Use and Legacy of Mercury in the AndesColin A. Cooke,*,†,‡ Holger Hintelmann,∥ Jay J. Ague,† Richard Burger,§ Harald Biester,⊥ Julian P. Sachs,#

and Daniel R. Engstrom∇

†Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, United States§Department of Anthropology, Yale University, New Haven, Connecticut 06520, United States∥Department of Chemistry, Trent University, Peterborough, Ontario K9J 7B8, Canada⊥Institute for Geoecology, Technical University-Braunschweig, Langer Kamp 19c, 38106 Braunschweig, Germany#School of Oceanography, University of Washington, Seattle, Washington 98195, United States∇St . Croix Watershed Research Station, Science Museum of Minnesota, Marine-on-St. Croix, Minnesota 55047, United States

*S Supporting Information

ABSTRACT: Both cinnabar (HgS) and metallic mercury (Hg0) wereimportant resources throughout Andean prehistory. Cinnabar was usedfor millennia to make vermillion, a red pigment that was highly valued inpre-Hispanic Peru; metallic Hg0 has been used since the mid-16thcentury to conduct mercury amalgamation, an efficient process ofextracting precious metals from ores. However, little is known aboutwhich cinnabar deposits were exploited by pre-Hispanic cultures, and theenvironmental consequences of Hg mining and amalgamation remainenigmatic. Here we use Hg isotopes to source archeological cinnabar andto fingerprint Hg pollution preserved in lake sediment cores from Peruand the Galapagos Islands. Both pre-Inca (pre-1400 AD) and Colonial(1532−1821 AD) archeological artifacts contain cinnabar that matchesisotopically with cinnabar ores from Huancavelica, Peru, the largestcinnabar-bearing district in Central and South America. In contrast, the Inca (1400−1532 AD) artifacts sampled are characterizedby a unique Hg isotopic composition. In addition, preindustrial (i.e., pre-1900 AD) Hg pollution preserved in lake sedimentsmatches closely the isotopic composition of cinnabar from the Peruvian Andes. Industrial-era Hg pollution, in contrast, is distinctisotopically from preindustrial emissions, suggesting that pre- and postindustrial Hg emissions may be distinguished isotopicallyin lake sediment cores.

■ INTRODUCTION

Cinnabar (HgS) forms a bright red pigment (vermillion) whenpowdered. In the South American Andes, vermillion is found ingraves of high-status individuals and as a paint coveringfunerary masks and adorning ceremonial artifacts (Figure 1A).Vermillion has been recovered in association with a range ofarcheological artifacts spanning one of the first (Chavın) to thelast (Inca) pre-Hispanic Andean civilizations. Deposits ofcinnabar are known from a range of hydrothermal ore depositslocated across Central and South America,1 the largest of whichis the Huancavelica quicksilver district in central Peru (Figure1B).2,3 It has been suggested that Huancavelica cinnabar wasmined and traded for in pre-Hispanic times,4 but clearconfirmation is lacking, as is information regarding otherpossible cinnabar sources.A renewed interest in cinnabar, this time as a source of

metallic mercury (Hg0), occurred after Spanish conquest of theAndes in 1532 AD. By ∼1570 AD, metallic Hg0 was relied uponacross Central and South America to conduct mercuryamalgamation, a technological development that allowed forthe extraction of silver and gold from even low-grade ores.5,6

The rapid adoption of mercury amalgamation across theAmericas stimulated cinnabar mining on an unprecedentedscale, and the cinnabar mines within the Huancavelicaquicksilver district, the largest of which was the Santa Barbaramine,2,3 supplied much of the metallic Hg0 used foramalgamation. Mercury amalgamation dominated silverproduction globally until ∼1900 AD,7 and it is estimated tohave emitted >100 Gg of gaseous Hg0 to the globalatmosphere.6,8 Resolving the geographic scope and biogeo-chemical impact of preindustrial mercury mining and emissionsis important because mercury can be recycled repeatedlybetween various earth-surface compartments9 and may persistfor centuries in biogeochemically active pools before beingsequestered in soils or sediments.10,11

High-precision measurements of Hg isotopes have affordednew insight into source apportionment and the biogeochemical

Received: November 26, 2012Revised: April 1, 2013Accepted: April 3, 2013Published: April 18, 2013

