Speciation of Arsenic, Selenium, and Chromium in Wildfire 

Impacted Soils and Ashes

By Ruth E. Wolf, Todd M. Hoefen, Philip L. Hageman, Suzette A. Morman, and Geoffrey S. Plumlee

Open-File Report 2010–1242

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia 2010

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Suggested citation:

Wolf, Ruth E., Hoefen, Todd M., Hageman, Philip L., Morman, Suzette A., and Plumlee, Geoffrey S., 2010, Speciation 

of arsenic, selenium, and chromium in wildfire impacted soils and ashes: U.S. Geological Survey Open-File Report 

2010–1242, 29 p.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
1

Speciation of Arsenic, Selenium, and Chromium in Wildfire Impacted Soils 

and Ashes

By Ruth E. Wolf, Todd M. Hoefen, Philip L. Hageman, Suzette A. Morman, and Geoffrey S. Plumlee

Abstract 

In 2007-09, California experienced several large wildfires that damaged large areas of forest and 

destroyed many homes and buildings. The U.S. Geological Survey collected samples from the Harris, 

Witch, Grass Valley, Ammo, Santiago, Canyon, Jesusita, and Station fires for testing to identify any 

possible characteristics of the ashes and soils from burned areas that may be of concern for their impact 

on water quality, human health, and endangered species. 

The samples were subjected to analysis for bulk chemical composition for 44 elements by 

inductively coupled plasma mass spectrometry (ICP-MS) after acid digestion and de-ionized water leach 

tests for pH, alkalinity, conductivity, and anions. Water leach tests generated solutions ranging from pH 

10-12, suggesting that ashes can generate caustic alkalinity in contact with rainwater or body fluids (for 

example, sweat and fluids in the respiratory tract). Samples from burned residential areas in the 2007 

fires had elevated levels for several metals, including: As, Pb, Sb, Cu, Zn, and Cr. In some cases, the 

levels found were above the U.S. Environmental Protection Agency (USEPA) preliminary remediation 

goals (PRG) for soils.

Speciation analyses were conducted on de-ionized water and simulated lung fluid leachates for 

As(III), As(V), Se(IV), Se(VI), Cr(III), and Cr(VI). All species were determined in the same analytical 

run using an ion-pairing HPLC-ICP-MS method. For leachates containing high levels of total Cr, the 

majority of the chromium was present in the hexavalent, Cr(VI), form. Higher total and hexavalent 

chromium levels were observed for samples collected from burned residential areas. Arsenic was also 

generally present in the more oxidized, As(V), form. Selenium (IV) and (VI) were present, but typically 

at levels below 2 ppb for most samples. Stability studies of leachate solutions under different storage 

conditions were performed and the suitability of different sample preservation methods for speciation 

analysis will be discussed. 

Introduction

This report contains slides and speaker’s notes used for an oral presentation given at the 2010 

National Environmental Monitoring Conference (http://www.nemc.us/) held in Washington, D.C., in 

August 2010. 

The slides discuss the growing concern for the high number of acres burned each year in the 

United States by wildfires and work done by the U.S. Geological Survey in evaluating the potential 

effects on human and ecosystem health. The U.S. Geological Survey has collected samples of ash and 

burned soils from a variety of locations in southern California during the 2007 and 2009 fire seasons. 

Data from samples collected from the Harris, Grass Valley, Jesusita, and Station fires have been 

analyzed for total metal content. Selected samples with elevated levels of arsenic, selenium, and 

chromium were analyzed to determine the speciation or chemical form of these elements present. 

Several tables of results taken from Plumlee and others (2007) are presented in the slides as well as 

maps depicting locations of the 2007 fires in southern California. The slides also contain preliminary 

results for the speciation analysis of arsenic, selenium, and chromium by High Performance Liquid 
2

Chromatography (HPLC) coupled to Inductively Coupled Plasma Mass Spectrometry (ICP-MS) using a 

modified version of the method discussed by Wolf and others (2007). The slides discuss the 

modifications made to the method including the use of nitrogen as the reaction gas used in the ICP-MS 

to remove interferences affecting low-level chromium analyses. The use of nitrogen as a reaction gas 

allows As(III), As(V), Se(IV), Se(VI), Cr(III), and Cr(VI) to be determined under the same 

chromatographic conditions under the same run with Practical Quantitation Limits (PQLs) in the 50 – 

100 ppt range. The Practical Quantitation Limit for this study was defined as the lowest level standard 

that was recovered within ±20 percent of the true value. The slides also discuss issues encountered 

during speciation analysis including calibration standard purity and stability, sample stability, and vial 

contamination. The use of an analytical spike on every sample is discussed as a means of assessing 

overall data quality and determining sample matrix effects on species stability and possible species 

interconversions. Preliminary results for a study on sample storage conditions are presented which 

indicate that refrigeration at 1-10o C may be the best alternative as analyte losses were seen with room 

temperature storage (20o C) and freezing (-21o C) in the 24-48- hour timeframe. Initial testing indicated 

that the selenium species were not stable under any storage conditions after 48 hours. These studies 

indicate that the speciation analysis and the sample extraction process should be closely coordinated and 

the analysis of extracts should begin as soon as possible after extraction. 

