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Persistent organic pollutants (POPs) and Polycyclic Aromatic Hydrocarbons (PAHs)
As described in a recent critical review (Daly and Wania, 2005), interest on the identification of organic contaminants in mountain regions has been recently increased. The reasons for studying these compounds in mountains are various and principally relate to the potential pollution impact to the human health and to the alpine ecosystem (Kallenborn, 2006). The snow cover in alpine regions works as a temporary storage reservoir that releases massive quantity of the accumulated chemicals in the snowpack into lakes or fresh waters representing a significant load of contaminants over the short snow cover melting period. In addition, many alpine areas are not directly influenced by close anthropogenic activities and thus they are suitable for studying the sources, the transport mechanisms and the fate of pollutants from urban to remote areas (Daly and Wania, 2005; Fernandez, 2003).
The works on the investigation of the presence of POPs, principally pesticides and PCBs, in snow and ice samples are few and essentially restricted to the Arctic regions (Leuenberger et al., 1988; Rahm et al., 1995; Franzen et al., 1994; Jaffrezo et al., 1994; Masclet and Hoyau, 1994; Masclet et al., 2000; Garbarino et al., 2002). Only sporadic studies were conducted in the European (Carrera et al., 1998; Carrera et al., 2001; Kiss et al., 1997; Herbert et al. 2004), Chilean-Argentinean Andes (Quiroz et al., 2008), Himalaya (Wang et al. 2008a; Wang et al., 2008b), US and Canada mountain regions (Hageman et al., 2006; Blais et al., 1998; Gregor et al., 1996; Gregor and Gummer, 1989). In Wang et al. (2008a), the concentration of 5 light PAHs and some organochloride pesticides (OCPs) were determined in a 10 m firn core recovered from Dasuopu Glacier (6720 m a.s.l.) in the Central Himalayas. In a 21 m ice core recovered from Everest at an altitude of more than 6500 m a.s.l.; the samples have been analysed for major ions, stable O and H isotopic ratios and some POPs, obtaining detailed concentration profiles of DDT, hexachlorocyclohaxanes and PAHs for the last 40 years (Wang et al., 2008b).
The only study regarding POPs in an alpine ice-core was carried out by Villa et al. (2003, 2006) on the Colle del Lys (Mont Blank) but it was limited to concentrations of some pesticides prior to the 1950s.
Recently, the release of organic contaminants from melting snow have been studied because it poses risks to aquatic and terrestrial organisms and to humans who rely on drinking water and food production from regions that are seasonally snow-covered (Meyer and Wania, 2008; Meyer et al., 2009a; Meyer et al., 2009b).
The release of persistent organic pollutants (PCBs, HCB, HCHs and DDTs) accumulated in Alpine glaciers, was studied in glacial and non-glacial fed stream in the Italian Alps (Bizzotto et al, 2008). To our knowledge this work is the first PAHs concentration record to be published for an Alpine firn and ice core.
Elemental composition of aerosol particles
Larger particles emitted from coal-fired furnaces are primarily oxides of Al, Si, Ca, Fe, Na, Mg, and K, while smaller particles are highly enriched in volatile trace elements such as As, Sb, Se, Cd, Pb, and Zn.
The multimodal shape of trace element size distributions is also found in the ambient atmosphere. Pb, Cd, and Zn are present predominantly in the accumulation mode (AD 0.3-0.8 mm), Ca, Mg, and Al generally follow the shape of the coarse mode (AD >2.5 mm) whereas Mn, V, Cu, and Cr exhibit an intermediate behaviour with ADs of about 1-5 mm, according to the compilation by Davidson and Osborn (1986). Data concerning the chemical speciation of larger particles are rather sparse (Noll et al., 1990), as most studies of the size distribution of individual elements in the atmospheric aerosol have been limited to particle sizes up to 10 µm. Eleftheriadis and Colbeck (2001) found that a number of common earth and trace metals including K, Mn, Fe, Ca, Ti, Cr show their concentration maximum in the coarse mode at around 3-7 mm, and only a small fraction of the mentioned metals’ mass was present in particles larger than 10 µm. With newer instrumentation, trimodal mass-size distribution of the atmospheric aerosol can be observed, with three groups of trace metals: elements with most of their mass in fine particles (V, Zn, As, Sb, Pb), elements with roughly equal amounts of their mass in fine and coarse particles (K, Mn, Cu) and elements with most of their mass in the coarse mode (Na, Mg, Ca, Al, Si, Ti, Fe). The mass size distributions and the relative content in the fractional aerosol mass of some trace metals in a rural environment is shown in figure 2.2 (Allen et al., 2001).