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cycling of Hg.12−14 There are seven stable isotopes of Hg(196−204 amu), and mass-dependent fractionation (MDF) ofHg isotopes is expressed as δ202Hg, which is derived usingstandard delta notation: δxHg (‰) = ([(xHg/198Hg)unknown/( xHg/1 9 8Hg)N I ST SRM 3 1 3 3 ] − 1) × 1000 , where(xHg/198Hg)NIST SRM 3133 is the average Hg isotope ratio ofbracketing standards.15 MDF of Hg is known to occur duringreduction−oxidation transformations, biological cycling, andvolatilization of Hg. Hg isotopes can also undergo mass-independent fractionation (MIF) in which the even- and odd-mass-number isotopes fractionate from each other.12 MIF ofHg isotopes is reported as the deviation of a measured δ202Hgvalue from that theoretically predicted on the basis of MDF.MIF is thus reported as Δ199Hg and Δ201Hg in per mil (‰),and for variations ≤5‰ can be calculated using the following:Δ199Hg = δ199Hg − (δ202Hg × 0.252) and Δ201Hg = δ201Hg −(δ202Hg × 0.752);15 we use Δ199Hg as the default value toreport MIF. MIF of Hg is largely produced by photochemicalreactions and remains unchanged by most dark and biologicaltransformations.12,16

Here we present the results of an interdisciplinary studyusing Hg isotopes to link resource exploitation, thearcheological record, and environmental pollution. Our newHg isotope data offer unprecedented insight into artisanalcinnabar mining and exchange and the environmental legacy ofmercury mining in the Andes.

■ MATERIALS AND METHODSMercury Stable Isotopes. Hg isotopic compositions were

measured using Thermo-Finnigan Neptune continuous-flowcold vapor generation MC-ICP/MS at Trent University and in

accordance with published methodologies.17,18 Additionaldetails are provided in the Supporting Information. Analyticaluncertainty was evaluated using replicate analyses of both theUM-Almaden standard and the certified standard referencematerials (CRM) MESS-3 (marine sediment) and NIST 1944(New York/New Jersey waterway sediment); the CRM wereprocessed and analyzed in the same manner as our samples.The results for these standards (Table S1) were indistinguish-able (within uncertainty ranges) from published values.15,17,19,20

We estimate a typical analytical uncertainty of a given isotoperatio as 2 SD of the measurement of the ratio in proceduralstandards (e.g., δ202Hg uncertainty = 0.09‰). Digestionduplicates yielded δ202Hg values with 2 SD uncertainty rangesspanning ±0.02‰ to ±0.56‰ (δ202Hg); ±0.02‰ to ±0.09‰(Δ199Hg) and 0.01‰ to ±0.09‰ (Δ201Hg) (Table S1). Whilewe cannot readily explain the relatively large δ202Hgheterogeneity observed in sample H5, it seems likely that thisreflects heterogeneity within the original deposit (discussedbelow).

Cinnabar Ores and Archeological Artifacts. Toconstrain the Hg isotopic signature of cinnabar sources acrossthe South American Andes, we obtained 12 samples of cinnabarore from eight deposits (Table 1; Figure 1B). Our samples,

which were obtained from museum mineral collections, are byno means a complete sampling of Andean cinnabaroccurrences. But they offer an initial evaluation of Hg isotopeheterogeneity across the Andes and include the only twodeposits (Huancavelica and Chonta, Peru) mined historically(i.e., since 1532 AD).1

We hypothesized that Hg isotopes might be used toprovenance archeological cinnabar. To test this hypothesis,we obtained samples of cinnabar found either as an offering(samples A1−7) or as a pigment covering ceramic (sample A8),metal (sample A9), or wooden (samples A10−17) artifacts(Table 2; Figure 1). A complete list of the objects sampled,including information about the archeological site, culturalaffiliation, and age, is provided in Table 2; additional detailsabout each item are provided in the Supporting Information.The artifacts sampled include a number of pre-Inca (i.e., pre-1400 AD), Inca (ca. 1400−1532 AD), and Colonial (1532−1821 AD) objects.

Lake Sediment Core Mercury Content. To reconstructthe history of Hg deposition, we collected sediment cores fromtwo lakes, one located in the Peruvian Andes (Laguna Negrilla:13° 09′ S, 72° 58′ W; 4125 masl) and one located on SanCristobal Island, Galapagos archipelago, Ecuador (El JuncoLake: 0° 53′ S, 89° 28′ W; 660 masl) (Figure 1B). Detailsabout the recovery, chronology, and Hg measurements of theLaguna Negrilla sediment core have been published pre-

Figure 1. Artifact photos and sample locations. (A) Photographs ofsome of the artifacts included in this study; the red pigment on eachitem is cinnabar. Details about the provenance, cultural affiliation, andage of each artifact are provided in Table 2; photographs of theartifacts not shown here (samples A7−8, A10, A12−13, and A15−16)are included in the Supporting Information. (B) Map showing thelocations of cinnabar samples (C#; white squares), archeologicalartifacts (A#; gray squares), and lake sediment cores (red stars). Alsoindicated is the approximate extent of the Inca Empire at the time ofSpanish conquest (1532 AD), which extended across much ofmodern-day Peru and Ecuador, and parts of Colombia, Bolivia,Chile, and Argentina. Sample labels in both panels correspond toTables 1 and 2.

