Monitoring of the natural environment by chemical speciation of elements in aerosol and sediment samples

Abstract

The development of a monitoring network for chemical speciation of elements of aerosol and sediment samples collected at Lake Balaton has been carried out. Sequential leaching procedures for the determination of the distribution of elements in aerosols (3 steps) and sediments (4 steps) were used. These methods were recently successfully applied to describe environmentally mobile and stable fractions of toxic metals. In aerosol matrices the partition of elements was accomplished by particle size and chemical bonding. In sediments the distribution was performed by chemical bonding. The processes are called fractionation of elements. Particular attention was paid to distinguishing between environmentally mobile and environmentally immobile fractions because these represent the two extreme modes by which the metals are bound to solid matrices. The monitoring objectives were to assess pollution effects on man and his environment and to identify any possible cause and effect relationship between pollutant concentrations and health effects. The results of dry and wet deposition rates showed that most of the toxic metals were dissolved in an aqueous phase and the wet deposition played an important role. It has been found that, while the concentration of Cd and Pb in aerosols is low (0.7 and 29 ng m⁻³, respectively), environmentally mobile fractions are considerable. Based upon the data it can be concluded that the effect of the anthropogenic sources on the quality of the lake is minor. This has been the first attempt to correlate speciation results between aerosols and sediments.

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Introduction

The chemical analysis of environmental samples gives answers to several questions like an analyte's quality and quantity, the analyte's distribution between the surface and the bulk of materials, change of the analyte's concentration with time (monitoring system), and determination of an analyte's forms (speciation). In environmental sciences the development of monitoring systems and estimation of an analyte's chemical form are important. Monitoring is usually done to gain information on the concentration of pollutants.¹ Objectives can be, e.g. to identify any possible cause and effect relationship between pollutant concentrations and health effects or climate changes. Furthermore, it is fundamental to obtain a historical record on the state of the environment and provide a database for future use.

For a reliable monitoring program the sampling of analytes from the environment is crucial.² Sampling is accompanied by uncertainty, which may contain systematic and random components arising from the sampling procedure itself. Sampling errors can not be controlled by the use of reference materials, sampling is always an error generating process.² In principal, the problem in the environmental sampling is that with the sample removal from its natural environment the stable or metastable equilibrium can be disturbed and, after the measurement, the entire population might be characterized. This uncertainty is even further increased when the speciation analysis is performed since an analyte's original form has to be kept during sampling and sample preparation.

Presently, it is evident that element speciation has become a major aspect in analytical and bioinorganic chemistry.³ In the past few years a number of impressive new methods have been developed, however a vast amount of questions has not been answered yet. Consequently, the element speciation is one of the main targets in research laboratories. For example, concerning natural waters (lakes and rivers), the mobility, transport and partitioning of trace elements in a natural aquatic system are the function of the chemical form of elements. Solid matter in sediments governs the concentration of these elements in the water phase via sorption–desorption and dissolution–precipitation reactions. The environmental impacts of a pollutant can be assessed by the estimation of the reactivity of metals introduced with solid materials from anthropogenic activities (hazardous waste, sewage sludge, atmospheric deposits, etc.).

The concept of elemental speciation by leaching is based on the thought that a particular solvent is either specific to a discrete phase or specific in its action. Fractionation is the process of classification of an analyte or a group of analytes in a certain matrix according to physical (size, solubility) or chemical (bonding, reactivity) properties.⁴ Fractionation is usually performed by a sequence of selective extraction techniques, which include successive removals or dissolution of the mineralogical phases and their associated elements. Whatever extraction procedure chosen, the validity of extraction results depends primarily on the sampling and preservation of samples prior to analysis. Care should be taken to collect sediment samples from the same layers during monitoring.

The atmospheric speciation of metals has several difficulties.⁵ Measurement of the total concentration of most metals in atmospheric samples is even hampered by the lack of proper quality assurance programs. The speciation of trace metals in the atmosphere is different than of those applied in the hydrosphere. Metals are transported in the atmosphere primarily on aerosols, which can be removed by wet and dry deposition process. Therefore, an element's forms are determined by the interaction mechanism of the biosphere and the atmosphere, and by the mechanism of transport in the atmosphere. The deposition, transport and inhalation processes are controlled predominantly by the size of the atmospheric aerosols. For estimation of the elemental budget in the atmosphere dry and wet deposition rates have to be calculated. Furthermore, to investigate the equilibrium of elements between atmosphere and hydrosphere, the composition of bottom sediments of lakes or rivers should also be determined.