Preliminary results are presented for several samples from the 2007 and 2009 fires. In addition 

to the de-ionized water leaching method discussed by Hageman (2007), the samples were also leached 

using a near-neutral pH simulated lung fluid (Plumlee and others, 2006) to model potential chemical 

interactions of inhaled particles with fluids lining the respiratory tract. The preliminary results 

presented in the slides show that in the de-ionized water leachate, all of the chromium present is in the 

form of Cr(VI) and the resulting high pH tends to stabilize Cr(VI) from reduction to Cr(III). Analysis of 

the simulated lung fluid leachates indicates that the predominant form of chromium present in the nearneutral pH of lung fluid would be Cr(VI), which is of concern because of the high possibility of 

inhalation of the small ash and soil particulates, particularly by fire or restoration crews. The presence 

of hexavalent chromium, Cr(VI), in leachates from the fire ash samples is of particular concern because 

of its known toxicity and carcinogenicity (Agency for Toxic Substances and Disease Registry, 2008). 

References Cited

Agency for Toxic Substances and Disease Registry, 2008, Toxicological profile for chromium – draft 

for public comment: U.S. Department of Health and Human Services, Public Health Service, 

September 2008, 610 p., http://www.atsdr.cdc.gov/toxprofiles/tp7.html. 

Hageman, P.L., 2007, U.S. Geological Survey field leach test for assessing water reactivity and leaching 

potential of mine wastes, soils, and other geologic and environmental materials: U.S. Geological 

Survey Techniques and Methods, book 5, chap. D3, 14 p. 

Plumlee, G.S., Martin, D.A., Hoefen, T., Kokaly, R., Hageman, P., Eckberg, A., Meeker, G.P., Adams, 

M., Anthony, M., and Lamothe, P.J., 2007, Preliminary analytical results for ash and burned soils 

from the October 2007 southern California Wildfires: U.S. Geological Survey Open-File Report 

2007-1407. 
3

Plumlee, Geoffrey S., Morman, Suzette A., and Ziegler, Thomas L., 2006, The toxicological 

geochemistry of earth materials: an overview of processes and the interdisciplinary methods used to 

understand them: Reviews in Mineral Geochemistry, vol. 64, Chapter 2, p 5-57. 

Wolf, Ruth E., Morrison, Jean M., and Goldhaber, Martin B., 2007, Simultaneous determination of 

Cr(III) and Cr(VI) using reversed-phased ion-pairing liquid chromatography with dynamic reaction 

cell inductively coupled plasma mass spectrometry, Journal of Analytical Atomic Spectrometry, vol. 

22, p. 1051-1060. 
4 

Slide 1

Note: This presentation uses two equivalent forms of notation to express the identity of individual species of an element:

Cr(III) = Cr+3 , Cr(VI) = Cr+6

As (III) = As+3 , As(V) = As+3 

Se(IV) = Se+4 , Se(VI) = Se+6 

U.S. Department of the Interior

U.S. Geological Survey

Speciation of Arsenic, Selenium, 

and Chromium in Wildfire 

Impacted Soils and Ashes

Ruth E. Wolf, Todd M. Hoefen, Philip L. Hageman, Suzette A. Morman, and Geoffrey S. Plumlee

U.S. Geological Survey, MS 964D, Denver Federal Center, Denver, CO 80225 

U.S. Department of the Interior

U.S. Geological Survey

Speciation of Arsenic, Selenium, 

and Chromium in Wildfire 

Impacted Soils and Ashes

Ruth E. Wolf, Todd M. Hoefen, Philip L. Hageman, Suzette A. Morman, and Geoffrey S. Plumlee

U.S. Geological Survey, MS 964D, Denver Federal 

Center, Denver, CO 80225 
5 

Slide 2

Wildfires a Growing Concern

 More land affected by wildfires in recent years since 1960s

 In 2003 fires burned over 5700 structures (4090 homes)

Source: http://www.nifc.gov/fire_info.html

Every year millions of acres of land are affected by wildfires in the United States. The 2006 and 2007 fire seasons were the 

worst on record since 1996.

