MERCURIO Y LOS MALES

Over three millennia of mercury pollution in the Peruvian Andes Colin A. Cookea,1, Prentiss H. Balcomb, Harald Biesterc, and Alexander P. Wolfea
aDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E3; bDepartment of Marine Sciences, University of Connecticut, Groton, CT 06340; and cInstitute of Environmental Geology, Technical University of Braunschweig, Pockelsstrasse 3, 38106 Braunschweig, Germany
Edited by Mark Brenner, University of Florida, Gainesville, FL, and accepted by the Editorial Board April 13, 2009 (received for review January 16, 2009)
We present unambiguous records of preindustrial atmospheric mercury(Hg)pollution,derivedfromlake-sedimentcorescollected near Huancavelica, Peru, the largest Hg deposit in the New World. Intensive Hg mining first began ca. 1400 BC, predating the emergence of complex Andean societies, and signifying that the region served as a locus for early Hg extraction. The earliest mining targeted cinnabar (HgS) for the production of vermillion. PreColonial Hg burdens peak ca. 500 BC and ca. 1450 AD, corresponding to the heights of the Chavı´n and Inca states, respectively. During the Inca, Colonial, and industrial intervals, Hg pollution became regional, as evidenced by a third lake record 225 km distant from Huancavelica. Measurements of sediment-Hg speciationrevealthatcinnabardustwasinitiallythedominantHgspecies deposited, and significant increases in deposition were limited to the local environment. After conquest by the Inca (ca. 1450 AD), smelting was adopted at the mine and Hg pollution became more widely circulated, with the deposition of matrix-bound phases of Hgpredominatingovercinnabardust.Ourresultsdemonstratethe existence of a major Hg mining industry at Huancavelica spanning the past 3,500 years, and place recent Hg enrichment in the Andes in a broader historical context.
cinnabar Inca Chavín vermillion Cinnabar (HgS) is the primary mineralogical source of mercury(Hg),andformsabrightredpigment(vermillion)when powdered. In the Andes, the use of vermillion is closely tied to that of precious metals, and vermillion has been recovered in burials of the elite from the first (Chavı´n) to the last (Inca) Andean empires, where it was used as either a body paint or a coveringonceremonialgoldobjects(1).DuringtheColonialera (1532–1900 AD), large-scale Hg mining began in earnest with the invention of Hg amalgamation in 1554 AD (2). For the next 350 years, Hg amalgamation became the dominant silver processing technique because it allowed for the extraction of silver from low-grade ores (2, 3). Nriagu (2, 3) estimated Colonial Hg emissions totalled 196,000 tons, averaging 600 tons year 1; approximately equivalent to current emissions from China (4). Estimates of Colonial Hg emissions represent minimum values fortheregionbecausetheyonlyincorporatestate-registeredHg used during amalgamation. Hg emissions associated with early Hgminingthereforeremainentirelyunknown.Huancavelica,in the central Peruvian Andes, served as the single largest supplier of Hg to New World Colonial silver mines, and thus represents a potentially major source of preindustrial Hg pollution. Study Region HuancavelicaisontheeasternslopeoftheCordilleraOccidental in central Peru (Fig. 1). Hg deposits are related to high-grade Cenozoic magmatism intruding Mesozoic and Cenozoic sedimentary rocks. Cinnabar is the dominant mercuric ore, and 90% of historically documented cinnabar production has been from the Santa Ba´rbara mine, immediately south of Huancavelica (5). Frequent cave-ins and extensive Hg poisoning throughoutHuancavelica’s450-yearColonialhistoryhavemade
it one of the most sinister examples of human exploitation and disastrousminingenvironmentseverdocumented,earningitthe nickname mina de la muerte (mine of death) (5, 6). We recovered lake-sediment cores from 3 lakes to reconstruct the history of mining at Huancavelica. Two of the study lakes presentedherearenamedLagunaYanacocha(hereafterLY1and LY2;seeFig.1).LY1is10kmsoutheastofHuancavelica,whereas LY2is 6kmsouthwestandisdirectlyup-valleyfromHuancavelica and the Santa Ba´rbara mine. Both lakes are small (LY1: 0.03 km2; LY2: 0.05 km2) and relatively deep (maximum depths for LY1: 14 m; LY2: 11 m) headwater tarns that occupy undisturbed catchmentsof0.71km2 and0.31km2,respectively.LagunaNegrilla (hereafter Negrilla) is 225 km east of Huancavelica in the Cordillera Vilcabamba (Fig. 1A). There are no major Hg deposits orminingcentresinthislatterregion.Negrillaisasmall(0.06km2), deep (33 m) headwater lake that occupies an undisturbed catchment of 0.32 km2. Lakes with undisturbed catchments were deliberately targeted to minimize confounding impacts associated with catchmentdisturbance,andtomaximizesensitivitytoatmospheric deposition of Hg. Sediment cores were recovered from the deepest part of each lake, using a percussion corer fitted with a 7-cm-diameter polycarbonatetube.Coreswereextrudedintocontinuous0.5-cm