Dissolved trace metals

As is the case with assessments of the toxicity of dissolved trace metals, the development of sediment quality criteria (SQC) must be based on the fraction of sediment-associated metal that is bioavailable. Bulk sediments consist of a variety of phases including sediment solids in the silt and clay size fractions, and sediment pore water. Swartz et al. (1985) demonstrated that the bioavailable fraction of cadmium in sediments is correlated with interstitial water cadmium concentrations. More recent work (e.g., Di Toro et al, 1990 Allen et al., 1993 Hansen et al, 1996 Ankley et ai, 1996, and references therein) has demonstrated that the interstitial water concentrations of a suite of trace metals is regulated by an extractable fraction of iron sulfides. 

In the determination of cadmium in seawater, for both operational reasons and ease of interpretation of the results it is necessary to separate particulate material from the sample immediately after collection. The dissolved trace metal remaining will usually exist in a variety of states of complexation and possibly also of oxidation. These may respond differently in the method, except where direct analysis is possible with a technique using high-energy excitation, such that there is no discrimination between different states of the metal. The only technique of this type with sufficiently low detection limits is carbon furnace atomic absorption spectrometry, which is subject to interference effects from the large and varying content of dissolved salts. 

Achterberg et al. [961] have described an electrochemical monitor for near real-time determination of dissolved trace metals in marine waters, and also in surface seawater [962],... 

Under relevant conditions (neutral pH, presence of carbonate) the concentrations of dissolved trace metals are limited by the solubility of their solid hydroxides or carbonates. A prominent example is the solubility of Fe(III), which is very low (around 10 10 mol dm 3) under relevant conditions of fresh water or seawater at neutral pH [96]. Iron(III) occurs primarily as solid or colloidal iron hydroxide at neutral pH. 

Table 11.2 gives some representative examples of dissolved trace metal concentrations in rivers, especially in large impolluted rivers. 

Table 11.2 Examples of Dissolved Trace Metal Concentrations in Rivers... 

The atmospheric load is delivered to the sea surface via two processes dry and wet deposition. Dry deposition is mostly gravitational when winds weaken, solid particles fall to the sea surface. Wet deposition involves incorporation into a raindrop that falls to the sea surfece. Particulate trace elements can become entrained in raindrops and thereby carried to the sea surfece. Along the way, some of the trace elements can dissolve. Gaseous trace elements, such as mercury, can also be dissolved directly into raindrops. Thus, rainwater can contain dissolved trace metals. 

Vertical profiles of O2 and particulate and dissolved trace metal concentrations at 32.5°E and 44.5°N in the Black Sea. (a) Temperature, salinity, fluorescence, and O2 (b) ammonium, silica, nitrate+nitrite, and phosphate (c) Fe (d) Mn (e) Co (f) Pb (g) Cu (h) Zn (I) Cd and Ni. In the trace metal profiles, the dissolved concentrations are represented as solid circles, the total particulate concentrations by open circles, the acid-leachable particulate concentrations by open squares, and the suspended particulate matter concentrations by the solid triangles. Source-. After Tankere, S. P. C., et al. (2001). Continental Shelf Research, 21, 1501-1532. 

Shiller AM, Boyle EA. 1987. Variability of dissolved trace metals in the Mississippi River (USA). Geochim Cosmochim Acta 51 3273-3278. 

Bourg, A.C.M. and Vedy, J.C., Expected speciation of dissolved trace metals in water of acid profiles, Geoderma, 38, 279, 1986. 

Transport of dissolved trace metals in the Transport of the particulate trace Amazon mainstream elements in the Amazon mainstream... 

Shiller, A. M., and E. A. Boyle. 1987b. "Variability of dissolved trace metals in the Mississippi River." Geochimica et Cosmochimica Acta 51 3273-3277. 

Zhang J. and Huang W. W. (1992) Dissolved trace metals in the Huanghe, the most turbid river large river in the world. 