Table 1. List of Cinnabar Ores, with Sample IDsCorresponding to Labels in Figures 1 and 2

sample ID location

H1−5 Huancavelica, PeruC1 Jalaca, HondurasC2 Antioquia, ColombiaC3 Quindio, ColombiaC4 Chonta, PeruC5 Cerro Colorado, BoliviaC6 Mina de Pedernal, BoliviaC7 Algarrobo Mine, Chile

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viously.21 El Junco Lake occupies an extinct volcanic crater onthe southwest summit San Cristobal Island in the GalapagosArchipelago. The lake, which is roughly circular with a diameterof ∼220 m, lies within a ∼320-m diameter crater.Stratocumulus cloudswhich are an efficient scavenger ofatmospheric Hg2+ (ref 22)usually conceal the lake in a densefog (locally called garua), and strong surface winds channel airyear round from the southeast. El Junco Lake is thus ideallysituated to record the long-range atmospheric transport of Hgemitted from the South American mainland.The sediment cores from both lakes were dated using both

210Pb (Table S2) and 14C (Table S3) radioisotopes, and age-depth models for the sediment cores (Figure S2) weregenerated using the CLAM software package.23 To quantifythe total sediment Hg content, we freeze-dried andhomogenized ∼200 mg of sediment from 1-cm intervals andmeasured the Hg content using a DMA-80 direct mercuryanalyzer. Duplicate analyses and the CRM MESS-3 weremeasured after every 10th sample and were always within 5% ofeach other (for duplicates) and certified values (for CRM). Wealso measured a suite of other sediment parameters includingorganic carbon and nitrogen contents (%C and %N), and theconcentration of aluminum (Al), titanium (Ti), sodium (Na),and manganese (Mg) (Figure S3).

■ RESULTS AND DISCUSSIONAncient Cinnabar Mining and Exchange. Many of the

cinnabar ores we analyzed exhibit both MDF and MIF of Hg(Figure 2; Table S1). Cinnabar δ202Hg values span ∼3.5‰, andΔ199Hg and Δ201Hg values span ∼0.4‰. There is, furthermore,greater variability in δ202Hg values within the Huancavelica oresthan among the different deposits, reflecting the heterogeneityof this district.Our cinnabar samples were obtained from museum

collections that are largely devoid of information concerningtheir geological provenance beyond their general location ofcollection. Formation conditions are, therefore, unknown forthe majority of the samples we analyzed, making it difficult toexplain the wide range of isotopic compositions observed(Figure 2). However, MDF of Hg has been observed previously

within a variety of hydrothermal ores, including cinnabar,24−28

and is thought to result from a combination of processesassociated with the emplacement of Hg-bearing minerals.25,26

In contrast, significant MIF of Hg has not been observedpreviously in cinnabar, and we observe a linear relationshipbetween MDF and MIF within Huancavelica ore (r2 = 0.99, p =0.001). MIF of Hg is thought to be initiated by either thenuclear volume effect (NVE) or the magnetic isotope effect(MIE). The NVE, which generates smaller MIF (≤0.4‰) anda Δ199/201Hg ratio of 1.60−1.65, has been observed during

Table 2. List of Archaeological Cinnabar Samples: Sample IDs Correspond to Labels in Figures 1 and 2a

sample id objectarchaeological site or

region cultural affiliation age estimate

Pre-IncaArtifacts

Al−2 cinnabar in grave Kuntur Wasi Chavın Early Horiozn (800−300 BC)A3−6 funerary offering Chongoyape Chavın Early Horizon (800−300 BC)A7 cinnabar in ceremonial

offeringLas Huacas Cupisnique Initial Period (1200−800 BC)

A8 bottle rim Cerro Blanco Chavın Early Horiozn (800−300 BC)A9 gold funerary mask Northern Peruvian

coastLambayeque(Sican)

Late Intermediate Period (1000−1250 AD)

A10−11 wooden mummy bundlemasks

Central Peruvian coast unknown A10: 1020−1150 AD All: 890−1020 AD

Colonial ArtifactsA12−14 wooden drinking vessels

(qeros)Cusco Colonial A12: 1670−1890 ADA13: 1670−1950 AD A14: 1520−1790 AD

Inca ArtifactsA15−17 wooden digging boards Southern Peruvian

coastInca A15: 1400−1440 AD A16: 1460−1630 AD

aArchaeological samples occur either as pure cinnabar entombed within a burial or offering (A1−7) or as a decorative pigment (A8−17). SamplesA10−17 were radiocarbon dated, and the calibrated 2σ age ranges are also provided. More details about each artifact and the radiocarbon results areprovided in the Supporting Information.