intervals in the field. At all 3 lakes, sediment excess 210Pb activities decline in near-monotonic fashion (Table S1). To constrain ages beyond the limit of 210Pb, accelerator mass spectrometry (AMS) 14C measurements of discrete carbonized grass macrofossils were obtained on 5 samples from LY1, 3 samplesfromLY2,and3samplesfromNegrilla(Fig.2andTable S2). AMS 14C ages were calibrated using SHCal04 (7) within Calib 5.0 (8). Concentrations of total Hg were determined on a DMA80 direct mercury analyzer (Table S3). Measurements of sediment-Hg speciation were done by solid-phase Hg thermodesorption (9), which produces temperature-dependent Hg release curves enabling identification of species such as Hg0, matrix-bound Hg, and inorganic HgS by comparison with reference materials (Fig. S4). Results and Discussion Despitedifferentsedimentationrates(Fig.2),theLY1andLY2 geochemicalprofilesarehighlyconcordant(Fig.3)whenplotted on their respective age-depth models. For approximately 1 millennium before ca. 1600 BC, Hg accumulation within LY2 sedimentisstableandlow,averaging6( 1) g m 2 year 1.This represents the natural, background accumulation of nonpollutionHgwithinLY2sediment.TheHgprofileoftheNegrillacore
Authorcontributions:C.A.C.designedresearch;C.A.C.,P.H.B.,H.B.,andA.P.W.performed research; H.B. contributed new reagents/analytic tools; C.A.C., P.H.B., H.B., and A.P.W. analyzed data; and C.A.C., P.H.B., H.B., and A.P.W. wrote the paper. The authors declare no conflict of interest. ThisarticleisaPNASDirectSubmission.M.B.isaguesteditorinvitedbytheEditorialBoard. 1To whom correspondence should be addressed. E-mail: cacooke@ualberta.ca. This article contains supporting information online at www.pnas.org/cgi/content/full/ 0900517106/DCSupplemental.
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is somewhat different; however, background Hg accumulation rates are of similar magnitude [7 ( 2) g m 2 year 1] for much of this lake’s early record. Background Hg levels do not appear tohavebeenreachedatLY1,althoughHgaccumulationratesof 6 g m 2 year 1 arenotedinthedeepestintervals(Fig.3).Thus,
we conclude that the accumulation of natural, nonpollution Hg in these lakes is 6–7 g m 2 year 1. Although this range is consistentwithnearlyallotherlake-sedimentreconstructionsof preanthropogenic Hg deposition from around the globe (10), mechanisms such as catchment export and sediment focusing ultimatelyservetoconfoundreconstructionsofHgdepositionto varying degrees (11). Therefore, to enable comparability betweenthese,andotherlake-corerecords,sampletobackground flux ratios were calculated for each lake (Fig. 3). AtbothLY1andLY2,dramaticincreasesinHgaccumulation rates are initiated ca. 1400 BC, and by 600 BC both lakes exceed background by 10-fold (Fig. 3). The accumulation of Hg subsequently decreases in both lakes until ca. 1200 AD at LY1 and ca. 1450 AD at LY2, before increasing once again. By the mid-16th century, sediment Hg accumulation rates at LY1 and LY2 are enriched by factors of 55 and 70 relative to background, respectively (Fig. 3). Only the latter increase in Hg depositionispreservedatNegrilla,whereHgaccumulationrates rise dramatically ca. 1400 AD to over 30 times background. After 1600 AD, the Hg records for all 3 lakes are all characterized by Hg accumulation rates and flux ratios well above background (Fig. 3). The earliest (ca. 1400 BC) rise in Hg at LY1 and LY2 is characterizedbya3-to5-foldincreaseinHgaccumulation(Fig. 3), and occurs during a period of stable sedimentation with respecttobothorganicandinorganicsedimentfractions(Fig.S1 and Fig. S2). Consequently, these increases cannot be explained by a rapid influx of catchment material or enhanced Hg scavenging by organic matter. Moreover, lake sediment burdens of total Hg are largely unaffected by diagenetic processes (12, 13), andrepresentminimumestimatesoftotalHgdepositedtoalake surface because of reductive losses before final burial (14). Becauseweknowofnonaturalmechanismcapableofreplicating such large and synchronized increases in Hg deposition in 2 adjacent lakes, and given their proximity to a major cinnabar deposit, we attribute with confidence the early increases of Hg observed at LY1 and LY2 to the emergence of regional-scale cinnabar mining at Huancavelica. Lessthan20kmfromHuancavelica,thearchaeologicalsiteof Atalla is the earliest example of large-scale ceremonial architectureinthecentralAndes.AlthoughAtallalacksdirectdating and excavation, surface remains suggest the site served as a regional Center for procuring and distributing cinnabar (15). CeramicssuggestAtalladatestotheEarlyHorizon(ca.800–300
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Fig. 1. Map of the study region. (A) Map of Peru with study region and location of Negrilla. (B) Detailed map of Huancavelica region with locations of Santa Ba´rbara mine, the 2 study lakes (LY1 and LY2), and remains of Colonial Hg retorts.