Not only are accurate data for trace metals in rivers sparse, there are complications that exist at the river-sea interface. The increase in salinity occurring at the river-sea water interface, with its concomitant increase in the concentrations of the major seawater cations, can lead to flocculation and sedimentation of trace metals such as iron (Boyle et al., 1978 Sholkovitz and Copeland, 1983) or to desorption from suspended riverine particles of trace metals such as barium (Edmond et al., 1978). In organic-rich rivers a major fraction of dissolved trace metals can exist in physiochemical association with colloidal humic acids. Sholkovitz and Copeland (1983) used product-mode mixing experiments on filtered Scottish river water, and observed that iron removal was almost complete due to the flocculation of strongly associated iron-humic acid colloids in the presence of the increased... 

Morley N. H., Statham P. J., and Burton J. D. (1993) Dissolved trace metals in the southwestern Indian Ocean. Deep-Sea Res. 30, 1043-1062. 

Table 10.2. Distribution of Dissolved Trace Metals in Surface Marine Waters...

Apparatus and techniques for the sampling and concentration of particulate and dissolved trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) from seawater were used to monitor ambient trace metal concentrations and heavy metal dis charges. Particulate trace metals were collected in 0.4 fim Nuclepore filter bags, and dissolved metals were concentrated on Chelex-100 chelating resin. The apparatus is constructed of polyethylene and polypropylene plastics to reduce possible sample contamination. 

Table III presents results obtained from the sampling and concentration apparatus for both particulate and dissolved trace metals. The percentage of the ratio of dissolved-to-total trace metals also was computed. These results compare with values reported by others for Narra-gansett Bay (7).

An advantage of this sampling configuration is that particulate matter can be trapped on the column packing or removed by filtration prior to chelation. This allows analysis of either the total trace element concentration or the dissolved trace metal concentration. 

In the last few decades many studies have been carried out to evaluate the distribution of dissolved trace metals in sea water (12, 119 122) and more recently studies of metal speciation have been reported (24, 33, 34, 108 110, 123). However, few data sets are available for the Southern Ocean (124—133), and studies of trace metal speciation are limited to a few papers (35, 57, 69, 134). 

TABLE 13.1 Concentrations of Dissolved Trace Metals from the North Atlantic and the Baltic Sea... 

The influence of anoxic deepwater conditions on the solubility of dissolved trace metals has been demonstrated by using a comprehensive data set from the main Station 271 in the Gotland Deep, which has been evaluated in view of trace metal concentration changes due to saltwater inflow events. 

For trend calculations, we considered the slopes of the linear regression, shown in Fig. 13.5, related to the mean dissolved trace metal concentrations in surface waters as given in Table 13.3. For Pbdiss, a significant negative trend of 5%/year (—0.005 nmol/ (kg/year)) was calculated in the water masses Above Halocline between 1993 and 2005. 

Internal particulate trace metal fluxes were obtained from an experimental sediment trap flux study (Pohl et al., 2004) (Section 13.4), and internal dissolved trace metal fluxes across the redox interface were considered as estimated above. 

Atmospheric input of trace metals, 2. Lateral transport from adjacent masses of surface water, 3. Diapycnal fluxes of dissolved trace metals at the halocline, 4. Sinking of... 

Kremling, K., Petersen, H., 1984. Synoptic survey on dissolved trace metal levels in Baltic surface waters. Marine Pollution Bulletin, 15(9), 329-334. 

Figure 3.4 The removal of dissolved trace metals and chlorinated organic compounds as a function of added particle concentration (SP/Vf ) in the river end-member of the Humber Estuary, calculated according to Equation (3.10) for SP/Vf° = 5mg H and a = 0.50.

Balls, P.W. (1989) Trend monitoring of dissolved trace metals in coastal sea water- a waste of effort Marine Pollution Bulletin 20, 546-8. 

Mechanism 3. Alternatively, the main route for accumulation of the trace metals may involve the uptake of dissolved trace metals (e.g., via the gills and mantle). In this case, the protective role of the sink could be explained by invoking adsorption in the external medium as the principal factor controlling the dissolved metal concentrations to which the organisms are exposed. Clearly, as the concentration of adsorbing substrate increases, the concentration of dissolved metals will decrease. 

---