Metallic elements, airborne

The Analytical Chemistry Branch (ACB) of the Environmental Mon-itoring and Support Laboratory of the U.S. Environmental Protection Agency has a number of responsibilities for analytical support. Analyses of fuels, sources, and ambient samples are performed along with the analyses of divers other types of specimens including tissue, both plant and animal. One of the major areas of support rendered by the ACB is in support of the National Air Siurveillance Networks (NASN) a portion of this support consists of the analysis of collected material for airborne metallic elemental content. This chapter will, in the main, be a summary of the work done by the ACB with respect to the collection and analysis of airborne metallic elements. 

The analysis of tetramethylammonium hydroxide (TMAH) solutions manufactured by SACHEM Inc. of Cleburne, Texas, includes the determination of trace elements. These elements cause less-than-optimum performance of integrated circuit boards manufactured by SACHEM s customers that use these solutions in their processes. Alkali and alkaline earth metals (e.g., Li, Na, K, Mg, Ca, and Ba) can reduce the oxide breakdown voltage of the devices. In addition, transition and heavy metal elements (e.g., Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, and Pb) can produce higher dark current. Doping elements (e.g., B, Al, Si, P, As, and Sn) can alter the operating characteristics of the devices. In SACHEM s quality control laboratory, ICP coupled to mass spectrometry is used to simultaneously analyze multiple trace elements in one sample in just 1 to 4 min. This ICP-MS instrument is a state-of-the-art instrument that can provide high throughput and low detection Emits at the parts per thousand level. Trace elemental determination at the parts per thousand level must be performed in a clean room so that trace elemental contamination from airborne particles can be minimized. 

The collection and analysis of airborne metal components encountered in air is categorized by physical state. Mercury, lead, and manganese are considered as metallic elements which can be found as components of ambient air. No examples are given for the liquid state. Attention is focused on particulate matter and its trace metal constituents—methods of evaluation considered include AAS, NAA, SS/MS, OES, XRF, and XRD, Elemental compositional levels and ranges of metals are considered. Fluctuations in the composition of samples taken at a site at differing times are noted concen-trational differences between sites can vary by 10 . 

It is possible to distinguish whether airborne metals arise from crustal sources, e.g., windbome soil and rocks, or from anthropogenic sources by comparing the elemental concentration patterns of airborne... 

The environmental scientist has at his disposal a variety of sensitive, multi-elemental analytical methods that can lead to a massive amount of data on airborne metals. Optimum use of these tools for environmental monitoring calls for focusing resources only on those metals that are environmentally important. Considerations of toxicity along with their ability to interact in the air, leading to the formation of secondary pollutants, and their presence in air have led to the identification of 17 environmentally important metals nickel, beryllium, cadmium, tin, antimony, lead, vanadium, mercury, selenium, arsenic, copper, iron, magnesium, manganese, titanium, chromium, and zinc. In addition to the airborne concentration, the particle size of environmentally important metals is perhaps the major consideration in assessing their importance. 

Efforts have been made over the past several years to identify airborne metals with specific emission sources by the use of enrichment factors, and by comparing the trace element profile of airborne particles with characteristic components in particulate matter from various sources. Measurements of particle size and the application of sophisticated statistical techniques should increase the accuracy of these "fingerprinting approaches. 

Lichens were applied to delineate the distribution of airborne chemical elements emitted by industrial plants such as metal works and foundries (Belandria et al., 1991 Kansanen and Venetvaara, 1991 Manninen et al., 1991 Perkins, 1992 Zanini et al., 1992 Galley and Lloyd, 1993 Caniglia et al., 1994 Jovanovic et al., 1995), chlor alkali plants (Makholm and Bennett, 1998), fertilizer manufacturers and strip mines (Palomaki et al., 1992 Tynnyrinen et al., 1992), mercury mines (Bargagli, 1990 Lupsina et al., 1992) and uranium mines (Fahselt et al., 1995 Jeran et al., 1995). 

Pellizzari ED, Clayton CA, Rodes CE, Mason RE, Piper LL, Fort B, Pfeifer G, Lynam D (1999) Particulate matter and manganese exposures in Toronto. Canada Atmos Environ 33 721-734 Pfeifer GD, Harrison RM, Lynam DR (1999) Personal exposures to airborne metals in London taxi drivers and office workers in 1995 and 1996. Sci Total Environ 235 253-260 Ro C-U, Osan J, Van Grieken R (1999) Determination of low-Z elements in individual environmental particles using windowless EPMA. Anal Chem 71 1521-1528 Ro C-U, Osan J, Szaloki I, Van Grieken R (2000) Determination of chemical species in individual aerosol particles using ultra-thin window EPMA. Environ Sci Technol 34 3023-3030... 