Wet and bulk deposition
For wet deposition, rainfall rate and the concentration of the component of interest in the liquid phase determine the wet deposition flux. A simple model to express the concentration of a metal component in the liquid phase (CL) as a function of the atmospheric concentration (CA), the liquid water content of the cloud (L), the density of water (d), and the scavenging efficiency (ES) has been described by Junge (1963): CL = C A × ES × d L Eq. 2.2 Model for wet deposition The output of substances from the atmosphere depends on the intensity and duration of the rain. For wet deposition, it is necessary to collect and to analyze the rain water to study the matter input or the mass flow in soils and surface waters.
Wet deposition to forests can be measured using wet-only samplers situated in a clearing next to the forest. They are open only during precipitation, and so do not record that part of the dry deposition which is taken up during the periods free of precipitation by always-open collectors. Bulk samplers collect both wet and dry deposition, and are continuously open. The wet deposition measured as bulk precipitation will only represent the total deposition at open field conditions where dry deposition is of minor importance. The bulk precipitation flux will underestimate the total deposition to forests, because it neglects the filtering effect by the forest (Legrand et al., 1992).
Two types of biogenic sources exists: biomass burning and emissions from marine and continental activity.
Elements such as V, Cr, Mn, Cu, Zn, Cd and Pb occur in trace amounts in plants, some of which are essential for their growth and development. In plant tissues, concentration ranges of essential elements such as V, Cr, Mn, Cu, Zn and Cd are in ppb order whereas non-essential elements such as Bi, Pb and U are about ppb. The major components of biomass burning are forests (tropical, temperate, and boreal); savannas; agricultural lands after harvesting and wood for cooking, heating, and the production of charcoal. The burning of tropical savannas is estimated to destroy three times as much dry matter per year as the burning of tropical forests. The immediate effect of burning is the production and release into the atmosphere of gases and particulates such as trace elements that result from the combustion of biomass matter (Kaufman et al., 1992).
Vegetal organisms desorb many chemical volatile compounds emitted into the atmosphere. Amongst these numerous compounds, we recognize non-methanated hydrocarbons (NMHC) like isoprene and terpenes, particulate carbon, sulphur compounds (DMS), pollens and spores. These compounds can form various complexes containing trace elements, and so favour their emission into the atmosphere.
The source strength for the atmospheric emission of a metal compound is calculated from emission factors available for the different emitting processes. While most of the national emission inventories are focused on SO2, NOx, and total particulate matter, data on the emission of metal compounds are relatively sparse. Pacyna (1986a) has reviewed the available trace element emission factors for natural and anthropogenic sources.
On the global scale, compilations have been made for metal emissions by Nriagu (1979), Lantzy and Mackenzie (1979), and Weisel (1981). The divergence of the data reflects the uncertainties in estimating global emissions from very sparse data sets on natural and anthropogenic sources. Pacyna (1986b) and Salomon (1986) presented the first comparison of estimated global anthropogenic emissions of trace metals with emissions from natural sources.
A compilation of recently reported data for metal emissions (Pacyna and Pacyna 2001) is shown in table 2.3. Global anthropogenic emissions of metals greatly exceed the emissions of several trace elements from natural sources. On a regional scale in densely populated areas, anthropogenic emissions of metals are by far the dominant contributors as compared to natural sources. This is reflected by the fact that ambient concentrations of trace elements in source regions are some orders of magnitude higher than in remote regions. In table 2.4 the worldwide annual emissions of trace elements from major anthropogenic (mid 1990s) source categories is reported (Pacyna and Pacyna, 2001).
Polycyclic Aromatic Hydrocarbons (PAHs)
Polycyclic aromatic hydrocarbons (PAHs), considered “prioritant pollutants” by the EPA (2009), are incomplete combustion products of biomass and fossil fuel and for this reason they can be used as tracers of combustion activities (Masclet et al., 1986; Masclet et al., 1987; Masclet et al., 1995; Khalili et al., 1995; Subramanian et al., 2006). They are characterized by 2 or more condensed aromatic rings (sharing of at least two carbon atoms). The vapour pressure is variable in function of molecular weight and chemical features, ranging from 10.4 Pa (at 25°C) for Naphthalene to 1 .3.10-8 for Dibenzo[a,h]anthracene.
Sources of PAHs
Some PAH may be generated at the same time by several sources but others are often related to a particular combustion typology. The utility of using PAHs as an environmental marker depends on how different the PAHs pattern is from each source.
