University of Zagreb, Faculty of Science, Department of Geology, Zagreb, Croatia. Andrija Štampar Teaching Institute of Public Health, Zagreb, Croatia

Geochemistry of Croatian superhigh-organic-sulphur Raša coal, imported low-s coal, and bottom ash: their Se and trace metal fingerprints in seawater, clover, foliage, and mushroom specimens Gordana Medunić

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Geochemistry of Croatian superhigh-organic-sulphur Raša coal, imported low-s coal, and bottom ash: their Se and trace metal fingerprints in seawater, clover, foliage, and mushroom specimens Gordana Medunić 1*, Željka Kuharić 2, Adela Krivohlavek 2, Željka Fiket 3, Ankica Rađenović 4, Kristina Gödel 1, Štefica Kampić 1, Goran Kniewald 3 1 University of Zagreb, Faculty of Science, Department of Geology, Zagreb, Croatia 2 Andrija Štampar Teaching Institute of Public Health, Zagreb, Croatia 3 Ruđer Bošković Institute, Division for Marine and Environmental Research, Zagreb, Croatia 4 University of Zagreb, Faculty of Metallurgy, Sisak, Croatia Abstract The Labin city area has represented the major Croatian coal mining, metal industry, and coal-fired electricity centre for more than two centuries. The domestic superhigh-organic-sulphur (SHOS) Raša coal is a unique variety compared to other coal types worldwide, based on its highest organic sulphur values, up to 11%. It was utilized in the Plomin coal-fired power plant during the period , and was replaced by an imported low-s coal afterwards. This paper presents the levels of S, Se, V, U, Hg, Sr, Cd, Cr, Pb, Cu, and Zn in the two coal types, their bottom ash, seawater, and plant (clover, mushroom, and foliage) specimens collected from the Labin city area, while the sulphate was measured in surface stream water. Their levels were compared with relevant legislative as well as the published data from different world localities. Data analysis was interpreted in the context of past and recent coal combustion activities. Keywords: SHOS Raša coal, low-s coal, bottom ash, sulphur, selenium, uranium, vanadium, seawater, clover, foliage, mushroom, trace elements 1. Introduction Coal accounts for the most important energy source in many parts of the world. It is the most complex geological material, composed of organic matter, water, oil, methane gas, and virtually all the elements in the periodic table, together with a wide variety of minerals (Finkelman, 1994; Rađenović, 2006; Vejahati et al., 2010). Low-quality coals are characterised by high sulphur, high ash, and high levels of potentially toxic trace elements. Among them, sulphur is a particularly interesting component, which, along with nitrogen and phosphorous, is an essential element for all living matter. Its characterisation, occurrence, ecotoxicology, and environmental fate have been studied extensively using 1 various scientific approaches (Oden, 1976; Zerklea et al., 2010; Senko et al., 2011; Kuklińska et al., 2013; Saikia et al., 2015; Sołek-Podwika et al., 2016). It is ubiquitously present on Earth, existing in soils, seawater, and plants in organic, sulphate, and sulphide forms, whereas in gaseous and solid states in the atmosphere (Badr and Probert, 1994). Since SO 2 has been emitted whenever fuels containing sulphur, like coal, coke, and oil, are burnt, its main anthropogenic emission sources are coal-fired power plants, central-heating stations, and industrial furnaces in the iron and steel industry (Speight, 2013). Herewith, a considerable amount of research of sulphur emission processes, pathways, budgets, and environmental issues has been published so far (Speight, 2005; Baruah and Khare, 2010; Bläsing et al., 2015; Saikia and Ninomiya, 2011; Saikia et al., 2015; Dutta et al., 2017). Although the sulphur content in coal varies considerably, its total levels most commonly range from 0.50% to 5.00% (Rađenović, 2004; Chou, 2012). Fulekar and Dave (1986) reported that the total S content in major Indian coals (except those of Assam, Jammu, and Kashmir which contain S up to 14.0%, and are not used in power plants) are