Earthworms as a Bioindicator of Mercury Pollutionin an Artisanal Gold Mining Community:

Cachoeira do Piriá, Brazil

Jennifer J. HintonB.A.Sc. Geological Engineering

The University of British ColumbiaDept. of Mining Engineering

Marcello VeigaProfessor of Mining Engineering

Outline of Discussion

Mercury and Artisanal

Gold MiningMercury

in the Environment

Mercuryin Cachoeira

do PiriáThe

Earthworm Protocol

Results

Implications

Worldwide: 13 million artisanal miners in 55 countries.

Continent Number of Miners (million)

Asia/Pacific 6.7 - 7.2Africa 3.0 - 3.7Latin America 1.4 - 1.6Developed countries 0.4 - 0.7Total 11.5 - 13.2

Source: International Labour Organization (1999)

Gold is the main substance extracted:~ 6 million people extracting 300 - 500 tonnes Au/year.

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

Mercury and Artisanal Gold Mining

Mercury (Hg) Emissions:

• Discharged as tailings, vapour, pure Hgo

• 3000 – 4000 tonnes of Hg emitted in the Brazilian Amazon

Exposure Pathways

1. Inhalation

Fish may be contaminated several years after mining activities have ceased

Exposure Pathways

2. Ingestion

Mercury Transformations

Hg(II)Hgo CH3Hg+

(CH3 ) 2HgCH3SHgCH3[HgS, HgS2- HgS2H-...]

Hg-humates, Hg-tannates, Hg-fulvates

[HgCl2, HgOHCl Hg(OH)2...] CH3HgCl

CH3HgOH

?

After Veiga et al. (1999)Bioaccumulation and Biomagnification

Mercury Transformations

70 to 90% of Hg is methylated

Bacteria

MetallicHg

Organic Acids Bacteria

Solublecomplexes

Colloids

CH3Hg+

CH3Hg+

?

Thesis

Cachoeira do Piriá, Brazil

BRAZILBELÉM

Capanema

Cachoeira

Atlantic Ocean

Pará State

BR-316

Gold Rush: 1980 – 1990-attracted 10,000 people (5000 miners) - extracted around 4 tonnes

of gold

“An island of prosperity in a sea of poverty” (Veiga, 1999)

Cachoeira do Piriá, Brazil

More than 4 tonnes of Hg emitted to the environment Elevated Hg levels in biota (fish, pigs, cattle, humans)

Cachoeira do Piriá, Brazil

Wetland Zones

Cachoeira do Piriá

Approx. 1 km

Two Main Mining Areas

RioMacaco

N

Bela Vista

Downstream ~2.5 km

Important Fishing Areas

Soil/Sediment/Tailings Samples(collected 1999-2000)

Cachoeira do Piriá, Brazil

1000

1000

0

Cachoeira – Mercury Distribution

Mercury Concentration (ppb)

1805295

32

397

385

455

700

3730

39201045

189

104401210

135

455

320

202

6

5

13

32

55

15

10

7

55

6

4

513

227

155140

445

4140

120

1720 1230

3120

1435 2950

1090

756

100

1910

905

10500

3120

Approx. 1 km

CurrutelaCreek

BarriquinhaCreek

Lake Cachoeira

Cachoeira

Tailings

Soil/Sediment/Tailings Samples(collected 1999-2000)

Cachoeira – Mercury Distribution (cont…)

Tailings – Revegetation in progress

Effluent from active mining area entering Barriquinha Creek

Cachoeira – Mercury Distribution (cont…)

1000

1000

0

Cachoeira – Mercury Distribution

Mercury Concentration (ppb)

Approx. 1 km

CurrutelaCreek

BarriquinhaCreek

Lake Cachoeira

Cachoeira

Cachoeira – Mercury in Fish

Traíra 925 ppb 68%

Jejú 1274 ppb 100%

Mãe Rosa 667 ppb 63%

Mandi* 108 ppb 0%

Acará 347 ppb 21%

Piaba 215 ppb 0%

FISH Hg (ppb) % > 500 ppb

Herbivorous

Carnivorous

* Mandi omnivorous

CachoeiraAdult Male 2Adult Female 4Child (1-4 yrs) 14

Bela VistaAdult Male 6Adult Female 17Child (1-4 yrs) 56

Exposure Times aboveGroup Safe Limit

A Comparative Methodology

How do materials influence bioavailability?