Many studies have suggested that specific compounds or ratios between different PAHs may be used for source identification (Masclet et al., 1987; Masclet et al., 1995; Li et al., 1993; Pistikoupolos et al., 1990; Duval et al., 1991; Harrison et al., 1996; Simcik et al., 1999; Park et al., 2002; Yunker et al., 2002; Venkataraman et al., 1994a; Venkataraman et al., 1994b; Khalili et al., 1995; Subramanian et al., 2006). There are three significant concerns regarding the use of PAHs in source apportionment studies:
– characteristic source signatures.
– partitioning of various PAHs between gas and particulate phase (see section 2.3.2).
– loss of the source signature by destruction of PAHs by photochemical process.
PAHs can also be used together with trace elemental data for source apportionment studies (Harrison et al, 1996).
Parental PAHs ratios have been widely used to detect combustion derived PAH. To minimize confounding factors such as volatility differences, water solubility, adsorption, etc. ratio calculations are restricted to PAHs within in a given molecular mass range. For parental PAHs, inputs are often inferred from an increase in the proportion of the less stable kinetic PAH isomer relative to the more stable thermodynamic isomers. The photochemical reactions in the atmosphere play a key role in source signatures and for this reason, as demonstrated in various studies (Masclet et al., 1986), atmospheric PAH ratios could vary from those seen in source emissions. In Gaga (2004) PAH ratios for several single-source and environmental material combustions is presented.
Gas to particle distribution in atmosphere
The different volatility is reflected by the environmental behaviour of these compounds which can be present both in gas phase and adsorbed to the carbonaceous aerosol particles. The repartition is function not only of molecular weight but also of meteorological and climatic parameters (temperature, pressure, relative humidity, incident radiation, air masses circulation) and carbonaceous aerosol chemical-physical features. Adsorption of PAHs on black carbon particles often increases their chemical stability, reducing the photo-degradation rate (Schauer et al., 2003). The atmospheric lifetime of PAHs absorbed on fine/ultra-fine particles (<1.0 µm) can be estimated as several days compared to a few hours when in the gas phase. In general, low molecular weight PAHs are primarily in the gas phase while high molecular weight PAHs are in particulate phase.
Repartition of PAHs between gas and particulate phase strongly affects their toxicological properties, primarily carcinogenic effects. In fact, of 49 PAHs tested by IARC (International Agency of Cancer Research), 1 is listed as certainly carcinogenic for humans, 3 probable, 12 possible while the others not classifiable yet (IARC, 2008). If associated with ultra-fine particles, PAHs can be introduced deeply into the lungs (respirable fraction) with long residence times.
Table of contents :
CHAPTER ONE Ice cores from Alps and temperate regions as climatic and environmental archives
1.1 Glaciochemical records in temperate regions
1.2 Glaciological proxies for environmental and climatic studies
1.3 The history of ice core drilling on Colle Gnifetti
1.4 The 2003 Colle Gnifetti cores: the state of art
1.4.1 Drilling campaign
1.4.2 Density profile
1.4.3 Processing of firn / core ice section
1.4.5 Stable H and O isotopic analysis
126.96.36.199 Calibration of isotopic ratio as paleo-thermometer
1.4.6 Major ions analysis
1.5 Literature review
1.5.1 Trace elements
188.8.131.52 Tibetan Plateau
1.5.2 Persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs)
CHAPTER TWO Aerosol, trace elements and PAHs: sources, transport pathway and sequestration
2.1.1 Modal distribution of aerosol
2.1.2 Elementar composition of aerosol particles
2.1.3 Transport processes
2.1.4 Deposition processes
184.108.40.206 Dry deposition
220.127.116.11 Occult deposition
18.104.22.168 Wet and bulk deposition
2.2 Trace elements
2.2.1 Natural emissions
22.214.171.124 Mineral aerosol and Enrichment Factor (EF)
126.96.36.199 Sea-salt spray
188.8.131.52 Volcanic emissions
184.108.40.206 Biogenic emissions
2.2.2 Anthropogenic emissions
2.3 Polycyclic Aromatic Hydrocarbons
2.3.1 Sources of PAHs
