A Moropoulou,^ K Bisbikou,™ K Torfs, ™ R. Van Grieken^

Risk analysis for the protection of cultural

heritage from industrial pollution

A Moropoulou, K Bisbikou,™ K Torfs, ™ R. Van Grieken^ National Technical University of Athens, Faculty of ChemicalEngineering, Dpt. of Materials Science and Engineering, 9, IroonPolytechniou St., 157-73 Athens, Greece. E-mail:amor'[email protected]^ Department of Chemistry, University of Antwerp, Universiteitsplein 1,2610Antwerpen, Belgium. E-mail: [email protected]

Abstract

The Sanctuary of Demeter in Eleusis, Greece, presents a characteristic case ofthe attack of an industrial atmosphere attack to ancient marbles. The growth ofweathering crusts has already been studied, attributed to principalphysicochemical phenomena, like gypsum formation, dissolution andreciystallization of calcite or oxidation of the iron- bearing phases. The presentwork concerns the analysis of the risks, which threaten cultural heritage whenexposed to industrial atmosphere, as investigation of the origin of weathering crustson ancient marbles in relation to the triggering environmental factors. Crustsand encrustation samples from the monuments' surfaces, as well as aerosols andtotal depositions samples have been investigated by Ion Chromatography (1C),Atomic Absorption / Atomic Emission Spectrometry (AAS/AES) and EnergyDispersive X-Ray Fluorescence (EDXRF). The estimation of enrichmentfactors permits the determination of the possible sources of the identifiedelements as soil, underlying rock, marine spray and anthropogenic activities.The study of sulfur isotopes permits the investigation of the sources of sulfur-rich pollutants triggering gypsum formation. Gypsum crusts and dusts on themonument marbles and crusts on buildings in the city were sampled, andaerosol samples were collected from the emissions of the nearby industries. Theisotopic ratio S/ S, in terms of delta values (5 S) of the sulfur-rich pollutantsfrom industry shows that the main impact of suspended particles to thearchaeological site, is caused by the industry; cement industry in particular. Theadvanced analysis of the weathering risks by this interdisciplinary approachprovides tools for the proper planning of environmental management andspecifically of the industrial emissions in order to prevent weathering of historicstructures and complexes by industrial pollution.

Transactions on the Built Environment vol 39 © 1999 WIT Press, www.witpress.com, ISSN 1743-3509

476 Structural Studies, Repairs and Maintenance of Historical Buildings

Introduction

The Sanctuary of Demeter in Eleusis, Greece, presents a characteristic case ofthe industrial atmosphere attack to cultural heritage. The analysis of theweathering risks due to the industrial emissions is necessary for preventiveenvironmental management.

In order to study reliably the origin of atmospheric depositions as decayfactors, enrichment factor analysis was used. The enrichment factors of variouselements with respect to carbonate rock have been calculated by Sabbioni andZappia to identify the components due to the deposition of atmospheric gasesand aerosols on the stone surfaces. Enrichment factors were used as well toidentify the sources of the aerosols and total deposition (Torfs & Van Grieken ).The contribution of seawater and mineral dust to each element is assumed to berepresented by the concentrations of indicator elements, which are Na and Al,respectively (Schneider*). The average composition of seawater was taken fromRiley and Chester*, and the composition of mineral dust from Mason . Theextent to which the aerosol is affected by mixing with seawater and crustalmaterial is estimated using enrichment factors :

=: \ >™™sol rr ( y\ _( \r i *r\ ' ^^ crust V* )~

erosolFF^ seawater

where X is the concentration of the investigated element in the aerosol, in seawateror in crustal material, as indicated by the subscript; Na is the indicator element forseawater and Al is the indicator element for crustal material. Particularly in the lattercase, other indicator elements, like Si, Fe and Ti, might be chosen and justified aswell. By convention, a "cut-off" EF value of 10 is used to distinguish between twotypes of participates in the atmosphere. This is a purely arbitrary value, but it offers aconvenient classification. An EF<10 is taken as an indication that elements have asignificant sea or dust source and they are termed non-enriched An EF>10 isconsidered to indicate that a significant proportion has a significant non-sea or non-mineral dust source (Chester et al.).

