Characterisation and analysis of persistent organic pollutants and major, minor and trace elements in Calabash chalk

Characterisation and analysis of persistent organic pollutants and major, minor and trace elements in Calabash chalk

Chemosphere 57 (2004) 21–25 Characterisation and analysis of persistent organic pollutants and major, minor and t...

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Chemosphere 57 (2004) 21–25

Characterisation and analysis of persistent organic pollutants and major, minor and trace elements in Calabash chalk J.R. Dean *, M.E. Deary, B.K. Gbefa, W.C. Scott School of Applied Sciences, Northumbria University, Ellison Building, Newcastle upon Tyne, NE1 8ST UK Received 30 July 2003; received in revised form 7 May 2004; accepted 19 May 2004

Abstract Analysis of Calabash chalk has been done using energy dispersive X-ray fluorescence spectroscopy (EDXRF), X-ray diffraction (XRD) and pressurised fluid extraction (PFE) followed by gas chromatography (GC) with mass selective detection (MSD). It was found by XRD that the composition of Calabash chalk was an aluminium silicate hydroxide from the kaolin clay group with the possible formula Al2 Si2 O5 (OH)4 . Multi-elemental analysis by EDXRF was able to quantify 22 elements in Calabash chalk including lead at a mean concentration of approximately 40 mg/kg. A range of persistent organic pollutants were identified and quantified in Calabash chalk including alpha lindane, endrin, endosulphan II and p,p0 -DDD using PFE-GC-MSD.  2004 Elsevier Ltd. All rights reserved. Keywords: Calabash chalk; Metals; Persistent organic pollutants; Geophagia; Energy dispersive X-ray fluorescence spectroscopy (EDXRF); Gas chromatography with mass selective detection (GC-MSD)

1. Introduction Calabash chalk, also known as Calabar stone, La Craie, Argile, Nzu, Mabele, Ebumba and Ulo, is available in a variety of forms including powders, moulded shapes and blocks. It has traditionally been eaten by some pregnant women in the Nigerian and West African Community to alleviate the symptoms of morning sickness. It is available in the UK in ethnic stores and markets. Concern with regard to it safety has arisen (Chief Medical Officer, 2002), and in particular its lead content. This concern is in line with recommended dietary intake of lead from a variety of sources. The European Union recommends (Commission Regulation, 2001) that the highest concentration of lead permitted in


Corresponding author. Tel.: +44-191-227-3047; fax: +44191-227-3519. E-mail address: [email protected] (J.R. Dean).

specific foods should not exceed 1 mg/kg. However, lead levels in Calabash Chalk have been reported (Codex Committee on Food Additives and Contaminants, 2003) in the range 10–50 mg/kg. Geophagia, derived from the Greek words, geo(earth) and phag- (eat), has been defined (Halsted, 1968) as the practice of eating earth including soil and chalk. A recent review (Reilly and Henry, 2000) indicates that the practice of geophagia is neither new nor outdated. In fact soils can be consumed for a variety of reasons including religious belief, medicinal purposes, or as part of a regular diet. The practice however, does leave the consumer susceptible to ingestion of toxic constituents and parasites. The availability of nutrients from soil is nothing new (Oliver, 1997; Abrahams, 2002). Food crops grown on soil provide part of the nutritional dietary requirements that humans require for living. Indeed elevated or deficiency of certain elements in soil can have severe health implications. For example, it has been postulated