Figure 2. Three-isotope plot of δ202Hg and Δ199Hg values forcinnabar. The sample numbers correspond to the sample ID numbersin Table 1 (for the cinnabar ore) and Table 2 (for the artifacts) butwithout the capital letters. A significant and linear (r2 = 0.99, p =0.001) relationship is noted within cinnabar samples fromHuancavelica (black line). The majority of the pre-Inca (pre-1400AD) and Colonial (1532−1900 AD) archeological cinnabar samples(circled) plot within the 2σ uncertainty ranges for the Huancavelicacinnabar ores (gray shading), suggesting Huancavelica was the sourceof cinnabar on these objects. In contrast, cinnabar from Inca-era (ca.1400−1532 AD) artifacts plot away from the Huancavelica, pre-Inca,and Colonial cinnabar samples.

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liquid−vapor Hg0 evaporation, Hg2+ reduction in the absenceof light, and Hg2+−thiol complexation.29−31 In contrast, theMIE produces larger MIF with a Δ199/201Hg ratio between 1.0and 1.3, and is initiated during photoreduction of Hg2+ ormethyl-Hg (ref 12). Our cinnabar samples are characterized bya Δ199/201Hg ratio of 1.23 ± 0.09 (Figure S1), suggesting thatthe MIE drives MIF in these samples. While photochemicallyinitiated reduction of oxidized Hg2+ (to gaseous Hg0) isthought to be the main driver of MIF of Hg in naturalsamples,13,32 it cannot explain the MIF observed within ourcinnabar samples. Instead, the MIF anomalies preserved withinCentral and South American cinnabar may indicate isotopicinheritance from interactions with sedimentary source-rocks,which, for example, are found in close association with thecinnabar deposits at Huancavelica.2 Coal, peat, and marinesediments all exhibit MIF of Hg generated by the MIE,13,32 anda similar suggestion was made by Sonke et al. to explainsignificant MIF anomalies of trace Hg found within sphalerite(ZnS).20 We also note that, given our small sample size, wecannot rule out the existence of other isotopic end-members.Regardless of the exact cause of MIF within cinnabar, the

relatively high degree of isotopic variability among cinnabardeposits raises the possibility that Hg isotopes can be used tosource cinnabar preserved as part of the archeological record.The archeological artifacts we analyzed can be broadly groupedaccording to their antiquity and Hg isotopic signatures. Thefirst group (samples A1−11) includes all of the artifactspredating the Inca Empire (i.e., pre-1400 AD). Most of thesepre-Inca artifacts do not reveal significant MIF of Hg, and, withthe lone exception of sample A2, plot within the 2σ uncertaintyrange of the Huancavelica data (gray band) (Figure 2). Thesecond group of artifacts (samples A15−17), which contains allof the Colonial era (1532−1821 AD) samples, is characterizedby δ202Hg and Δ199Hg values that overlap closely withHuancavelica cinnabar. This is consistent with historical recordsthat indicate Huancavelica was the only significant source ofcinnabar exploited by the Spanish.2 The final group of artifactsall date to the Inca era (ca. 1400−1532 AD). The cinnabaradorning these items is characterized by Hg isotopiccompositions that are significantly different from both theHuancavelica cinnabar ore and the other artifacts.The isotopic overlap between the Huancavelica ores and the

majority of the artifacts is consistent with previous suggestions4

that the Huancavelica region was an important prehistoricsource of cinnabar. However, we cannot eliminate thepossibility that some of the archeological cinnabar might havecome from deposits at Chonta in the Department of Huanuco,Peru (sample C4), Cerro Colorado in the Nor Chicas Province,Bolivia (sample C5), or other deposits that we did not analyze.We are also unable to constrain the Hg isotopic heterogeneitythat may be present in these other cinnabar deposits.Historically, Chonta was exploited only briefly (<100 years),and the Cerro Colorado mine was not utilized at all, despite itsproximity to the huge silver deposit in Potosı, which was animportant center of silver mining and mercury amalgamation.The pre-Inca artifacts we analyzed were recovered from

