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The Arsenic Project Chemical Measurements in Support of Studies of the Biogeochemistry of
ArsenicJulian Tyson
Department of ChemistryUMass Amherst
http://courses.umass.edu/chemh01/
Outline of “The Arsenic Project” talk
Background to my involvement.Background on arsenic: environment and health
Pressure treated woodArsenic in water Other sources of arsenic
Middle school and undergraduate researchers.
Measurement problems: soils and waterHigh tech: HPLC- HG-ICP-OES; low tech: test stripsWhat is research?
Background to “The Arsenic Project”
J. F. Tyson , S. G. Offley, N. J. Seare, H. A. B. Kibble and C. Fellows, "Determination of arsenic in a nickel based alloy by flow injection hydride generation atomic absorption spectrometry incorporating by continuous flow matrix isolation and stopped flow pre-reduction procedures," J. Anal. At. Spectrom., 1992, 7, 315-322.
Peter Yehl: my first student to work on issues of arsenic (from pressure-treated wood) obtained hisPh.D. in 1996. Since then, at least one Ph.D. student has worked on arsenic-related topics every year.
Loughborough U. 76 - 89: UMass 89 - present
Started with trying to answer the question, “What happens to the arsenic that leaches out of wood pressure-treated with chromated copper arsenate?”
Three hypotheses: (1) it forms insoluble compounds with soil, (2) it is washed away by surface water run-off, and (3) it evaporates, because soil bacteria convert it to volatile methylated compounds.
Needed methods to measure the various arsenic compounds in soils. Turned out to be very difficult!
Background to “The Arsenic Project”
This led to my suggestion that tracking the arsenic from PTW as part of an “arsenic in the environment” theme would be a suitable for our GK-12 program. Started in summer of 2002.
Needed a procedure for the determination of arsenic to support studies by the middle-school student participants.
Issues: cost, safety, limit of detection (LOD), speed
Picked the Hach version of the “Gutzeit” test designed to measure As in drinking water.
Background to “The Arsenic Project”
Awareness of the PTW source led to my suggestion that tracking the arsenic from PTW as part of an “arsenic in the environment” theme would be a suitable for our GK-12 program. Started in summer of 2002.
Needed a procedure for the determination of arsenic to support studies by the middle-school student participants.
Issues: cost, safety, limit of detection (LOD), speed
Picked the Hach version of the “Gutzeit” test designed to measure As in drinking water. But it has limitations.
Background to “The Arsenic Project”
Can we do better? This led to a research project, supported by NSF, into the possibility of pervaporation with visible spectrophotometry. Started in fall 2003.Also an interest in the general need for inexpensive, reliable, field-deployable, simple, technologies for the determination of arsenic at realistic concentrations i.e. with an LOD of < 10 ppb (or ng mL-1 or g L-1)Fall 2004. Creation of authentic research experiences for first-year undergraduates--more info at the arsenic project website: http:://courses.umass.edu/chemh01/
Background to “The Arsenic Project”
Mandal and Suzuki, “Arsenic around the world” Talanta, 2002, 58, 201-235.Uses: insecticides, herbicides, desiccant (cotton production), wood preservative, feed additive, medicine, poison, bullets, electronics, glass, paints, wallpapers and ceramics.
Background to “The Arsenic Project”
Our quality of life affected by the extent to which we can (a) minimize the harmful effects of naturally occurring chemicals, (b) exploit beneficial effects of chemicals with which we choose to interact.
Update on “The Arsenic Project”
“The World Health Organization (WHO) recommends a tolerable daily intake of 50 µg/kg body weight from food and no more than 20 µg/L in the drinking water (WHO, 1983).”
http://www.prn.usm.my/sites/arsenic.html (accessed April 2005).
Update on “The Arsenic Project”
Chemical form or speciation is all important.
E.g. Sodium is nasty, chlorine is even worse.
But swap an electron between them and make sodium chloride, and the resulting compound is essential.
Not quite the same for As, as there are no known essential compounds (in humans).