0045-6535/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2004.05.023


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that a common cardiac disease (endomyocardial fibrosis) in tropical climates, including parts of Uganda, may be related to the presence of elevated levels of cerium, and deficiency of dietary magnesium (Smith et al., 2000). This has been attributable to local variations in soil geochemistry and the practice of geophagia. Similar deficiency concerns have been reported in a study (Hooda et al., 2002), using geophagic materials collected from Uganda, Tanzania, Turkey and India. The results showed that all geophagic materials were able to sorb large amounts of Fe and Zn. However, these findings were contrasted by the results for Ca. In this situation significant amounts of Ca desorption were observed from calcareous soil samples. Thus indicating that while calcareous geophagic materials may supplement Ca, the deliberate eating of soil can potentially cause Fe- and Zn-deficiency. This is consistent with mineral nutrient deficiency problems observed in clinical nutrition studies conducted amongst geophagic populations. This situation is in fact not restricted to humans. For example, a recent study (Elsenbroek and Neser, 2002) has highlighted a specific enzootic form of geophagia that effects young cattle and sheep in a manganese-rich soil in the Northern Cape and North West Provinces of the Republic of South Africa. This resulted in severe, subacute to chronic hepatitus and jaundice, with a high mortality rate in untreated cases. Energy dispersive X-ray fluorescence (EDXRF) provides direct element analysis (major, minor and trace) on samples with minimal sample preparation. Sample preparation typically involves air-drying of sample followed by grinding and pelletising with a binder. This is in direct contrast to other elemental techniques i.e. atomic spectroscopy. Atomic spectroscopy techniques including atomic absorption spectroscopy, inductively coupled plasma (ICP) atomic emission spectroscopy and ICP-mass spectrometry all require aggressive acid digestion of soil samples prior to analysis (Dean, 2003). The process of acid digestion can result in incomplete dissolution of soil samples (Dean, 1997). The digestion process is dependant upon the acid or acid combination used. For example, complete digestion of soil samples containing silicates requires the use of hydrofluoric acid (Dean, 1997). Acid digestion can also result in loss of volatile elements unless special precautions are undertaken. Extraction of persistent organic pollutants (POPs) from soils has traditionally been done using Soxhlet extraction (Dean, 1998). However modern extraction techniques including pressurised fluid extraction (PFE) (sold under the trade name of accelerated solvent extraction) are able to effectively remove POPs from soil rapidly, reproducibly and with minimal organic solvent useage (Dean, 1998). Pressurised fluid extraction was first reported (Dean, 1996) for the extraction of POPs

from environmental matrices. The use of PFE has been extensively reviewed (Dean and Xiong, 2000; Fitzpatrick et al., 2000 ; Dean and Cresswell, 2002). This paper proposes to investigate the composition of Calabash chalk in terms of its metal composition and presence of persistent organic pollutants e.g. pesticides. Metal composition has been determined using an energy dispersive X-ray fluorescence spectrometer while pesticide determination has been assessed by extracting chalk samples using pressurised fluid extraction followed by gas chromatography with mass selective detection. X-ray diffraction was used to elucidate structural information.

2. Experimental 2.1. Chemicals/reagents The solvents used were certified analytical grade, obtained from Fisher Scientific (Loughborough, Leicestershire). The pesticide standard (18 component mixture) in toluene:hexane (50:50 v/v) was obtained from Sigma-Aldrich Company Ltd. (Supelco UK, Dorset, UK). Internal standard (pentachloronitrobenzene) was obtained from Sigma-Aldrich Co. Ltd. Hydromatrix (Varian Ltd., Surrey, UK) was used to fill the head space of the ASE extraction cells (Dionex). Kaolin was obtained from Sigma-Aldrich Co. Ltd. Samples of Calabash chalk were obtained from a local retail outlet in Newcastle upon Tyne. 2.2. GC-MSD analysis The GC-MSD (HP G1800A GCD system, Hewlett Packard, Palo Alto, USA) was operated in single ion monitoring mode with a splitless injection volume of 1 ll. The column was a DB-5 ms purchased from SigmaAldrich Company Ltd. with dimensions; length 30 m · 0.25 mm internal diameter · 0.25 lm film thickness. For all analyses the injection port temperature was set at 250 C and the detector temperature was set at 280 C. Selected standards for the analytes were run daily to assess analytical performance. Pesticides were analysed using the following temperature programme: initial temperature 120 C for 2 min then to 250 C at 4 C/min. The separation of all the target pesticides was achieved in approximately 34 min. 2.3. Energy dispersive X-ray fluorescence spectroscopy (EDXRF) EDXRF analysis was performed on a Spectro Analytical X-Lab 2000 instrument fitted with a Gresham Si(Li) detector. The instrument uses polarised radiation to excite fluorescence in the sample, drastically reducing the scattering background in the collected spectrum and

