Trace metals partitioning

Another approach to assess the partitioning of metals among the phases comprising natural particulate matter is to sequentially and selectively extract or dissolve portions of natural particulate matter. Based on the release of trace metals accompanying each step, associations between the trace metal and the extracted phase are inferred. Both of the above approaches have drawbacks, and at this time it is impossible to predict in advance how and to what extent metals and particulate matter will bond to one another in a natural system. Despite the uncertainties, empirical results can often be interpreted using the framework provided here. 

Chung Y, Finkel R, Bacon MP, Cochran JK, Krishnaswami S (1983) Intercomparison of °Pb measurements at GEOSECS station 500 in the northeast Pacific. Earth Planet Sci Lett 65 393-405 Chung Y, Finkel R (1988) Po-210 in the Western Indian-ocean - distributions, disequilibria and partitioning between the dissolved and particulate phases. Earth Planet Sci Lett 88 232-240 Clegg SL, Whitfield M (1991) A generalized model for the scavenging of trace metals in the open ocean -... 

The partition index (IR, which will be discussed in details below) of Cd, Cu, Cr, Ni and Zn in both soils rapidly increased from time zero (calculated value) to one day and further to one year. This was especially true for Cr, Cu and to some extent Ni and Cd (Table 6.5). This result indicates that added trace metals are initially and rapidly transferred from the labile EXC fraction into the more stable fractions. Furthermore, IR of trace metals in native arid soils incubated under the saturated paste regime decreased at the end of year. This indicates mobilization of trace elements in these soils as saturation (Table 6.5). Also, it can be seen that IR decreased, for any given time, with an increase of the loading level (Table 6.5, Fig. 6.5). This means that higher additions of soluble metals result in higher metal content in the labile fractions and lower metal binding intensity in soils. 

Table 6.5. Reduced partition index (IR) of trace metals in arid-zone soils incubated under saturated paste regime (after Han and Banin, 1997. Reprinted from Water Air Soil Pollut, 95, Han F.X., Banin A., Long-term transformations and redistribution of potentially toxic heavy metals in arid-zone soils. I Incubation under saturated conditions, p 411, Copyright (1997), with permission from Springer Science and Business Media)...

Gupta S.K., Chen K.Y. Partitioning of trace metals in selective chemical fractions of nearshore sediments. Environ Lett 1975 10 129-158. 

Levy, D.B., Barbarick A., Siemer E.G., Sommers L.E. Distribution and partitioning of trace metals in contaminated soils near leadville, Colorado, J Environ Qual 1992 21 185-195. 

Horowitz, A. and B J. Presley. 1977. Trace metal concentrations and partitioning in zooplankton, neuston, and benthos from the south Texas Outer Continental Shelf. Arch. Environ. Contam. Toxicol. 5 241-255. 

Bordin, G., J. McCourt, and A. Rodriguez. 1994. Trace metals in the marine bivalve Macoma balthica in the Westerschelde estuary, the Netherlands. Part 2 intracellular partitioning of copper, cadmium, zinc and iron — variations of the cytoplasmic metal concentrations in natural and in vitro contaminated clams. Sci. Total Environ. 151 113-124. 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

In addition to the dependence of sorption on the organic fraction of the sorbent, and the KQw of the sorbate, Chiou et al. (13) cite the following observations as support for the hypothesis that the sorptive mechanism is hydrophobic partitioning into the organic (humic) fraction of the sediments (1) the linearity of the isotherms as the concentration approaches solubility, (2) the small effect of temperature on sorption, and (3) the lack of competition between sorbates for the sorbent. These arguments also illustrate the applicability of the approach for modeling sorption on hydro-phobic compounds an approach which has been criticized when used in the context of adsorption of trace metals onto oxides (17). 

Tsai WT, Lai CW, Hsien KJ (2003) Effect of particle size of activated clay on the adsorption of paraquat from aqueous solution. J Coll Interface Sci 263 29-34 Turner A (1996) Trace-metal partitioning in estuaries Importance of salinity and particle concentration. Marine Chemistry 54 27-39... 

Turner A, Martino M, Le Roux SM (2002) Trace metal distribution coefficients in the Mersey Estuary UK Evidence for salting out of metal complexes. Environ Sci Technol 36 4578 584 Turner A, Millward GE, LeRoux SM (2001) Sediment-water partitioning of inorganic mercuries in estuaries. Environ Sci Technol 35 4648-4654... 

Palumbo, B. Bellanca, A. Neri, R. Roe, M.J. (2001) Trace metal partitioning in Fe-Mn nodules from Sicilian soils, Italy. Chem. Geol. 173 257-269... 

The effectiveness of a partition coefficient (Kd) approach in predicting trace metal residence times in Lake Michigan was demonstrated by Shafer and Armstrong (20). Nearly 99% of the variation in residence time among five trace elements was modeled on the basis of Kd. The same concepts can... 

Giusti, L., Yang, Y.-L., Hewitt, C.N., Hamilton-Taylor, J. and Davison, W. (1993) The solubility and partitioning of atmospherically derived trace metals in artificial and natural waters a review. Atmos. Environ., 27A, 1567-1578. 

Mouneyrac, C., J.C. Amiard, C. Amiard-Triquet, A. Cottier, P.S. Rainbow, and B.D. Smith. 2002. Partitioning of accumulated trace metals in the talitrid amphipod crustacean Orchestia gammarellus A cautionary tale on the use of metallothionein-like proteins as biomarkers. Aquat. Toxicol. 57 225-242. 

Figure 14.5 Particle concentration effect showing negative relationship between particle/solution partition coefficient (X,j) of selected trace metal ions and suspended particulate matter (SPM). Data are from six Texas estuaries (USA). (Modified from Benoit et al., 1994.)...

The partitioning of trace metals between the dissolved and particulate fractions in estuaries can be affected by variability in river flow, tidal and wind energy, storms, coagulation, and flocculation in the estuarine turbidity maximum (ETM), resuspension events (of sediments and porewaters), and inputs from wetland and mudflat processes. 

Turner, A., Millward, GE., and Le Roux, S.M. (2004) Significance of oxides and particulate organic matter in controlling trace metal partitioning in a contaminated estuary. Mar. Chem. 88, 179-192. 

Zhang, J.G, Huang, W.W., and Wang, Q. (1990) Concentration and partitioning of particulate trace metals in the Changjiang. Wat. Air Soil Pollut. 52, 57-70. 

---