Potentially toxic trace elements

Sediment Analysis. Sediment is the most chemically and biologically active component of the aquatic environment. Benthic invertebrate and microbial life concentrate in the sediment, a natural sink for precipitated metal forms, and an excellent sorbent for many metal species. TTie extent to which potentially toxic trace element forms bind to sediment is determined by the sediment s binding intensity and capacity and various solution parameters, as well as the concentration and nature of the metal forms of interest. Under some conditions sediment analyses can readily indicate sources of discharged trace elements. 

The following chapter is a case study of how the three problem areas illustrated (dissolved oxygen depletion, erosion/deposition, and potentially toxic trace elements) may be successfully addressed on a major river system using quantitative, semi-quantitative and qualitative approaches respectively. 

The goals of this chapter do not include a "state of the art" literature review which would be appropriate for a more in-depth discussion of one particular problem area. Rather the intent is to illustrate mechanistic approaches to river quality assessment using the three globally relevant water quality problem areas discussed in the previous chapter dissolved oxygen depletion, erosion/deposition, and potentially toxic trace elements. The information provided does not include all rationale, methology or approaches used in the study as this is beyond the scope of the chapter. Additional general information on application of the intensive river quality assessment approach in the Willamette River basin may be found elsewhere (4-9, 11-14, 17). 

Potentially Toxic Trace Elements - A Qualitative Approach... 

Methods. As discussed in the previous chapter, a number of approaches have been used to assess the presence of potentially toxic trace elements in water. The approaches used in this assessment include comparative media evaluation, a human health and aquatic life guidelines assessment, a mass balance evaluation, probability plots, and toxicity bioassays. Concentrations of trace elements were determined by atomic absorption spectrometry according to standard methods (21,22) by the Oregon State Department of Environmental Quality and the U.S. Geological Survey. 

Comparative Media Evaluation. Table 4 is a summary of trace element occurrences for water, sediment, fish and rocks in Oregon as compared with concentrations measured elsewhere in the world. Details of the comparison parameters are provided in the footnotes to Table 4. The table indicates that no excessively high concentrations of potentially toxic trace elements exist in Willamette River water relative to "uncontaminated sites. 

Caroli S, Forte G, Iamiceu AL, Galoppi B 1999) Determination of essential and potentially toxic trace elements in honey by inductively coupled plasma-based techniques. Talanta 50 327-336. Chiswell B, Johnson D (1994) Manganese. In Seiler HG, Sigel A, Sigel H, eds. Handbook on metals in clinical and analytical chemistry. Dekker, New York. 

Table 8.10 shows the concentration range of potential toxic trace elements in U.S. sewage sludges, as summarized by Chaney (1989). In this table, data on maximum concentration of toxic trace elements in dry, digested sewage sludges are compared to concentrations of the elements in median sludges and in soils. The subsurface contamination that may result from uncontrolled disposal on land surfaces... 

The environmental risk leachates from the retort residue represent on the ecosystem is not only related to the absolute content of various potentially toxic trace elements in the semicoke, which in most cases may not be significantly higher than the content of the natural oil shales. It also depends on the leachability of these elements when the residue comes in contact with water, and on the elemental speciation. Important factors to consider in this context are ... 

Preliminary studies have shown that it is possible to remove over half of the potentially toxic trace elements present in coal when the mineral matter is reduced by coal washing. When coal is burned in a power plant, about 13% of the mercury and about 50% of the lead and cadmium may remain with the fly ash. Analytical chemical techniques have been developed to determine Hg, Cu, Cr, Mn, Ni, Cd, Pb, and F in coal and fly ash. These techniques produce accurate and precise results despite the fact that there are no coals with established trace element content, except for mercury. 

Feng, X., Hong, Y., Hong, B. and Ni, J. (2000) Mobility of some potentially toxic trace elements in the coal of Guizhou, China. Environmental Geology, 39(3-4), 372-77. 

Toxic and essential trace elements intakes were computed from food consumption data of the population in northern Italy and element concentration measurements. The results (Table 10.6) were compared with the Italian Recommended Dietary Allowance (RDA) for essential trace elements and with the Provisional Tolerable Daily/Weekly Intake (PTDI/PTWI) for toxic elements. Finally, an assessment was made of the extent to which each food contributes to the total intake of trace elements by the population under study and the most contaminated foods were also detected. On the whole, mean intake values satisfied the Italian RDA for all the essential trace elements [31], while the potentially toxic trace elements were below the relevant threshold limits. 

ARSENIC AND OTHER POTENTIALLY TOXIC TRACE ELEMENTS IN RICE... 

P, 819-2589 and 789-1440 and Zn, 14.6-30.1 and 13.8-22.8. It could be concluded that Vietnamese rice has elemental concentration ranges largely overlapping those of Australian rice. Another fact worth mentioning is that Vietnamese rice has rather high concentrations of nutritional elements such as K, Mg, and P, whereas the levels of potentially toxic trace elements (e.g., Cd) are very low. Finally, the concentration of Ni was found to be higher in white than in brown... 

The issues of method validation and assessment of measurement uncertainty in the determination of potentially toxic trace elements in rice are of permanent interest for the scientific community. In this context, the sources of uncertainty associated with the determination of Cd, Cu, Pb, and Zn have been recently estimated in rice through an interlaboratory comparison [30]. Four Brazilian laboratories participated in the proficiency test. The analytical technique used were FAAS, ET-AAS, and ICP-AES. The rice samples were supplied by the Institute for Reference Materials and Measurements (IRMM), Joint Research Center of the European Commission, within the scope of the interlaboratory comparison International Measurement Evaluation Programme (IMEP) 19 Trace Elements in Rice (see also Chapter 7 in this book). Three out of the four laboratories reported values close to the reference values. It was emphasized that, in order to establish a reliable uncertainty budget, all significant sources of uncertainty should be identified. 