How to identify/prioritize “hot spots”?

Simple, Low-Cost Methodology Using Earthworms:• Accumulate Heavy Metals from soil and other media

• Ingest large quantities of soil and are in full contact with the substrate they consume

• Participate in many food chains

• Constitute up to 92% of Invertebrate Biomass in soils

• Eisenia foetida species recognized for toxicity testing by several international organizations (Including: European Economic Community, U.S. EPA, ASTM, etc.)

Can bioavailability be reduced?

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

{ }Jars

20 Worms 60g Soil/sand + 80 ml 20 g. cellulose #1

Distilled Water Organic Acids { }

Earthworm Methodology

28d Exposure

CVAADigested tissuesanalyzed#4

DepurationWorms removed, cleaned, weighedand starved for 24 hrs. #2

AcidDigestion

Worms cleaned, weighed andtissues dissolved in 0.7M HNO3#3

Experimental Program

Earthworm Protocol

Solutions Soils / Sediments / Tailings

1. Evaluate the efficacy of the methodology.

6 Series of Tests

2. Determine influence of specific variables.

3. Assess the bioavailability of Hg-organic complexes.

1. Evaluate the efficacy of the methodology.

7 Series of Tests

2. Compare the effectiveness of different soils in inhibiting Hg bioavailability.

3. Assess the influence of organic acids on Hg bioavailability.

B-1

B-2

B-3

B-4

B-5

B-6

B-7

Moisture content assessment

Organic-rich soil and tailings

Humic acid (3) and tailings

3 different soils mixed w. tailings

Humic and tannic acid tailing and lateritic soil

Soils, seds and tails of Cachoeira

Tannic acid tailing / lateritic soil / tails-lat mix

A-1

A-2

A-3

A-4

A-5

A-6

Exposure time / depuration time / experimental design{

Verify A-2 / Hg dose vs. uptake

Humic acid habitability

Hg uptake in humic, tannic acid

MeHg in worms exposed to Hg in humic, fulvic and tannic acid

1. Organic acids and Hg Bioaccumulation

2. Hg Bioaccumulation in Cachoeira

3. Reducing Hg Bioaccumulation in Cachoeira

Solution Tests – Effect of Organic Acids

Metallic Hg Solubility:

0.56 ng g-1 in water

After 24 hr stirring(1-6 g of metallic Hg – excess removed):

1150-8150 g L-1 in tannic acid

3780 g L-1 in humic acid

Solubility directly linked to bioaccumulation

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) 7

Test Description Hg in Tissues* Hg Substrateppb ppb

* Average of replicates shown

Solution Tests – Effect of Organic Acids

Solution Tests - Methylation and Organic Acids

Description

Worms Substrate

MeHg(ppb)

% of Total Hg

MeHg(ppb)

% of Total Hg

HA + Hg 5.22 0.005 0.033 2 x 10-7

HA + Hg 6.19 0.005 0.018 1 x 10-7

TA + Hg 7.42 0.009 0.008 5 x 10-8

TA + Hg 4.22 0.005 0.009 5 x 10-8

TA + Hg 32.2 0.012 0.013 4 x 10-3

FA + Hg 3.14 0.020 0.007 2 x 10-5

FA + Hg 3.11 0.010 0.006 2 x 10-5

Average 4.88 0.009 0.014 7 x 10-6

TA = tannic acid; HA = humic acid; FA = fulvic acid

Methylation Potential of Earthworms

CONTROLS WORMS(with Hg)

WORMS(no Hg)

WORMS(TA, no Hg)

WORMS(HA, no Hg)

WORMS(culture bin)

SRB Innoculant

++ SRB- SRB + SRB ++ SRB + SRB + SRB ++ SRB

- No SRBs+ SRBs probable++ SRBs present

The potential for intestinal methylation of Hg(or direct bioaccumulation of Hg-organic complexes)

warrants further study!!