between 0.20% and 1.40%. Superhigh-organic-sulphur (SHOS) coal is a special class of coal, characterised by remarkably elevated values of organic S, usually in the range of %. Due to its limited distribution in the world, there are only several papers concerned with such unusual coal. These are following: the Cenozoic coals of the Gippsland Basin, Victoria, Australia (Smith and Batts, 1974), a Permian coal seam in the Cranky Corner Basin, eastern Australia (Marshall and Draycott, 1954; Ward et al., 2007), and some Lopingian coals preserved within marine carbonate successions in southern China Guiding (Guizhou Province), Yanshan (Yunnan Province), Heshan and Fusui (Guangxi Province) (Dai et al., 2008, 2013a,b, 2015). Chou (1997) compared organic S in Chinese SHOS coals Guidin (up to 9.18%), and Yanshan (up to 10.3%), with Croatian SHOS Raša coal (10.5%). According to Sinninghe Damsté et al. (1999), SHOS Raša coal is characterised by unusually high amount of sulphur (11.8%), which is largely present in the form of anomalously high level of organic S (11.4%). The authors concluded that Raša coal is not a typical coal, as the organic matter had not been derived from the higher terrestrial plants. White et al. (1990) carried out the petrographic, proximate, and ultimate analyses of Raša coal, and they also reported information on the vitrinite reflectance, carbon aromaticity, sulphur and carbon isotopic abundances, ash analysis, and forms of sulphur. They stated that 'for the scientist interested in characterizing organic sulphur components in coal, Raša coal is a good starting point'. The paper comprehensively referes on previously published publications (since early 1950s) pertinent to Raša coal geology and organic geochemistry. Briefly, the Raša coal-bearing strata represent the Upper Paleocene lacustrine and brackish facies. 2 Recently, Medunić et al. (2016a) reviewed historical, geological, geochemical, and environmental aspects of the Raša coal mines located on the eastern part (Fig. 1) of the Istrian Peninsula (Labin city area, North Adriatic, Croatia). They had been by far the most important and economically the most valuable deposits of the lignite (a high volatile B bituminous rank) coal reserves in Croatia since the 18th century till 1999, when their excavation and use in the local Plomin coal-fired power plant (PPP) ceased. The characteristics of Raša coal were reported as follows: total moisture wt%, ash content wt%, combustibles wt%, low heat value 18,400-26,300 kj/kg, carbon wt%, hydrogen wt%, S (org.) wt%, oxygen wt%, and nitrogen wt% (Limić and Valković, 1986). Raša coal had powered not only local households, but also many various industries in Croatia and in Italy. Due to the lack of a proper desulphurisation technology, during each hour of operation the PPP had emitted nearly 8.50 tons (18,080 mg/m 3, or 6,900 mg/kg) of SO 2 during the period (Mohorović, 2003). This has resulted in the soil pollution with S, PAHs, Se, and Cd (Medunić et al., 2016b), and prominent soil REE patterns (Fiket et al., 2016). As the Raša coal was characterised by an enhanced radioactivity, soil around an ash waste site (near the PPP) was also found to have elevated radioactivity (Ernečić et al., 2014). Marović et al. (2004) reported that the activity of U-238 was Bq/kg in 1970s and Bq/kg in 1980s, which was times higher than the average of other coal types in the world. Bauman and Horvat (1981) reported natural U ranges in Raša coal from 14.0 mg/kg to 100 mg/kg (occasionally up to 1500 mg/kg), whilst natural radioactivity of ash and slag was enhanced by a factor of ten. Also, the authors found higher values of 210 Pb in urine and chromosome aberrations of an exposed group of workers in the PPP. Also, high uranium SHOS coals from China were reported by Dai et al. (2008, 2013a, b, 2015). Stergaršek et al. (1988) reported that Raša coal was characterised by increased levels of S, Ca, U, and V. The authors found out that the ash had also very specific characteristics, particularly high levels of U and V, thus serving as a potential