Since the sulfate concentration in the crust composition, in the total depositsand in the aerosol samples as well, has been found to be very high (Moropoulouet al.\ the study of sulfur isotopes was performed to investigate the sources ofsulfate pollutants. Isotope effects and differences in geochemical history ofcompounds are the actual reason why the sources (fossil fuels e.g.) havedifferent (and typical) isotope composition (Buzek& Sramek*). The feasibility ofapplying sulfur isotope measurements to elucidate the origin of sulfur and themechanism of crust formation on monuments has already been proved (Torfs,Van Grieken & Buzek ). Atmospheric SO: and various local anthropogenic SC>2emitters have been investigated. Effects of sulfur isotopes are considered by theratio S/ S and are commonly expressed as differences in isotopic ratio to thestandard Canyon Diablo Troilite (CDT), for which **S/ S is 1 / 22.22 :


Structural Studies, Repairs and Maintenance of Historical Buildings 477

sample-1 xlOOO

'CDT

Stable isotope measurements are a useful tool in determining the source of acertain element.

The integrated risk analysis is demonstrated in the characteristic industrialatmosphere of Eleusis threatening the ancient marbles. According to theHomeric Hymn, the first temple of Demeter at Eleusis was founded in the lateHelladic period (1500-1425 BC). The present ruins are the rests of the newTelestirion, built during Pericles' reign (500 BC), (Preka-Alexandri ). Systematicmineralogical, petrographical and chemical examination of the buildingmaterials of the Sanctuary has already been performed (Moropoulou et ai.").Pentelic marble has been mainly used together with some limestone. Pentelicmarble is well-recrystallized, fine to medium grained, presenting a low totalporosity of interparticle-type, with a high calcitic content (96%) (Moropoulou etal. ). The type and growth of the weathering crusts on the ancient marbles havealready been investigated (Moropoulou et al/). In particular, the environmentalimpact of the industrial and marine atmosphere to the ancient marbles has beencharacterized by (a) disintegrated "washed-out" surfaces, where weatheringproducts were taken away through dissolution, (b) rusty yellow patinas rich inFe and Cu, (c) firmly attached black-grey crusts in contact with percolatingwater, where recrystallized calcite shields amorphous deposits rich in S, Si, Feand carbonaceous particles, (d) black loose deposits on the water shelteredareas, consisting mainly of gypsum and fly ash particles and (e) cementitiouscrusts, coating and pitting the horizontal surfaces. The interconnected evolutionof the various physicochemical processes records characteristically the riskswhich the industrial pollution presents to the cultural heritage. Monitoring ofthe deteriorating environmental factors (Moropoulou & Bisbikou ), totaldeposition, aerosols and the meteorological data of the area has been carried outfor more than one year. Total deposition refers to both, particles from dust falland to material deposited with the rain. Aerosols comprise all solid or liquidsubstances that are airborne, for a reasonably long time, in the gaseous medium.The particles can be produced either by disintegration of solid or liquid matteror by condensation from the gas phase. The variety of sizes and chemicalcompositions is due to the variety of sources; some of them are natural (soildispersion, sea spray, volcanic activity, etc.), while others are anthropogenic.(Moropoulou et al. ). In the Thriasian plain, several sources of anthropogenicactivity are encountered, like cement industry, refineries and metallurgies,quarries, combustion of coal, fuels, etc., along with urban activities, like caremissions, central heating, etc. (Christidis ). However, the transport anddispersion of the pollutants are difficult to be studied because the airflow ishighly complex. The combination of sea breezes, heat inland effects, andpronounced topographic relief, results in a highly variable atmospheric structurein the Athens area, with short time stratifications (Valaoras ).