Soils Tests – Effect of Organic Acids

Hg Solubility - Shake Flasks:

Tailing (10500 ppb) Tannic Acid 210 g/LHumic Acid 110 g/LDistilled Water 12 g/L

Tailing (10500 ppb) 5590 2930 1373Lateritic Soil (150 ppb) 3180 3399 121

Substrate Tannic Acid Humic Acid Water

*Average of replicates shownConcentrations shown are Hg in worm tissues in ppb (g/kg)

Hg Bioavailability – Earthworm Experiments*:

Soils Tests – Effect of Organic Acids

Hg Bioavailability in association with Tannic Acid (TA):Tailing (3180 ppb), Lateritic Soil (135 ppb), and Tail/Lat Mixture (1933 ppb)

Tailing + TA > Lateritic Soil + TA > Tailing:Lat Soil + TA

Increasing bioaccumulation

Tailing (1180 ppb) 129 97 98 48

Humic Acid Distilled Substrate 0.25 g/L 0.125 g/L 0.05 g/L Water

*Average of replicates shownConcentrations shown are Hg in worm tissues in ppb (g/kg)

Hg Bioavailability in association with Humic Acid *:

1. Organic acids and Hg Bioaccumulation

2. Hg Bioaccumulation in Cachoeira

3. Reducing Hg Bioaccumulation in Cachoeira

Bioaccumulation in Cachoeira

Tailings 710 2925 190 3151373 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

Test Description Hg in Worm Tissues* Hg in Soilppb ppb

*Average of replicates shownDistilled water applied to Jars

Wetland Zones

Cachoeira do Piriá

RioMacaco

N

Downstream ~2.5 km

Important Fishing Areas

Bioaccumulation inCachoeira

Mining Areas

Bela Vista

Moderate Vegetation

Dense Vegetation

150(120)

270(1630)

3730(380)

2925(710)

1180(1370) 315

(190)

10500(1373)

90(120)

205(330)

20(430)

440(250)

70(37)

70 (37) clay

20 (430) organic soil

270 (1630) lateritic soil

315 (190) tailings

Hg (ppb) in SoilHg (ppb) in Worms

Options for Mitigation

Information-Based Measures

- Communication of health risks

Wetland Remediation? May exacerbate problem

Permeable or Impermeable walls? Costly; maintenance/monitoring

Phytoremediation/Phytoextraction? Promising but not yet proven

Appropriate Technical Measures

- Use of local materials to cap “hot spots”

- ‘Clean’ lateritic soils or clayey sediments

Reduction of Hg Bioaccumulation

Hg in Tissues* 1370 1247 918 840(ppb)

Tailing Org-rich soil Lateritic Soil Clayey Sediment+ tails + tails + tails

*Average of replicates shown

Hg Bioavailability – Earthworm Experiments*:

Rel. Influence ++ ++ - -on Hg uptake

++ Relatively strong, positive influence on Hg Bioaccumulation+ Positive influence on Hg Bioaccumulation- Negative influence on Hg Bioaccumulation

Hg-organic acid complexation definitely important pathway for Hg bioavailability:

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

Conclusions:

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

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

Significant in terms of current understanding of

biogeochemical cycling of Hg in darkwater systems!

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

Hg pollution in Cachoeira presents hazards to area residents:

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

Conclusions:

Fish Consumption:

Residents of Cachoeira – 2 to 14 times safe ingestion levels

Residents of Bela Vista – 6 to 56 times safe ingestion levels

Soils, Sediments and Tailings:

Hg concentrations range from 5 ppb to 10500 ppb (ave. 695 ppb)

How can Hg pollution in artisanal mining communities

be mitigated?

Appropriate responses to effectively mitigate impacts from artisanal mining activities are critically needed:

Capping using Local Materials:

Clayey sediments highly effective; Lateritic soils also effective (except in the presence of organic acids)

Conclusions:

Non-technical Measures also needed:

- Educational campaigns

- Consumption advisories

Earthworm Methodology:

Low cost, simple method to assess hazards and mitigation measures

Integrated approaches are the most effective!

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!

Dr. Ken Hall – Civil Engineering

Many Thanks:

NSERC Operating Grant #217089

Dr. Malcolm Scoble – Mining Engineering

Dr. Kevin Telmer – University of Victoria

Dr. Marcello Veiga – Mining Engineering

Colleagues and Faculty in the Mining Department

Research Committee:

My Family and Friends