source of the two metals. Furthermore, the authors reported that Raša coal had 15.0% of ash, which was alkaline and distributed as 70:30 fly ash: bottom ash (slag). An average composition (%) of the Raša coal ash was following: SiO , Al 2 O , Fe 2 O , CaO 64.2, MgO 3.79, Na 2 O 1.42, K 2 O 0.19, and SO (Stergaršek et al., 1988). Dai et al. (2013b, 2015) also discussed the enrichment of V-Cr-Mo-Se-Re-U in SHOS coals. Considering the ash, Valković et al. (1984) analysed the Raša coal fly ash by X-ray emission spectroscopy and proton microbeam facilities, and reported the following element data (mg/kg): S 1.3E04, Ca 7.8E04, Ti 1200, V 969, Cr 439, Fe 2.2E04, Ni 65.0, Cu 72.0, Zn 37.0, Ga 10.0, As 21.0, Se 78.0, Pb 19.0, Rb 16.0, U 207, Sr 1800, and Y 3 11.0. Regarding the mineral composition of analysed fly ash, the authors reported following phases: CaSO 4, CaO, FeS 2, FeSO 4 x H 2 O, Ca(OH) 2, and amorphous material. Limić and Valković (1986) analysed two Raša coal regions, 400-m apart, where coal samples (n = 265) were collected simultaneously with the exploitation. Element ranges (all in mg/kg except for S, Ca, and Fe in %) were as follows: S , Ca , Fe , Ti , V , Cr , Ni , Cu , Zn , Ga , As , Se , Pb , Rb , U , and Sr By applying geostatistical methods on the data, the authors established the same genesis for Ca, S, Fe, Ti, and V in the investigated coal seam. To the best of our knowledge, the Labin city area has not been studied as regards the distribution of potentially toxic trace elements and dissolved sulphate in the aquatic and vegetative environmental compartments related primarily to the past Raša coal mining and industrial activities. Therefore, the aim of this study is to report the sulphur, selenium, and trace metal levels in two coal types (SHOS Raša coal, and low-s imported coal), and the respective bottom ash specimens. In order to get an insight into their possible trace metal(loid) influence on the local environment, seawater (the Plomin bay, Adriatic Sea) and plant (clover, mushroom, and foliage) communities were sampled and analysed. Additionally, the sulphate levels were measured in surface streams (natural stream as well as municipal sewage effluent water) from the old coal mining towns of Raša and Krapan (Fig. 1). All data were compared with legislative and other relevant published data from different world localities. Their interpretation was carried out based on the past Raša coal combustion as well as the recent low-s coal combustion activities. 2. Materials and methods 2.1. Study area and sampling description The study area (Fig. 1) is situated inside the 10-km radius around the Labin city (45 06 N E). Regarding the geological, hydrological, and hydrographical setting, more details can be found elsewhere (Durn et al., 1999; Peh et al., 2010; Halamić et al., 2012; Frančišković-Bilinski et al., 2014). Briefly, the most prominent geological characteristic of the study area is the karst topography and carbonate bedrock. The local and regional terrain is overlain by thin reddish or brownish clay-loam soil, which belongs to the class of Cambic soils. The area is characterised by the Mediterranean climate, with mild 4 humid winters, and hot dry summers. According to the wind rose issued by the Croatian Meteorological and Hydrological Service (presented in Medunić et al., 2016b), the dominant NE winds carry airborne gases and dust load from the PPP ( N E) towards the city of Labin, which is situated on a m tall plateau. Four Raša coal (SHOS) samples (mined and collected in early 1980s) were selected from the Ruđer Bošković Institute archive (Zagreb, Croatia), while two imported low-s coal (C) samples were obtained in late An old bottom ash waste site (A (SHOS)), which had been accumulated due to the Raša coal combustion until 1950s, is situated at the Štrmac village locality ( N E), 2 3-km north of Labin city (Fig. 1B, C). Its various surface parts were randomely sampled with a clean sampling shovel in June Two samples (one of a grey/light colour, and the other one of a dark/black colour) of the