archeological sites spanning thousands of kilometers and nearly3000 years of Andean prehistory. The oldest artifacts weanalyzed date either to the Initial Period (ca. 1200−800 BC) orEarly Horizon (ca. 800−300 BC) cultural periods and werefound in association with the remains of high-status individualsfrom Northern Peru (Table 2). For example, samples A1 andA2 were excavated in secure archeological contexts from two

different burials of elite individuals at the site of Kuntur Wasi inthe upper Jequetepeque drainage (Figure 1A). Artifactassemblages from Kuntur Wasi indicate that the center engagedin long-distance trade with Chavın de Huantar and othercenters of the Chavın Horizon, which was the first pan-regionalcultural phenomenon in the Andes.33 Four jars of differentshades of cinnabar (samples A3−6; Figure 1A) were similarlyrecovered from Chongoyape in the Lambayeque drainage ofPeru’s north coast in association with a large collection of goldand silver funerary items fashioned in the distinctive Chavınstyle.34 Other cinnabar samples from north coast archeologicalsites include Las Huacas in the middle Jequetepque Valley(sample A7) and Cerro Blanco in the lower Nepena Valley(sample A8). All of these samples show an isotopic signatureconsistent with that of the Huancavelica ores. Thus, our isotopedata suggest cinnabar from the Huancavelica district could havebeen actively traded from deposits in the south centralhighlands of Peru to as far away as the far north coast ofPeru (a distance of over 800 km) almost three thousand yearsago.Mining and metallurgy along Peru’s northern coast increased

dramatically during the Late Intermediate Period (ca. 1000−1250 AD) by communities belonging to the Lambayeque (orSican) culture.35 Lambayeque burials contain some of thelargest caches of precious metals yet discovered in the Americas(e.g., sample A5), and cinnabar pigment is often found coatingtheir gold death masks and other jewelry (Figure 1A). Our Hgisotope data from a Lambayeque burial mask strongly suggestthat Huancavelica remained an important source of cinnabarduring this period of increased metallurgical production.The exchange of cinnabar during the late Middle Horizon/

Late Intermediate Period (ca. 800−1200 AD) extended to thecentral coast of Peru as well. Two wooden burial masks(samples A10 and A11), which radiocarbon date to 890−1150AD (Table S2), are painted red with cinnabar that matchesclosely both Huancavelica ores and the other pre-Inca artifactsfrom northern Peru (Figure 2). Thus, it appears that northernPeruvian cultures did not have exclusive access to Huancavelicacinnabar.Cinnabar from Huancavelica was similarly used for

ceremonial objects after conquest of the Inca (in 1532 AD)as well. Three incised and painted wooden drinking cups calledqeros (samples A12−14; Figure 1A), which radiocarbon date tothe 17th and 18th centuries AD (Table S2), have Hg isotopiccompositions that span nearly the full range of isotopic valuesobserved within the Huancavelica ores (Figure 2). Colonialcinnabar mining of the Huancavelica quicksilver districtexploited three types of deposits, which are classified accordingto their host rock (sandstone, limestone, or igneous rocks).1

The largest of these mines (the Santa Barbara mine) exploitedore contained within the sandstone; however, all three types ofdeposits were mined historically. Thus, the isotopic variabilitywe observe within these qeros and our samples of Huancavelicaores may reflect Colonial mining of deposits unexploited duringpre-Hispanic times.A clear exception is noted in the isotopic composition of

cinnabar associated with a series of large and highly decoratedwooden digging boards (samples A15−17; Figure 1A). Theseitems, which are from the south coast of Peru (Figure 1B) andradiocarbon date to the Inca Empire (Table 2), plot well awayfrom all of the ores and archeological objects we analyzed(Figure 2). Our Hg isotope data therefore suggest that thecinnabar adorning these items was not obtained from

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Huancavelica, making them unique among the archeologicalobjects analyzed. These Inca-era artifacts are generallyinterpreted as digging boards used for agriculture, and elaborateones, such as the specimens we analyzed, probably were used inagricultural rituals associated with these agrarian activities.36