Source: http://www.nifc.gov/fire_info.html
6 

Slide 3

Effects of Fires on Health

 Immediate

 Exposure to gases and particulates

 Irritants to eyes and respiratory system

 Complicate chronic heart and lung diseases

 Post-fire and long-term

 Exposure to potentially caustic dusts

 Raise soil and water pH levels

 Exposure to chemicals/metals liberated 

 Impact on watersheds and ecosystems

Wildfires can have both immediate and long-term effects on human health. Exposure to the gases and particulates from a fire 

can cause immediate irritation to the eyes and respiratory system and can cause complications for those with chronic heart and 

lung diseases. Post-fire and long-term effects can be caused by exposure to potentially caustic ashes and dusts that are skin 

and eye irritants. They can also impact the environment and ecosystems by raising soil and water pH levels.
7 

Slide 4

Analysis of Fire Ash/Soil Leachates

 Large forest fires in 

California Fall 2007

 Burned many homes and 

outbuildings

 USGS asked to assess 

potential risks to human 

health from residential and 

nonresidential fire ash

 Expected to vary with particle 

size and speciation

The U.S. Geological Survey was asked by the California Burned Area Emergency Rehabilitation Team (BAER) to assess the 

potential impact of the large fires in 2007 on human health. The satellite image on the right (from NASA) shows the smoke 

plumes from these 2007 wildfires as seen from space. Of particular concern were any differences observed between residential 

and non-residential areas because of the large number of homes and buildings that were destroyed.
8 

Slide 5

2007 California Burn Areas

This map shows the major wildfires from the 2007 season in California. The green stars indicate sites studied by USGS that we 

will discuss in this presentation. More information on the USGS response to the California wildfires can be found at 

http://www.usgs.gov/hazards/wildfires/ca/.
9 

Slide 6

Fire Ash Studies – 2007 California Fires

 Samples from burned wildland and residential areas

 Primary focus on residential ash and soil samples at 

request of Burned Area Emergency Rehabilitation (BAER) 

Team

 Report available at: http://pubs.usgs.gov/of/2007/1407/

Source: http://pubs.usgs.gov/of/2007/1407/

The USGS issued a report on the potential impact of wildfire ash on human health and the environment from the work done on 

the 2007 fires. A wide range of testing was done on the samples, including elemental analysis of the ash materials as well as on 

leachates from the ash to determine possible impacts. The report is available on the USGS Web site listed above.
10

Slide 7

Key Findings 

Preliminary Fire Ash Study

 Water leach tests generate pH levels > 12

 Suggest ash can generate caustic alkalinity in contact with 

rainwater or bodily fluids (e.g., sweat, fluids in respiratory tract)

 Rate of neutralization has not been studied

 Residential ash has elevated levels of metals

 As (140 mg/kg), USEPA PRG (soil) 0.4-0.62 mg/kg

 Pb (344 mg/kg), USEPA PRG 150-400 mg/kg

 Sb (32 mg/kg), USEPA PRG 31 mg/kg

 Cu (1,370 mg/kg), USEPA PRG 3,100 mg/kg

 Zn (2,800 mg/kg), USEPA PRG 23,000 mg/kg

 Cr (354 mg/kg)

 USEPA PRG 210 mg/kg (Cr+6/Cr+3 = 0.17), 30 mg/kg if all Cr+6

 PRG = Preliminary Remediation Goal

Some key findings outlined in the report include the results of de-ionized water leach tests. This quick 5-minute leach in deionized water simulates what happens when the ash comes into contact with rainwater or body fluids such as sweat or in the 

respiratory tract. Several metals including arsenic (As), lead (Pb), antimony (Sb), and chromium (Cr) were found at levels in the 

leachate above the USEPA Preliminary Remediation Goals for soils. It is important to note that the PRG for chromium varies, 

depending on the species of chromium present, and is much lower if Cr+6 or hexavalent chromium is present.
11

Slide 8

Extractions Performed

 De-ionized water leaches – soluble Cr(VI)