low-s coal combustion bottom ash (A) were taken from several-kg material collected from the PPP's vicinity in April Surface municipal effluent stream water (Fig. 1E; non-filtered) and plants (one sample from each plant species, i.e. clover, foliage, and mushroom; Fig. 1B, D) samples were collected in November 2015, while one sample of seawater (non-filtered; SW) was taken from the Plomin bay ( N E; Fig. 1B) in June Coal and ash samples were disaggregated and crushed in an agate mortar. The plant parts were washed first with tap water, then with distilled water, and rinsed with deionized water. Afterwards, they were dried in an oven at 60 o C for a few days, and finally crushed in an agate mortar. The surface stream water (sulphate analysis, n = 5) and seawater (trace element analysis, n = 1) samples were collected in clean plastic bottles, where the latter one was spiked with suprapure HNO 3, and all the bottles were stored at 2 o C prior to analyses. 5 Figure 1: Map of the study area: A/ geographical position (square), B/ sampling sites: Š (Štrmac) the A (SHOS) site; SW seawater (Plomin Bay); F, M, C foliage, mushroom, and clover sampling sites, respectively, C/ field situation at the Š site, D/ the plant sampling site (PPP's stack is some m away), and E/ surface municipal effluent water (water samples for sulphate analysis) located in the Raša and Krapan towns (Fig. 1B; Krapan is located 1 2-km NE of Raša). A small village of Štrmac came out of anonymity at the 1880s when the nearby coalfields were discovered. In the vicinity of a coal mine, lots of buildings (houses, shops, factories, etc.) soon appeared. They had lasted until 1955, when the last tons of coal were excavated. Five years later, the coal-fired power plant's stack together with a mining tower were demolished. Furthermore, the activity of an old local foundry had gradually declined. Today, mostly descendants of miners live there. Also, the A (SHOS) site serves as a landfill for various nonhazardous wastes (Fig. 1C) Analytical methods Elemental composition of the C, A (SHOS), and plant specimens was determined by atomic absorption spectroscopy, while the SHOS, A, and SW specimens were analysed by high resolution inductively couppled plasma - mass spectroscopy. Subsamples (0.1 g) of SHOS and A were subjected to total digestion in the microwave oven (Multiwave 3000, Anton Paar, Graz, Austria). The two-step procedure consisted of digestion with a mixture of 4-mL nitric acid (HNO 3 ) 1-mL hydrochloric acid (HCl) 1-mL hydrofluoric acid (HF) followed by the addition of 6-mL of boric acid (H 3 BO 3 ). After digestion, each solution was transferred into a pre-cleaned plastic volumetric flask and diluted to 100 ml. Prior to analysis, SHOS and A digests and SW samples were further diluted 10-fold and acidified with 2% (v/v) HNO 3 (65%, supra pur, Fluka, Steinheim, Switzerland), whilst In (1 µg/l) was added as an internal standard. All SHOS, A and SW samples were analysed for total concentration of Se, V, U, Sr, Cd, Cr, Pb, Cu, and Zn using an Element 2 HR-ICP-MS instrument (Thermo, Bremen, Germany). Detailed method description is given elsewhere (Fiket et al., 2007; Fiket at al., 2016). Quality control was performed by simultaneous analysis of the blank and certified reference material soil (NCS DC 77302, also known as GBW 07410, China National Analysis Center for Iron and Steel, Beijing, China) 6 and water (SLRS-4, NRC, Canada). Good agreement (± 10%) between analysed and certified concentrations was obtained for all the measured elements. Mercury was determined by means of the mercury/hydride atomic absorption technique. Monovalent or divalent Hg and organic mercury are oxidized into divalent mercury with KBrO 3 and KBr. Then, it gets reduced to the elemental form with sodium borohydride in an acidic media. By using stream of argon, the dissolved elemental mercury is conveyed into the cuvette, heated at 100 C. The measurement conditions were following: Hg tube, the absorbance wavelength of nm, slit 0.7 nm, sample volume 500 µl, and measurement of peak heights. Flame