Earthworms as a Bioindicator of Mercury Pollution

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The University of British Columbia Dept. of
Mining Engineering
Earthworms as a Bioindicator of Mercury
Pollution in an Artisanal Gold Mining
Community Cachoeira do Piriá, Brazil
Jennifer J. Hinton B.A.Sc. Geological Engineering
Marcello Veiga Professor of Mining Engineering
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Outline of Discussion
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Mercury and Artisanal Gold Mining

• Worldwide 13 million artisanal miners in 55
  countries.

• Mercury (Hg) Emissions
• Discharged as tailings, vapour, pure Hgo
• 3000 4000 tonnes of Hg emitted in the Brazilian
  Amazon

• 80 to 100 million people worldwide depend on
  this activity
• for their livelihood.

Gold is the main substance extracted 6 million
people extracting 300 - 500 tonnes Au/year.
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Exposure Pathways
1. Inhalation
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Exposure Pathways
2. Ingestion
Fish may be contaminated several years after
mining activities have ceased
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Mercury Transformations
CH3SHgCH3
(CH3 ) 2Hg
HgS, HgS2- HgS2H-...
Hgo
Hg(II)
CH3Hg
HgCl2, HgOHCl Hg(OH)2...
Hg-humates, Hg-tannates, Hg-fulvates
CH3HgCl CH3HgOH
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Mercury Transformations
70 to 90 of Hg is methylated

Bioaccumulation and Biomagnification
After Veiga et al. (1999)
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Cachoeira do Piriá, Brazil
BRAZIL
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Cachoeira do Piriá, Brazil
An island of prosperity in a sea of poverty
(Veiga, 1999)

• Gold Rush 1980 1990
• attracted 10,000 people (5000 miners) -
  extracted around 4 tonnes
• of gold

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Cachoeira do Piriá, Brazil

• More than 4 tonnes of Hg emitted to the
  environment

• Elevated Hg levels in biota (fish, pigs,
  cattle, humans)

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Cachoeira do Piriá, Brazil
Bela Vista
Downstream 2.5 km
Cachoeira do Piriá
Rio Macaco
Approx. 1 km
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Cachoeira Mercury Distribution
Soil/Sediment/Tailings Samples (collected
1999-2000)
Cachoeira
Currutela Creek
Tailings
Lake Cachoeira
Barriquinha Creek
Mercury Concentration (ppb)
Approx. 1 km
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Cachoeira Mercury Distribution (cont)
Tailings Revegetation in progress
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Cachoeira Mercury Distribution (cont)
Effluent from active mining area entering
Barriquinha Creek
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Cachoeira Mercury Distribution
Cachoeira
Currutela Creek
Lake Cachoeira
Barriquinha Creek
Mercury Concentration (ppb)
Approx. 1 km
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Cachoeira Mercury in Fish
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A Comparative Methodology

• How to identify/prioritize hot spots?

• How do materials influence bioavailability?

• Can bioavailability be reduced?

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Invertebrate Protocols
ASTM 1676-95 Standard Guide for conducting
laboratory soil toxicity tests for the Earthworm
Eisenia foetida



US EPA 600R94024 Methods for measuring the
Toxicity and Bioaccumulation of
Sediment-Associated Contaminants with Freshwater
Invertebrates




ASTM 1383-93A Standard Guide for Conducting
Sediment Toxicity Tests with Freshwater
Invertebrates
Lockheed Martin Environmental Restoration
Program Development and Validation of
Bioaccumulation Models for Earthworms
Goats and Edwards (1988) Prediction of Field
Toxicity of Chemicals to Earthworms by Laboratory
Methods