2.3.2 Gas to particle distribution in atmosphere
2.3.3 Gas to particle distribution in atmosphere
CHAPTER THREE Instrumentation: principle of methods
3.1 Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
3.1.1 Sample introduction system
220.127.116.11 APEX™ desolvation unit
3.1.2 Plasma source
3.1.3 Interface region
3.1.4 Vacuum system
3.1.5 Ion focusing lenses
3.1.6 Mass analyzer
18.104.22.168 Quadrupole mass analyzer
22.214.171.124 Double focusing sector field analyzer
3.1.8 Resolution in ICP-MS
3.1.9 Interferences in ICP-MS
3.1.10 ICP-QMS: instrument and setting up
3.1.11 ICP-SFMS: instrument and setting up
3.2 ICP Optical Emission Spectroscopy (ICP-OES)
3.2.1 ICP excitation source
3.2.2 Dispersive optical system and spectral lines
3.2.4 Instrument and setting up
3.3 High Performance Liquid Chromatography (HPLC)
3.3.1 Pumps and introduction system
3.3.2 Separation column and stationary phases
126.96.36.199 Photodiode Array
3.3.4 Instrument and setting up
3.4 Coulter Counter
3.4.1 Instrument and setting up
CHAPTER FOUR The ice/firn core melting system
4.1 The decontamination of ice cores: from chiselling to melting system devices
4.2 Melting heads: design and manufacturing
4.3 The continuous flow analysis
4.3.1 Continuous ICP-Q-MS measurements
4.3.2 Continuous conductivity measurements
4.3.3 Discrete sampling
4.3.4 On-line SPE extraction of PAHs
4.3.5 SPE storage and elution procedure
4.3.6 Washing of melting head and tubing
4.4 Ice core melting procedure
CHAPTER FIVE Methods validation and quality control
5.1 Continuous ICP-QMS measurements
5.1.2 Procedural blanks
5.1.3 Detection limits
5.1.4 Decontamination efficiency
5.1.5 Instrumental accuracy and recovery tests
5.1.6 Instrumental repeatability
5.2 Discrete ICP-SFMS measurements
5.2.2 Procedural blanks
5.2.3 Detection limits
5.2.4 Instrumental precision, accuracy and recovery tests
5.3 Discrete ICP-OES measurements
5.3.2 Procedural blanks
5.3.3 Detection limits
5.3.4 Instrumental precision, accuracy and recovery tests
5.4 Solid phase extraction and HPLC analysis
5.4.2 Blanks value
5.4.3 Procedural blanks
5.4.4 Detection limits
5.4.5 Instrumental precision, accuracy and recovery tests
5.4.6 Procedural reproducibility
5.5 Coulter Counter
CHAPTER SIX Trace element profiles
6.1 Character of the data
6.2 Multivariate exploratory techniques for identifying patterns and different principal sources
6.2.1 Principal component analysis (PCA): princples
6.2.2 PCA on Colle Gnifetti firn/ice core
6.3 Short term variations
6.3.1 Contribution of anthropogenic and natural sources
6.3.2 Meteorological factors: air masses and boundary layer
6.3.3 Short-term intense emissions event
6.4 Crustal trace elements long-term variations
6.4.1 Concentrations profiles
6.4.2 Near-bedrock ice core samples
6.4.3 Natural emissions of trace elements
6.5 Anthropogenic metals long-term variations
6.5.1 Variations during Greek and Roman empires (500 BC – 400 AD)
6.5.2 Variations during Early Middle Ages (400 AD – 800 AD)
6.5.3 Variations during Late Middle Ages (800 AD – 1400 AD)
6.5.4 Variations during in pre-industrial period (1400 AD – 1700 AD)
6.5.5 Variations during in industrial period (1700 AD – 2000 AD)
188.8.131.52 European trace elements inventories: the state of art
184.108.40.206 Pb profile and European emissions
220.127.116.11 Cd profile and European emissions
18.104.22.168 Zn profile and European emissions
22.214.171.124 U profile and European emissions
CHAPTER SEVEN Polycyclic Aromatic Hydrocarbons profiles
7.1 PAHs concentrations in snow and ice samples
7.2 PAHs concentrations and profiles
7.3 PAHs pattern
7.4 European PAHs emissions inventories
7.5 Short-term PAHs variability
7.5.1 Global distillation or Grasshopper effect
7.5.2 PAHs short-term variability and climate linkage
CHAPTER EIGHT Radioactive 239Pu fallout record
8.1 Plutonium: a recent global pollutant
8.2 A novel ICP-MS direct injection method for 239Pu determination in alpine snow/ice samples
8.3 239Pu profile in Colle Gnifetti core
8.3.1 239Pu profile and nuclear tests in atmosphere
8.3.2 Comparison between CG core and other environmental records
CHAPTER NINE Lead isotopes profile
9.1 206Pb / 207Pb ratio profile 1
9.1.1 206Pb / 207Pb in the last three centuries
9.1.2 206Pb / 207Pb profile in 65-75 m of depth: an helpful tool for dating evaluation?