But there is a very wide range of toxicities.
Update on “The Arsenic Project”
Chemical form or speciation is all important.
The most toxic are arsenite, As(OH)3, arsine AsH3 and the methylated forms of AsIII. MMAIII and DMAIII
CH3
OH
OHAs CH3
CH3
OHAs
These are more toxic than the corresponding +5 species, which in turn are more toxic than arsenate, As(O)(OH)3
Intake of 70 to 300 mg of arsenic trioxide may be fatal. Death typically occurs between 12 to 48 hours but can occur within one hour. Those who survive arsenic trioxide poisoning may develop encephalopathy or severe peripheral neuropathies.
Symptoms of acute poisoning usually occur within one hour of ingestion but may be delayed for up to 12 hours, particularly in the presence of food. The principle toxic effects are hemorrhagic gastro-enteritis, profound dehydration, cardiac arrhythmias, convulsions, muscle cramps, shock and death.
http://www.gettingwell.com/drug_info/nmdrugprofiles/nutsupdrugs/ars_0026.shtml (accessed April 2005)
Toxicity from dietary intake of arsenic—up to 60 µg/day daily—is relatively low. Intakes of higher amounts of arsenic on a chronic basis may cause hyperkeratosis, especially of the palms and soles, skin pigmentation, eczematous or follicular dermatitis, edema (especially of the eyelids), alopecia, muscle-aching and weakness, stomatitis, excessive salivation, anemia, leukopenia, thrombocytopenia, jaundice, cirrhosis, ascites, peripheral neuropathy, paresthesias, proteinuria, hematuria and anuria. Chronic-high arsenic ingestion has been associated with various cancers, such as basal cell carcinoma and bladder, liver and lung cancers. The nail changes associated with arsenic toxicity are known as Mees' lines or transverse striate leukonychia.
Abnormal levels exist in:Argentina, Australia, Bangladesh, Chile, China, Hungary, India, Mexico, Mongolia, Peru, Thailand and the United States of America
Adverse health effects documented in:Bangladesh, China, India (West Bengal), Mongolia and the United States of America
Arsenic in drinking-water will cause 200,000 – 270,000 deaths per year from cancer in Bangladesh alone.
Arsenic contaminated water revealed in 1993 4.5 million tube wells Arsenic contamination in 20% of those tested
Environmental Health Perspectives, 2005, 113, A379
Recent studies estimate that 2-100 children per million exposed to PTW during early childhood may develop lung or bladder cancer later in life as a result of this exposureConsumer Product Safety Commission (2003)
Some arsenic compounds are not so bad.
Salvarsan: used to treat syphilis until the advent of penicillin in the 1950s
Some of the good guys
Neoarsphenamine: used in the treatment of syphilis until the advent of penicillin in the 1950s.
Melarsoprol: currently used in treatment of sleeping sickness, Trypanosoma brucei rhodense and gambiense. May also cure chromic lymphocytic leukemia.
As2O3 is used to treat acute promyelocyte leukemia, chronic myeloid leukemia and some cases of lymphoma or esophageal cancer.
J. Chem. Educ., 2003, 80, 497
Roxarsone: growth promoting and antibiotic agent in poultry. Annual emission estimated to be 900,000 kg.
4-hydroxy-3-arsanilic acid
p-arsanilic acid or 4-aminophenylarsonic acid
trimethylarsine oxide TMAO
tetramethylarsonium iodide
The end of the metabolic path?
Arsenosugars:Found in urine and seaweed.
arsenocholine AsC
arsenobetaine AsB
Present in high concentrations in seafood
Background to “The Arsenic Project”According to a recent NSF report: About 80% of school students decide, by the time they enter high school, that they are not interested in science.And: environmental topics improve student interest, attitude, achievement and attendance.
Can be applied at all stages of the curriculum from K-21.
