Depth profiles trace metals

TOF-SIMS can be applied to identify a variety of molecular fragments, originating from various molecular surface contaminations. It also can be used to determine metal trace concentrations at the surface. The use of an additional high current sputter ion source allows the fast erosion of the sample. By continuously probing the surface composition at the actual crater bottom by the analytical primary ion beam, multi element depth profiles in well defined surface areas can be determined. TOF-SIMS has become an indispensable analytical technique in modem microelectronics, in particular for elemental and molecular surface mapping and for multielement shallow depth profiling. 

Simple steady-state models can only predict mean concentrations. Seasonal variations and concentration depth profiles in the water column of lakes give further insight into the mechanisms governing the removal of metal ions. Data on depth concentration profiles of trace metals in lakes are however still scarce (Sigg, 1985 Sigg et al., 1983 Murray, 1987). In a similar way as in the oceans, it might be expected to observe in lakes different types of profiles for different elements, depending on the predominant removal mechanism (Murray, 1987 Whitfield and Turner, 1987). 

Trace metals are resolubilized from the biogenic hard and soft parts in much the same way as the macronutrients. Thus, the depth profiles of the trace metals with high EFs tend to be similar in shape to those of the nutrients. Efforts have been made to develop a Redfield-Richards type ratio far the trace metals in marine plankton. Surprisingly, field and lab work suggests that a relatively constant composition can be defined for whole... 

Metal profiles for two sediment cores from the Elizabeth River, VA, USA. Land use along the shores adjacent to collection site PC-1 (Paradise Creek) is primarily industrial and includes oil terminals, shipyard installations, coal transfer facilities, petroleum distribution and shipment operations, and wood treatment facilities. It has been identified as a toxic hot spot by the U.S. EPA. Land-use adjacent to WB-2 (Western Branch) is primarily residential. Excess lopb and profiles for (a) PC-1 and (b) WB-2 profiles. These were used to determine accumulation rates (1.1 to 2.3cm/y at PC-1 and <0.5cm/y at WB-2). Trace metal enrichment factor profiles (see Eq. 28.1 in text) are presented in profiles (c-g) in groups determined by the depth and shape of their concentration peaks. Source From Conrad, C. R, et al. (2007). Marine Pollution Bulletin 54, 385-395. 

By coupling flow field-flow fractionation (flow FFF) to ICP-MS it is possible to investigate trace metals bound to various size fractions of colloidal and particulate materials.55 This technique is employed for environmental applications,55-57 for example to study trace metals associated with sediments. FFF-ICP-MS is an ideal technique for obtaining information on particle size distribution and depth profiles in sediment cores in addition to the metal concentrations (e.g., of Cu, Fe, Mn, Pb, Sr, Ti and Zn with core depths ranging from 0-40 cm).55 Contaminated river sediments at various depths have been investigated by a combination of selective extraction and FFF-ICP-MS as described by Siripinyanond et al,55... 

Depth profile of elements in seawater near hydrothermal vents. [From T. Akagi and H. Haraguchi, Simultaneous Multielement Determination of Trace Metals Using W mL of Seawater by Inductively Coupled Plasma Atomic Emission Spectrometry with Gallium Coprecipitation and Microsampling Technique Anal. Chem. 1990, 62.81.]... 

Figure 12.2 SOFeX depth profiles of biomass (PN)-specific NO/ uptake rates, determined during 24-h incubations in Plexiglas acrylic incubators under simulated in-situ light and temperature conditions. Ultra-clean trace-metal techniques were used for sample collection within and outside (control waters) of the Fe-enriched patch north and south of the Antarctic Polar Front zone. The/-values [f = Fn03/(1 n03 + 1 nH4 + F n02 + F Urea)] were determined at the isolume depths of 47 and 16% surface irradiance, using tracer-level isotopic enrichments, and are not corrected for the effects of isotopic dilution. Error bars represent the range of duplicate samples (n = 2). Corrected from Coale et al. (2004).

As we have seen, trace metals are involved as cofactors of metalloenzymes and proteins, in all general metabolic processes of phytoplankton, including photosynthesis and respiration, and in assimilation of macronutrients. The vertical profiles of trace metal concentrations in open oceans (Figure 10.9) are like those of macronutrients that is, they show surface depletion resulting from algal uptake and partial release at greater depth due to mineralization. 

Vertical profiles of the trace metals (A) Fe, (B) Zn and (C) Cd in the Atlantic and Pacific Oceans and (D) the global dissolved Cd versus P relationship. The shape of the depth distributions indicates that these metals behave like nutrients in the ocean. (Data from Johnson et al. 

Anthropogenic inputs to intertidal environments are often direct, through point-source waste disposal, but they are also indirect, from riverine, marine and/or atmospheric sources. Trace metals are partitioned between each component of the intertidal sediment-water system they are found in solution ( bulk water or interstitial water) and associated with suspended and deposited sediments. This chapter is concerned with the biogeochemistry of trace metals in deposited intertidal sediments. Two main sections follow in the first, an overview of surface sediments and sediment depth profiles is presented, and in the second, a case study is given of the historic record of Zn from saltmarsh sediments in the Severn Estuary, UK. 

Finally, a recent approach to the study of trace metal distribution in sediment depth profiles deserves mention. This is a factor-analysis technique which is used to determine the main environmental condition prevailing at the place and time when the sediment was deposited, or the main process responsible for modification of the sediment after deposition (Buckley et al, 1995). The study in Halifax Harbour, Nova Scotia, (Buckley et al, 1995), established the following groups ... 

Trace metal concentrations in intertidal sediment depth profiles will no doubt continue to provide useful historic records of pollution in the future. In particular, dated profiles that take into account sediment characteristics and diagenetic processes (where appropriate) are of value. Future studies will perhaps be more process-oriented, e.g. by combining pore-water analysis with solid phase data and through a detailed investigation of the nature and significance of the organic matter present. 

Early work on trace metals in sediment depth profiles in the Severn Estuary provided an overview of trace metal concentrations in marsh sediments, in order to establish a chemostratigraphy (Allen, 1987c Allen Rae, 1987 Allen, 1988). Later work (Allen et al, 1990) provided a preliminary investigation of the post-depositional behaviour of Cu, Zn and Pb at one location (Tites Point). Subsequent intensive sampling of an adjacent profile has allowed a more detailed appreciation of trace metal concentrations and behaviour. 

ScHAULE BK and Patterson CC (1983) Perturbations of the Natural Depth Profile in the Sargasso Sea by Industrial Lead. Proceedings of NATO Advanced Research Workshop of Trace Metals in Seawater, Erice, Italy, 1981, pp. 407-504. Plenum Press, New York. 

Concentration profiles of trace metals in ancient bone. In many cases the concentrations of elements such as U, Th and the REE show marked heterogeneities with depth perpendicular to the external cortical (periosteal) surface. The shape of these concentration profiles has received considerable study, as calculations of the age of bone based on ESR and U-series dating techniques depend upon knowledge of the style of uptake of U into bone (e.g., Millard and Hedges 1999). 

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