In our work a monitoring system for chemical speciation of elements of aerosol and sediment samples was developed. The study area chosen was Lake Balaton which is situated in the western part of Hungary. Its surface area is 596 km², the mean depth is 3.25 m and the water volume is about 1.9 × 10⁹ m³, so the lake is a shallow one with a large surface area. Sequential leaching procedures were used for the determination of the elements' distribution in samples. These methods have recently been developed and successfully applied to describe environmentally mobile and stable fractions of toxic metals. In aerosol matrices the elements' classification was accomplished by particle size and chemical bonding, while in the case of sediments, the arrangement was performed by chemical bonding.^6–11 The processes have been defined as fractionation. The correlation of speciation results between aerosols and sediments has been attempted for the first time.

Experimental

Sampling

Sediment samples were collected from the top 10-cm layer of the bottom of Lake Balaton, rivers at the catchment area and major harbors in three seasons. The sampling procedure has been specified recently.^9–11 The samples taken were immediately carried to the laboratory and air-dried, then stones and plant fragments were removed by passing the dried sample through a 2 mm sieve. The sieved sample was powdered and finally passed through a 500 µm sieve and stored in glass bottles. Sieve nets were made from copper. The sample collection was carried out in spring, summer and fall between 1996 and 1998. Inside the lake 15 sampling points were set, while the sampling sites of rivers were selected as follows: north shore 5, south shore 2, west shore 1, while those of harbors: north shore 5, south shore 1, west shore 1. The map of the lake is shown in Fig. 1.

Fig. 1 Map of Lake Balaton and its catchment area with sampling points.

Aerosol samples were collected in Tihany (north shore), Siófok (south shore) and Keszthely (west shore) on 5 cm diameter Teflon filters (pore size 0.45 µm, diameter 47 mm) with a membrane pump of 1.2–1.5 m³ h⁻¹ of air. During a 2 day period 55–72 m³ of air was sampled and collected weekly. In the same survey period precipitation samples were collected in Tihany by a wet-only sampling device.¹² The precipitation sample was transferred to a polyethylene bottle, acidified with nitric acid to pH = 2, and kept in a refrigerator. The sampling apparatus was placed close to the aerosol sampler. Aerosol and precipitation samples were collected from 1995 to 1998.

Leaching procedures

The 4-step sequential leaching procedure for sediments was published earlier.^9–11 Fractions were collected as (i) exchangeable/bound to carbonate; (ii) bound to Fe/Mn oxide; (iii) bound to organic matter/sulfide; and (iv) an acid-soluble residue. Here, the summary of the procedure is briefly described: 1 Exchangeable/bound to carbonate fraction: 20 mL of 0.11 mol L⁻¹ CH₃COOH (pH 2.8) was added to 0.5 g sediment in a centrifuge tube and extracted by shaking for 16 h at room temperature. The extract was centrifuged for 15 min at 2500 rpm. The supernatant liquid was separated, 0.5 mL of conc. HNO₃ was added, and the solution was brought to 50 mL in a volumetric flask. Colloids were not included in the leaching solutions. The residue was washed with 20 mL of distilled water, shaken for 15 min, and centrifuged. The supernatant was decanted and discarded. The cake was broken up using a glass rod prior to the second step. 2 Bound to Fe/Mn oxide fraction: 20 mL of 0.1 mol L⁻¹ NH₂OH–HCl (pH 2) was added to the residue from step 1 and extracted for 16 h at room temperature. The extract was separated by centrifugation, washing and handling of the solution were carried out as in step 1. 3 Bound to organic matter and sulfide: 5 mL of 8.8 mol L⁻¹ H₂O₂, (pH 2–3) was added to the residue from step 2. The vessel was covered and digested at room temperature for 1 h. The digestion was continued for 1 h at 85 °C and the volume was reduced to a few milliliters. Another 5 mL of 8.8 mol L⁻¹ H₂O₂, (pH 2–3) was added and suspension was heated again to 85 °C, and the sample was digested for 1 h. To the cool residue 25 mL of 1 mol L⁻¹ NH₄OAc (pH 2) was added and the mixture was shaken for 16 h at room temperature. The extract was separated by centrifugation and decantation as in step 1. 4 Acid-soluble fraction: 3.75 mL conc. HNO₃ and 1.25 mL HClO₄ were added to the residue from step 3. The digestion was accomplished in 2 h at 100 °C in a water bath. After cooling, 1.5 mL conc. HNO₃ and distilled water were added to the mixture. The solution was filtered and made up to 50 mL.