The Hg isotope data indicate the exploitation of a new, perhapsextra-local, source of cinnabar. One possible source may becinnabar deposits in Colombia, two of which we sampled(samples C2 and C3). While additional assessment Colombiancinnabar heterogeneity is clearly needed before we canfingerprint the new source of cinnabar used to decorate theseInca artifacts, our Hg isotope data offer the potential to revealthe evolving exchange of mineral resources through time.Long-Range Transport of Hg Pollution. Cinnabar

mining at Huancavelica left not only a lasting cultural legacybut an environmental one as well. The geographic impact ofpreindustrial Hg emissions would have depended on the Hgspecies emitted. For example, emissions of particulate cinnabardust associated with early cinnabar mining and processingwould have been characterized by a short atmosphericresidence time (hours to days) and thus would have had alimited geographic impact. In contrast, emissions of gaseousHg0 would have the potential to influence the global Hg cyclebecause of the long atmospheric residence time (0.5−2 years)of gaseous Hg0. Preindustrial sources of gaseous Hg0 potentiallyincluded cinnabar retorting, mercury amalgamation, or thesmelting of nonferrous ores containing trace amounts ofmercury.To assess the potential for long-range atmospheric transport

of preindustrial mercury emissions, we measured theconcentration and isotopic composition of Hg in two sedimentcores from Laguna Negrilla and El Junco Lake (Figure 3). TheLaguna Negrilla Hg data have been published previously21 andare presented here on an updated age-depth model (Figure S2).Between about 1000 BC and 1400 AD, Hg concentration andflux are stable and low in both Laguna Negrilla (Hgconcentration: 178 ± 39 ng g−1; Hg flux: 7.1 ± 3.0 μg m−2

y−1) and El Junco Lake (Hg concentration: 76 ± 9 ng g−1; Hgflux: 6.0 ± 0.8 μg m−2 y−1). Increases in both Hg concentrationand flux are noted between 1400 and 1600 AD in both lakes.These increases in Hg, which are synchronous within the 2σuncertainties of the individual age-depth models (Table S4),represent clear departures from otherwise steady rates ofatmospheric Hg deposition over the late Holocene. Moreover,there is no synchronous influx of organic or inorganic materialto either lake or, for El Junco Lake, in the balance of regionalrainfall relative to evaporation.37 Thus, we assert that thesediment cores from both Laguna Negrilla and El Junco recordpreindustrial Hg pollution beginning between 1400 and 1600AD.Due to dating uncertainties, we cannot determine if the initial

rise in Hg pollution occurred during the latest stages of the IncaEmpire or shortly after Hispanic conquest of the Andes in 1532AD. In addition to cinnabar mining for pigment production,Inca metallurgists were highly skilled at smelting a range ofnonferrous ores; both of these activities release Hg to theatmosphere.38−40 In 1564 AD, the Spanish assumed control ofcinnabar mining at Huancavelica, Peru, in response to thedemand for metallic Hg0 for amalgamation. Historical recordsindicate that, over the next ∼250 years, metallic Hg0 productiongradually declined and effectively ended when Peru achievedindependence in 1821 AD (Figure 3A).3 Regional Hgdeposition appears to have declined concomitantly, as

Figure 3. Sediment core Hg results. (A) Sediment core Hgconcentration (symbols), Hg flux (lines), δ202Hg, and Δ199Hg profilesfrom Laguna Negrilla and El Junco Lake since 1500 BC (BC dates asnegative values). The gray shading spans the interval of preindustrialHg pollution (1400−1900 AD). (B) An expanded plot of Hg flux since1400 AD. Also shown in green is registered metallic Hg0 production atHuancavelica, Peru since 1564 AD.2 Time periods corresponding tothe Inca Empire (ca. 1400−1532 AD), the Colonial era (1532−1900AD), the Republican era (1821−1900 AD), and the industrial era(1990−today) are also indicated. (C) Plot of 1/Hg flux against δ202Hgfor both lake sediment cores in which the data can clearly be separatedinto pre- and post-Inca groupings. (D) Plot of 1/Hg flux againstΔ199Hg for both lake sediment cores. The sediment cores samples canbe grouped according to their age.

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evidenced by declining Hg burdens in Laguna Negrillasediment. However, Hg deposition to El Junco Lake increasesthroughout the preindustrial era, rising to over 20 μg m−2 y−1

by 1900 AD (Figure 3A). The steady rise in Hg deposition toEl Junco throughout the preindustrial era suggests the lakereceived Hg from a range of activities (e.g., cinnabar mining,retorting, and mercury amalgamation) occurring at locationsacross the South American Andes. Thus, we suggest thatLaguna Negrilla records Hg emissions associated with cinnabarmining at Huancavelica while El Junco records the long-rangetransport of Hg emitted from a range of processes.Isotopic Legacy of Hg Pollution. The mercuric species