Airborne or splash zone attack is not normally a problem at freshwater facilities however, air pollution can cause potential problems. Under certain flow conditions, such as turbulent flow or cavitation, fresh water can cause severe corrosion to submerged metallic elements. Ice damage also can limit the effectiveness of coatings on bulkhead walls and support piling. 

Filter samples can be prepared to airborne workplace concentrations by spiking each filter with aqueous solution containing elements with concentrations gravimetrically traceable to ultrapure metals or stoidiiometricaUy well defined oxides. The amormts correspond for some of the materials to current threshold limit values of contaminants in workroom atmospheres provided that the simulated filter has been exposed to one cubic meter of air. The certified values are based on a gravimetric procedure, i.e. weight per volume composition of the primary reference material dissolved in high purity sub-dis-tiUed acids. The National Institute of Occupational Health in Oslo, Norway, has produced several batches of such materials certified for 20 elements. Additionally, information values are reported for four other elements see Table 6.2. 

The systematic removal of elements by runoff and the reimmobilization from solution by organic matter are continuously counterbalanced by the new input of chemical species, which maintain both biological and biogeochemical cycles. The main sources of water-soluble elements are oceanic aerosols deposited on the land surface and the weathering of rocks. The airborne input of the trace metals may be ranked as follows for the Spitzbergen island ecosystems (Table 4). 

We can see that for iron and manganese the annual fluxes of trace metals are an order of magnitude higher than airborne input. For copper this input is sufficient to supply the annual uptake, and for zinc is even in excess. All these trace metals are essential elements and their input with deposition can be considered as positive for... 

In may be of interest to compare the fluxes of elements in biogeochemical cycles of Oak Forest ecosystem with exposure to airborne deposition input. The latter were (inkg/ha/yr)forN, 17.7 forCa, 14.7 forMg, 1.8 for K, 4.2 for Na, 1.4 forP, 1.1 for Fe, 0.07 and for Zn, 0.14. The deposition input of these elements fall into a range of 20% (calcium) to 4.5% (potassium) relative to the respective biogeochemical fluxes (see Table 9). The airborne Fe input accounts for a mere 2.5%. Simultaneously, for some heavy metals, like zinc, the deposition input is commensurate with the fluxes of biogeochemical cycle. 

Elemental Be and its compounds are very poisonous by inhalation or intravenous route. Chronic inhalation of beryUium dusts or fumes can cause a serious lung disease, beryUiosis, after a latent period ranging from several months to many years. Inhalation of airborne dusts can also cause an acute disease manifested as dyspnea, pneumonitis and tracheobronchitis with a short latency period of a few days. Skin contact with soluble salts of the metal can cause dermatitis. Beryllium also is a carcinogen. There is sufficient evidence of its inducing cancer in animals and humans. 

An operational definition is considerably more practical. Operationally determined species are defined by the methods used to separate them from other forms of the same element that may be present. The physical or chemical procedure that isolates the particular set of metal species is used to define the set. Metals extracted from soil with an acetate buffer is an operational definition of a certain class. Lead present in airborne particles of less than 10 pm is another. In water analyses, simply filtering the sample before acidification can speciate the analytes into dissolved and insoluble fractions. These procedures are sometimes referred to as fractionation, which is probably a more properly descriptive term than speciation, as speciation might imply that a particular chemical species or compound is being determined. When such operational speciation is done, careful documentation of the protocol is required, since small changes in procedure can lead to substantial changes in the results. Standardized methods are recommended, as results cannot be compared from one laboratory to another unless a standard protocol is followed [124], Improvements in methodology must be documented and compared with the currently used standard methods to produce useful, readily interpretable information. 

A second pathway by which metals reach the continental shelf is through deposition of airborne particles. This mechanism has been implicated in explaining the elevated concentrations of such elements as Cu, Zn, Pb and Ni that may occur in the sea surface microlayer25, although bubble flotation also contributes to metal enrichment at the surface. Eventually, gravitational settling removes these particles to subsurface waters. 

Mercury is a naturally occurring metal that has several forms. Also known as quicksilver because it is a silver-colored liquid at room temperature, mercury is an element that does not break down. It occnrs natnrally and is fonnd in very small amounts in oceans, rocks, and soils. It becomes airborne when rocks erode, volcanoes erupt, and soil decomposes. Mercnry combines with carbon to make organic mercury compounds (methyl mercury).3 3 ... 

Intuitively, one expects that trace metal analysis will involve collection and analysis of particulate matter. It is convenient to consider the collection and analysis of airborne species for the elemental determination... 

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