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Monitoring Heavy Metals in River Water Receiving Mine Water Discharge using the Diffusive Gradients
in Thin-‐film technique (DGT)
Trang HUYNH and Sue VINK The University of Queensland, Australia
-‐ The Fitzroy River Basin (FRB) is the home to QLD’s major mining acKvity -‐ Since 2008-‐2009 wet season, the FRB catchment was subject to prolonged and intense periods of rainfall.
-‐ In order for the mines to operate water needs to be released from the mine-‐sites into the rivers.
-‐ Mining are permiUed to discharge mine water under condi2ons specified in EA issued under the EP Act 1994.
-‐ Water quality needs to be assessed based on QLD guidelines to protect the aqua2c biota of FRB.
-‐ Mul2ple grab samples analyses are required during and a@er mine water releases, this costly in term of both analyses and personnel Kme.
Background
Research QuesDon: DGTs vs Grab samples
Can the in-‐situ and Kme-‐integrated Diffusive Gradients in Thin Films technique (DGT) replace the series gab samples to determine metal concentraKons in river water receiving mine water discharge?
(Modified from Lorax, 2002)
tADgMC
d
DGTΔ
=Diffu
sive
gel
Res in gel
Δg
C
water M2+ diffusion
1 2 mm
CSOL
Filter Piston holder
M: measured mass
Δg: diffusive layer thickness
A: area of the exposure window
t: deployment Dme
D: diffusion coefficient
Principles of the DGT
ML
L M2+ M2+
M2+
M2+
M2+
M2+
M2+
M2+
M2+
M2+
(Zhang and Davison, 1995)
• Allow solutes to pass easily • No reacKon with solutes • Defined thickness • Hydrophilic • Diffusion of metals similar to water
Diffusive Layer
ü Time integrated
ü Independent of pH, ionic strength
ü SpeciaKon (diffusion, reacKons)
ü Simple field deployment
ü MulKmedia
Key ProperDes of DGT
Trials Purposes Laboratory trial (5-‐15/1 2015)
• High fluctuaDon of metal concentraKons in the water
• Simulated changes in concentraKons to mimic water condiKon fluctuaKon when river receiving mine water
Isaac River (29/1-‐13/2 2015)
• InsensiKve DGT trial: before, during and a@er the mine water released program at upstream and downstream of mine release points during release events
• Coincident with mine site water quality monitoring Recycle water dams (24/4-‐ 8/5 2015)
• This trial is represenKng a lower fluctuaDon condiKon in mine water chemistry and metal concentraKons
Review of Metal/loid ConcentraDons monitoring data of river water (2/2010 to 5/2013)
Dissolved conc. (µg/L) Al As Cd Cr Cu Pb Ni Zn Mn Se
Min 1 0.001 0.0001 0.001 0.01 0.002 0.006 0.01 0 0.002 Max 127,000 76 232 331 537 820 31,000 4,670 7,730 5,000 Median 5,200 2 0.1 11 7 3 11 17 130 2.5 N 834 806 811 850 875 806 831 873 771 865 TV95% 55 24 0.2 10 1.4 3.4 11 8 1,900 11 N of Exceedance 785 1 338 432 824 331 394 646 5 54
% Exceedance 94 0 42 51 94 41 47 74 1 6
Laboratory ValidaDon Experiment
Sample RaDonale and Experimental Design -‐ River water (the Mackenzie) were spiked with different levels of metals (As, Cd, Cu, Ni, Pb & Zn) to create 5 test waters
-‐ Water columns were diluted (by simulated rain waters) -‐ 12 grab samples per test water were collected for analysis -‐ 3 replicates per treatment and 7 replicates for in-‐house QA/QC
Chemical ProperDes of Test Waters Parameters! Ranges!pH! 7.7 -‐ 8.2!EC (mS/cm)! 0.4 -‐ 0.5!TDS (mg/L)! 284 – 300!WH (mg/L CaCO3)!
100 – 112!SAR! 1.9 -‐ 2.0!Cl (mg/L)! 62 – 67!SO4
2-‐ (mg/L)! 14 – 22!TSS (mg/L)! 6 -‐ 45!
Metal/ metalloids
Ranges (µg/L) Total Dissolved
Al 44 – 380 1 – 26 As 0.5 – 81 2 – 71 Cd 1 – 56 1 – 45 Cr 0.1 -‐ 0.5 0.1 -‐ 0.12 Cu 2 – 195 2 – 102 Ni 3 – 42 3 – 23 Pb 0.2 – 71 5 – 8 Zn 43 – 94 2 – 37
Laboratory ValidaDon Results
0
20
40
60
80
100
Cd (µ
g/L)
Grab sample dissolved conc. Labile DGT conc. Mean grab samples +SD Mean grab samples -‐SD Mean grab samples
0
40
80
120
1 2 3 4 5 6 7 8 9 10 11 12 Zn
(µg/L)
Times (12hrs interval)
0
40
80
120
1 2 3 4 5 6 7 8 9 10 11 12
Cu (µ
g/L)
Times (12hrs interval)
0
50
100
150
As (µ
g/L)
Bioavailability of Copper in Water: DGT Measurements and MINTEQ Modelling
0 20 40 60 80
100 120 140
1 2 3 4 5 6 7 8 9 10 11 12
Cu (µ
g/L)
Times (12hrs interval)
Grab sample 0.45um
Mean grab samples
Labile DGT conc.