S. Pfirman and the AC-ERE “Environmental Education in the Complex Environmental Systems: Synthesis for Earth, Life and Society in the 21st Century, A report summarizing a 10-year outlook in environmental research and education for the National Science Foundation, 2003, p. 44. http://www.nsf.gov/geo/ere/ereweb/acere_synthesis_rpt.cfm (accessed April 2005).
Student Activities in “The Arsenic Project”http://courses.umass.edu/chemh01/Undergraduates: Now in 5th semester. Each group has 2-3 freshmen and 1-2 juniors and a graduate student mentor.
Final reports from spring semester 2006.
1. Removal of Arsenic from Drinking Water: Chemical Means: Arsenic Removal by Iron Precipitation in Alkaline Solutions
2. Arsenic (III) Removal from Water via Coagulation with an Iron Species
3. Measurement of Arsenic in Hair and Nails
4. Spectrophotometric Determination of Arsenic in Water: Flow injection molybdenum blue method
5. Spectrophotometric Determination of Arsenic in Plants: The Molybdenum Blue Method
Student Activities in “The Arsenic Project”
http://courses.umass.edu/chemh01/
6. Spectrophotometric Determination of Arsenic in Pressure-Treated Wood: Silver diethyldithiocarbamate method
7. Determination of arsenic in wood by inductively coupled plasma mass spectrometry using oxalic acid extraction: the mapping of copper chromated arsenate wood on the University of Massachusetts Amherst Campus
8. Metabolism of Arsenic in E. Coli
9. Analyzing the spatial distribution of arsenic in soil using the Hatch Test Kit and soil from the Amherst area
10. Effectiveness of Solvents in the Removal of Arsenic from Soil
11. Evaluating and Improving a Commercial Test Kit for the Determination of Arsenic in Drinking Water
Student Activities in “The Arsenic Project”
http://courses.umass.edu/chemh01/
Current arsenic-related research in the Tyson group.
Primary topics
Fate of arsenic leached from CCA pressure-treated wood.
Study of the transformations of arsenic compounds by microorganisms.
Study of the uptake of arsenic by plants.
Study of the interaction of the in vivo interaction of arsenic and selenium
Graduate Student Activities
Improved procedures for the determination of arsenic and arsenic compounds in waters, soils, plants and other biological systems.
Improved against the usual criteria: cost, speed, accuracy, precision, multi-analyte capability, detection limit, selectivity, sensitivity, signal-to-noise ratio, cost effectiveness,
Both at high tech end (HPLC with plasma source emission or mass spectrometry) . . .and at the low tech end (naked eye detection).
Graduate Student ActivitiesSecondary Topics
Mapping of As distribution in local communities.PTW, soil and ground water
Removal of arsenic from drinking water.Waste biomass
Biomarkers of arsenic exposureHair, nails, and earthworms
Rahman et al.,“Effectiveness and Reliability of Arsenic Field Testing Kits: Are the Million Dollar Screening Projects Effective or Not?” Env. Sci. Technol, 2002, 36, 5385-5394.
290 samples: FTK vs HG-AAS vs Ag-DDTC; false negatives were as high as 68% and false positives up to 35%.
2,866 samples from previously labeled wells: HG-AAS; 45% mislabeling in the lower range (< 50 ppb), for 70 - 600 ppb, 4 - 10% mislabeled
“Millions of dollars are being spent without scientific validation of the field kit method. Facts and figures demand improved, environmentally friendly laboratory techniques to produce reliable data.”
Caldwell, et al. “Searching for an optimum solution to the Bangladesh arsenic crisis,” Social Science & Medicine, 2003, 56, 2089–2096..
“the most urgent need is not changing the source of water but comprehensive national water testing providing essential information to households about which wells are safe and which are not . . . all progress depends on nationwide testing and retesting of all tubewells, a process that has hardly started.”
“The reason for caution about precipitating a great suspicion of tubewells or a rapid turning against them is that no alternative source of water may prove very satisfactory.”