emitted during Colonial and pre-Colonial cinnabar mining,smelting (retorting), and mercury amalgamation carryimplications for the size of the impacted airshed and theisotopic composition of the atmospheric Hg pool. SignificantMDF and MIF of Hg is observed in both the El Junco andNegrilla sediment cores (Figures 3 and 4; Table S1). Sedimentδ202Hg values range from −1.7 to 0.4‰ in Negrilla and from−0.9 to 0.4‰ in El Junco. Sediment Δ199Hg values rangedfrom −0.13 to 0.30‰ in Negrilla and from −0.21 to 0.41‰ inEl Junco.Both sediment cores are characterized by considerable down-

core variability in δ202Hg. This variability implies either the

input of mercury from multiple sources with different Hgisotopic signatures or varying amounts of in situ Hg isotopicfractionation through time, or both. Nonetheless, periods ofhigh Hg delivery to the lakes also tend to be associated withhigher δ202Hg values. For example, peak δ202Hg, Hgconcentration, and Hg flux values co-occur during the Incaperiod in Negrilla and during the industrial era in El Junco(Figure 3). High rates of anthropogenic Hg deposition appearto have similarly shifted sediment Δ199Hg signatures. In ElJunco, preindustrial Hg deposition resulted in Δ199Hg valuesshifting from negative values to near 0‰ (Figure 3). InNegrilla, no significant MIF of Hg was detected in preindustrialsediments. Both lakes record positive Δ199Hg values in 20thcentury sediments.Comparing the lake sediment Hg isotope data with the

results from both the Huancavelica and archeological cinnabarprovides support for the suggestion that anthropogenic Hgemissions can be fingerprinted using Hg isotopes. In general,older (i.e., pre-Inca) sediments within the El Junco Lake andLaguna Negrilla sediment cores tend to be characterized bynegative MDF and MIF of Hg (Figure 4). This implies that Hgdeposited during pre-Inca times underwent recycling within theglobal pool of Hg prior to deposition. In contrast, most of theInca, Colonial, and Republican aged (i.e., 1400−1900 AD)samples overlap with the isotopic composition of cinnabar fromthe Andes, including both the Huancavelica ores and thearcheological artifacts. The preindustrial Hg pollution preservedwithin our sediment cores was likely transported to the lakes aseither particulate cinnabar dustemitted during cinnabarmining and processingor as gaseous Hg0emitted duringthe production of metallic Hg0 or during amalgamation. Weexpect that emissions of cinnabar dust would preserve theisotopic composition of the original ore. In contrast, previousresearch has demonstrated that roasting cinnabar imparts aMDF signature that allows for isotopic distinction betweenroaster mine waste (calcine) and unroasted ore.27,28,41

However, Yin et al. showed that, even with a substantialdifference (up to 8‰) in δ202Hg values between calcine andunroasted cinnabar, an insignificant difference of only ∼0.05‰in δ202Hg values is expected between the released gaseous Hg0

and the unroasted ore.28 Thus, we would not expect asignificant difference in δ202Hg values between gaseous Hg0 andthe starting cinnabar. We, therefore, cannot use Hg isotopes toascertain which species of Hg was emitted during preindustrialtimes; emissions of both particulate cinnabar dust and Hg0

would likely closely match the isotopic composition of theoriginal cinnabar ore. The lack of any significant MIF of Hgassociated with preindustrial Hg pollution indicates that therewas also relatively little MIF associated with preindustrial Hgemissions. Nonetheless, the lake sediment data suggestpreindustrial Hg emissions shifted the Hg isotopic compositionof regional lake sediments.Similar relationships between anthropogenic Hg input and

Hg isotope enrichment have been noted in aquatic sedimentsdirectly impacted by point sources of anthropogenic Hgpollution, with contaminated sediments commonly character-ized by Δ199Hg and Δ201Hg values near 0‰.42 In contrast,mid-Pleistocene marine sediments43 and most terrestrialreservoirs, including soils,19,44 peat,45 lichen,46 and snow,47

commonly display both negative MDF and MIF (Figure 4).This suggests that the release of Hg by industrial activities doesnot impart MIF into sediments, likely because most crustal andmantle Hg sources reveal little, if any, MIF of Hg.25−28 In

Figure 4. Three-isotope plot of δ202Hg and Δ199Hg values from theLaguna Negrilla (circles) and El Junco Lake (diamonds) sedimentcores. Also indicated are the ranges of Huancavelica, pre-Inca, andColonial cinnabar data from Figure 2, and published Hg isotopicvalues for various terrestrial reservoirs (including soil, peat, lichen, andsnow) and precipitation.19,45−50 Lake sediment intervals predating∼1400 AD (i.e., pre-Inca) overlap with published values for terrestrialreservoirs and typically exhibit negative MDF and MIF of Hg.Preindustrial intervals dating to 1400−1900 AD, in contrast, typicallyexhibit small (<0.2‰) or no significant MIF of Hg; these intervals alsotend to overlap with cinnabar ores and artifacts. Industrial-era intervals(i.e., post-1900 AD) overlap with published precipitation values anddo not overlap with either the cinnabar data or published values forterrestrial materials.