Aerosol leaching was done by a 3-stage sequential leaching procedure. Details of the leaching experiments were published elsewhere,⁸ and (i) environmentally mobile; (ii) bound to carbonate/oxide, and (iii) bound to organic matter/silicate fractions were separated. The procedure is briefly summarized as follows: 1 Environmentally mobile fraction: filters were folded and placed in centrifuge tubes. Extractions were carried out at room temperature for 15 min with 25 mL of 1 mol L⁻¹ NH₄OAc at pH 7, then suspensions were centrifuged for 15 min at 3000 rpm. Supernatant phases were separated and stored for analysis. Colloids were not included in the leaching solutions. 2Bound to carbonate and oxide fraction: residues from fraction 1 were extracted at room temperature for 6 h with 25 mL of 1 mol L⁻¹ hydroxylamine hydrochloride + 25% v/v acetic acid and, after leaching, the suspensions were centrifuged. Supernatant liquids were stored for analysis. 3Bound to silicate and organic fraction: residues from fraction 2 were transferred to PTFE beakers and 10 mL of conc. HNO₃ was added to each sample. The beakers were placed on a water-bath at a temperature of 95 °C and 2 mL of conc. HF was added, and left until all particles have dissolved. Portions of 4 mL conc. HNO₃ were repeatedly added for the evaporation of the HF, and cold solutions were transferred to 50 mL volumetric flasks and made up to volume with 0.1 mol L⁻¹ HNO₃ and stored for analysis.

The solutions were stored at 4 °C prior to analysis. Analytical blanks were performed on filters from the same batch, on centrifuge tubes and on PTFE beakers. The sequential procedure was run on unexposed filters in the same way as the exposed samples. The blank obtained is a reagent + beaker + filter blank and the values have been subtracted from the atomic absorption measurements. The amount of a single sample was found to be small, so it was not possible to perform parallel measurements. Nor was it conceivable to directly verify the accuracy of the analysis since appropriate filter-collected aerosol standards have not been available yet. Sampling uncertainty was partly estimated using blank samples. Before extraction, all glassware and plastic vessels were treated in a solution of 10% v/v HNO₃ for 24 h and washed with doubly-distilled ion-exchanged water.

Atomic absorption spectrometry (AAS) measurements

The elemental concentrations of the solutions were determined by AAS in an electrothermal atomization mode using Perkin-Elmer 5100 PC, HGA 600 graphite furnace (GEM software) and Perkin-Elmer 303, HGA 70 graphite furnace instruments. Standard solutions were prepared from 1 g L⁻¹ of each metal (Merck standard solutions) and freshly diluted before use. All elements were determined by AAS in a graphite furnace. Arsine was measured at 193.7 nm (0.015 mg Pd + 0.05 mg Mg(NO₃)₂), Cr at 357.9 nm (0.05 mg Mg(NO₃)₂), Ni at 232.0 nm, Pb at 283.3 nm (0.2 mg (PO³⁻₄ + 0.01 mg Mg(NO₃)₂, Cd at 228.8 nm (0.05 mg Mg(NO₃)₂, Al at 309.3 nm, Fe at 248.3 nm, Mn at 279.5 nm, (0.05 mg Mg(NO₃)₂), Cu at 324.8 nm, and Zn at 213.9 nm. The concentration of an element was measured with an RSD < 5% from solutions. The limit of detection (LoD) for elements was found to be as (µg L⁻¹): As 0.5; Cr 1; Ni 0.5; Pb 0.1; Cd 0.1; Al 5; Fe 5; Mn 0.2; Cu 1; Zn 50.

Results and discussion

The average geometric concentration of elements in aerosol samples collected at the three stations, and the ratios of mobile fractions are summarized in Table 1. The chemical speciation data of elements in aerosols are presented as a geometric mean concentration being calculated by the sum of the concentrations determined in each fraction of an individual element found in 92 measurements at Tihany, and 23 at Keszthely and Siófok, respectively. From the average concentration of elements dry deposition budget (mg m⁻² y⁻¹) can be calculated.

Table 1 The geometric mean of the elemental content of aerosol samples collected around Lake Balaton, and distribution of mobile fractions

Element	North Tihany/ng m^−3	West Keszthely/ng m^−3	South Siófok/ng m^−3	Average/ng m^−3	Mobile, average/ng m^3	Mobile, average (%)
Al	51.4	38.2	47.3	45.6	12.2	26.7
Fe	82.2	95.3	150	109	23.6	21.7
Mn	53	35	74	54	8.8	16.3
Pb	29.5	29.8	26.4	28.6	14.3	50.0
Cd	0.67	0.55	0.74	0.65	0.3	44.7
Cr	1.11	1.7	0.78	1.2	0.2	18.7
Cu	4.9	3.8	4.4	4.3	1.4	33.3
Ni	5.1	3.3	3.0	3.8	1.3	34.7
Zn	37.0	8.7	14	19.9	6.9	34.7
As	6.8	5.3	7.0	6.4	1.8	28.3