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resulting in improved limits of detection and reduced measurement times. Three Barkla scatterer targets are used for this purpose: boron carbide, which is optimised for elements from manganese to molybdenum; aluminium oxide, optimised for trace element analysis for the elements from molybdenum to cerium; and HOPG (highly ordered pyrolytic graphite) for other elements. In addition to the Barkla scatterer target, two secondary targets are used by the instrument: cobalt, which enables optimal excitation of the elements from potassium to manganese, independent from the iron content of the sample (an iron filter before the target absorbs the cobalt Kb radiation so that iron cannot be excited by this line); and the Compton/secondary molybdenum target. Pelletised samples (see EDXRF sample preparation section) are fitted into aluminium cuvettes and placed into the carousel of the instrument. Each sample is subjected to the following programme of targets: Compton/ secondary molybdenum, 40 kV tube voltage, 150 s measurement time; Barkla scatter, aluminium oxide, 53.5 kV, 250 s; Barkla scatter, boron carbide, 44 kV, 250 s; cobalt secondary, 35 kV, 200 s; and Barkla scatter, HOPG, 15 kV, 50 s. Element concentrations are determined from the internal calibration data of the instrument using the above programme, which comprises 71 standard geological reference materials. Calibration data is in the form of given concentration against count intensity for each element after correction for background and interelement matrix effects. The element energies used for quantification are shown in Table 1.


Table 1 EDXRF data for Elemental Analysis Line


Energy (KeV)

Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka Ka La Lb

Al K Ti Cr Mn Fe Ni Cu Zn As Rb Sr Y Zr Nb Cd Sn Sb Ba Ce Hg Pb

1.4866 3.3138 4.5108 5.4147 5.8988 6.4038 7.4782 8.0478 8.6389 10.5437 13.3953 14.1630 14.9584 15.7730 16.6120 23.1700 25.2670 26.3550 32.1880 34.7140 9.9899 12.6137

was approximately 13 min per sample. The extract was transferred to a 25 ml volumetric flask, internal standard (pentachloronitrobenzene) was added (50–100 ll) and made up to the mark with acetone. The extract was then analysed by GC-MSD. 2.6. EDXRF sample preparation

2.4. X-ray diffraction The sample was analysed using a Siemens D5000 X-ray powder diffractometer. The sample (1 g) was irradiated using a copper source, Ka1, at a wavelength  The scan time was 2.5 h. Substance idenof 1.5405 A. tification was achieved using an automatic search using information supplied from JCPDS, the International Centre for Diffraction Data. 2.5. Extraction procedure All samples were extracted using pressurised fluid extraction using an Accelerated Solvent Extractor, ASE 200 (Dionex (UK) Ltd., Camberley, Surrey). Sample cells 11 ml were used for all the extractions. The ASE 200 is an automated system capable of 24 sequential extractions. Typical extraction conditions are based on a pressure of 2000 psi (1 psi ¼ 6894.76 Pa), a temperature of 100 C and a total extraction time of 10 min (5 min plus 5 min static) using acetone. A single static flush cycle was used. Additional time was required for rinsing with fresh solvent and N2 hence the total extraction time

Grinding and pelletisation of samples prior to EDXRF analysis results in a uniform grain size, improving the quality of the analysis. Samples were prepared by weighing approximately 4.0 g into a zirconium oxide ball mill chamber. The chamber was then fitted into a Retsch mm 200 shaker and the milling procedure initiated at 30 cycles per second for 60 s. Approximately 4.0 g of the ground sample was accurately weighed into a disposable plastic sample tube, together with 0.6 g of Hoechstwax HWC binder (supplied by Spectro Analytical Ltd.). The sample and binder were mixed at high speed in the capped sample tube using the Retsch mm 200 shaker and then made into a 32 mm pellet using a Graseby Specac press at an operating pressure of 10 tonnes.

3. Results and discussion 3.1. Characterisation of Calabash chalk Characterisation of the sample is one of the important steps in selecting the most important extraction