Sampling - Experimental procedures and techniques

1. Enrichment factors analysis

Different stone samples have been investigated, according to their differentweathering state. Samples were taken on the surrounding wall, facing the sea,where the marble is disintegrated. Washed-out areas, where reaction productsmay be removed by rain, were studied together with black-grey crusts, shelteredfrom direct rainwater, and black gypsum formations on the marble surfaces, incontact with percolating rainwater, but not washed out. Surface encrustations,especially on the pavements, where the marble is pitted by cementitious'encrustations, were investigated together with the dust deposits, which werefound on horizontal surfaces.

The chemical composition of the leachable stone fraction was measured aftercrushing the samples and dispersing the powder in demineralized water. Thesuspension was filtered and the filtrate is analyzed for soluble compounds using1C, AAS and AES. To apply EDXRF, the stone was wet ground in a mill and afew millilitres of the suspension were brought on a Mylar foil. The foil wasdried and analyzed.

Cl~, NCV and SO/ were determined by 1C, using a Dionex 40001 ionchromatograph, equipped with a ASH separator column; the eluent was 20 mMNaOH. Ca^ and M^~ were determined by means of AAS, whereas Na* and K+were measured by AES, both with a Perkin Elmer 3030 spectrometer. Thesamples were acidified to pH 2 with HC1 and 100 ul 10% La solution wasadded to 10 ml of the samples to avoid interferences. EDXRF analyses werecarried out using a Tracor Spectrace 5000 instrument. The instrument isequipped with a Si(Li) detector and a low power X-ray tube with a Rh target.The X-ray spectra were accumulated during 3000 s and analyzed using theAXEL software (Van Espen et al. ). The calculation of the concentrations in thestones has been checked with soil standards : IAEA Soil-5 and BCR 142.

2. Sulfur isotopes analysis

Sampling was performed (Figure 1) on black gypsum crusts on the monumentssurfaces and on dust gathered on the marble surfaces (El, E4, E7), as well as oncrusts from the city within an approximate 1 km radius from the archaeologicalsite at a height of 2.0 m above the ground and at different directions (north andsouth) to study the possible effect of the sample location on its isotopecomposition (BC1, BC2, FN1, FN2, FS1, FS2). Sampling areas should besheltered from rain, without lichens or other plants growing on it. Aerosolsamples were also collected, directly at the chimneys of two refineries(PETROLA and ELD A) and the Cement Industry TITAN, by using Tecobags of5 L (Tesseraux Container, Boersdadt, Germany), constructed of PE and Al, inwhich alkaline filters were put. The fume was then kept in contact with thefilters during 6 weeks.



3ROUTEI MAP OF THE THRIASIAN PLAIN! T

PETRQLA

Figure 1 : Map of the Thriasian Plain - Sampling points

About 1.5 f of crust was homogenized in a mortar, dissolved in HC1 (10%),treated in an ultrasonic bath (30 min) and boiled under reflux (30 min). Non-dissolved parts were filtrated and the solution was precipitated as BaSO, usingBaCL washed with deionized water, dried and stored for sulfur isotope analysis.

The isotope analyses were carried out with a Finnigan MAT 251 isotope ratiomass spectrometer. The accuracy of the measurements is checked frequently byinserting standards. The reproducibility of the analyses reaches 0.2-0.15 V .

Results and Discussion

1. Enrichment factors analysis

Analogously to the enrichment factors of the deposition and the aerosols(Moropoulou et al."), the fraction due to deposition of atmospheric gases andaerosols on the stone surfaces is identified by the determination of enrichment factors(Sabbioni & Zappia\ Sabbioni ). The enrichment of the crusts versus the originalrock material was obtained by using the average carbonate rock composition ofMason ) and Ti as an indicator element (Sabbioni & Zappia\ Sabbioni ), although apart of Ti may be deposited on the stones, from the cement industry.

