Metals background concentrations

Hamon RE, McLaughlin MJ, Gilkes RJ, Rate AW, Zarcinas B, Robertson A, Cozens G, Radford N, Bettenay L. 2004. Geochemical indices allow estimation of heavy metal background concentrations in soils. Global Biogeochem Cycles 18 GB1014. 

The background concentrations at which metals occur in seawater are extremely low, and much work has been done on preconcentration procedures in attempts to improve detection limits for these metals. Various preconcentra-... 

While most of the noble metal stays on the catalyst, small amounts do end upon the road, causing diverse environmental effects [115-117]. The concentration of Pt metals in urban road dust (especially on roundabouts) can be 100-fold higher than the normal background concentration. There is even a company in the UK that sweeps up this dust, with the aim of recovering the Pt group metals ... 

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). 

In view of these considerations, one can adopt practical and reasonable, though arbitrary, criterion A ferrous ion concentration of 10 6 mol liter 1 and higher implies the occurrence of considerable dissolution, i.e., of corrosion. With these considerations as background, it is conventional in using a potential-pH diagram for deciding whether a metal can possibly corrode, to calculate the equilibrium potential for the M + + ne M reaction for a metal-ion concentration of 10 6 mol liter 1. 

In Europe, the notion that it may be possible to determine a natural background concentration of a metal at most sites may be unrealistic. Many hundreds of years of industrial activity, urbanization, and widespread aerial deposition mean that it is best to consider background concentrations as those determined at sites of relatively low anthropogenic impact. These concentrations will still vary considerably from site to site due to geological influences. 

A crucial difference between the total and added risk is in treatment of the eco-toxicity data. The added risk methodology requires the production of a PNECadd, which is calculated by subtracting the background concentration of metal in the control from the effect/no-effect concentration from that test. These data are then used for the derivation of the PNECadd. The ambient background concentration at the site is then added to the PNECadd to produce the standards to which the measured concentration is then compared. 

Note that in Australia, Canada, and some other jurisdictions, the added risk procedure is not followed, and the EQS instead defaults to the background concentration if this is greater than the calculated EQS at a particular site (ANZECC/ARMCANZ 2000 CCME 2007). In nearly all jurisdictions, speciation and bioavailability considerations are taken into account, but for some metals this is not currently possible. 

FIGURE 4.2 Summary of the added risk approach for dealing with background concentrations of metals. 

Zhao FJ, McGrath SP, Merrington G. 2007. Estimates of ambient background concentrations of trace metals in soils for risk assessment. Environ Pollut 148 221-229. 

Some substances, such as metals and some organics (e.g., polycyclic aromatic hydrocarbons), occur naturally, with background concentrations in soils that can vary widely (Table 5.1). An overview of the European background concentrations of metals and other inorganic elements was provided by Salminen et al. (2006). Maps and the raw data can be found in the Geochemical Atlas of Europe at http //www.gsf.fi/publ/foregsatlas/. 

Crommentuijn T, Polder MD, van de Plassche EJ. 1997. Maximum permissible concentrations and negligible concentrations for metals, taking background concentrations into account. RIVM report no. 601501001. 

Namral background concentrations for heavy metals can be identified by the nearly stable or constant values below the sediment depth, which represents about the change from the nineteenth to the twentieth century. A comparison of natural background values of the heavy metals Cu, Pb, Zn, Hg in different Baltic Sea Basins, based on the cores of this study and completed by former investigations (Brugmann, 1998), is given in Table 14.5. 

TABLE 14.5 Natural Background Concentrations of Heavy Metals in Different Basins... 

Analytical Techniques. The primary method used to determine the metallic element concentration in the tailings was IX Plasma Atomic Emission Spectrometry (IXP). It was used for the determination of both major and minor components. In the former case, the analysis is straightforward, but in the case of minor constituents, it was necessary to use matrix matching, i.e., to use standard solutions having the same concentration of the major component as the unknown, to compensate for the background emission interference of the other solutes. This requires the initial determination of the major components to define the appropriate doping levels. The... 

---