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In a 2 year sampling period it has been observed that there was not serious pollution from the dry deposition on Lake Balaton. Since there is no considerable industrial activity in the close neighborhood of the lake and its catchment area, and samples were collected on the beach, the toxic metals were transported from foreign sources with a long-range transport. About 27% of the aluminium compounds can be found in the mobile fractions (12.2 ng m⁻³), and concerning the low concentration of total Al (45.6 ng m⁻³), this average value is much smaller than it has been found recently at different domestic sampling sites.^6–8 No considerable differences were observed in the fractionation of Al either by particle size or chemical bonding in aerosols collected at the Hungarian background station.¹³ In the fine fractions 26 ng Al m⁻³ (range 9.3–132 ng m⁻³), while in the course ones 27 ng Al m⁻³ (range 13–254 ng m⁻³) were identified. Particles bigger than 1.0 µm are generally produced during mechanical processes and these are primarily the result of low-temperature crustal weathering termed as natural sources. The similar total concentration of Al and the comparable distribution between the fine and course fractions have originated as a combination of natural and anthropogenic sources.

Iron compounds were considerably concentrated in the fractions where bound to carbonate/metal oxide and bound to organic matter/silicate, and only 22% were found in the environmentally mobile fractions. The average concentration was quite low (109 ng m⁻³), higher values were only achieved in samples collected at the south shore. So, the dry deposition of iron is low, the lake is not polluted by Fe-compounds. These findings slightly differ from our earlier conclusion of an investigation at a moderately polluted city and regional background station, since much higher concentrations (433 ng m⁻³ at Veszprém, and 243 ng m⁻³ at Kabhegy) were previously determined.⁷

In natural systems manganese has two dominant oxidation states, Mn(IV) which is insoluble in water, and Mn(II) which is water soluble. Knowledge of the oxidation state is of importance since it can govern either the biological availability or the toxicity of an element once it enters the natural waters. The amount of manganese compounds in aerosols was found to be on average 54 ng m⁻³ (range 35–74 ng m⁻³), these values have been much less compared to a recent survey in Hungary.⁶ The variance among the samples collected at different sites is either due to the re-suspension of the dust from the street by traffic and from the upper soil layer or to the effects of combustion. Manganese ions are highly concentrated in the stable fractions (only 16% in the environmentally mobile fraction) and do not have any direct impact on the environment.

The lead pollution around Lake Balaton is 28 ng m⁻³ on average, and it is at least one order of magnitude less than those found in large cities,¹⁴ due to smaller traffic. Emissions from vehicle exhausts have dominated in the lead contribution to the atmosphere, although smelting operations also contribute to the atmospheric lead load, emitting both Pb⁰ and PbO.¹⁵ Since there is no smelting activities close to this area, the pollution has mostly originated from the traffic. The environmentally mobile fraction is about 50%, and the distribution of Pb-compounds among the three sampling sites is rather even. The relative significance of lead sources in the atmosphere is currently changing as a result of the decline in the use of leaded vehicle fuels. The actual lead compounds in a particular aerosol will depend on the other constituents in the atmosphere and the age of aerosols.

The concentration of Cd in aerosols depends considerably on the location, pollution sources, time, meteorological conditions, etc. and ranges from 1–300 ng m⁻³ in major cities.¹⁶ Around the lake the Cd-pollution is minor, 0.65 ng m⁻³ on average. The fractionation of cadmium resulted in association with the environmentally mobile fractions, 51% at the north shore, and less amount of Cd-compounds was found at the other two locations, (39% at the west shore and 44% at the south shore, respectively). Cadmium, liberated mostly during combustion processes, has been shown to occur in elemental and oxide forms whereas emissions from refuse incineration were predominantly CdCl₂.^17,18

Concentrations of Cr, Cu, Ni, Zn, and As were usually found in lower levels than those identified at other national sampling sites.^6–8 About 33–34% of the total Cu, Ni and Zn was determined in the environmentally mobile fractions. Lum et al.¹⁹ identified high proportions of Ni and Cu in soluble and/or exchangeable forms and of Cr in a bound-to-silicate fraction in urban particulate matter analysed by a sequential extraction procedure.

For evaluation of the atmospheric budget for Lake Balaton and the environmental effects of the trace metals on the biosphere the calculation of the dry and wet depositions is of vast importance. The dry deposition rates were calculated by means of the dry deposition velocities and the amount of annually deposited elements was estimated for the 596 km² area. Dry deposition velocities were recently calculated by Molnár et al.²⁰ using the size distributions of metals. These values are used in Hungary for the calculation of dry deposition rates. The results are summarized in Table 2.

