2011-07-11

1

Predicting toxicity of future combined pit lakes at the former Steep Rock Iron Mine

near Atikokan, Ontario

Amy L. Godwin1, Peter F. Lee1, Andrew G. Conly2 and Andrea R. Goold1

1Department of Biology2Department of Geology

LUMINX-LUEL-ATRC

Location

Hogarth

Caland

Errington

Robert’s

Hogarth Pit looking southeast, ca. 1970’s

Original Lake Level

History

Courtesy J. Baechler

The Issues

West Arm

Middle Arm/Hogarth

East Arm/Caland

Atikokan

Nature of the Pit Lakes

• Typical pH for both pit lakes is 7 to 8• Caland

– Stratified (only upper 20 m oxygenated)– Non-toxic (hosted a fish farm)

• Hogarth– Previously non-stratified– Oxygenated– Toxic

Toxicity of the Hogarth Pit Lake

• Ten years of toxicity tests at Lakehead University:

1. Explore nature of toxicity (Daphnia magna LC50 test)

2. Determine changing nature and source of toxicity

• Ceriodaphnia magna LC50 test

• Toxicity Indicator Evaluation (TIE)

3. Predict future nature of toxicity

in merged pit lake with wall

rock interaction

• Lemna minor IC25 test

IMWA 2010 Sydney, Nova Scotia | “Mine Water & Innovative Thinking”

© by Authors and IMWA

2011-07-11

2

Acute and Chronic Tests

ACUTE

• May 1999: Daphnia magna

• June & July 2004:

– Rainbow trout

CHRONIC

• November 2004 – July 2006:

– Ceriodaphnia dubia– Lemna minor

• TIE tests

– Daphnia magna • Mock Effluent tests

– Ceriodaphnia dubia• Growth inhibition tests

– Lemna minor

PREDICTIVE MODELING: · Growth inhibition tests using Lemna minor

Predictive Modeling: Growth inhibition testsGrowth inhibition tests were conducted using Lemna

minor• Static column experiments:

• Varying water ratios from the two pit lakes• Geological influence of wall rocks

• Resultant water represented future water quality of the• Resultant water represented future water quality of the merged pits as they fill:• Used in Lemna minor growth inhibition tests

• Analysis and Alternate Endpoints:– IC25 (ToxCalc v5.0)– Dry weights– Chlorophyll-a concentration– Frond surface area

• (total, by colour – dark green, light green, yellow (chlorotic), white (necrotic)

Predictive Water Quality

Crushed (1-2 mm) wall rock(amount =

24 in exposed surface area of pit wall rock@ outflow)

Mix of Hogarth &Caland water

Water:rock ratio (by mass) = 10:1

Predictive Water Quality

1

10

Column 1 Column 2 Col 3 umnCol 4 umnCol 5 umnC l 6o

nc

entr

atio

n N

orm

aliz

ed

to

Cal

and

200

6 W

ate

r

pH SO4

2- Ca+Mg Na+K TotalMetal

0.1

Col 6 umnCol 7 umnCol 8 umnCol 9 umnCol 10 umn

Hog06 EC25 range (see Section 5)

Co

Column 1 2 3 4 5 6 7 8 9 10

Hogarth (water sample depth) n/a 2 m 30 m 30 m 30 m 2 m 2 m 2 m n/a 30 m

Caland (water sample depth) 2m n/a 2 m 2 m 2 m 30 m 30 m 30 m 30 m n/a

% Caland water 100% 0% 10% 25% 50% 10% 25% 50% 100% 0%

Acute Tests - Results

• 1999: Daphnia magna– LC50 = 100% mortality in

48 hours

– Source: fluctuations in SO4

2-, Ni2+, Mg2+, iron floc

• June and July 2004: Rainbow trout and D. magna– No mortality

floc

Chronic Tests - Results

• Nov. 2004: Ceriodaphniadubia– IC50 > 100% Hogarth 2m

• Jan., May, June, Nov. 2004; Jan., June, July 2006:– Highly variable results

• TIE Tests: January 2005– Only the EDTA 8 mg/L

manipulation reduced toxicity:

• Indicates toxicity due to cationic metals and/or some non-metal ions (Ca2+, Mg2+)

• Isolated elevated Pbt (0 0885 /L) >

• All subsequent tests showed IC25 > 100% except winter months:– Cond., Ca2+, Mg2+, SO4

2-, TDS elevated during winter months

event (0.0885 mg/L) > CWQG 0.007 mg/L

– January 2006 TIE manipulations resulted in no reductions in toxicity

• No sources determined

IMWA 2010 Sydney, Nova Scotia | “Mine Water & Innovative Thinking”

© by Authors and IMWA

2011-07-11

3

Mock Effluents - Results

• Investigations into TDS-related toxicity:– Elevated TDS levels in Hogarth account for the

majority of the toxicity

– BUT: The reduction in toxicity due to EDTA addition (TIE tests) indicates that metals may be a minor toxicant as well

• Lemna minor was less affected than other species tested– Signs of stress at greater concentrations of

Hogarth:• Small, unhealthy fronds, chlorotic tissue, shorter roots• Due to elevated TDS levels (2000 mg/L), mainly SO4

2-

Predictive Modeling - Results

Control

Caland 2 m + Hogarth 30 m

Caland 30 m + Hogarth 2 m

Predicted outflow water

EC25

86.7%

43.1%

Predictive Modeling - Results• Unexpected IC25 values

(>100 % Hogarth 30 m water)– Plants showed definite signs

of stress

• Small fronds, chlorotic and necrotic tissue, colony destruction

• One-way ANOVA: – No differences in dry weights

in any treatments

Compound side fronds

Side frond attaching narrowly

• One-way ANOVA:

– Lower total frond surface area in all treatments compared to controls

1 2 3 4 5 6 7 8 9 10 Control

Sur

face

Are

a (c

m2 )

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Dark Green areaLight Green areaYellow area White area

Predictive Modeling -Results

– More chlorotic and necrotic tissue in certain treatments

– Once the effect of dry weight was controlled, chlorophyll-a content was shown to be reduced by Hogarth 2 m water

Column

% Hogarth water0 20 40 60 80 100 120

Chl

orop

hyll

(ug/

g)

500

1000

1500

2000

2500

3000

3500

4000

4500ANCOVA-adjusted Hogarth 2 m x Caland 30 mANCOVA-adjusted Hogarth 30 m x Caland 2 mANCOVA-adjusted control values

Conclusions

• Frond counts + IC25 calculations– GREATLY underestimate toxicity

• Include small fronds and dead or chlorotic fronds

• Chlorophyll-a and surface area measurements give better estimates of toxicity:

F t it l k t lit ill ti l i t– Future pit lake water quality will negatively impact aquatic macrophytes

• Likely due to elevated Ca2+, Mg2+, and SO42-

• No longer acute toxic effects

• Dynamic nature of the pit lakes is producing a chronic toxic effect, now and in the future

IMWA 2010 Sydney, Nova Scotia | “Mine Water & Innovative Thinking”

© by Authors and IMWA