Modelling Inorganic Cu
Mean Modelling Inorganic Cu
Decision tree for metal specia2on guideline (ANZECC, 2000)
Applica2on of DGT in ANZECC
Field Trials – Isaac River, Central QLD
Water Chemistry Isaac River Waters
Sampling sites/dates
Cherwell Creek Bridge (CCB)
Isaac River upstream Cherwell Creek (IRCC)
Isaac River Down Stream (IRDS)
Isaac River Highway Bridge (IRHB)
29/01 to 12/02/15 29/01 to 19/02/15 29/01 to 19/02/15 29/01 to 12/02/15
pH 7.8 7.7 8.1 7.9 8.0 8.1 7.9 8.0 8.1 8.1 8.0 7.5 7.8
EC (µS/cm) 553 995 613 442 373 404 445 2270 408 491 496 214 358
TSS (mg/L) 67 524 17 83 30 35 87 524 16 <1 103 784 <1
WH (mg/L CaCO3)
106 142 112 70 83 93 72 300 89 105 78 58 85
SAR 2 5 3 3 2 2 3 9 2 2 3 1 2
Cl (mg/L) 105 168 82 73 49 53 67 390 58 62 116 31 40
SO42-‐(mg/L) 44 123 59 18 12 13 18 333 17 23 23 5 7
DOC (mg/L) 7.5 7.1 5.4 6.2 10.4 5.0 6.2 6.7 4.7 4.5 6.1 6.0 4.4
Field Trial Results: DGT vs Grab samples (Copper)
0.0
1.0
2.0
3.0
Cu (µ
g/L)
DGT CCB DGT-‐IRCC DGT-‐IRDS DGT-‐IRHB Grab CCB Grab IRCC Grab IRDS Grab IRHB Mean Grab CCB Mean Grab IRCC Mean Grab IRDS Mean-‐IRHB
LOR
0 1 2 3 4 5
CCB IRCC IRDS IRHB Cu (µ
g/L)
Grab-‐total Grab dissolved DGT ANZECC (TV 95%)
• The concentraDons of Cu measured by the DGT were significantly lower than total and dissolved Cu.
• The bioavailable Cu concentraDons at 4 sites are well above the lower of report value (LOR)
• High variaDon in total & dissolved Cu conc. during the trial.
DGT vs Grab samples: Zinc
0
1
2
3
4
Zn (µg
/L)
DGT CCB DGT-‐IRCC DGT-‐IRDS DGT-‐IRHB Grab CCB Grab IRCC Grab IRDS Grab IRHB Mean Grab CCB Mean Grab IRCC Mean Grab IRDS Mean-‐IRHB
LOR
0
2
4
6
8
10
CCB IRCC IRDS IRHB
Zn (µ
g/L)
Grab-‐total Grab-‐dissolved DGT LOR
• Total Zn concentraDons in water were high, however most of dissolved Zn were below the LOR
• The bioavailable Zn measured by DGT were detected and well above the lower of report value (LOR)
Water Chemistry of Recycle Water Dams
Sites Ranges pH 8.2 -‐ 9.2 EC (µS/cm) 8,000 – 11,000 TDS (mg/L) 5,450 -‐ 7,500 TSS (mg/L) 3 – 20 WH (as mg/L CaCO3)
900 – 980
SAR 20 – 35 Chloride (mg/L) 1,640 – 2,020 SO4
2-‐ (mg/L) 1,224 – 2,256 DOC (mg/L) 4.5 -‐ 12
Metal/ metalloids
Ranges Total (µg/L) Dissolved (µg/L)
Al 4 – 10 1 – 2 As 4 – 5 3 – 4 Cd BDL BDL Cr 0.1 – 0.4 0.1 – 0.4 Cu 0.4 – 0.6 0.3 – 0.5 Fe 7 – 22 4 – 6 Ni 2 – 9 2 -‐ 8 Zn BDL BDL
Recycle water dams (Al & As)
Recycle water dams (Co & Cu)
EsDmated Cost Comparison* ConvenKonal grab sampling Unit Per Unit Total
Analysis (AUD) 4 65 260 Deloyment/sampling 4 60 240 Total 500 Time-‐integrated DGT sampling Unit Per Unit Total DGT unit (AUD) 1 25 25 Analysis (AUD) 1 65 65 Deloyment/sampling 2 120 240 Total 330 Cost saving (%) for 4 days deployment 34 *This es<ma<on based on 4 days water release and grab samples are taken everyday and price based on research rate
Key Findings: Laboratory trial • The DGT measurement is comparable to the averaged concentraKon of 12 grab samples over the 7 days trial (except Cu).
• The labile concentraKons measured by the DGT were significantly lower, 13% and 23% respecKvely, than the measured total and dissolved Cu concentraKons.
• The bioavailable concentraKons of other metals including Cd, Ni and Zn ranged from 60% to 80% of the measured dissolved concentraKons.
Key Findings: Field trials • The bioavailable concentraKons heavy metals in Isaac river water measured by the DGT were significantly lower than that of total and dissolved concentraKons.
• Cd in water at 4 study sites was not detected by both DGT and grab sampling.
• In some cases, As and Zn was not detected by grab sampling but was detected by the DGT at a low concentraKon and well above LOR.
Mechanism of the CollaboraDon and Partnership
Decision tree for metal specia2on guideline (ANZECC, 2000)
Recommenda2on and Future Work DGT measurement will replace 4 steps for assessing metal/loid toxicant in water in the ANZECC decision tree
Thank You & Questions
Contact details: Dr. Trang Huynh [email protected] Dr. Sue Vink [email protected]
References: Reducing AnalyDcal and Water Quality Monitoring Costs using Diffusive Gradients in Thin Films (DGT) Technique (Project C23027 ACARP)