Hossain “Arsenic Contamination in Bangladesh—An Overview,”, Agriculture, Ecosystems and Environment, 2006, 113, 1-16
2.5 million tube wells, 128 million people
“Field kits used to measure As in the region’s groundwater are unreliable and that many wells in Bangladesh have been labeled incorrectly”
“No-one has devised practical methods of ground water remediation, most studies and actions have focused on testing tube well water for arsenic.”
Melamed, “Monitoring As in the environment: a review of science and technologies with the potential for field measurements”, Anal. Chim. Acta, 2005, 523, 1-13.“Accurate, fast measurement of arsenic in the field remains a technical challenge. Technological advances in a variety of instruments have met with varying success.
However, the central goal of developing field assays that reliably and reproducibly quantify arsenic has not been achieved.”
What’s the problem?A procedure capable of the reliable on-site determination of arsenic in ground water at single digit ppb concentrations is needed.Can be used on site by inexperienced operators.Costs nothing.Field deployable criterion rules out the best technique: atomic spectrometryCandidates: electrochemistry, solution spectrophotometry, and Gutzeit-type test kits
Spectrophotometric methods?
Two candidates: (a) molybdenum blue, and (b) silver diethyldithiocarbamate
Arsenate + molybdate + acid + reducing agent gives blue color due to formation of heteropoly species containing both MoIV and MoVI.
Arsenate converted to arsine, evolved and trapped in a solution of AgDDC in non-aqueous solvent containing a base. A red color forms due to colloidal silver formation
Spectrophotometric methods?
Two candidates: (a) molybdenum blue, and (b) silver diethyldithiocarbamate. Both have problems as basis of field deployable procedure.
Molybdenum blue has possibilities but reaction is slow and non-specific. There is current activity: e.g.
Dhar et al., “A rapid colorimetric method for measuring arsenic concentrations in groundwater,” Anal. Chim. Acta, 2004, 526, 203-209
AgDDC complicated.
Dhar et al., “A rapid colorimetric method for measuring arsenic concentrations in groundwater,” Anal. Chim. Acta, 2004, 526, 203-209
There are still some issues to be sorted out.
“one peculiarity of the formation of As-molybdate complexes encountered during this study is that samples containing very little P must be spiked to at least 2 µmol L-1 P (i.e. to ~0.05 absorbance for a reduced aliquot) because of a P dependence of the rate of color development for As.”
Could the method be adapted to a non-instrumental finish?
Maybe.
Matsunaga et al., “Naked-eye detection of trace arsenic in aqueous media using molybdenum loaded chelating resin having -hydroxypropyl-di(-hydroxyethyl)amino moiety” Talanta, 2005, 66, 1287-1293
The color developed fully after heating for 4 h at 40 oC.
The 20-min (45% max color) detection limit was 1 x 10-6 mol dm-3
But this is only 75 ppb.
Prospects:Cardwell et al. “Pervaporation flow injection determination of arsenic based on hydride generation and the molybdenum blue reaction” ACA, 2001, 445, 229-238. Determination of arsenic by pervaporation flow injection hydride generation and permanganate spectrophotometric detection, ACA 2004, 510, 225-230.
Our approach: Pervaporation into an acceptor solution containing iodate and permanganate with detection by visible spectrophotometry. Performance was superior to those of procedures based on (a) the molybdenum blue chemistry, which requires on-line heating, and (b) pervaporation into permanganate alone. LOD 0.5 ppb
Gutzeit test?Arsenate + zinc + acid produces AsH3. Soluble in water to 780 mg/L, but dissolved salts and H2 evolution transferAsH3 into head space. AsH3 reacts with mercuric bromide impregnated test strip. Yellow-brown color produced after set time is compared with preprinted chart.
Modifications to Hach Test
Speed up reaction by HG with borohydride?Improve accuracy and precision by increasing the time to 24 h?Read color by scanning and interrogating the RGB values of image pixels?Mathews et al, “Quantitative assay for starch by colorimetry using a desktop scanner,” J. Chem. Educ. 2004, 81, 702-704.
“Field test kits offer the only plausible approach for mass screening” Kinniburgh & Kosmus, Talanta, 2002, 58, 165-180.