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BC), and was actively engaged in trade with Chavı´n de Hua´ntar in the Cordillera Blanca (15) (Fig. 1). Chavı´n influenced much of the Peruvian Andes at its apogee, and represents the cradle of complex Andean culture (16, 17). High-status burials at Chavı´n de Hua´ntar, and other Early Horizon sites, commonly contain prestigious materials including gold adorned with ver
million (17, 18). However, cinnabar mining at Huancavelica precedes even the earliest radiocarbon dates for Chavı´n (1), and thereforemustpredatetheriseandexpansionofChavı´nculture. The rate of Hg accumulation at both LY1 and LY2 declined duringthesubsequentEarlyIntermediatePeriod(ca. 200BCto 500 AD; Fig. 3). At LY1, Hg flux ratios briefly return to background ca. 200 AD; however, no parallel return to background is evident at LY2. This discrepancy likely indicates that watershed-scale Hg retention times vary between the 2 lakes. The steady export of legacy Hg from the catchment of LY2 may be therefore partially responsible for the maintenance of elevated Hg accumulation during this period. In any case, cinnabar mining does appear to have continued during the Early Intermediate Period, although at reduced intensity. Although the collapse of Chavı´n likely curtailed the demand for exotic goods includingcinnabar,highlystratifiedculturesfromthenorthcoast of Peru, such as the Moche (ca. 100–700 AD) and Sica´n (ca. 700-1200 AD), may have sustained some level of imperial demand for cinnabar. Burials of Moche and Sica´n nobles are some of the richest yet excavated in Peru, and vermillion is ubiquitous (19). Huancavelica is the likely source, given the scarcity of other cinnabar deposits in the Andes (20). By 800 AD, a brief renewal in cinnabar mining is indicated as Hg flux ratios increase to 3.5 and 5.5 at LY1 and LY2, respectively (Fig. 3). This increase occurs during the Middle Horizon (ca. 500 to 1000 AD), and is followed by larger increases in Hg depositionatLY1duringtheLateIntermediatePeriod(fromca. 1000 to 1400 AD). The Middle Horizon and the Late Intermediate Period witnessed the rapid development and expansion of mining and metallurgy in the Andes (21, 22). During the Late Intermediate Period, the archaeological site of Attalla appears to have been reoccupied (15), suggesting continuation, if not intensification, of local cinnabar processing. Inca expansion into the central Andes occurred ca. 1450 AD, and cinnabar production appears to have increased dramatically under Inca control. Hg accumulation at LY1 increases rapidly ( 55-fold), and is matched by the first increase in Hg at Negrilla, which exceeds background by 30-fold (Fig. 3). The appearance of Hg pollution atNegrillaindicatesIncaexploitationoftheHuancavelicacinnabar deposits exceeded all previous cultures, producing a broadly dispersed legacy of Hg pollution captured by all 3 study lakes. Incaminingcontinueduntil1564ADwhentheSpanishcrown assumed control, at which time the Santa Ba´rbara mine was established. In contrast to cinnabar extraction for vermillion, Spanish efforts concentrated on supplying elemental Hg (Hg0) to Colonial silver mines for use in Hg amalgamation. Hg amalgamationwasinventedin1554ADbyBartolome´deMedina in Mexico, and is considered one of the most remarkable technological advances of Ibero-America (2). Cinnabar ores fromHuancavelicaweresmeltedingrass-fired,clay-linedretorts (hornos;Fig.1),untilvaporizationyieldedgaseousHg0,aportion of which was trapped in a crude condenser and cooled, yielding liquid Hg0. Emissions of Hg thus occurred both during mining, as cinnabar dust, but also during cinnabar smelting, as gaseous Hg0. Historical records of Hg production at Huancavelica indicate declining Hg output while under Colonial control, and into the 20th Century (5). At LY1 and Negrilla, Hg accumulation decreases through the Colonial period, while increasing at LY2 (Fig. 3). The apparent discordance between the Hg profiles appears to support the suggestion that the watershed of LY2 continued to export legacy Hg to the lake during periods of declining atmospheric deposition, a mechanism that has also been observed in modern lake systems (23). The mine was permanently closed in 1975 AD, and currently the only mining of Hg at Huancavelica is artisanal. In response, Hg flux ratios at Negrillahavedeclined,andarecurrently 4.6timesbackground in the uppermost sediments (Fig. 3). This level of relative Hg enrichment is in agreement with the vast majority of sediment
