Hexavalent Chromium in Drinking Water - ftp.weat.orgftp.weat.org/Presentations/Jay_Gandhi_Hexchrom.pdf · • For DW, due to Chlorine as disinfectant, ammonium salt added to sample

Hexavalent Chromium in Hexavalent Chromium in Drinking WaterDrinking Water

myths and mysteries resolvedUSEPA Method 218.7

Presented byJay Gandhi, PhD – Metrohm USAJohnson Mathew – USEPA Region 6 (Houston)E. Prince – U of H – Clearlake (Houston)

WEAT 2012 - Austin TX (Dr. Jay Gandhi) 1


Disclaimer – working with USEPA

*Reference herein to any specific commercial products or nonprofit organization, process, or service by trade name, trademark, manufacturer, or other-wise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government and shall not be used for advertising or product endorsement purposes.


What weWhat we’’ll cover todayll cover today

• USEPA method for Chromium-6 Analysis – A Collaborative approach with USEPA• Principle of the method• Hexavalent Chromium Analysis• USEPA Method 218.7….. Updated from 218.6

• Sample Preservation Study• Various Buffer Chemistries• Data for Sample Preservation study• Data from common Drinking water matrix

• Summary


Background

• Environmental Working Group Study • www.ewg.org – December 2010 report (pdf)• 31 cities in US – affected by Cr+6 in drinking water• Watch group studies indicate that 89% of US water

utilities (water supply) have Cr+6 in their DW

• News media picked up this report http://thechart.blogs.cnn.com/2010/12/20/carcinogen-found-in-31-of-35-cities-water-supply/

• EPA’s response to investigation


Background

• Cr+6 & human health?• “This study clearly identifies a linear trend of increasing risk of

lung cancer mortality with increasing cumulative exposure to water soluble hexavalent chromium.”Park, et al , Risk Analysis, Vol 24, 2004

• Debate over Level (concentration exposure) vs Risk

• Is all Chromium bad for our health?• Chromium in oxidation state +3 is an essential

micronutrient to metabolize fat into energy•• Chromium in oxidation state +6 is a carcinogenChromium in oxidation state +6 is a carcinogen

• No EPA defined limit for Cr+6 … MCL - 100 ppb for Total Cr


Current USEPA MethodsCurrent USEPA Methods

For Drinking Water:USEPA Method 218.6

Updated in December 2011 to Updated in December 2011 to USEPA method 218.7USEPA method 218.7


Cr (VI) Cr (VI) --

ChromateChromateCrOCrO44

--22

CrCr22OO77--22

pH = 9.5 pH = 9.5 or higheror higher

In post column reactor

1N H2SO4 + Diphenyl Carbazide (DPC)

In post column reactorIn post column reactor

1N H2SO4 + Diphenyl Carbazide (DPC)

Cr (VI) Cr (VI) forms forms complex in complex in presence of presence of excess Hexcess H+ +

to form Magenta color

Principle of the MethodPrinciple of the Method


Typical instrument setup (Dosino for PCR)


Alternate instrument setup (HP pump for PCR)

Auto sampler IC System PCR/VIS (DPC)


Chromium System at work (USEPA, Cincinnati OH)


USEPA Method 218.7 – Option 1

• Current app notes (AW US6-0134, US6-0152 and CH6-1049)

• Metrohm:• Column: ASUPP5 – 150 (4mm ID Column)• Eluent: 12.8 mM Na2CO3 + 4.0mM NaHCO3 + 2.5mM

Amm.Sulfate

• Flow rate: 0.7 mL/min

• PCR: Diphenyl Carbazide

• PCR flow: 0.24 mL/min• Sample loop: 2 mL

• Reaction coil – 375uL Volume(optimized for correct reaction ratio)

• Vis Detector: 530nmWEAT 2012 - Austin TX (Dr. Jay Gandhi) 12

USEPA Method 218.7 – Option 2

• Metrohm:• Column: ASUPP10 – 100 (2mm ID column)• Eluent: 15g/L Amm.Sulfate + 6.5mL/L

Amm.Hydroxide

• Flow rate: 0.45 mL/min

• PCR: Diphenyl Carbazide

• PCR flow: 0.22 mL/min• Sample loop: 1 mL

• Reaction coil – 375uL Volume(optimized for correct reaction ratio)

• Vis Detector: 530nm


ChromatogramChromatogramColumn: ASUPP 10-250Loop size 2000 microlitersEluent: 15g/L (NH4)2SO4 + 6.5ml/L NH4OHFlow rate: 0.8mls per minutePCR: DPC reagentPCR flow: 0.4mls per minuteUV detection at 530nM

0.0

2.0

4.0

6.0

mAU

0.0 1.0 2.0 3.0 4.0 5.0 6.0 min

Chr

om-6

0.0

1.0

2.0

3.0

4.0

5.0

6.0

(mAU) x min

0.0 1.0 2.0 3.0 4.0 5.0 ppb

0.025 ppb in DW Calibration Range0.025 – 5.00 ppb


MDL Study DataMDL study (0.025ppb and 0.050ppb)