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contrast, Hg bound within ancient sediments has likelyexperienced significant recycling within the global pool,including photochemical reduction, which generates MIF ofHg. The same would apply to lake sediments that derive mostof their Hg from the erosion of catchment soils.42

The isotopic composition of 20th century sediments withinboth the El Junco and Laguna Negrilla sediment cores isdifferent than that at any time previous. In general, preindustrialintervals are characterized by Δ199Hg values that are negative ornear 0‰, while post-1900 AD core intervals are characterizedby positive MIF (Figures 3 and 4). The Δ199/201Hg slope ofsediment Hg remains unchanged (0.92 ± 0.12) across thesetransitions (Figure S1), suggesting that the evolution ofatmospheric MIF cannot be explained by a change in theinitiating mechanism of atmospheric Hg MIF. Moreover, thisshift occurs at different depths within each core and, therefore,is not due to the in situ reduction−oxidation cycling ofsedimentary Hg. Instead, we hypothesize that this positive shiftin the MIF of atmospheric Hg reflects the large-scale industrialrelease of gaseous Hg0 into the global atmosphere, initiated bythe global adoption of high-temperature fossil-fuel combustionor by a large-scale change in the cycling of low-latitudeatmospheric Hg. Measurements of Hg in precipitation, whichtoday is dominated by anthropogenic sources, are commonlycharacterized by positive MDF and MIF.47−50 We, therefore,suggest that, in lakes where the rate of Hg sequestration andsedimentation exceeds the rate of Hg loss (via Hg2+ reductionand volatilization of Hg0), sediment cores can faithfully recordthe past isotopic composition of atmospheric Hg. In contrast,the Hg isotopic composition of terrestrial archives, at leastthose that are subaerially exposed for long periods of time (e.g.,peat, lichen, snow, soil), likely incorporates some degree ofphotochemical alteration. We, therefore, conclude that whilethe magnitude of Hg release from New World metal extractionwas comparable to that from later industrial activities, its impacton the global mercury cycle was far less significant and morelocal in nature. Additional Hg isotopic records fromatmospherically sensitive archives (e.g., crater lake sedimentcores) are clearly required to better characterize the uniquenature of 20th century Hg emissions.The cinnabar deposits at Huancavelica, Peru, were among

the most important mercuric deposits ever exploited. The longand complex history of mining and metallurgy produced anarcheological and environmental legacy that we have delineatedusing Hg isotopes. This geochemical fingerprinting providesnew opportunities to decipher the cultural and environmentallegacies of early Hg emissions in this and potentially othermetallogenic provinces.

■ ASSOCIATED CONTENT*S Supporting InformationAdditional experimental details, a list of archaeological materialsincluded in this study, a table of stable Hg isotope results forstandards and samples, a table of radiocarbon results forartifacts and lake sediment samples, a table of 210Pb activitiesand constant flux/constant supply (cf/cs)-derived ages for theEl Junco sediment core EJ6-MW1, a table of [Hg] and Hg fluxdata for the El Junco and Negrilla sediment cores, a plot of199/201Hg ratio in (A) cinnabar and (B) lake sedimentsamples, age-depth models for the Laguna Negrilla and ElJunco sediment cores, and geochemical profiles from the ElJunco sediment core. This material is available free of charge viathe Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: colin.cooke@yale.edu.Present Address‡C.A.C.: Department of Geology and Planetary Science,University of Pittsburgh, Pittsburgh, PA 15260, USA.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis effort is dedicated to the memory of our friend andcolleague, Karl Turekian. Karl’s scientific interests, which didnot adhere to traditional disciplinary boundaries, set the courseof geochemistry that carries forward today and will do so fordecades to come. We thank Ellen Howe, Emily Kaplan, RamiroMatos, Yoshio Onuki, Yuji Seki, Koichiro Shibata, EiseiTsurumi, Yuichi Matsumoto, William Brooks, Mike Rumsey,and Jason Nesbitt for contributing samples. Dan Nelson, WillHobbs, Alex Wolfe, Joel Blum, and two anonymous reviewersprovided valuable feedback on an earlier draft of thismanuscript. The National Geographic Society and YaleUniversity provided funding for this project.

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