Speed up reaction by HG with borohydride?
Added a side-arm to vessel to add borohydride solution,
Needed to add a lot of borohydride to overcome the demand by “oxone”.
Without this reagent: color development in 15 min. More intense colors in 30 min.
Stirring also helps.
Twenty-four hour version of test
Current test kit does not detect below 10 ppbResponse in 10 – 50 ppb range inconsistent
Signals observed for 1, 3, 5, 7, 10, 15, 20 ppb
1 ppb response was clearly different from that of the blank
24-hr technique not reliable for 15 ppb.
Suggests a way of tuning the range of responses based on choice of time before reading strip.
RGB values of scanned test strips
Images of test strips from std 30-min tests on 0 ppb to 500 ppb As solutions obtained with a desktop flatbed scanner.
Images (in color JPEG format) evaluated by software developed by Mathews et al. COLORS.EXE that calculates the average red, green and blues intensities of the pixels within the area selected.
Three different resolutions: 400, 800 and 1200 dpi
Mathews, et al., “Quantitative assay for starch by colorimetry using a desktop scanner,” J. Chem. Educ. 2004, 81, 702-704.
0
50
100
150
200
250
0 100 200 300 400 500 600
Concentration (ppb)
B V
alue
Resolution 400 Resolution 800 Resolution 1200
Prospects. Maybe sensing based on quartz crystal microbalance is possible?
Frequency of oscillation of a piezoelectric quartz crystal is dependent on the mass. Manufacturer’s literature suggests that mass changes of 1 ng can be detected.
The referred literature does not really support this. Also suggests that frequency changes due to factors other than mass, such as visco-elasticities of interphases, are more important. We’ll find out.
Mirmohseni & Alipour, “Construction of a sensor for the determination of cyanide in industrial effluents: a method based on quartz crystal microbalance,” Sens. Actuators, 2002, 84, 245-251.
HPLC-HG-ICP-OES
Sample flow rate 1ml/minArgon flow 0.55 l/minNaBH4 0.5% in 0.1% NaOHNaBH4 flow rate 1.5 ml/minHCl 16 M flow rate 0.05 ml/min
J. Anal. At. Spectrom., 2002, 17, 1540–1548
ICP
HCl
Column
SampleInjection valve
2-ChannelHPLC pump
A B Mobile phases
Pump
Argon
Pump Waste
NaBH4
MSIS
Baseline separation of four key compounds
0.2 g soil to 15 ml centrifuge tube
5 ml 0.1 M phosphoric acid added and shake for 24 h
Centrifuged for 10 min at 70 rps
Supernatant filtered through 0.45 µm filter and inject
5 ml 0.1 M sodium hydroxide was added: shake for 24 h
Centrifuged for 10 min at 70 rps
Supernatant filtered through 0.45 µm filter, adjust pH to 2.5 and inject.
Sequential extraction procedure
Soil contain As(III)
0
5
10
15
20
25
As(III) DMA MMA As(V) Total
Con
cent
ratio
n (u
g/g)
Phosphoric acid
sodium hydroxide
Total extract
Soil contain As(V)
0
5
10
15
20
25
As(III) DMA MMA As(V) Total
Con
cent
ratio
n (u
g/g)
Phosphoric acid
sodium hydroxide
Total extract
Soil contain DMA
-5
0
5
10
15
20
25
As(III) DMA MMA As(V) Total
Con
cent
ratio
n (u
g/g)
Phosphoric acid
sodium hydroxide
Total extract
Soil contain MMA
-5
0
5
10
15
20
25
As(III) DMA MMA As(V) Total
Con
cent
ratio
n (u
g/g)
Phosphoric acid
sodium hydroxide
Total extract
Soil contain Mix
0
10
20
30
40
50
60
70
80
As(III) DMA MMA As(V) Total
Con
cent
ratio
n (u
g/g)
Phosphoric acid
sodium hydroxide
Total extract
The arsenic project: acknowledgements
NSF awards DUE 0139272 Graduate Students in GK-12 Education (GK-12) “STEM Connections”, June 2002 and is currently in a no-cost extension period. NSF 0316181 “Integrating Research and Education: tracking arsenic from pressure-treated wood” started in July 2003.UMass Center for Teaching: Faculty Grant for Teaching. Sept 2005.Camille and Henry Dreyfus Foundation: Special Grant Program in the Chemical Sciences. Feb 2006.