Chrom‐6 parts per billion

Chrom‐6 parts per billion

MDL‐1 day 1 0.026 MDL‐2‐Day 1 0.051MDL‐1 day 1 0.028 MDL‐2‐Day 1 0.044MDL‐1 day 2 0.029 MDL‐2‐Day 2 0.040MDL‐1 day 2 0.028 MDL‐2‐Day 2 0.046MDL‐1 day 2 0.031 MDL‐2‐Day 2 0.055MDL‐1 day 3 0.030 MDL‐2‐Day 3 0.051MDL‐1 day 3 0.024 MDL‐2‐Day 3 0.047

average 0.028 average 0.048std dev 0.0024 std dev 0.005

calculated MDL 0.007 calculated MDL 0.016*MDL = 3.14 x SD *MDL = 3.14 x SD


MRL Study DataMRL Data

Chrom‐6, ppbanalysis‐1 0.026analysis‐2 0.028analysis‐3 0.031analysis‐4 0.026analysis‐5 0.027analysis‐6 0.028analysis‐7 0.029

Mean 0.0279std.Dev 0.0018HPPIR 0.0070

True Concentration 0.025

Upper HPPIR 139.5311638

Lower HPPIR 83.32597905

Must be less than 150

Must be greater than 50


Sample Sample Preservation Preservation

StudyStudy


Work at US EPA to validate new method

• Cincinnati & Region 6 laboratories• Sample preservation study data

• Various preservatives were studied• NaHCO3/Na2CO3

• (NH4)2SO4/NH4OH• NaHCO3/Na2CO3 + amm. sulfate• Borate buffer• NaOH + Na2CO3


Sample Preservation Buffer Studied

Buffer Chemical CompositionInitial

measured pH

A 2 mM Na2CO3 + 10 mM NaOH in 1000 mL 12.0

B 1.25 mM Na2CO3 + 1.25 mM NaHCO3 in 1000 mL 10.2

C 0.4 g (NH4)2SO4 + 0.65 mL NH4OH in 1000mL 10.0

D1.25 mM Na2CO3 + 1.25 mM NaHCO3 + 0.15 g/L

(NH4)2SO4 in 1000 mL9.25

E5 mM NaHCO3 + 10 mM Na Tetra Borate in 1000

mL9.10

In each matrix In each matrix 1ppb Cr1ppb Cr+6+6 & & 1ppb Cr1ppb Cr+6+6 + 1ppb Cr+ 1ppb Cr+3+3


Buffer Study Data

Buffer A - pH ~ 12.02 mM Na2CO3 + 10 mM NaOH

Buffer B - pH ~ 10.21.25 mM Na2CO3 + 1.25 mM NaHCO3


Buffer Study Data

Buffer C - pH ~ 9.00.4 g (NH4)2SO4 + 0.65 mL NH4OH

Buffer D - pH ~ 9.71.25 mM Na2CO3 + 1.25 mM NaHCO3

+ 0.15 g/L (NH4)2SO4


Buffer Study Data

Buffer E - pH ~ 9.55 mM NaHCO3 + 10 mM Na Tetra Borate


Other Ions of Drinking water• Chloride (100ppm), Sulfate (150ppm) and

Total Hardness as CaCO3 (450ppm)


Reducing Agents• Fe+2 and Fe+3 (10ppm), Mn+2 (5ppm) and Humic

Acid (Total carbon 25ppm)


Reducing Agent – Only Humic Acid• Humic Acid (Total carbon 25ppm)


Summary• Sample preservation study concluded that

• pH greater than 9.5 is preferred for sample preservation• For DW, due to Chlorine as disinfectant, ammonium salt

added to sample preservation helps Chromium species inter-conversion issue

• Two buffers that worked best in this study are• Ammonium Sulfate + Ammonium Hydroxide• Sodium Carbonate + Sodium Bicarbonate + Ammonium Sulfate

• In Collaboration with USEPA – Metrohm developed simple yet robust method for Hexavalent Chromium in drinking water

• With modern Metrohm IC instrumentation trace level detection of Chromium-6 is possible• Metrohm Also has online analyzers for continuous

monitoring of Hexavalent chromium

26WEAT 2012 - Austin TX (Dr. Jay Gandhi)

Acknowledgements• Mr. Johnson Mathew – USEPA Region – 6• Mr. David Neliegh – USEPA Region – 6

• Dr. Melvin Ritter – USEPA Region – 6

• Ms. Marvyln Humphrey – USEPA Region – 6

• Dr. David Munch – Retired USEPA – ODW/OGW

• Dr. Steve Wendelken – USEPA – ODW/OGW

• Mr. Alan Zaffiro - Shaw Group/USEPA – Cincinnati OH

• Metrohm AG applications teamespecially, Dr. Katinka Ruth and Dr. Andrea Willie

• Dr. Hari Narayanan – Metrohm USA Applications Lab

• Dr. Chunlong Zhang– University of Houston - Clearlake

27WEAT 2012 - Austin TX (Dr. Jay Gandhi)

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Documents

Hexavalent Chromium in Drinking Water - ftp.weat.orgftp.weat.org/Presentations/Jay_Gandhi_Hexchrom.pdf · • For DW, due to Chlorine as disinfectant, ammonium salt added to sample