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Fig. 3. Lake-sediment profiles of Hg deposition and Andean archaeology. (A) Compilation of central Andean archaeology (EIP, Early Intermediate Period;LIP,LateIntermediatePeriod).(B)ProfilesofHgaccumulationratesand flux ratios for lakes LY2, LY1, and Negrilla. Two intervals of marked Hg enrichmentareshaded.Pre-ColonialHgdepositionpeaksduringtheheightof the Chavı´n culture, whereas the later rise occurs under Inca and subsequent Colonialcontrol.Thissecondperiodofextensiveminingactivitywitnessedthe long-rangetransportofHgemissions,asshownbytheonsetofHgdeposition to Negrilla, 250 km east of Huancavelica.
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core studies from remote lakes, which collectively suggest an average increase in global Hg deposition rates of 3–5x background values (10). In contrast, Hg flux ratios at both LY1 and LY2 in 1975 AD were 105 times background. Although modern flux ratios at LY1 have declined by 60% (to 42 times background), no such decline is recorded at LY2. The elevated Hg accumulation rates still present at these lakes likely reflect the legacy of 3,500 years of regional Hg pollution residing within their catchments. The mercuric species emitted during Colonial and preColonialminingactivitieshavedirectimplicationsforthesizeof the impacted airshed. Atmospheric Hg0 has long atmospheric residence times ( 0.5–1.5 years) and is the most important Hg species at the global scale (24). In contrast, oxidized reactive species of mercury can be rapidly scavenged from the atmosphere, whereas coarse particulate forms (including cinnabar dust) predominate in direct proximity to Hg point-sources (25). Measurements of Hg speciation within LY2 sediments confirm that major changes in Hg extractive technology occurred at Huancavelica (Fig. S4). Solid-phase thermal desorption reveals 2 predominant Hg phases: cinnabar and noncinnabar (i.e., matrix-bound), which are variably expressed down-core (Fig. 4). During the pre-Inca era, cinnabar was the dominant Hg species inallsedimentsamples,averaging78%ofthetotalsedimentHg inventory.Althoughnotprecludingtheemissionofotherspecies
of Hg, these results suggest that pre-Inca Hg pollution, although important locally, exerted little influence beyond the range of particulate dust transport, a conclusion supported by the apparent lack of any pre-Inca Hg pollution at Negrilla. A progressive decline in the cinnabar fraction is noted in sediments that postdate ca. 1450 AD, and the majority of sediment Hg burdens remain matrix-bound through the remainder of the LY2 sediment record. This is despite absolute increases in the concentration of total Hg (Fig. S2) and of the fraction that is cinnabar (Fig.4).Theonsetoflong-rangetransportofHgduringtheInca hegemony suggests a shift in Hg extractive technology and associated Hg emissions. Indeed, to transport Hg the 225 km to Negrilla, at least some emissions must have been in the form ofgaseousHg0 (orpossiblyreactiveHg2 ).Incontrasttocoarse particulatecinnabardust,gaseousatmosphericHgspeciescanbe broadcast atmospherically over far greater distances, can undergoatmosphericoxidation/reductioncycling,andHg2 canbe methylated once delivered to aquatic systems. A growing number of cores from remote lakes suggest an approximately 3-fold increase in Hg deposition over the last 100–150years(10,24).Theserecordsarepredominantlyfrom the northern hemisphere, and do not reveal any significant preindustrialHgenrichment.Incontrast,ourresultssuggestthat considerable preindustrial Hg pollution occurred in the Andes. TheonsetofcinnabarminingatHuancavelicaca.1400BCplaces