«Dissertation zur Erlangung des Grades “Doktor der Naturwissenschaften” Im Promotionsfach Geowissenschaften Am Fachbereich Chemie, Pharmazie und ...»
Thallium emissions were observed in West-Germany cement plants due to thalliumbearing roasted pyrite (average 400 ppm) additive to limestone. A cement plant at Lengerich showed emitted flying-dust being enriched with Tl content up to ~ 50,000 ppm with other German plants like Erwitte, Geseke and Paderborn all demonstrated high Tl contents (Ewers, 1988; MAGS, 1980). Soil in an area of 1-2 km radius from the cement plant in Lengerich, Germany showed maximum concentration of 6.9 mg/kg (LIS, 1980). In agricultural soil 4 mg/kg of Tl was found and 6 mg/kg of Tl was reported in house garden soils (Crössmann, 1984). The Tl level in soil samples showed highest Tl concentrations in the upper soil layer and gradually decreased with increasing depth (LIS, 1980). The source of the pyrite roasting residues used by the cement plant in Lengerich, Germany demonstrated high Tl concentration of 160 µg/l (LIS, 1980).
According to FRG General Administration Regulation thallium as a constituent of dust fall-out cannot be exceeding 10 µg/m2/day (Ewers, 1988). The potential risk for human of excessive Tl contents in soils is in 1 mg/kg according to North-Rhine Westphalia (FRG). Swiss Ordinance on Soil contaminants suggested the maximum admissible level of thallium in agricultural soil is 1 mg/kg dry weight. In uncontaminated areas, air concentration of thallium is usually less than 1ng/m3, in water less than 1µg/l and in water sediments less than 1 mg/kg. The maximum contaminant level in the drinking water is 2 µg/l according to the United States Environmental Protection Agency. For adults the LD50 is between 10 to 15 mg/kg (Schoer, 1984;
Gosselin et al., 1984). The International Programme on Chemical Safety (IPCS) of the World Health Organisation (1996) suggested in a monograph with the total general population intake of thallium should not be more than 5 µg/day (WHO, 1996).
(2.0) Aim (2.1) Aim of arsenic project The aims of this project were: (1) to determine the physicochemical behaviour of arsenic presents in limestone oxide as impurities. (2) to understand the adsorption of heavy metals into the soil system by investigating (i) the form of metal enters the soil (solid particulate in wet or dry deposition or solution), (ii) range of metal species, (iii) charge on the metal entering the soil, (iv) the pH of the receiving environment, (v) the percentage of organic matter in the soil and the redox condition of the receiving environment. (3) to partition metals in different metal-bearing phases in order to gain better understanding of the arsenic’s behavior.
(2.2) Aim of copper project The aims of this project were: (1) to determine the physicochemical behaviour of copper presents in limestone Fe and Mn oxide impurities. (2) to predict copper mobility in soils. (3) to detect the main host phase(s) and soild copper speciation accumulated in agricultural lime samples. (3) to evaluate the risks of soil and ground water contamination when such lime samples are applied to soil pH amendments. (4) to understand long term fate of copper species in environment. (5) to provide information of managing copper contaminated soils in future development.
(2.3) Aim of thallium project The aim of this project was to determine the mobility of thallium in soil samples in the vicinity of a cement factory at Lengerich, Germany and hence determining the toxic effect of the element.
Exchangeable and sorbed thallium metal was extracted by ammonium nitrate solution and the total thallium contents were found by applying aqua regia acid digestion. The two sampling areas have been using for farming and various purposes. The investigation of the soil thallium concentrations could help to identify the effects of mobile thallium on the farm products producing in the areas and the long term health impact to local inhabitants.
(3.0) Method (3.1) Sequential extraction technique Chemical extraction is complicated by the fact that no chemical solution uniquely extracts trace elements out of one pool. Sequential extractions, in which a soil samples is reacted with a series of carefully selected chemical solutions of increasing strengths, were developed to increase extraction selectivity of the distinct geochemical fractions.
