Electrochemical Measurement of Toxic Metal

Report
Electrochemical Measurement of
Toxic Metal Contaminants in the
Waters of the Golden Triangle Area
By: Progga Chirontoni
Mentor: Dr. Andrew Gomes
Dan F. Smith Department of Chemical Engineering,
Lamar University
Texas STEM Conference-2014, Beaumont, TX
Overview
• About Heavy Metals
• Detection Techniques
• Nano-band electrode system and electrochemistry
• Optimization
• Results
• Conclusion
Heavy metals in the environment
• Toxic metals such as lead, cadmium, copper and
arsenic are referred to as heavy metals
• Widespread Occurrence (regulated by federal and
regional agencies)
• Presence of chemical, petrochemical and metal-work
industries in Golden Triangle area
Effects on Human Health
Metals
Main source
Health effects
Maximum
Permissible
Limit (mg/L of
water)
Lead (Pb)
natural deposits,
plumbing of old
households
poor physical growth and 0.015
learning disabilities in
children, kidney problems,
and high blood pressure in
adults
Cadmium (Cd) phosphate fertilizers,
iron, and steel industry,
batteries
Carcinogenic, kidney
problems, poor growth
rate, anemia and
hypertension
0.005
Copper (Cu)
household plumbing
materials and industrial
manufacture
Gastro-intestinal distress
and in the long run,
experience liver or kidney
damage.
1.30
Arsenic (As)
volcanoes, weathering
of arsenic-containing
minerals and ores
skin and internal cancers,
diabetes and
cardiovascular diseases
0.010
Detection Techniques
LABORATORY-BASED
1. Spectrometric techniques (Hydride generation atomic absorption spectrometry
(HG-AAS), Graphite furnace atomic absorption spectrometry (GFAAS), Atomic
fluorescence spectrometry (AFS))
2. Inductively coupled plasma (ICP) techniques (ICP-Atomic emission spectrometry
(AES), ICP-Mass Spectrometry (MS))
3. High performance liquid chromatography (HPLC) and ICP-MS
4. Laser induced breakdown spectroscopy (LIBS)
FIELD-DEPLOYABLE
1. X-ray fluorescence
2. Colorimetric assays (spectrophotometers)
3. Electrochemical methods (Polargraphic techniques, Cathodic stripping
voltammetry (CSV), Anodic stripping voltammetry (ASV))
Anodic Stripping Voltammetry (ASV)
• Principle
Deposition step:  2+ + 2 − →  0
 2+ + 2 − →  0
2+ + 2 − → 0
 3+ + 3 − →  0
Stripping step:  0
 0
0
 0
→  2+ + 2 −
→ 2+ + 2 −
→ 2+ + 2 −
→  3+ + 3 −
ADVANTAGES OF ASV
Large linear concentration range- from few mg/L to 0.1μg/L.
Sensitivity of less than 0.1 ppb
Selectivity
Matrix effect immunity to samples with high ionic content
Automated analysis and battery powered portable devices can be developed
Extremely safe for monitoring, does not require vigorous heating,
concentrated acid, etc.
7. Rapid analysis (10-15 min)
8. Inexpensive Analysis
1.
2.
3.
4.
5.
6.
DISADVANTAGES OF ASV
1. As(V) in the sample has to be chemically reduced to As(III), increasing the sample
analysis time.
2. Interferences
Instrumentation- Nano-band electrode system
• Nano-Band™ Explorer Portable instrument
• Explorer Software to operate the instrument
• Iridium electrode (for Lead, cadmium, copper)
Carbon Nano-Band™ Electrode (for Arsenic)
• Auxiliary electrode (Platinum)
• Reference electrode (Ag/AgCl)
Pictures of the Nano-Band electrode
developed and fabricated at TraceDetect
http://www.envirotechpubs.com/pdf/iet/2005/03/iet200503_046.pdf
Advantages of Nanoelectrodes
• Enhanced mass transport
• Signal amplification
• Greater number of measurement points
• Great scope for parallel measurements
• No requirement of removal of dissolved oxygen
• More inert and much less sensitive to accidental overvoltage conditions
Disadvantages of Nanoelectrodes
• Surface-fouling
• Fragility
Procedure
• Cleaning the Electrodes
• Electrode Set up and Thin film plating
- Carbon electrode and gold plating solution for As
- Iridium electrode and mercury plating solution for Pb,
Cd and Cu
• Conditioning
• Verification
• Screening the sample for dissolved metal ion
• Method of Standard addition
Method of Standard Addition
Voltammograms for lead standards (left) and the calibration curve
(right).
