Electrochemical Measurement of Toxic Metal Contaminants in the Waters of the Golden

Triangle Area

By: Progga ChirontoniMentor: 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 HealthMetals Main source Health effects Maximum

PermissibleLimit (mg/L of water)

Lead (Pb) natural deposits, plumbing of old households

poor physical growth and learning disabilities in children, kidney problems, and high blood pressure in adults

0.015

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 TechniquesLABORATORY-BASED1. 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-DEPLOYABLE1. X-ray fluorescence2. 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 + 2 +

Stripping step:

ADVANTAGES OF ASV 1. Large linear concentration range- from few mg/L to 0.1μg/L. 2. Sensitivity of less than 0.1 ppb 3. Selectivity 4. Matrix effect immunity to samples with high ionic content 5. Automated analysis and battery powered portable devices can be developed 6. Extremely safe for monitoring, does not require vigorous heating, concentrated acid, etc. 7. Rapid analysis (10-15 min)

8.  Inexpensive Analysis

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 over-voltage 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

Arsenic (III) stripping current vs. depositionpotential

Effect of deposition potential on stripping current

020406080100120140160180

-1000-800-600-400-2000

Deposition potential (mV)

Str

ipp

ing

cu

rren

t (n

A)

Stripping Current Vs Plate time

0

50

100

150

200

250

300

350

400

0 30 60 90 120 150 180 210

Plate Time (sec)

Str

ipp

ing

Cu

rren

t (n

A)

Arsenic (III) stripping current vs. plate time

Optimization: Effect of Supporting Electrolyte Concentration

Hydrochloric acid conc. vs Stripping current

0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2 2.5

Hydrochloric acid conc. (Molarity)

Str

ippi

ng c

urre

nt (n

A)

Plot of Stripping current of As (III) versus the HCL concentration

Interference Peaks• The concentration of copper metal

in drinking water is higher thanother 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 andSabine 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 river2. Filtration of sample

Sample Locations

Sampling locations [A-E] (about every 5 miles upstream)

ResultsMetals Sample

A (ppb)Sample B (ppb)

Sample C (ppb)

Sample D (ppb)

Sample E (ppb)

Beaumont Tap water (ppb)

Port Arthur Tap 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 limitArsenic 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.