Hazardous Materials Assessment Team (HMAT)
14-Day Soil Test using Earthworms
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Earthworm Methodology
28d Exposure
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Experimental Program
Earthworm Protocol
Solutions
Soils / Sediments / Tailings
7 Series of Tests
6 Series of Tests
1. Evaluate the efficacy of the methodology.
1. Evaluate the efficacy of the methodology.
2. Compare the effectiveness of different soils
in inhibiting Hg bioavailability.
2. Determine influence of specific variables.
3. Assess the bioavailability of Hg-organic
complexes.
3. Assess the influence of organic acids on Hg
bioavailability.
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Solution Tests Effect of Organic Acids
Solubility directly linked to bioaccumulation
Metallic Hg Solubility 0.56 ng g-1 in water
After 24 hr stirring (1-6 g of metallic Hg
excess removed) 1150-8150 mg L-1 in tannic
acid 3780 mg L-1 in humic acid
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Solution Tests Effect of Organic Acids
Test Description Hg in Tissues Hg
Substrate ppb ppb
Series A-1 2693 (sd 244) 828 2655 (sd
1041) 828 Series A-2 2499 (sd 875)
828 5680 (sd 1625) 828 Series A-3 4359
(sd 1463) 1424 Control worms 178 (sd 15)
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Average of replicates shown
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Solution Tests - Methylation and Organic Acids
TA tannic acid HA humic acid FA fulvic
acid
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Methylation Potential of Earthworms
The potential for intestinal methylation of
Hg (or direct bioaccumulation of Hg-organic
complexes) warrants further study!!
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Soils Tests Effect of Organic Acids
Hg Solubility - Shake Flasks
Tailing (10500 ppb) Tannic Acid 210
mg/L Humic Acid 110 mg/L Distilled Water
12 mg/L
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Soils Tests Effect of Organic Acids
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Bioaccumulation in Cachoeira
Test Description Hg in Worm Tissues Hg in
Soil ppb ppb
Tailings 710 2925 190
315 1373 10500 Lateritic Soil 120
150 1630 270 1370 1180 120
90 Organic-rich Soil 380 3730
330 205 430 20 Clayey
Sediment 37 70 250 440
Average of replicates shown Distilled water
applied to Jars
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Bioaccumulation inCachoeira
70 (37)
Bela Vista
440 (250)
Downstream 2.5 km
20 (430)
205 (330)
Wetland Zones
90 (120)
Cachoeira do Piriá
2925 (710)
3730 (380)
10500 (1373)
270 (1630)
1180 (1370)
315 (190)
150 (120)
Rio Macaco
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Options for Mitigation

• Wetland Remediation?

• Permeable or Impermeable walls?

• Phytoremediation/Phytoextraction?

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Reduction of Hg Bioaccumulation
Hg Bioavailability Earthworm Experiments
Tailing Org-rich soil Lateritic Soil Clayey
Sediment tails tails
tails
Hg in Tissues 1370 1247 918
840 (ppb)
Average of replicates shown
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Conclusions
Hg-organic acid complexation definitely important
pathway for Hg bioavailability

• Solutions Concentrations in Worm Tissues of 2499
  - 6296 ppb following exposure to Hg in tannic
  acid.

• Tailings 200-540 more uptake in association
  with humic and tannic acids than with distilled
  water.

• Lateritic Soil 100-2810 more uptake in
  association with humic and tannic acids than
  distilled water.

• Intestinal Methylation? Methylmercury
  bioccumulation orders of magnitude higher in
  worms than substrate. Also presence of SRBs.

Significant in terms of current understanding
of biogeochemical cycling of Hg in darkwater
systems!
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Conclusions
Hg pollution in Cachoeira presents hazards to
area residents

• Soils, Sediments and Tailings
• Hg concentrations range from 5 ppb to 10500 ppb
  (ave. 695 ppb)

• Tailings-associated Hg Mobilizing from mining
  areas into organic-acid rich watercourses.

• Fish Consumption
• Residents of Cachoeira 2 to 14 times safe
  ingestion levels
• Residents of Bela Vista 6 to 56 times safe
  ingestion levels

How can Hg pollution in artisanal mining
communities be mitigated?
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Conclusions
Appropriate responses to effectively mitigate
impacts from artisanal mining activities are
critically needed

• Earthworm Methodology
• Low cost, simple method to assess hazards and
  mitigation measures

• Capping using Local Materials
• Clayey sediments highly effective Lateritic
  soils also effective (except in the presence of
  organic acids)

• Non-technical Measures also needed
• - Educational campaigns
• - Consumption advisories

Integrated approaches are the most effective!
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Recommendations

• Replicate earthworm experiments statistical
  confidence in results.

• Assess the methylation potential of earthworms.

• Explore mechanisms influencing Hg uptake from
  lateritic soils in conjunction with organic acids.

• Conduct Risk Assessment in Cachoeira and Bela
  Vista.

• Develop remediation technologies appropriate to
  artisanal mining communities.

• Develop educational programs and consumption
  advisories.

Artisanal Mining is an essential economic
activity concrete solutions must be developed!
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Many Thanks

• NSERC Operating Grant 217089

• Colleagues and Faculty in the Mining Department

• My Family and Friends

Research Committee

• Dr. Marcello Veiga Mining Engineering

• Dr. Ken Hall Civil Engineering

• Dr. Malcolm Scoble Mining Engineering

• Dr. Kevin Telmer University of Victoria