Table 1 : Enrichment factors of the weathering layers on the stones tocarbonate rock (Ti as indicator element)

Wall facingthe seaWashed-outareaBlack-greycrustGypsumformationSurfaceencrustationDust deposit

Na+

23

2.1

3.8

7.1

53

4.5

M^0.05

0.04

0.01

0.02

0.01

0.01

Si

-

2.0

2.1

1.8

2.1

1.4

SO/

380

4.7

470

570

390

77

cr

31

120

12

29

20

16

K+

1.9

15

3.5

4.8

2.2

0.87

Ca

3.2

6.8

1.4

2.1

0.91

0.17

Cr

-

-

7.9

6.2

2.3

3.6

Mn

-

0.94

0.42

0.41

0.32

0.09

Fe

0.29

0.87

1.5

1.2

1.9

1.4

Ni

-

-

0.78

1.2

1.2

1.1

Cu

3.92

-

12

12

6.7

5.8

Zn

4.1

5.2

6.7

6.4

7.2

5.0

Sr

0.54

1.5

0.5

0.61

0.32

0.12

Pb

5.8

-

14

21

28

11



Table 1 presents the enrichment factors of the different weathering types, whichwere found in the Demeter Sanctuary, versus the average composition of carbonaterock. The elements, showing enrichment factors close to 1, have an origin, whichmust be attributed to the underlying rock (Sabbioni ), as in the case of Ca, Si, K%Mn, Fe and Sr. The components with enrichment factors greater than 1 are of non-carbonate origin and are due to atmospheric deposition, as in the case of Cl, 884,Na* and Pb. For all samples, SO/ is the compound with the greatest enrichmentfactor; it is mainly deposited on the surfaces as both gaseous SOz and sulfateparticles. With regard to heavy metals, Pb seems to be the most enriched element.Even the concentration of Fe in the black crust, black-grey crust, surface encrustationand dust samples must be conditioned by the underlying rock, by dissolution of thestone (Sabbioni & Zappia*). In the case of Mg*", which has values of EF < 0.1 at allsamples, a non-caibonate contribution is to be excluded The deposition of SO/" isless on the washed-out surface, while Cl is highly enriched in this area Na* presentsmost deposition on the wall facing the sea and on the horizontal surface encrustationon pavements. The deposition of Pb, Cu and Zn is most distinct on the black-greycrust, the black gypsum formations and the surface encrustations. To estimate theimportance of sea-derived elements and elements deposited on the stones by soil dust,the enrichment factors to the average seawater composition (Riley & Chester*®),using Na as tracer element, and to soil dust (Mason ), using Si as indicator element,were determined The results are presented in Table 2. Ca and SO/ are, besidesthe heavy metals, the components with the highest enrichment factors, with respectto the seawater contribution. Cl, Mg*" and K* in some samples may be originatedfrom the sea (EF close to 1), while also a small fraction of Sr is sea-derived Thewashed-out area presents the highest EF to Cl and the lowest for SO/, suggestingthat the low amount of SO/ deposited on the area (Table 1) may be sea derived,while the high deposition of Cl (Table 1), in comparison with other samples, doesnot originate from the sea. For the 1C deposition, sea salt particles do not seem to bethe most important source. For Mg*~, K% Ni, Cu and Sr, enrichment factors wereobserved close to 1 with respect to soil dust, indicating that soil dust is their majorsource. The enrichment factors were smaller than 1 for Fe, suggesting again that weunderestimate the contribution of soil dust, if Si is used as tracer element. Pb and Znare the only heavy elements, which are clearly enriched to soil dust, and are thereforeattributed to an industrial or in general anthropogenic source. The deposition of Cuon the stones must be related to anthropogenic influences as well.

Very high amounts of SO/ were observed in the total deposition, stone crustsand aerosols. The origin of SO/ is almost purely anthropogenic and not marinespray. The crust formation on the stones is not merely caused by aerosols, butgaseous SQz influences this process. The major part of the collected SO/ aerosolsmust be classified as secondary aerosols and not as originating from sea spray; onlythe fine particles contain SO/, which originates partly from marine spray. Ca ,found in the weathered stone layer, originates from the underlying carbonate rock(Pentelic marble), from deposited calcite particles of the ruins and only partly fromsoil dust. Cl in the total deposition originates mainly from the sea, while for the