our lake-sediment records among the earliest evidence for mining and metallurgy in the Andes, of comparable antiquity to the oldest known hammered and annealed objects from welldated contexts (26). Before Inca control of the mine, Hg emissions appear to have been restricted to the environment surrounding Huancavelica. Over the past 550 years however, emissions of Hg have been transported long distances. Materials and Methods Sediment Geochemistry. Blank values, average relative standard deviations, and recoveries of standard reference materials [NRCC PACS-2 (marine sediment, certified value 3040 200 ng g 1) and MESS-3 (marine sediment, certifiedvalue91 9ng g 1)]associatedwithDMA80measurementofHgare presentedinTableS3.Solid-phaseHgthermo-desorption(SPTD)isanindirect methodinwhichHgspeciesaredeterminedbythermaldesorptionordecompositiontemperatures(9).Themethodhasadetectionlimitof0.4 g g 1 Hg, andamaximumsamplesizeof 200mg.InSPTDanalysis,thesampleisplaced in a quartz furnace and heated at a rate of 0.5 °C s 1. Volatilized Hg compoundsarecarriedfromthefurnacewithN2200mL min 1,andreducedtoHg0 bythermalreductioninaquartztubeheatedto800 °Cbeforebeinganalyzed by flameless AAS. This method produces temperature-dependent Hg release curvesthatarespecies-andmatrix-specific.Thesereleasecurvesenableidentification of species such as Hg0, matrix-bound Hg, and inorganic cinnabar (HgS) by comparison to pure Hg phases and reference materials (Fig. S4). Quantification of Hg species was made by peak integration (27). The sample volume used was between 20 and 200 mg of dry sediment depending on sediment-Hg concentrations. Relative standard deviation on replicate measurements of Hg binding forms in sediments (matrix-bound noncinnabar Hg compounds and cinnabar) of each sample (n 3–4) ranged 2.8% to 15.4% (mean 8.0%). Total organic matter was determined by loss-on-ignition (28). Sediment chlorophyll a was inferred using visible-near infrared reflectance (VNIR) spectroscopy (29).
ACKNOWLEDGMENTS. We thank W. Hobbs, A. Reyes, J. Vargas, and P. Tapia for assistance in the field; A. Hutchins and S. Castro for assistance in the laboratory;D.Froese,V.StLouis,W.Fitzgerald,andJ.Wisefortheirinsightful discussions; and 2 anonymous reviewers. This work was supported by grants fromtheNationalGeographicSociety,theGeologicalSocietyofAmerica,and the Natural Sciences and Engineering Research Council of Canada.
1. Burger RL (1992) Chavı´n and the origins of Andean civilization (Thames and Hudson, London), pp 248. 2. Nriagu JO (1994) Mercury pollution from the past mining of gold and silver in the Americas. Sci Total Environ 149:167–181. 3. Nriagu JO (1993) Legacy of mercury pollution. Nature 363:589. 4. Wu Y, et al. (2006) Trends in anthropogenic mercury emissions in China from 1995 to 2003. Environ Sci Tech 40:5312–5318.
5. Wise JM, Fe´raud J (2005) Historic maps used in new geological and engineering evaluation of the Santa Ba´rbara Mine, Huancavelica mercury district, Peru. De Re Metallica 4:15–24. 6. BrownKW(2001)Workers’healthandColonialmercuryminingatHuancavelica,Peru. Americas 57:467–496. 7. McCormacFG,etal.(2004)ShCal04SouthernHemispherecalibration,0–11.0calkyrBP. Radiocarbon 46:1087–1092.
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Fig. 4. Measurements of Hg speciation within LY2 sediment. (A) Plot of relative percentage cinnabar and matrix-bound phases of Hg. (B) Concentration of Hg as cinnabar down-core. Before anthropogenic enrichment a combination of cinnabar dust and matrix-bound Hg make up the sediment Hg record. During the height of Chavı´n mining (ca. 400–800 BC), cinnabar dust wasthevastmajorityofsedimentHg.AfterIncacontrolofthemine(ca.1450 AD), matrix-bound phases of Hg predominate, despite a synchronous rise in the concentration of Hg as cinnabar. This relationship suggests a shift in the phaseofHgemitted,fromcinnabardusttoHg0(orpossiblyHg2 ).Bothwould subsequently be available for oxidation/reduction cycling within the atmosphere,sorptionbyorganicmatter,methylation,andsubsequentbioaccumulation within aquatic food-webs.