Table 2 Dry deposition rates (D_dry), the mobile fraction of dry deposition rates (D_dm), total dry deposition and mobile fraction of total dry deposition for samples collected around Lake Balaton^a

Element	North Tihany Ddry/ mg m^−2 y^−1	West Keszthely Ddry/mg m^−2 y^−1	South Siófok Ddry/mg m^−2 y^−1	v total/cm s^−1	D dry average/mg m^−2 y^−1	D dm average/mg m^−2 y^−1	Total Ddry/kg y^−1	Total Ddm/kg y^−1
a D dry/mg m^−2 y^−1) = (v/cm s^−1) × (c/ng m^−3) × 0.315.
Al	15.0	13.8	11.1	0.950	13.3	3.5	7980	2131
Fe	24.0	43.8	27.8	0.926	32.9	7.1	19740	4284
Mn	11.3	15.9	7.5	0.680	11.6	1.9	6960	1134
Pb	1.06	0.95	1.07	0.114	1.03	0.52	618	309
Cd	0.02	0.02	0.02	0.096	0.02	0.009	12	5.4
Cr	0.02	0.02	0.04	0.067	0.03	0.006	18	3.4
Cu	0.14	0.21	0.11	0.092	0.15	0.05	900	300
Ni	0.35	0.21	0.23	0.220	0.26	0.09	156	54
Zn	2.44	0.41	0.25	0.23	1.03	0.36	618	214
As	0.24	0.25	0.19	0.235	0.23	0.065	138	39

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Dry deposition rates obtained for the three sampling sites show a variable picture. In the case of one element, the south part is more polluted, while for other, deposition has been found at a greater extent in the west or east area. Considering the average values of the dry deposition rates it can be seen that along with the main elements (Fe, Mn, Al), less amount of toxic metals has been deposited into the lake. The yearly 12 kg of Cd and 18 kg of Cr are much less than the lake receives from the rivers and creeks coming from the water catchment area. Referring to the environmentally mobile portion of elements it can definitely be concluded that the lake water has not yet been largely polluted from the dry deposition. The soluble part of the toxic elements is negligible since 5.4 kg Cd, 3.4 kg Cr, 54 kg Ni, or 39 kg As yearly, do not change the quality of the water. The Fe content (4284 kg y⁻¹) is probably transformed to iron(III) hydroxide in oxygenated environment and settles to the sediment layer.

Along with the dry deposition of aerosols, atmospheric removal occurs also by wet deposition of aerosol particles in rain, fog, hail and snow. The relative importance of the two depositional processes varies between locations and is primarily a function of the rainfall intensity in that area. Wet deposition is a very important removal process for those elements associated with small particles and which are predominantly anthropogenic in origin. Wet deposition rates are based upon the concentration of trace metals in precipitation samples collected by a wet-only sampler in Tihany in three years. Weighed mean concentrations were calculated by taking into account the volume of precipitation collected in each case, and the annual precipitation amounts. The results are shown in Table 3.

Table 3 Wet deposition rate (D_wet, mg m⁻² y⁻¹) and the amount of rain (mm) from samples collected at Tihany, Lake Balaton, June, 1995–December 1997 (92 samples)

Element	1995/mg m^−2 y^−1 (435 mm)	1996/mg m^−2 y^−1 (735 mm)	1997/mg m^−2 y^−1 (490 mm)	Mean/mg m^−2 y^−1	D wet/kg y^−1
Al	18.5	15.6	33.3	22.5	5670
Fe	60.7	5.8	21.7	29.4	13482
Mn	2.7	0.9	24.7	9.4	17634
Pb	1.8	1.2	3.9	2.3	1374
Cd	0.015	0.016	0.1	0.04	54
Cr	<0.7	<0.7	<0.7	<0.7	—
Cu	1.1	0.2	0.4	0.6	336
Ni	0.2	0.7	1.7	0.9	516
Zn	7.4	0.7	19.9	9.3	5604
As	0.2	0.1	2.6	1.0	582

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A number of factors can influence the level of deposition in any area, such as the locality, i.e. remote, rural, urban or industrial. Wet precipitation depends on the existence of rain, its volume, duration and intensity. The concentration of elements in the precipitation decreases mostly with increasing the intensity of the rain. So, the comparison of data derived from different sources is very difficult, and sometimes no relevance has been noticed. However, by collecting rain samples at one location for three years, the data can be compared. In 1996, there was 735 mm of rain and this was much higher than it was experienced in 1995 and 1997 (435 mm and 490 mm, respectively). Except Ni, other elements were deposited in amounts of sometimes one order of magnitude less (Fe, Zn) than those in the other two years. So, the dilution effect was observed and only minor pollution was deposited into the lake.