aerosols, other sources of Cl are present beside sea spray (e.g. combustion of coal).The Cl", which was found in the weathered stone layers, can be attributed mainly to amarine source, suggesting that the composition of the total deposition reflects betterwhat is really deposited on the stones than solely the aerosol composition. Thedeposition of Pb, Zn, Cu and Cr is most distinct on the black-grey crusts, blackgypsum formation, surface encrustations and dust deposits. Zn and Pb are highlyenriched to soil dust and must therefore be attributed to anthropogenic depositions,while a part of Cu and Cr derive from soil dust. The high concentrations of Mn, Ni,Ti and Fe in the weathered stones are due partly to the underlying rock and partly toindustrial activities of the area; only a small percentage is due to aerosol deposition.On the wall facing the sea, a high deposition of Na% Cl and SO/ is observed on thedisintegrated marble. Na* and Cl originate from marine spray, while SO/ isenriched relative to the average composition of seawater, and must be related toaction of anthropogenic SO/ The washed-out area presents deposition of Cl", 1C,Ca and SO/; only for this sample, some marine source can be identified for SO/.The four other weathered stone types (black-grey crusts, black gypsum formations,surface encrustations and dust deposits) present a high deposition level of Pb, Zn andSO/, attributed to the effects of the local industry.

Table 2 : Enrichment factors of the weathering layers on the stones to seawater(Na* as indicator element) and soil dust (Si as indicator element)

[NCVlNa+lMg*" si | so/| crK+ Ca Ti |Cr|Mn Fe |Ni Cu |Zn Sr PbEF to seawater (Na* as indicator element)Wall facingthe seaWashed-outareaBlack-greycrustGypsumformationSurfaceencrustation

Dust deposit

1100

-

-

10"

10'

4200

1,0

1,0

1,0

1,0

1,0

1,0

EF to soil dust (Si as inWall facingthe seaWashed-outareaBlack-greycrustGypsumformationSurfaceencrustation

Dust deposit

250

-

-

2100

2100

320

3.6

0.17

0.30

0.67

8.0

0.64

2,1

17

3,1

3,1

1,0

2,6

-

10*

10*

10*

10*

10*

580

80

4400

2600

1300

2300

dicator element

1.2

0.47

0.15

0.33

0.11

0.22

1.0

1.0

1.0

1.0

1.0

1.0

10'

120

10'

10'

1300

1500

0,28

12

0,67

0,82

0,33

2,0

21

-

6,9

24

6,5

14

990

7000

5000

2500

14000

2800

)

400

750

79

210

180

130

2.1

9.0

2.0

3.4

1.5

0.67

290

320

64

120

50

10

10*

10*

10*

10*

10*

10*

-

-

10*

10*

10'

10*

-

10*

10*

10*

10*

10*

10*

10*

10?

10*

10*

10'

-

-

10'

10'

10'

10*

6200

-

10*

10'

10'

10*

1.0

0.51

0.51

0.63

0.75

0.69

-

-

4.9

4.5

2.8

3.0

-

6.1

2.7

3.6

2.6

0.88

0.24

0.37

0.63

0.62

1.3

0.83

-

-

1.2

2.0

2.7

2.3

3.1

-

5.1

5.1

3.8

3.2

10'

10*

10*

10*

10*

10*

46

1500

260

170

62

110

10*

-

10'

10'

10'

10'

13

8.4

11

12

16

11

9.6

14

4.6

6.7

3.7

1.5

44

-

55

100

140

51



2. Sulfur isotopes analysis

The results obtained by the enrichment factors analysis lead to the conclusionthat the sulfate concentration is very high in the crust composition, in the totaldeposits and in the aerosol samples as well, and that it is anthropogenic and notseawater spray derived. Sulfur isotopes measurements were performed and thedelta value 5 S of the isotopic ratio was estimated (Table 3). Hence, sources ofatmospheric sulfur can be identified and monitored by stable isotopes of sulfur.Sulfate aerosols can form crusts directly by means of a rapid, heterogeneousreaction, catalyzed by transition metal oxides. In this case the sulfate reactionproducts should always be isotopically lighter than the participating sulfates.This mechanism involves isotopic fractionation in which the rate of oxidativetransformation of sulfur is proportional to the concentration of sulfur dioxide.

