Potentially toxic elements

Table 12.6 Potentially toxic element limits and allowed in the EU (mg kg 1 DM) (in ECN 2008) ...

Wiersema JM, Wright L, Rogers B, et al. 1984. Human exposure to potentially toxic elements through ambient air in Texas. In Proceedings of the 77th Meeting of the Air Pollution Control Association, San Francisco, CA, June 24-29, 1984. 

Saether (1980), Saether Runnells (1980), and Stollenwerk Runnells (1981) studied the leaching of various retorting residues from US Green River oil shales. Alkaline pH values were established even before 25% of the first pore-volume had passed through the waste, and were maintained at high levels for the first 15 pore-volumes. The main potentially toxic elements mobilized under such alkaline conditions were found to be As, B, F, Mo, and Se. In contrast, base metals such as Cu, Ni, Pb, and Zn will be immobilized under such alkaline conditions (Baes Mesmer 1976 Bell 1976). 

Al-Hwaiti, M., Matheis, G. and Saffarini, G. (2005) Mobilization, redistribution and bioavailability of potentially toxic elements in Shidiya phosphorites, southeast Jordan. Environmental Geology, 47(3), 431-44. 

Lee, J.-S., Chon, H.-T., Kim, J.-S. et al. (1998) Enrichment of potentially toxic elements in areas underlain by black shales and slates in Korea. Environmental Geochemistry and Health, 20(3), 135-47. 

Statutory legislation to control the levels of such substances in food has been introduced in the UK and elsewhere. In more recent years, other potentially toxic elements have come into focus. Lead, cadmium and mercury have been the subject of much monitoring of the food chain and other metals, in particular aluminium, are continuing to attract attention. Nitrate and nitrite in food from food additive use is regulated across the European Union, but its presence in food crops has raised concerns. 

The existence of an element in different chemical forms in the gaseous, solid or aqueous solution phase provides the conceptual basis for speciation in soils. More particularly, a chemical species in soil refers either to a specific molecular arrangement of the atoms of an element or, quite often, to the result of an operational process of detection and quantitation aimed at elucidating chemical forms (Bernhard et at., 1986, pp. 7-14). In principle, the former definition should be the outcome of the latter, methodological definition. In practice, this connection is difficult to achieve in natural systems (Bernhard et al., 1986) (see Chapter 1 for a definition of speciation). Understanding speciation is important in assessing the availability of plant nutrients, plant uptake of potentially toxic elements (e.g. Al, Cd), and the movement of both nutrient and toxic substances into waterways or other parts of an ecosystem (Da Silva et al., 1991). 

The assessment of plant-available soil contents can frequently be achieved and validated by field experiments for nutritionally essential elements, and, for a few potentially toxic elements such as chromium, nickel and molybdenum, at the moderately elevated concentrations that can occur in agricultural situations. The validation of extraction methods, devised for agricultural and nutritional purposes, is much less easy to achieve when they are applied to heavy metals and other potentially toxic elements, especially at the higher concentrations obtained in industrially contaminated land. This is not surprising in view of the fact that for some heavy metals, for example lead, there is an effective root barrier, in many food crop plants, to their uptake and much of the metal enters plants not from the root but by deposition from the atmosphere on to leaves. In these circumstances little direct correlation would be expected between soil extractable contents and plant contents. For heavy metals and other potentially toxic elements, therefore, extraction methods are mainly of value for the assessment of the mobile and potentially mobile species rather than plant-available species. This assessment of mobile species contents may well, however, indicate the risk of plant availability in changing environmental conditions or changes in land use. 

A further area in which sequential extraction continues to be applied successfully is in assessment of the likelihood of mobilisation of metal contaminants from sediment-derived soil. When dredged sediment is used to reclaim land from the coastal margins or applied to arable soil to improve fertility, there is concern that potentially toxic elements accumulated under reducing conditions may be released on exposure to an oxygen-rich environment. Sequential extraction can be used to characterise the sediment prior to application, or to monitor changes in metal availability in the soil with time (e.g. Singh et al, 1998). 

Afterfilter data. As indicated in Table I, the minimum D50 in this study was about 0.5 pm, and particles smaller than this were collected on an afterfilter. Aerosols from combustion of pulverized coal typically are distributed bimodally, with a fine-particle mode at about 0.1 pm and a large-particle mode at supermicrometer sizes the modal diameter of the latter depends strongly on the efficiency characteristics of the control device. The elemental concentrations in the fine-particle mode are of interest in health-impact and source-apportionment studies because of the typically high enrichment of the concentrations of many potentially toxic elements and useful tracer elements in particles in this size range. Large-particle con-taimination of the afterfilter due to particle bounce can, however, limit the value of these data. 

The use of ICP-MS for the analysis of foods has been reviewed recently [270]. Food analysis can provide information on potentially toxic elements, nutrient elements, or geographical origin of the food. The application of ICP-MS to experimental nutrition has recently been reviewed [271]. The importance of quality control for multielement analysis of complex sample matrices like foods by ICP-MS was shown [272]. 

In this context, modern geographical information systems (GIS) represent an indispensable tool for better understanding the distribution, dispersion and interaction processes of some toxic and potentially toxic elements. Discussion on the use of GIS in the urban environment is, therefore, also provided. 

Siegel, F. R. (2002). Environmental Geochemistry of Potentially Toxic Elements, p. 218. Springer-Verlag, Berlin. 

Overview of Selected Soil Pore Water Extraction Methods for the Determination of Potentially Toxic Elements in Contaminated Soils Operational and Technical Aspects... 

Chemical elements that are either present naturally in the soil or introduced by pollution are more usefully estimated in terms of availability of the element, because this property can be related to mobility and uptake by plants. A good estimation of availability can be achieved by measuring the concentration of the element in soil pore water. Recent achievements in analytical techniques allowed to expand the range of interest to trace elements, which play a crucial role both in contaminated and uncontaminated soils and include those defined as potentially toxic elements (PTE) in environmental studies. A complete chemical analysis of soil pore water represents a powerful diagnostic tool for the interpretation of many soil chemical phenomena relating to soil fertility, mineralogy and environmental fate. This chapter describes some of the current methodologies... 

Table 11.5 Threshold levels of potentially toxic elements (PTEs) in Water for crop production (modified from Pescod, 1992 and references therein)...

Table 11.8 Potentially toxic element (PTE) concentrations in soils, sludges and soil pore water, including the free ion forms in solution (from Di Bonito, 2005)... 

Table 11.10 Comparison of potentially toxic element (PTE) concentrations (mg kg ) in sewage sludge applied to agricultural land in Germany and in the UK in 1996 (EC, 2001a)...

Incineration is often regarded as a very efficient technique for municipal solid waste (MSW) management. However, the environmental impacts of MSW incineration need to be carefully taken into account. The most relevant problem with MSW incineration is flue gas treatment. However, another often overlooked issue is the disposal of solid byproducts of the incineration process. MSW incinerators essentially produce two types of solid by-products, that is, slag, or bottom ash, and fly ash, often mixed with various other chemicals used for flue gas treatment. Bottom ash and—even more—fly ash are regarded as dangerous wastes mainly due to their potentially toxic elements (PTE) content and their tendency to leach such PTE to the environment. 

The species that are the most hazardous to humans and other animals as poisons are those that have a toxic effect on the body and that are soluble in water or mild acid. Some species, like realgar, contain a potentially toxic element (arsenic), but have such a low solubility potential that their toxicity as a poison is considered to be low under normal circumstances. 

In view of the role that milk plays in the nutrition and well-being of newborns, elemental speciation of both essential and potentially toxic elements in this... 

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