The comparison of dry and wet depositions shows an interesting picture (Table 4). It has been published recently²⁰ that the ratio of D_dry/D_wet is significant, for Pb and Zn in particular, and usually higher for the others (V, Cr, Ni, Cu, As). In our case it has been found that for elements like Fe, Al, and Cu, the ratio of the two depositions gives an opposite appearance; namely, the dry deposition plays a more important role in the pollution of the environment. On the other hand, ratios of D_dry/D_wet entirely indicated that elements like Mn, As, Cd, Pb, and mainly Zn, were deposited in much higher amount by wet deposition than by dry one.

Table 4 Dry (D_dry) and wet (D_wet) deposition rates, ratio of dry and wet deposition rates (D_dry/D_wet), mobile fraction of dry deposition rate (D_dm) and ratio of mobile fraction of dry and wet deposition rates (D_dm/D_wet) of elements in samples collected around Lake Balaton

Element	Total Ddry/kg y^−1	Total Dwet/kg y^−1	D dry + Dwet/kg y^−1	D dry/Dwet	Total Ddm/kg y^−1	D dm + Dwet/kg y^−1	(Ddm/Dwet) × 100 (%)	[Ddm/ (Ddm  + Dwet)] × 100 (%)	[Ddm + Dwet/ (Ddry + Dwet)] × 100 (%)
Al	7980	5670	13650	1.4	2131	7801	37.6	27.3	57.1
Fe	19740	13482	33222	1.46	4284	17766	31.8	24.1	53.5
Mn	6960	17634	24594	0.39	1134	18768	6.4	6.0	76.3
Pb	618	1374	1992	0.45	309	1683	22.5	18.3	84.5
Cd	12	54	66	0.22	5.4	59.4	10.0	9.1	90.0
Cr	18	—	—	—	3.4	—	—	—
Cu	900	336	1236	2.68	300	636	89.3	47.2	51.5
Ni	156	516	672	0.30	54	570	10.5	9.4	84.8
Zn	618	5604	6222	0.11	214	5818	3.8	3.7	93.5
As	138	582	720	0.23	39	621	6.7	6.2	86.2

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In Table 4 environmentally mobile fractions of dry deposition rates of elements are also tabulated and compared to wet deposition rates (column 8). It is obvious that the contribution of mobile fractions of the dry deposition to the pollution of the lake is, except for Cu, minor. Copper compounds are mainly removed from the atmosphere by dry deposition and one-third of the amount of Cu is environmentally mobile. However, if mobile fractions are compared to the total soluble deposition (D_dm + D_wet), less than 50% of Cu come only from dry deposition and much less (3.7–27%) from all other elements. It means that in the budget of soluble compounds the wet deposition plays the more important role. In case of elements like Al, Fe, Cu, the dry deposition has been found to be the major source of pollution (column 5), but the mobile parts of dry deposition performed a minor role compared to the total soluble deposition.

Furthermore, the soluble fractions of depositions (D_dm + D_wet) were compared to the total depositions (D_dry + D_wet). The water quality of Lake Balaton is influenced by the soluble part of atmospheric depositions, and it has been found that 85–94% of toxic elements (Pb, Cd, Ni, Zn, As) are dissolved in the water. The other portions of elements are stable compounds formed in natural environmental conditions and after precipitation, they settle to the bottom of the lake. So, the metal compounds, sooner or later, become part of the bottom sediment, since the fate of dissolved metals greatly depends on the physical and chemical conditions of the bulk water (pH, complex forming capacity, adsorption on clays, quartz, organic matter, biological activities, etc.). In long-term studies the concentrations of same elements of the lake water have been found at very low levels, even lower than the Hungarian standards permit for drinking waters. Sediments are recognized as a sink and reservoir for metals, metalloids, and other contaminants. Therefore, the accumulation of metals in a lake can be followed by the analysis of bottom sediments.

Recently, investigation on bottom sediments of Lake Balaton, rivers on its catchment area and harbors were extensively carried out in spring, summer and fall.¹¹ The average concentration of the sum of 4 fractions, the minimum and maximum values for all sediments, as well as the comparisons to other background values are summarized in Table 5. The results were compared to the sediment quality values (SQVs) and sediment background values (SBVs) published by Chapman et al.²¹ Globally, SQVs for metals and metalloids vary over several orders of magnitude and can be below background values. Regional SQVs can be useful as an initial step in a sediment hazard/risk assessment. The SQVs are numerical, based on total dry weight concentrations of sediments collected from more than 50 different sampling points in all over the world (North-America, Asia, Europe and Australia). The SBVs for freshwaters include background values summarized for lakes and streams and the global shale average values.