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technique for recovering POPs from environmental matrices, particularly soil samples. Of particular concern in recovering POPs from environmental soil samples has been the soil organic matter and clay minerals, particularly those of the kaolin and montmorillonite groups (Sanchez-Camazano and Sanchez-Martin, 1988; Kozak, 1996). Previous work from this group (Dean et al., 1996) has identified that recovery of POPs from soil can be influenced by the choice of extraction technique e.g. supercritical fluid extraction. Data has subsequently been reported (Frost et al., 1997) that has indicated that the use of PFE can overcome POP-matrix interactions. On that basis Calabash chalk was subject to X-ray powder diffractometry to elucidate structural information. The results indicated that the major component of the Calabash chalk was an aluminium silicate hydroxide from the kaolin clay group. The kaolin group consists of kaolinite, dickite and nacrite. The structures are composed of sheets and differ only in the way these sheets are stacked upon each other. A possible formula indicated was Al2 Si2 O5 (OH)4 which is kaolinite. This was confirmed using a standard of kaolin. Similar findings have been previously reported (Reilly and Henry, 2000). 3.2. Analysis of Calabash chalk EDXRF results are summarised in Table 2 for within-sample and between-sample variation. A statistical comparison was made of the two experimental means using a t-test (Miller and Miller, 2000). It was found that in the majority of cases no significance, at the 95% confidence level, was found for elements compared for within-sample and between-sample variation. Significance, at the 95% confidence level, was noted for potassium, titanium, rubidium and niobium. It was found that lead levels in all samples tested exceed the European Union recommended guidelines (Commission Regulation, 2001) for dietary intake by approximately 40-fold. Levels of lead were identified as 36.4 ± 2.8 mg/ kg for between-sample variation and 42.5 ± 1.2 mg/kg for within-sample variation. It was also noted that other toxic elements including arsenic, cadmium and mercury were not detected in any of the samples analysed. However, potentially toxic chromium (depending on oxidation state) was determined at a concentration of 49.6 ± 5.9 mg/kg (between-sample variation). Five sub-samples of Calabash chalk were analysed for persistent organic pollutants. It was noted that no POPs were found in four sub-samples. However, it was possible to identify and quantify four POPs in one subsample. The results are shown in Table 3. In this one sub-sample, significant levels (<1 mg/kg) of alpha lindane, endrin, endosulphan II and p0 ,p0 -DDD were identified and quantified. This result is perhaps not extra-ordinary because even though the samples of Calabash chalk were obtained from the same local retail

Table 2 EDXRF analysis of Calabash chalk Element

Al K Ti Cr Mn Fe Ni Cu Zn As Rb Sr Y Zr Nb Cd Sn Sb Ba Ce Hg Pb

Withinsample variation

Betweensample variation

Mean ± sd (mg/kg) (n ¼ 5)

Mean ± sd (mg/kg) (n ¼ 5)

8856 ± 176 1618 ± 25 8052 ± 134 52.5 ± 1.6 24.1 ± 2.2 14 770 ± 86 15.5 ± 0.8 1.8 ± 0.5 26.9 ± 0.9 nd 13.4 ± 0.2 85.9 ± 1.1 17.4 ± 0.3 355.3 ± 1.4 72.9 ± 0.6 nd 6.2 ± 0.7 nd 226.5 ± 6.0 266.2 ± 7.4 nd 42.5 ± 1.2

8630 ± 152 1372 ± 63 7230 ± 98 49.6 ± 5.9 24.0 ± 2.1 14 402 ± 155 15.0 ± 1.3 3.1 ± 0.5 25.6 ± 1.8 nd 12.0 ± 0.6 78.2 ± 3.8 19.8 ± 1.6 337.7 ± 24.2 67.1 ± 2.6 nd 6.2 ± 0.7 nd 230.9 ± 5.9 243.6 ± 9.6 nd 36.4 ± 2.8

Comparison of two experimental means t-Test significant No Yes Yes No No No No No No Yes No No No Yes No No No No

Table 3 PFE-GC-MSD analysis of Calabash chalk POP

Within-sample variation Mean ± sd (mg/kg) (n ¼ 5)

Alpha lindane Endrin Endosulphan II p,p0 -DDD

0.050 ± 0.008 0.840 ± 0.095 0.475 ± 0.039 0.937 ± 0.089

outlet and had the same overall appearance no specific information was available on the actual source of the samples. It is therefore evident that one sample had been contaminated at source by POPs. This may be indicative of specific land use in this area e.g. agricultural, for the source of this particular sample of Calabash chalk. Dietary intake of POPs at any level is not recommended. 4. Conclusion A range of elements and persistent organic pollutants have been identified in Calabash chalk using a range of analytical techniques. In addition, it has been possible to identify by X-ray diffraction the structure of Calabash chalk.

