Trace elements in seawater

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In contrast to their rather low dissolved concentrations in seawater, some of the trace metals, e g., iron and aluminum, along with oxygen and silicon, comprise the bulk of Earth s crust. Some trace elements are micronutrients and, hence, have the potential to control plankton species composition and productivity. This provides a connection in the crustal-ocean-atmosphere fectory to the carbon cycle and global climate. 

Most of our understanding of the marine chemistry of trace metals rests on research done since 1970. Prior to this, the accuracy of concentration measurements was limited by lack of instrumental sensitivity and contamination problems. The latter is a consequence of the ubiquitous presence of metal in the hulls of research vessels, paint, hydrowires, sampling bottles, and laboratories. To surmount these problems, ultra-clean sampling and analysis techniques have been developed. New methods such as anodic stripping voltammetry are providing a means by which concentration measurements can be made directly in seawater and pore waters. Most other methods require the laborious isolation of the trace metals from the sample prior to analysis to eliminate interferences caused by the highly concentrated major ions. 

Periodic Tabie of Elements showing dominant oxidation states of each eiement and concentration ciassifications. Oxidation Numbers from 

Whitfieid, M. (2001). Advances in Man ne Biology 41, 3-128 and Bruiand, K. W. (1983). Chemical Oceangraphy, Academic Press, pp. 157-220. Concentrations from MBARi Chemicai Sensor Program, Monterey Bay Aquarium Research institute. Periodic Tabie of Eiements in the Ocean, (http //www.mbari.org/chemsensor/summary.htmi) accessed Juiy 2008. 

Two interlaboratory studies were organised prior to the certification campaign. The first one dealt with the analysis of artificial seawater and the second exercise concerned the analyses of natural and spiked seawater. The results obtained for Cd, Cu, Pb and Zn are compared in Table 8.23. The CV between all the laboratories appeared to be quite high in the second round-robin exercise. However, the participation in such intercomparison combined with critical discussions of methods and results was found to be a most useful tool in obtaining a high level of accuracy (which is reflected in the 

CVS OF THE MEASUREMENTS OBTAINED BETWEEN THE LABORATORIES IN THE INTERCOMPARISONS AND CERTIFICATION (CONCENTRATIONS GIVEN IN nmol kg ) 

CVs obtained in the certification stage). Only those laboratories that demonstrated a high level of accuracy were invited to participate in the certification. 

The 3000 L tank was filled to such a level that by rolling the tank over to the different sides, all sides were soaked with acid. For the final step the tank was filled up to the top with Milli-Q water acidified with pH= 1.6 (HNO3, Supra pure, Merck). All operations 

The sample collection was performed on 20-21 March 1988 in the central part of the Southern Bight of the North Sea. The ship was kept drifting during the sampling to stay away from the hull and from the bottom sediment, it was decided to collect the sample at a depth of 20 m. Investigation on the lateral and vertical composition variations had revealed that the water body was homogeneous within narrow limits. 

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Iieser et al. [628] studied the application of neutron activation analysis to the determination of trace elements in seawater. The rare earths included in this study were cerium and europium. The element concerned were adsorbed onto charcoal. Between 75% and 100% of the elements were adsorbed onto the charcoal which was then subjected to analysis by neutron activation analysis. Cerium (300 p,g/l) and europium (0.00082 pg/1) were found in North Sea water by this method. 

Chong et al. [742] have described a multielement analysis of multicomponent metallic electrode deposits, based on scanning electron microscopy with energy dispersive X-ray fluorescence detection, followed by dissolution and ICP-MS detection. Application of the method is described for determination of trace elements in seawater, including the above elements. These elements are simultaneously electrodeposited onto a niobium-wire working electrode at -1.40 V relative to an Ag/AgCl reference electrode, and subjected to energy dispersive X-ray fluorescence spectroscopy analysis. Internal standardisation... 

Bruland KW (1983) Trace elements in seawater. In Riley JP, Chester R (eds) Chemical oceanography, vol 8. Academic Press, London... 

H. Louie, M. Wu, P. Di, P. Snitch, and G. Chappie. Determination of Trace Elements in Seawater Using Reaction Cell Inductively Coupled Plasma Mass Spectrometry. J. Anal. Atom. Spectrom., 17(2002) 587-591. 