Table 5 The comparison of average (maximum and minimum) concentrations of metals in sediments to SQVs,²¹ SBVs,²¹ and the average metal content of Hungarian soils²² (mg kg⁻¹)

Elements	Sediments average (min–max)	SQVs average (min–max)	SBVs average (min–max)	Average metal content of Hungarian soils
Pb	16.9 (2–61)	142.5 (31–720)	59.9 (50–130)	100
Cd	0.6 (0.1–4.3)	5.7 (0.6–41)	0.8 (0.3–1.1)	1–3
Cr	12.0 (3–28)	104.4 (20–360)	30.3 (10–90)	75–100
Cu	34.6 (4–150)	119.4 (16–840)	20.0 (15–45)	74–130
Ni	37.0 (5–113)	38.0 (16–92)	25.5 (17–150)	50
Zn	81.3 (10–265)	463.0 (90–2750)	86.3 (50–130)	10–300
As	7.9 (1–29)	41.6 (3–404)	12.1 (4–29)	7–15

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Data in Table 5 clearly show that the average concentration of elements have been found to be less than the SQVs and other background data for soils.²³ This means that the sediment is not polluted and, after removing from the bottom, its disposal on the soil is feasible. SQVs do not fully consider factors influencing the availability and toxicity of metals and metalloids in sediments. Chemical speciation can be a tool for the assessment of bioavailability of metals. In our study the 4-step sequential leaching procedure was applied.^9–11 Fractions were collected as (i) exchangeable/bound to carbonate; (ii) bound to Fe/Mn oxide; (iii) bound to organic matter/sulfide; and (iv) acid-soluble residue. The results of the leaching are summarized in Table 6.

Table 6 Distribution of elements by chemical bonding in sediments of Lake Balaton, rivers and harbors (%)

	Cu	Zn	Pb	Ni	Cr	As
Exchangeable/bound to carbonate	8.6	1.4	8.9	8.5	3.5	16.8
Bound to Fe/Mn oxides	5.3	3.1	5.7	13.3	3.5	5.2
Bound to organic matter + sulfide	34.4	14.0	36.4	37.6	6.2	12.3
Acid-soluble	51.7	81.5	49.0	40.6	86.8	65.7

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It can be seen that the fraction exchangeable/bound to carbonate is minor—less than 10%, except for As. This refers to the strong bonding of elements to oxides, organic matters and silicates. This chemical bonding is strong enough to accumulate metals in the sediments and, under natural environmental conditions, the release of these elements is not significant.

The phenomenon of the low metal concentration of sediments correlates well with, as it has been pointed out, the fact that the major part of the dry and wet depositions is water soluble and metals are not concentrated in the sediment phase. Consequently, based on the results, it can definitely be confirmed that the water and the sediment of Lake Balaton are not polluted from the elements studied.

Conclusion

A simple sequential leaching method has been successfully applied to aerosols for determination of elements' distribution patterns in three fractions. Particular attention was paid to distinguishing between the environmentally mobile and environmentally immobile portions, because these represent the two extreme modes by which the metals are bound to the aerosols. The environmentally mobile elements are being most susceptible to release into aqueous solution after deposition of the aerosols to the surface of lakes. The fine fractions are characteristic of the anthropogenic pollution sources, and if the samples are collected continuously at one particular site, the data create the possibility to assess the dynamic processes having taken place in the atmosphere. The results of the sequential leaching give an indication of the mobility of the elements once the aerosol is mixed directly into natural waters or during scavenging of the aerosol by wet deposition. Aerosols sampled within the urban environment usually exhibit a greater solubility than aerosols with a crustal origin and this is important to interpret the results of sequential leaching.

The aim of collecting precipitate and aerosol samples at the same site in the same period was to determine the distribution of elements in two depositions. Nevertheless, the calculations are affected by the dry deposition velocities and some emission sources along with the air trajectory. While, e.g., Cd-compounds have been found largely in the environmentally mobile fractions, As-compounds accumulated almost evenly among portions. The comparison of dry and wet depositions showed that the ratio of D_dry/D_wet is significant, particularly for Fe, Al, and Cu, indicating that dry deposition plays an important role. Elements like Mn, As, Cd, Pb, and mainly Zn, were deposited in much higher amount by wet deposition. It has been observed that the contribution of mobile fractions of the dry deposition to the pollution of the lake was, except for Cu, minor.

Moreover, the soluble fractions of depositions (D_dm + D_wet) were compared to the total depositions (D_dry + D_wet) and it has been found that 85–94% of toxic elements (Pb, Cd, Ni, Zn, As) were dissolved in the water. These depositions, however, are negligible in the bulk of the water of Lake Balaton because its water volume, on average, is 1.9 × 10⁹ m³ and therefore the buffer capacity is huge. The elements' concentrations in the lake water have been found at even lower level than the Hungarian drinking water standards allow.