Chemical speciation analysis in soils and sediments is defined by BCR as: the process of identification and quantification of the different defined species, forms or phases in which an element occurs in the material. Speciation also represents the actual description of the quantity and variety of species. Chemical speciation can be sub-divided in three classes: (1) functionally defined species (e.g. plant available species) where the species are defined by their role or as (2) operationally defined species, characterized by the procedure of isolation and identification (e.g.
acid ammonium oxalate extractable fraction) or finally as (3) specific chemical compounds or oxidation states (e.g. AsH3).
The chemical compounds composition is responsible for the ecological functions of soil.
Sequential extraction is a method based on dissolving the chemical substances. It determines groups of compounds (but not individual ones) with identical properties that are dissolved by the same extractants and these compounds have a similar behavior in the environment.
Fractionation is a direct way of obtaining the main compounds content of any element in soils. There are numerous phases which can be pre-defined by this method which are listed in following table (9). The following components permanently interact and characterize the soils in specific manners in natural environment. The following five classification phases demonstrate different fundamental unit of elementary system of chemical compounds in a minimal soil volume (pedon, horizon).
Method Table (9) Table shows different phases that main element compounds can resident
According to Bureau of Standards of the European Union (BCR) stated in 1987 that fractionation is a quantification of different kinds, forms, or phases of chemical compounds including the studied elements. International Union of Pure and Applied Chemistry (IUPAC) also defines fractionation as a taxonomic separation of substances by their physical (e.g. size, solubility) and chemical (e.g. bonding and reactivity) properties using corresponding physical and chemical methods.
Chemical reagents tailored for extraction purpose are often applied for fractionation of chemical element compounds and these reagent’s interactions with definite groups of chemicals are important. The use of an extractant is to dissolve the investigated fraction and keep it soluble.
The characteristic reagents can be broadly classified as inorganic, organic, acid and alkaline hydrolysis complex formation, reduction of oxides and hydroxides of Fe and Mn, and displacement of ions from soil exchange complexes by solutions of electrolytes. Reagents can either completely dissolving a certain group of substance or establish an equilibrium solutions in which particular groups of substances are investigated. Microelements in soils do not form independent phases and these elements are constituents of marcoelement compounds.
Application of fractionation can dissolve those macro compounds such as C, Fe, and Al compounds and the microelements in the solution can be determined. The biggest obstacle to extractive fractionation of compounds of microelements is non-selective due to interaction between micro- and macro-elements in soils. The assessment and forecast of the ecological status of contaminated soils are impossible without information about the compounds containing pollutants absorbed by the soils. Many fractionation schemes have been developed over the past fifty years and the underlying principles are summarized in following table (10).
Table (10) Table shows association between extractants and different soil solid phases
The efficiency of extraction schemes depend on several factors which are (1) sample preparation (e.g. under reducing condition, labile phases can be converted to other phases); (2) concentration of the extractants; (3) sequence of extractants which apply to soil fraction; (4) soil solution ratio; (5) time and temperature of the extraction.
The key of the fractionation is to get further information about the contents of the As and Cu compounds with examples whether they are mobile, weakly mobile and intermediate between two. The As compounds can be stationed in following four different phases which are (1) Substances of the liquid phase of soils; (2) The mobile one of soil solid phase; (3) Mobile forms of the solid phase are easily soluble; (4) Nonspecifically sorbed (exchangeable) and the specifically sorbed compounds are in equilibrium with soil solution. Extraction of these compounds from soils is based on the mechanisms of their bonds with soil components depending on the properties of each microelement (or their groups) and irrespective of the specific features of the macroelements (organic and mineral).