Optimization: Deposition Potential and Plate Time
Stripping Current Vs Plate time
180
160
140
120
100
80
60
40
20
0
400
Stripping Current (nA)
Stripping current (nA)
Effect of deposition potential on stripping current
350
300
250
200
150
100
50
0
0
-200
-400
-600
-800
-1000
Deposition potential (mV)
Arsenic (III) stripping current vs. deposition
potential
0
30
60
90
120
150
180
210
Plate Time (sec)
Arsenic (III) stripping current vs. plate
time
Optimization: Effect of Supporting Electrolyte
Concentration
Hydrochloric acid conc. vs Stripping current
Stripping current (nA)
80
70
60
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
Hydrochloric acid conc. (Molarity)
Plot of Stripping current of As (III) versus the HCL
concentration
Interference Peaks
• The concentration of copper metal
in drinking water is higher than
other metals
• So ASV scans usually have Copper
interference peaks
Ways to remove interference:
• KI solution
• Peak separation and Analysis
software
ASV scan of 20 ppb arsenic (III) in 2 M HCl having
copper interference peak around 450 mV
Sampling
•
•
•
•
•
Samples were collected from
1.
29 different locations in the
Golden Triangle area.
From both upstream and
downstream Neches river and
Sabine lake, samples were collected.
pH and conductivity were measured.
Hydrochloric acid was added until
their pH was 2.
Filtered with PTFE membrane filter.
2.
1. Neches river
2. Filtration of sample
Sample Locations
Sampling locations [A-E] (about every 5 miles upstream)
Results
Metals
Sample
A (ppb)
Sample
B (ppb)
Sample
C (ppb)
Sample
D (ppb)
Sample
E (ppb)
Beaumont Port
Tap water Arthur Tap
(ppb)
water
(ppb)
Max.
Permissible
limit (ppb)
Pb
3.4
2.8
4.2
8.1
4.9
2.9
4.2
15.0
Cd
**
**
0.004
0.075
**
**
**
5.000
Cu
379.4
168.0
573.5
686.2
298.3
312.7
483.6
1300.0
Concentration of heavy metals found in water samples in parts per billion
** Below detection limit
Arsenic could not be detected in any of the samples
Conclusions
• Heavy metals such as Pb, Cd, Cu are present in the waters of
golden triangle area
• Within the permissible limit determined by EPA
• No immediate danger of metal contamination in this area
• Should be monitored in both day and night
Future Works
•
•
•
Extend this research outside Golden Triangle Area in South
Texas
Analysis of organic chemicals in waters of Golden triangle
area: organoarsenic, atrazine, diazinon, metalachor, and
trenbolone
Explore different detection techniques like Liquid
chromatography and Mass spectrometric methods
Acknowledgements
• Department of Chemical Engineering, Lamar University
• Department of Chemistry and Biochemistry, Lamar University
• Office for Undergraduate Research (OUR), Lamar University
• Research Enhancement Grant, College of Engineering
References
•
Bryan, G.W., W.J. Langston, “Bioavailability, accumulation and effects of heavy
metals in sediments with special reference to United Kingdom estuaries; a review”,
•
Environmental Pollution, 76 (1992), pp. 89–131.
•
Millward, G.E., A. Turner, Metal pollution ,in: J.H. Steele, S.A. Thorpe, S.A. Turekian
Encyclopedia of Ocean SciencesAcademic Press, San Diego, CA (2001), pp.
1730–1737.
•
CSEM (Case Studies in Environmental Medicine), Agency for Toxic Substances and
Disease Registry, Lead Toxicity, WB 1105, August 20 (2010).
•
Hem, J.D. Water Resources Res (1972), 8, 661-679.
•
Environmental Protection Agency, www.epa.gov.
•
Texas Annual Water quality report 2012, City of Beaumont, Water Utilities Department.

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