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8. Stuiver M, Reimer PJ (1993) Extended 14C database and revised CALIB radiocarbon calibration program. Radiocarbon 35:215–230. 9. Biester H, Scholz C (1997) Determination of mercury binding forms in contaminated soils: Mercury pyrolysis versus sequential extractions. Environ Sci Tech 31:233–239. 10. Biester H, Bindler R, Martinez-Cortizas A, Engstrom DR (2007) Modeling the past atmospheric deposition of mercury using natural archives. Environ Sci Tech 41:4851– 4860. 11. EngstromDR,BaloghSJ,SwainEB(2007)HistoryofmercuryinputstoMinnesotalakes: Influences of watershed disturbance and localized atmospheric deposition. Limnol Oceanogr 52:2467. 12. Rydberg J, et al. (2008) Assessing the stability of mercury and methylmercury in a varved lake sediment deposit. Environ Sci Tech 42:4391–4396. 13. Lockhart WL, et al. (2000) Tests of the fidelity of lake sediment core records of mercury depositiontoknownhistoriesofmercurycontamination. SciTotalEnviron 260:171–180. 14. Southworth G, et al. (2007) Evasion of added isotopic mercury from a northern temperate lake. Environ Toxicol Chem 26:53–60. 15. BurgerRL,MendietaRM(2002)Atalla:AcenterontheperipheryoftheChavı´nhorizon. Lat Am Antiq 13:153–177. 16. Rick JW (2004) The evolution of authority and power at Chavı´n de Hua´ntar, Peru. Archeolog Pap Amer Anthro Assoc 14:71–89. 17. BurgerRL(2008)inHandbookofSouthAmericanArchaeology,edsSilvermanH,Isbell W (Springer, New York), pp 681–703. 18. Onuki Y, Kato Y Excavations at Kuntur Wasi, Peru: The First Stage 1988–1990, trans Cooke C (1993) (University of Tokyo Press, Tokyo). 19. ShimadaI,etal.(2004)Anintegratedanalysisofpre-Hispanicmortuarypractices.Curr Anthropol 45:369–402.
20. PetersenU(1989)inGeologyoftheAndesanditsrelationtohydrocarbonandmineral resources, eds Ericksen GE, Theresa Can˜as PM, Reinemund JA (Circum-Pacific Council for Energy and Mineral Resources, Houston), pp 213–232. 21. CookeCA,AbbottMB,WolfeAP(2008)Late-Holoceneatmosphericleaddepositionin the Peruvian and Bolivian Andes. Holocene 18:353–359. 22. ShimadaI,EpsteinS,CraigAK(1982)Bata´nGrande:Aprehistoricmetallurgicalcenter in Peru. Science 216:952–959. 23. Harris RC, et al. (2007) Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition. Proc Natl Acad Sci USA 104:16586–16591. 24. Lindberg S, et al. (2007) A synthesis of progress and uncertainties in attributing the sources of mercury in deposition. Ambio 36:19–33. 25. Fitzgerald WF, Lamborg CH (2005) Geochemistry of mercury in the environment. Treatise Geochem 9:107–148. 26. AldenderferM,CraigNM,SpeakmanRJ,Popelka-FilcoffR(2008)Four-thousand-yearold gold artifacts from the Lake Titicaca basin, southern Peru. Proc Natl Acad Sci USA 105:5002–5005. 27. Biester H, Gosar M, Covelli S (2000) Mercury speciation in sediments affected by dumped mining residues in the drainage area of the Idrija mercury mine, Slovenia. Environ Sci Tech 34:3330–3336. 28. HeiriO,LotterAF,LemckeG(2001)Lossonignitionasamethodforestimatingorganic and carbonate content in sediments: Reproducibility and comparability of results. J Paleolimnol 25:101–110. 29. WolfeAP,VinebrookeR,MicheluttiN,RivardB,DasB(2006)Experimentalcalibration of lake-sediment spectral reflectance to chlorophyll a concentrations: Methodology and paleolimnological validation. J Paleolimnol 36:91–100.
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