More recently, Wells and Goldberg (1991) report that very small marine colloids (d < 120 nm) are, by at least three order of magnitudes, more abundant. A vertical stratification of these particles was found (very high concentrations in the thermodine and season-dependent in the bottom-waters). This stratification indicates that these very small colloidal particles are reactive. The apparent close association of metals with these colloids suggests that they may play an important part in the transport and fate of trace elements in seawater (Wells and Goldberg,... 

Piro, A. (1970) Physicochemical states of some trace elements in seawater which are of interest from the radiocontamination standpoint. Rev. Intern. Oceanogr. Med. Tome, 20, 1-17. 

Closely related to the behavior of trace elements in seawater is the composition of pelagic sediments, also covered by some parts of the program. 

The concentrations of trace elements in seawater varies geographically, spatially, and in depth [7j. Such variations are generally caused by the biological activities and physicochemical processes in the oceans. Thus, readers should note that the concentrations of trace elements given in Table 1 are not representative of those for all oceans. However, the extremely low levels of elements in concentrated salt matrix make accurate and precise analysis of seawater difficult. In recent interlaboratory investigations of seawater analysis by skillful marine or analytical chemists, a wide range of... 

Contamination of the analytes from the carriers (the precipitates) should be first examined, and the blank test carried out carefully. Great care should also be taken in terms of the recoveries of the analytes, because the procedures in the coprecipitation are sometimes time-consuming and irre-producible. Some efficiencies of recovery for Zr(IV) coprecipitation along with the determined values of trace elements in seawater are summarized in Table 7, where inductively-coupled plasma (ICP) emission spectrometry was applied for the simultaneous multielement analysis [45]. In this experiment, 10 mg of Zr(IV) was added to 11 of seawater, the precipitation made... 

DETERMINATION OF TRACE ELEMENTS IN SEAWATER AND RECOVERIES USING THE ZIRCONIUM-COPRECIPITATION TECHNIQUE... 

Trace elements in seawater are taken to be those that are present in quantities less than 1 mg excluding the nutrient constituents. The distribution and behaviour of minor elements have been reviewed in the light of data that conform to an oceanographically consistent manner. 

It would be difficult to find more comprehensive or more detailed studies on the physical chemistry of seawater than those done at the University of Miami (Millero, 2001). Several programs were developed for calculation of activity coefficients and speciation of both major ions and trace elements in seawater. The activity coefficient models have been influenced strongly by the Pitzer method but are best described as hybrid because of the need to use ion-pair formation constants (Millero and Schreiber, 1982). The current model is based on Quick Basic computes activity coefficients for 12 major cations and anions, 7 neutral solutes, and more than 36 minor or trace ions. At 25 °C the ionic strength range is 0-6 m. For major components, the temperature range has been extended to 0-50 °C, and in many cases the temperature dependence is reasonably estimated to 75 °C. Details of the model and the parameters and their sources can be found in Millero and Roy (1997) and Millero and Pierrot (1998). Comparison of some individual-ion activity coefficients and some speciation for seawater computed with the Miami model is shown in Section 5.02.8.6 on model reliability. 

Finally, we must somehow resolve the vexing problem of the chemical speciation of trace elements in seawater what is the chemical nature of the various metal chelators whose existence has been demonstrated by electrochemistry Is the chemistry of several metals in surface seawater really controlled by metallophores released by prokaryotes Or are dissolved metals chiefly present as parts of metalloproteins in the process of remineralization How do metal chelators affect the residence times of metals (in particular, scavenged elements such as iron and cobalt) and in turn how do those chelators influence the global carbon cycle via changes in marine primary productivity ... 

Figure 7 The excess trace element composition in black shales compared with that of calculated marine phytoplankton, and the relationship between trace elements in seawater and phytoplankton (inset) (source Quigg...

Bruland, K. W. (1983) Trace Elements in Seawater. In Chemical Oceanography J. P. Riley and R. Chester, Eds., Academic Press, New Yoric. 

Considerations in the Design of in Situ Sampling Techniques for Trace Elements in Seawater... 

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