AAS was used for the determination of other trace elements (Cd, V, Se, Pb, Sr, Cr, Zn, Cu, and U). The acidified samples were directly introduced in the flame atomic absorption spectrophotometer. When a ray of light passes through a cloud of free atoms in flames, the light absorption of selected elements occurs. The measurement conditions were following: an element tube, element specific absorbance wavelengths, slit 0.7/0.2, flame acetylene-air, and measurement of peak heights. Plant samples were digested in a microwave ETHOS SEL Milestone device. The procedure was as follows: about 0.1 g of a sample was placed in a Teflon cuvette, and 4 ml of aqua regia (1 ml HNO 3 (65%), and 3 ml of HCl (37%) was added. The digestion program included 4 min at 300 W, 1 min at 600 W, 1 min at 0 W, and finally 2 min at 300 W. Following the digestion, the cuvettes were removed from the microwave device, left to cool to room temperature, and the content was transferred into a volumetric flask of 25 ml, and then diluted with distilled water to the mark. Total sulphur content (%) in coal and ash samples was determined using the Eschka's mixture according to the standard test method ASTM E (1996). Sulphate in fresh surface water was determined by volumetric method that is based on the amount of sulphate which can be determined by the deposition of sulphate anions in excess of barium chloride. An excess of barium cations is deposited with an excess of potassium chromate, while an excess of chromate anions is measured by iodometric titration with sodium thiosulphate. Reagents included: indicator methylorange, hydrochloric acid (0.1 M), barium chloride solution, potassium chromate, a solution of aluminum chloride (10%), a solution of potassium hydroxide (0.1 M), a solution of potassium iodide (10%), hydrochloric acid (25%), a standard solution of sodium thiosulfate pentahydrate, and a starch solution as an indicator. The procedure was as follows: 1/ 100 ml of a water sample was placed in the Erlenmeyer flask, then 0.1 ml of methyl orange indicator was added, and the solution was titrated with 0.1 M HCl until the orange colour of the sample was obtained; 2/ in this solution 1 ml of 0.1 M HCl in excess was added, and 25 ml of the barium chloride solution. It was 7 necessary to put in a few glass beads for boiling, cover and heat to boiling; 3/ then, the flask was rapidly cooled in a water bath; 4/ following the standing for 30 minutes, 25 ml of potassium chromate solution, one drop of potassium chloride, and 1.6 ml of 0.1 M potassium chloride solution were added, and left to stand for about an hour; 5/ the solution was filtered without washing the residue, until 100 ml of the filtrate was ready in the Erlenmeyer flask for the determination of iodine. Then, 10 ml of freshly prepared solution of potassium iodide, and 5 ml of HCl were added to the filtrate, and allowed it to stand. The last step was titration with standard solution of sodium thiosulphate using starch as an indicator until a significant change in colour. 3. Results and discussion The previous paper (Medunić et al., 2016b) is an example of the integration of data from several disciplines which should contribute to the canon of knowledge about potential health effects of the SHOS coal combustion. The authors confirmed that soil surrounding the PPP had been polluted primarily by the SHOS Raša coal combustion decades ago. The downwind soil locations were found to be severely polluted with S (up to 4.00%) and PAHs (up to 13,500 ng/g), while moderately polluted with Se (up to 6.80 mg/kg) and Cd (up to 4.70 mg/kg). Also, the cytotoxic effects on fish cells of water extracts of the most polluted soil and ash (the black A sample) were statistically significant. The most important issue is the fact that the investigated locality is situated inside the coastal karst environment (Fig. 1), which is well known for its vulnerability. Therefore, it is important to evaluate the environmental quality of other local sites previously or recentl
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