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Acknowledgements The Engineering and Physical Sciences Research Council are acknowledged for the award of an Industrial case award to one of us (WCS) in collaboration with LGC limited, London, with support from the Department of Trade and Industry under the National Measurement System Valid Analytical Measurement (VAM) Programme. In addition, the Bayelsa State Government of the Federal Republic of Nigeria is acknowledged for the award of a scholarship to one of us (BKG). The technical support of Mr. E. Ludkin and Mr. J. Crighton, Northumbria University, is also acknowledged. References Abrahams, P.W., 2002. Soils: their implications to human health. Sci. Total Environ. 291, 1–32. Commission Regulation (EC) No. 466/2001, 2001. Setting maximum levels for certain contaminants in foodstuffs. Dean, J.R., 1996. Accelerated solvent extraction of polycyclic aromatic hydrocarbons from contaminated land. Anal. Comm. 33, 191–192. Dean, J.R., 1997. Atomic Absorption and Plasma Spectroscopy. John Wiley and Sons, Chichester, UK. Dean, J.R., 1998. Extraction Methods for Environmental Organic Analysis. John Wiley and Sons, Chichester, UK. Dean, J.R., 2003. Methods for Environmental Trace Analysis. John Wiley and Sons, Chichester, UK. Dean, J.R., Cresswell, S.L., 2002. Extraction techniques for solid samples. In: Pawliszyn, J. (Ed.), Sampling and sample preparation for field and laboratory. In: Barcelo, D. (Ed.), Wilson and Wilson’s Comprehensive Analytical Chemistry, vol. XXXVII. Elsevier, Amsterdam, pp. 559–586. Dean, J.R., Xiong, G., 2000. Extraction of organic pollutants from environmental matrices: selection of extraction technique. TrAC 19 (9), 553–564. Dean, J.R., Barnabas, I.J., Owen, S.P., 1996. Influence of pesticide–soil interactions on the recovery of pesticides using supercritical fluid extraction. Analyst 121, 465–468. Elsenbroek, J.H., Neser, J.A., 2002. An environmental application of regional geochemical mapping in understanding


enzootic geophagia of calves in the Reivilo area, South Africa. Env. Geochem. Health 24, 159–181. European Community Comments for the Codex Committee on Food Additives and Contaminants, 35th Session, Arusha, Tanzania, 17–21 March 2003. Agenda Item 16(c)––CX/ FAC 03/28. Proposed draft code of practice for the prevention and reduction of lead in food. Fitzpatrick, L.J., Zuloaga, O., Etxebarria, N., Dean, J.R., 2000. Environmental applications of pressurised fluid extraction. Rev. Anal. Chem. XIX (2), 75–122. Frost, S.P., Dean, J.R., Evans, K.P., Harraadine, K., Cary, C., Comber, M.H.I., 1997. Extraction of hexaconazole from weathered soils: a comparison between Soxhlet extraction, microwave-assisted extraction, supercritical fluid extraction and accelerated solvent extraction. Analyst 122, 895– 898. Halsted, J.A., 1968. Geophagia in man: its nature and nutritional effects. Am. J. Clin. Nut. 21, 1384–1393. Hooda, P.S., Henry, C.J.K., Seyoum, T.A., Armstrong, L.D.M., Fowler, M.I., 2002. The potential impact of geophagia on the bioavailability of iron, zinc and calcium in human nutrition. Env. Geochem. Health 24, 305– 319. Kozak, J., 1996. Soil organic matter as a factor influencing the fate of organic chemicals in the soil environment. In: Piccolo, A. (Ed.), Humic Substances in Terrestrial Ecosystems. Elsevier, Amsterdam, pp. 625–664. Message from the Chief Medical Officer, Department of Health (15th October 2002). CEM/CMO/2002/13. Miller, J.N., Miller, J.C., 2000. Statistics and Chemometrics for Analytical Chemistry. John Wiley and Sons, Chichester, UK. Oliver, M.A., 1997. Soil and human health: a review. Eur. J. Soil Sci. 48, 573–592. Reilly, C., Henry, J., 2000. Why do humans consume soil? Brit. Nut. Found. Nut. Bull. 25, 41–144. Sanchez-Camazano, M., Sanchez-Martin, M.J., 1988. Influence of soil characteristics on the adsorption of pirimicarb. Env. Toxicol. Chem. 7, 559–564. Smith, B., Rawlins, B.G., Cordeiro, M.J.A.R., Hutchins, M.G., Tiberindwa, L., Sserunjogi, L., Tomkins, A.M., 2000. The bioaccessibility of essential and potentially toxic trace elements in soils from Mukono District. J. Geol. Soc. 157, 885–889.