 

The exposure of soil to phosphorus aerosols will upset the pH of the soil and create a more acidic layer of soil. This decrease in pH often can exceed the buffering capacity of the surface layer of the soil depending upon the amount of applied phosphorus. This process can be mitigated by a larger soil volume area so that phosphorus speciation on a field scale will be minimal. The interaction of metals with phosphorus condensates could lead to their leachability and possible trace metal migration from the soil (Van Vorris et al. 1987). 

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. 

Boruvka, L., Kristoufkova, S., Kozak, J. and Huan Wei, C. (1997a) Speciation of cadmium, lead and zinc in heavily polluted soils. Rostlinna Vyroba, 43, 187-192. 

Cordos, E.A., Frentiu, T., Rusu, A.-M. and Vatca, G. (1995) Elemental speciation of lead, zinc and copper in sedimented dust and soil using a capacitively coupled plasma atomic emission spectrometer as detector. Analyst, 120, 725-731. 

Sauve, S., McBride, W.B. and Henderskol, W.H. (1997) Speciation of lead in contaminated soils. Environ. Poll., 98,149-155. 

An operational definition is considerably more practical. Operationally determined species are defined by the methods used to separate them from other forms of the same element that may be present. The physical or chemical procedure that isolates the particular set of metal species is used to define the set. Metals extracted from soil with an acetate buffer is an operational definition of a certain class. Lead present in airborne particles of less than 10 pm is another. In water analyses, simply filtering the sample before acidification can speciate the analytes into dissolved and insoluble fractions. These procedures are sometimes referred to as fractionation, which is probably a more properly descriptive term than speciation, as speciation might imply that a particular chemical species or compound is being determined. When such operational speciation is done, careful documentation of the protocol is required, since small changes in procedure can lead to substantial changes in the results. Standardized methods are recommended, as results cannot be compared from one laboratory to another unless a standard protocol is followed [124], Improvements in methodology must be documented and compared with the currently used standard methods to produce useful, readily interpretable information. 

The lead contents of 206 soil samples determined by AAS indicated that such determination provides a useful parameter for soil comparison and discrimination in forensic science (Chaperlin 1981). Soil investigations near a former smelter in Colorado revealed that historic use of arsenical pesticides has contributed significantly to anthropogenic background concentrations of arsenic on certain residential properties. A variety of forensic techniques including spatial analysis, arsenic speciation and calculation of metal ratios were successful in the separation of smelter impacts from pesticide impacts (Folkes, Kuehster, and Litle 2001). 

It is very important to understand that this kind of speciation calculation indicates that certain redox reactions can occur in soils, but not that they will occur a chemical reaction that is favored by a large value of log K is not necessarily favored kinetically. This fact is especially applicable to redox reactions because they are often extremely slow, and because reduction and oxidation half-reactions often do not couple well to each other. For example, the coupling of the half-reaction for 02(g) reduction with that for N2(g) oxidation leads to log K = -0.3 for the overall redox reaction ... 

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