The arsenic project: facts and figures CCA
Percentage of Component
Type Amin max
Type Bmin max
Type Cmin max
CrO3 59 - 69 33 - 38 44 - 51
CuO 16 - 21 18 - 22 17 - 21
As2O5 15 - 20 42 - 48 30 - 38
300,000 metric tons of inorganic arsenic have been used for wood preservation since 1975.
The arsenic project: facts and figures
PTW. As of December 2003 is no longer sold.Up till then about 2 x 108 ft3 of wood pressure-treated with CCA was made every year.Depending on formulation the material contains 4.0, 6.4 or 13 kg m-3 of CCA.
The acute lethal oral dose is 1 - 2.5 mg kg-1.For 75 kg adult this is 75 - 188 mg.
This is, for best case scenario, 313 cm3 or a cube 7 cm on the side. Worst case scenario: 2.3 cm cube.
The arsenic project: facts and figures
Total arsenic in PTW was measured to be 0.2% i.e. 2,000 ppm i.e. 2,000 mg kg-1 or 2 g kg-1
To get a minumum lethal dose: eat 3.8 g of wood.If density is 0.5 g cm-3. This is a 2-cm cube.
Katz and Salem, J. Appl. Toxicol., 2005, 25, 1-7.
The density of arsenic trioxide is 3.74 g cm-3. A 100 mg lethal dose is a cube of side 3 mm.
The arsenic project: facts and figures
About 35 µg cm-2 of As can be dislodged from aged PTW.
The Hach test kit can detect 500 ng (just). 35 µg in 50 mL is 700 ppb (top end of the scale).
Contaminated soil might contain 40 ppm. If a 1-g sample is taken, the mass in test kit would be 40 µg (800 ppb).
The arsenic project: facts and figures
Cost of Hach EZ test kit: $50.60(100 tests and 2 reaction vessels with caps, plus reagent to eliminate sulfide interference)
Reagent set for 100 tests: $33.00Reaction vessel (one): $5.50Cap (one): $2.50
Shipping; $14.00
Research: Creation and Dissemination of New knowledge
How is research done?
By: scientists working in industry, government labs, and universities and colleges.
Most organizations have a large number of research groups, whose members collaborate. Most groups are relatively small (< 10). Groups are dynamic. New members join; older members move on. Leadership is stable.
New members learn from the more experienced members.
Research: Creation and Dissemination of New knowledge
New members need training:
Background to problem (big picture, what is already known), How to find out (library)Techniques to be used, Hypothesis to be tested, Plan of action (experimental design)Communication skills (written and oral)
Research: Creation and Dissemination of New knowledgeHow is new knowledge communicated?
Within members of research group.Conference presentations (oral or poster).Scientific literature: reviewed journal articles.
Researchers write manuscripts, submit to journal editor. Editor sends to reviewers.Reviewers send back comments (anonymously).Researchers revise.Article is published and work is scrutinized.Recent work is reviewed periodically by experts who write “review articles”.Important stuff eventually finds its way into textbooks.
Research: Creation and Dissemination of New knowledge
Importance of chemical analysis.
Many investigations need information about chemical composition of relevant materials.
Often it is difficult to provide this information.
All researchers need to know about the scope and limitations of chemical measurement methods.
Often these are set by the instrument that is to be used.
An authentic research experience involves:
Working on a real problem, Over an extended time period, Working in a team with more experienced workers, Finding out about your topic, Devising a plan of work, Conducting experiments and interpreting the results, Devising new experiments, Sharing your findings by writing and talking about what you are doing/have done.