Table 3: 5 S%o - Sulfur isotope composition per crusts and aerosol samples atthe various industrial sulfur emission sources

SampleElE4E7BC1BC2FN1FN2FS1FS2PETROLAELDATITAN

8 5--+++----+++

* <224231122671

°/oo)142841102926

short descriptionblack-grey crustloose depositiondustbuilding crust from thbuilding crust from thaerosol samples fromaerosol samples fromaerosol samples fromaerosol samples fromrefineryrefinerycement industry

ecityecityfilterfilterfilterfilter

SofthNoftf-north-north- south- south

e archaeologicalic archaeologicalsidesidesideside

sitesite

(E4O-OE1

rsi

Titan

BC1 0-0 BC2

FS2 ##—*# FN1,FN2

Refineries

OE7

£1E4E7BC1BC2FN1FN2FS1FS2Petrolo *EldaTitan +

OoOoo#*##

- 3 - 2 - 1 0 1 2 3 4 5 6 7 8 9 0

Figure 2 : Fractionation of the sample - Values of 5 **S %the ordinate between -2.07oo and +4.0%o.

are distinguished at



In Figure 2 the fractionation of the samples is observed. Values of 5 S7ooare distinguished at the ordinate between -2.07oo and +4.07oo. The 5 S valuesin the city center and the surrounding area of Antwerpen range from -8.07 to+17™ (Torfs, Van Grieken & Buzek*). In Venice, values ranging from +4.67<>oto +5.67oo in gypsum crusts on the clock tower of San Marco square wereobserved (Longinelli & Bartelloni ). In Prague, the composition of the crustson various buildings varied between +1.87oo and +4.57oo (Buzek & Sramek®),while in Salt Lake City values between -0.67oo and +1.87oo were observed(Dequasie ). Grey and Jensen ™ reported for automobile exhaust a 8 S value of+12.l7oo to +177oo- Our sample presents less heavy sulfur. The ranges of 5 Sfrom petroleum and between -307o<> and +30%* for coal (Faure ). The resultsof our sampling fall within this range. The isotopic factor **S / S, in terms ofdelta values (5 S) shows intermediate values in the zone determined by thecrust values for the case of cement products, while the delta values from therefineries are left aside. Hence, the main impact of suspended particles to thearchaeological site, is caused by the industry; cement industry in particular.Taking into consideration that the isotopic factors attain more negative deltavalues in the case of sea aerosols in comparison to the more positive ones in theurban atmosphere, it is deduced that the marine atmosphere presents moreimportant impact on the archaeological site in vicinity to the sea, whereascentral heating and urban traffic are responsible for the weathering of thearchaeological site in vicinity to the urban center.

Conclusions

Through enrichment factor evaluations, conclusions can be drawn concerningnot only the origin of the elements in the total deposition and aerosols of aaheavily polluted industrial atmosphere, but also the importance andcontribution of each of these parameters and their possible correlation as decayfactors to the ancient marbles. The isotopic factor S/ S, in terms of deltavalues (5 S) of the sulfur-containing pollutants from industry shows that themain impact of suspended particles to the archaeological site is caused by theindustry; cement industry in particular. The advanced analysis of theweathering risks to cultural heritage by this interdisciplinary approach providestools for preventive environmental management regarding industrial emissions.

Acknowledgments

This work was partially supported by the European Union under contract EV5V-CT92-0102 (sci. co-ordinator Prof. Fulvio Zezza, Institute of Applied and Geotechnical Geology,Polytechnic of Ban, Italy). Acknowledgments are also attributed to the 3"* Superintendanceof Classical Antiquities, to the Hellenic Archaeological Society, for their permission towork at the archaelogical site of Eleusis, to Petrola S A. for co-funding and ELDA andTITAN S.A. for the permission to perform sampling, as well as to Dr. F.Buzek (CzechGeological Survey) for the isotope measurements.



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A Moropoulou,^ K Bisbikou,™ K Torfs, ™ R. Van Grieken^

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