The results of the sum of 4 fractions of bottom sediments of Lake Balaton, rivers on its catchment area and harbors were compared to SQVs and SBVs. The data showed that the average element concentration was usually less than that of SQVs and other background data for soils and geochemical values. So, the sediment is not polluted and its disposal on the soil is feasible. The fact of the low metal concentration of sediments correlates well with the finding that the main part of the dry and wet depositions is water-soluble. Based on the results, it can be definitely confirmed that the quality of the water and sediment of Lake Balaton is satisfactory.

Acknowledgment

The authors are indebted to the OTKA T 029250, the FKFP 0084/1999, and the Balaton Secretariat of the Prime Minister’s Office for their financial support.

References

1. C. N. Hewitt and R. M. Harrison, in Understanding our Environment, ed. R. E. Hester, The Royal Society of Chemistry, London, 1986, p. 1–10..
2. J. K. Taylor, in Principles of Environmental Sampling, ed. L. H. Keith, American Chemical Society, Washington, DC, 1988..
3. A. M. Ure and C. M. Davidson, Chemical Speciation in the Environment, Blackie Academic & Professional, London, 1995..
4. D. Templeton, F. Ariese, R. Cornelis, H. P. van Leeuven and L.-G. Danielsson, Speciation of trace elements: Definitions, structural aspects and analytical methods, presented at the IUPAC General Assemply Meeting, IUPAC Working Group, Berlin, 1999..
5. L. J. Spokes and T. D. Jickells, in Chemical Speciation in the Environment, ed. A. M. Ure and C. M. Davidson, Blackie Academic & Professional, London, 1995, pp. 137–168..
6. J. Hlavay, K. Polyák, I. Bódog, Á. Molnár and E. Mészáros, Fresenius' J. Anal Chem., 1996, 354, 227.
7. J. Hlavay, K. Polyák, I. Bódog and Á. Molnár, Idojaras, 1996, 100(1–3), 69.
8. J. Hlavay, K. Polyák, Á. Molnár and E. Mészáros, Analyst, 1998, 123(5), 859.
9. I. Bódog, K. Polyák and J. Hlavay, Int. J. Environ. Anal. Chem., 1997, 66, 79.
10. J. Hlavay and K. Polyák, Microchem. J., 1998, 58, 281.
11. K. Polyák and J. Hlavay, Fresenius' J. Anal. Chem., 1999, 363, 587.
12. J. Hlavay, K. Polyák, Á. Molnár and E. Mészáros, Acta Biol. Hung., 1999, 50(1), 89.
13. M. Bikkes, K. Polyák and J. Hlavay, J. Anal. At. Spectrosc., 2001, in the press..
14. Á. Molnár, E. Mészáros, L. Bozó, I. Borbély-Kiss, E. Koltay and Gy. Szabó, Atmos. Environ., Part A, 1993, 27A, 2457.
15. J. M. Pacyna, J. Münch and F. Axenfeld, in Heavy Metals in the Environment, ed. J. P. Vernet, Elsevier, Amsterdam, 1991, ch. 1, pp. 1–20..
16. J. E. Ferguson and D. E. Ryan, Sci. Total Environ., 1984, 34, 101.
17. J. O. Nriagu, in Cadmium in the Environment. Part I. Ecological Cycling, ed. J. O. Nriagu, Wiley, New York, Tokyo, Amsterdam, 1980, pp. 71–114..
18. J. M. Pacyna, in Lead, Mercury, Cadmium and Arsenic in the Environment, ed. T. C. Hutchinson and K. M. Meema, Wiley, New York, Tokyo, Amsterdam, SCOPE, 1987, pp. 69–87..
19. K. R. Lum, J. S. Betteridge and R. R. Macdonald, Environ. Technol. Lett., 1982, 3, 57.
20. Á. Molnár, E. Mészáros, K. Polyák, I. Borbély-Kiss, E. Koltay, Gy. Szabó and Zs. Horváth, Atmos. Environ., 1995, 29, 1821.
21. P. M. Chapman, F. Wang, W. J. Adams and A. Green, Environ. Sci. Technol, 1999, 33, 3937.
22. M. Kádár, Chemical pollution of soil, plant, animal and human food chain in Hungary, Műszaki Kiadó, Budapest, 1995..
23. E. Gromet, Geochim. Cosmochim. Acta, 1984, 48, 2469.

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Footnote

† Presented at the Whistler 2000 Speciation Symposium, Whistler Resort, BC, Canada, June 25–July 1, 2000.

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