The names of the microelement compounds more firmly bound with soil attest to the composition of the macrocomponents. Compounds of microelements that are held by the main products of soil formation (organic substances and nonsilicate forms of Fe, Al, and Mn) may be called specific soil ones. Elementary soil-forming processes provide the distribution of these products along soil profiles. In technogenic soils, these components are assumed to retain pollutants.
Trace elements occur in soils in certain “pools” or “sinks” of different solubility and mobility in six different soil phases which can be outlined in following table (11).
Table (11) Table shows trace elements in different soil phases
It is therefore understandable that arsenic and copper distribution or fractionation in different soil solid phases can be examined by an instrumental surface analytical technique or a selective sequential extraction (SSE) technique.
(3.2) Atomic absorption spectroscopy The invention of atomic absorption spectroscopy is based on the discovery of the absorption of radiation by atoms since the early part of the nineteenth century. It involves valence electron transitions yielding radiation with wavelengths in the ultraviolet-visible region of the spectrum. Electron orbits in an atom are characterized by the major and azimuthal quantum numbers n and l respectively. An electron undergoes a transition from a higher energy level (Enl) to a lower energy level (En1l1) with light of frequency is given off (eq.1).
The constants h and c in these equations are Planck’s constant and the velocity of light respectively. Thus, electronic transitions can be discussed in terms of frequency v, energy E and wavelength λ. All the ΔE, v and λ contain unique values for a given electronic transition and the resultant spectrum demonstrates a series of characteristic sharp lines which represents the particular element.
Absorption can be described with a parallel beam of continuous radiation of intensity I o passes through a cell containing atomic species of an element. The transmitted radiation I v will show a frequency of distribution. The atomic species is said to possess an absorption line at frequency vo, where vo is the frequency at the center of the line. The absorption coefficient of the atomic vapor kv is defined by (eq.3).
The relation between absorption and concentration are further explained by Beer-Lambert law in monochromatic radiation absorption. Lambert’s law states that light absorbed in a transparent absorption cell is independent of incident light intensity with an equal fraction of the light is absorbed by each successive layer of absorbing medium. Beer’s law suggests the absorption of light is likewise exponentially proportional to the number of absorbing species in the path of the light beam. In following figure(3), it shows with an incident beam of monochromatic radiation Io falls on an absorption cell length b. The transmittance (T) is equal to T = e-kbc and therefore in (eq.4)
where A is the absorbance and A = abc. a is a constant for a given system and c is the concentration of the analyte atoms in the flame. The above Beer-Lambert law predicts a linear relationship between absorbance and concentration with a and b stays constant. This relationship only is valid when the concentration of analyte atoms in the atomizer is equivalent to the analyte concentration in the sample solution.
(3.3) Flame atomic absorption spectroscopy (F-AAS) The fundamental principles underlying the flame atomic absorption spectroscopy (FAAS) is the same as HG-AAS described in above. Analytical liquid sample is aspirated, aerosolized and mixed with combustible gases. The mixture is ignited in a flame and during combustion, atoms of the element of interest in the sample are reduced to free, unexcited ground state atoms, which absorb light at characteristic wavelengths. The amount of light absorbed can be directly related to the amount of the element in the sample.
Hollow-cathode atomic spectral lamps (HCL) are the most common radiation sources for atomic absorption spectroscopy. These lamps can produce resonance radiation of narrow linewidth 0.01 Å, for most elements that are determinable by atomic absorption. The lamp is evacuated and filled with 2 torr of either argon or neon. A small current is passed between the anode and the cathode resulting in ionization of inert-gas atoms. Atoms of the cathode metal (analyte) are sputtered from the surface due to interactions with these ions. Resonance radiation results when the ground-state atoms are excited and then decay back to the ground state.
Although the discharge may appear to the eye to be hot, the cathode temperature is usually only 300-400oC. Excitation results from collisions between analyte atoms and inert-gas ions in the discharge. The cathode is constructed from the metal or an alloy of the element being determined.
The spectrum of a good lamp consists mainly of spectral lines of the element of interest.