Mercury deposition in a tidal marsh downstream of the historic New Almaden

mining district, CA

Christopher H. Conawaya, Elizabeth B. Watsonb, John R. Flandersa, and A. Russell Flegala

a WIGS Laboratory, Department of Environmental Toxicology, University of California at Santa Cruz

b Department of Geography, University of California at Berkeley

Overview

• San Francisco Estuary contaminated by historic mining

– Hydraulic gold mining in Sierra Nevada 1852–1884

– Mercury mining in Santa Clara Valley 1845–1975

Introduction

• Background data

• Mining history at New Almaden

• Current study

Background Sediment Data

• 20 –200 ng/g worldwide average in uncontaminated soils (Adriano 2001; Faure 1998)

• 50 –100 ng/g Northern Coast Range streams (Domagalski 2001)

• 1 –20 ng/g Pacific Coast Ranges (Kerin 2002)

• 200 ng/g upstream of New Almaden (Thomas et al., 2002)

• Surface sediments of estuary 200–600 ng/g (Hornberger et al., 1999; Conaway et al., 2003, Marvin-Dipasquale et al., 2003)

Mining History at New Almaden

• Pre-mining– Native Americans mined cinnabar for

vermilion (D’Itri and D’Itri, 1977)

• Mining era– Large scale development began 1845

– Produced 37 million kg of mercury (Cargill et al., 1980)

• Remediation by DTSC– Contaminated soils 10–1000 ppm on

mine site (Dames and Moore, 1989)

– Downstream concentrations 1–5 ppm (Thomas et al., 2002)

Current Study

• Mercury concentrations exceed regulatory criteria (Davis, 1999; Thompson et al., 2000)

– Water, sediment, fish

• Effect on biota– Humans (Davis 1999)

– Birds (Lonzarich et al., 1992; Hothem et al., 1995, 1998; Hoffman et al., 1998; Hui, 1998)

• What is the natural background?– i.e., what is the contribution of

natural weathering of mercury-rich rocks?

Methods

• Sampling

• Lab analysis

• Dating methods

Sampling

• San Francisco Bay– Gravity coring

– 3 cores in South Bay

• Triangle Marsh– Piston coring

– Tidal marsh where Coyote Creek and Guadalupe River enter estuary

Analysis

• Subsamples sieved to <63 microns to account for grain-size effects

• Digested in hot HNO3/H2SO4

• SnCl2 reduction, Au-amalgamation, CVAFS (Bloom and Crecelius, 1987)

Dating Methods

• AMS 14C dating of shell and organic material

• Appearance of non-native pollen– Eucalyptus

– Plantago lanceolata

• Abundance of Cyperaceae (sedge family) pollen related to ENSO events

Results and Discussion

• Description of core trends

• Assessment of pre-mining

mercury concentrations

• Interpretation of core profile

– Impact of mining

– Other factors

0

50

100

150

200

250

300

0 200 400 600 800 1000 1200 1400 1600

mercury (ng g-1)

de

pth

(c

m)

1983 ± 2 years: dramatic peak in Cyperacea pollen and seeds corresponding to the 1982/83 ENSO event (35 cm)

1945 ± 10 years: beginning of increase in sediment lead concentration (125 cm)

1870 ± 10 years: first appearance of Eucalyptus and Plantago lanceolata pollen (140 cm)

1570 ± 70: 14C date for Spartina foliosa rhizome (240 cm)

Description of Core Trends0

50

100

150

200

250

300

0 200 400 600 800 1000 1200 1400 1600

mercury (ng g-1)

de

pth

(c

m)

1983 ± 2 years: dramatic peak in Cyperaceae pollen and seeds corresponding to the 1982/83 ENSO event (35 cm)

1945 ± 10 years: beginning of increase in sediment lead concentration (125 cm)

1870 ± 10 years: first appearance of Eucalyptus and Plantago lanceolata pollen (140 cm)

1570 ± 70: 14C date for Spartina foliosa rhizome (240 cm)

Assessment of Pre-mining Concentrations

Hornberger et al. 1999 60 ± 10 ng/g

Triangle Marsh 80 ± 30 ng/g

Southern reach 70 ± 10 ng/g

Sample ID and location Depth(cm)

HgT(ng g-1)

Approximate age(y)

±250

San Mateo SM-4 71 128

N37 35.917'W122 15.268'

143 75 1500

242 51 1600

270 72

Oyster Point OP-5 133 61 4000

N37 39.014'W122 16.835'

280 77 4300

Oyster Point OP-6 226 85 3600

N37 40.395'W122 21.049'

232 87 2200

0

50

100

150

200

250

300

0 200 400 600 800 1000 1200 1400 1600

mercury (ng g-1)

de

pth

(c

m)

1983 ± 2 years: dramatic peak in Cyperacea pollen and seeds corresponding to the 1982/83 ENSO event (35 cm)

1945 ± 10 years: beginning of increase in sediment lead concentration (125 cm)

1870 ± 10 years: first appearance of Eucalyptus and Plantago lanceolata pollen (140 cm)

1570 ± 70: 14C date for Spartina foliosa rhizome (240 cm)

Interpretation of Core Profile

• Impact of Hg mining– Dominant contributor

• Other factors– Hydraulic mining debris

– Wastewater

– Hydrography

– Subsidence

Impact of Hg Mining

0

50

100

150

200

250

300

0 200 400 600 800 1000 1200 1400 1600

mercury (ng g-1)

de

pth

(c

m)

1983 ± 2 years: dramatic peak in Cyperacea pollen and seeds corresponding to the 1982/83 ENSO event (35 cm)

1945 ± 10 years: beginning of increase in sediment lead concentration (125 cm)

1870 ± 10 years: first appearance of Eucalyptus and Plantago lanceolata pollen (140 cm)

1570 ± 70: 14C date for Spartina foliosa rhizome (240 cm)

• Production from New Almaden reaches 100 million kg in 1880

• Little production from 1910 to 1940

• Brief renaissance of production in 1940s– surface ore dumps

– open cuts

• Mines close in 1975

Other Factors

• Hydraulic Mining– Contemporaneous– Little sediment transported to

from northern to southern reach (Krone, 1979; Ritson et al., 1999)

• Industrialization– Hydrography

• Increased erosion• Changing sediment sources

– Wastewater• Santa Clara Water Pollution Control

Plant

– Subsidence

Conclusion• Pre-mining mercury concentration

in estuary is about 70 ng/g

• Clear anthropogenic influence in Hg-deposition history

• Complex history beneath profile

• Contribution of natural weathering of Hg-rich rocks to contamination in SFB is relatively small

0

50

100

150

200

250

300

0 200 400 600 800 1000 1200 1400 1600

mercury (ng g-1)d

ep

th (

cm

)

1983 ± 2 years: dramatic peak in Cyperacea pollen and seeds corresponding to the 1982/83 ENSO event (35 cm)

1945 ± 10 years: beginning of increase in sediment lead concentration (125 cm)

1870 ± 10 years: first appearance of Eucalyptus and Plantago lanceolata pollen (140 cm)

1570 ± 70: 14C date for Spartina foliosa rhizome (240 cm)

Acknowledgements

• UCSC

– Liz Kerin, Miranda Spang, Allison, Luengen, Andy Fisher, Glen Spinelli

• UCB

– Roger Byrne, Liam Reidy, Brenda Hamilton

• Others

– Clyde Morris, Gordon Smith, Richard Looker, Khalil Abu-Saba, Roberto Anima, John Callaway, and Tom Grieb

• Funding by the San Francisco Bay Regional Water Quality Control Board, SFEI, UCTSR&TP, and the

W. M. Keck Foundation