The continuously increasing pollution of the environment with potentially toxic trace elements, among them heavy metals, is a problem of particular concern (Nriagu, 1992, 1996). However, one may ask, whether part of the reported increase results from the application of more and more sensitive analytical techniques in recent years. Such methods enable us to find most of the elements of the periodic table in all kinds of analyzed materials (Markert, 1992, 1993). Therefore, the question arises is the environment today actually more polluted with heavy metals than it was in the past To find an answer, we need methods to determine pollution levels of the past as a comparison... 

Well over 10,000 papers dealing with activation analysis have appeared in the literature. Most of these (99%) have been published since 1955. Some of the more interesting applications have been determining potentially toxic trace elements in natural waters and environmental samples, authenticating paintings and other objects of art, and studying impurities in semiconductor materials, trace elements in plant and animal metabolism, and trace-element abundances in terrestrial rocks, meteorites, and lunar samples. In the analyses of lunar samples, more than twice as many trace-element determinations have been reported by activation analysis than by any other technique. In fact, the activation-analysis determinations on these rare samples probably exceed those by all other techniques combined. 

The deposition and accumulation of fly ash downwind from coal-combustion sites is a concern because it may be significantly enriched in potentially toxic trace elements, including lead (Pb) and arsenic (As), compared to the burned coal (Coles et al, 1979 Eary et al, 1990 Hower et al, 1999 Kaakinen et al, 1975). Other elements such as zinc (Zn) and germanium (Ge), of less environmental concern, may also be enriched in fly ash. The relatively high concentrations of As in fly ash reflect partly its presence in pyrite in coal from the Appalachian Basin (Goldhaber et al, 2002). More importantly, the concentration of these metals and metalloids occurs during the combustion process itself. A suite of elements including As, Ca, Cr, Cu, Ga, Mo, Ni, Pb, Sb, Se, V, and Zn is enriched in the fine fraction of coal fly ash (Coles et al, 1979), because of vaporization in the furnace and subsequent condensation or absorption onto ash particles (Kaakinen et al, 1975). 

In general, the coal-mining and coal-consuming industries determine coal quality for immediate or near-term use, whereas federal and state governments analyze coal (1) to characterize large areas of unmined coal (resources) for future reference, (2) to support policy decisions related to future coal use, and (3) to supply federal and state regnlatory agencies with information about the quality or special characteristics of future coal supplies, such as the presence, amounts, and modes of occurrence of sulfur and potentially toxic trace elements (Table 8.1). 

To some extent, this process is already under way and some unessential potentially-toxic trace elements now appear to be present in human protoplasm in unnaturally high concentrations. Hecker et at. [7], in a comparison of 100 acculturated and 90 unacculturated individuals, have found that the levels of lead and cadmium were markedly lower in the hair, blood and urine in the unacculturated population. Since the latter was composed of Yanomamo Indians living in remote areas of Venezuela, the levels associated with this population can probably be taken to reflect an environment uncontaminated by trace elements derived from industrial sources. 

Problems arising from the presence of natural soils containing abnormally high levels of potentially toxic trace elements have provided valuable information on the ecological consequences of enhancement of soil levels with a number of elements which are industrial pollutants. The elements, lead, molybdenum, nickel and selenium are in this category. 

Fluorine is another potentially-toxic trace element which is dispersed by atmospheric pollution and it has long been recognised that damage to plants occurs and that there is a hazard to man and farm stock, in the vicinity of industrial plants processing fluoride-containing minerals. Such plants include factories for the production of aluminium, superphosphates and compound fertilisers based on the liberation of phosphoric acid from rock phosphate. In October 1976, ten cows had to be destroyed on two farms in the vicinity of the British Aluminium Company s aluminium smelter at Invergorden in the north of Scotland, and problems of fluoride toxicity have been commonly associated elsewhere with the production of aluminium. 

The effects of soil contamination with potentially toxic trace elements on plant composition has attracted a great deal of attention from research workers in recent years and there has also been an increase in interest in the relationship between plant uptake and the concentration of particularly toxic elements, such as cadmium, in soil solutions. For example, Lagerwerff [297] has reported work on the uptake of cadmium, lead and zinc by radishes from the soil and... 

To summarise our consideration of the consequences of the substantial contamination of soils which has already occurred, particularly in urban and industrial areas, we can conclude that a general enhancement of the levels of potentially toxic trace elements in plants grown in urban areas could lead to deleterious effects both on the plants and on the health of animals or humans eating them. The enhancement of trace-element levels in soils resulting from contamination can also have effects on biochemical processes occurring in the soil, and Tyler and co-workers [359] have reported increased nitrate accumulation in soil in which the cadmium and lead levels had been experimentally enhanced. 

No general conclusions can be drawn about nutritional hazards arising at localised sites where the soil has been very heavily contaminated as a result of the direct application of metal-containing industrial wastes, such as wastes from smelting or electro-plating operations. In such situations, the levels of several potentially-toxic trace elements may be substantially enhanced in... 

International standards should be established for particulate emissions into the atmosphere from industrial, public and domestic sources and these should limit both the rate of total particulate dispersal and the individual rates of dispersal of potentially toxic trace elements. 

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