 1g in 20 mL DI water, shaken 5 minutes, centrifuge (3,000 

rpm), 0.45 μm filter

 Simulated lung fluid leach

 Estimates effects of particulates (<38 μm) taken into lungs 

and in contact with pulmonary fluids at near neutral pH

 0.5 g sample to 20 mL at 37oC for 24 hours

 150mM Na, 0.2mM Ca, 10 mM NH4

+, 6mM glycine, 67mM 

formaldehyde, 20mM methanol, 126mM chloride, 0.5mM sulfate, 

27mM hydrogen carbonate, 1.2 mM phosphate, 0.2mM citrate, 

adjusted to pH 7.4

During the USGS studies, two different extractions were performed on the ash samples. The first was a de-ionized (DI) water 

leach test where 1 g of ash was added to 20 mL of de-ionized water and shaken for 5 minutes and filtered. The second was a 

simulated lung fluid leach which uses a solution similar to lung fluid (the recipe is given above) to estimate the amount of metals 

leached out when the ash is in contact with the fluids in the respiratory tract and the lungs. This is a 24-hour leach performed at 

body temperature (37° C).
12

Slide 9

Elemental Content in DI-Leaches

 Total elemental analysis in 5 minute De-ionized (DI) water leach

 Limited information on actual potential for toxicity or impacts on 

human heath and environment

 Toxicity depends of chemical form of element

 Cr(VI) >> Cr(III), Cr(VI) a known carcinogen (lung)

 Cr(VI) regulated in several industries with potential for inhalation of 

Cr(VI) containing dusts, e.g., welding, refining, plating

 As(III) > As(V), aquatic species

Sample Location Description pH

 As 

(μg/L)

 Cr 

(μg/L)

 Se 

(μg/L)

Harris 06 Ash S teep hillside 10.9 1 1.5 7.2

G rass V alley 02 S oil Hillside 8.2 1 <1 <1

G rass V alley 02 Ash Hillside 9.8 1 1.4 3.1

G rass V alley 01 S oil Modern Hom es 10.9 2 7.7 1.6

G rass V alley 01 Ash Modern Hom es 12.7 2 31.9 3.6

Harris 07 S oil R esidential, m obile hom es 10.6 219 3 2.7

Harris 07 Ash R esidential, m obile hom es 12.5 13.5 32.4 6.3

Blank De-ioniz ed water 6 <1 <1 <1

These data show the total content of 3 potentially toxic elements in the ash from the Harris and Grass Valley fires. In general the 

soil and ash samples from residential areas had higher levels of arsenic (As) and chromium (Cr) than the non-residential areas. 

However, knowing the total concentrations gives us limited information on the potential toxic effects since the toxicity often 

depends on the chemical form or speciation of the element. For example hexavalent chromium, Cr(VI) or Cr+6 is more toxic 

than trivalent chromium, Cr(III) or Cr+3 , and is a known lung carcinogen.
13

Slide 10

Analytical Method1

 HPLC – reversed phase, ion-pairing

 Column: Brownlee C8

 3.3 cm X 3um, Si-based2

 Column Oven 35o C

 Mobile Phase:

 2 mM tetrabutylammonium hydroxide (TBAOH) 

+ 0.5mM K2EDTA, pH = 7.4 – 7.6

 EDTA converts Cr(III) to an anionic EDTA-Cr(III) 

complex so it can be separated under same 

conditions as Cr(VI) species

 5% MeOH added online

 Autosampler 10o C

 Required for sample stability

 DRC-ICP-MS

 Reaction gas: N2 (removes 40Ar12C 

interference on 52Cr)

 Sample Introduction: Baffled quartz cyclonic 

spray chamber and Meinhard TQ-30-A3 

nebulizer

1 Complete description in J. Anal. At. Spectrom., 2007, 22, 1051-1060 2 Stated column working range to pH=7; however, have run up to pH=8 without significant column 

life issues

The use of company, trade, and/or 

product names is for identification 

purposes only and does not imply 

endorsement by the United States 

Government.

The method we have been using for speciation at our laboratory is a reversed ion-pairing HPLC separation method followed by 

ICP-MS detection. We use a small, 3 cm, C8 column with tetrabutylammonium hydroxide as the mobile phase. Elution is 

isocratic and methanol is added to enhance peak shapes. EDTA is added to the mobile phase and to the samples to complex 

the Cr+3 cationic species to an anionic Cr(III)-EDTA complex. The ICP-MS has a dynamic reaction cell that uses nitrogen 

reaction gas to remove the 40Ar12C interference at mass 52 that interferes with low-level chromium detection. The method has 

been modified from the version published in J. Anal. At. Spectrom., 2007, v. 22, p. 1051-1060 to allow determination of arsenic, 

chromium and selenium species in the same run.
14

Slide 11

DRC Reaction Schemes

 N2 Reaction Gas offers best compromise conditions for all three elements

 If Cr DLs important and [Cl-] is low, N2 or NH3 can be used

 If As DLs important and [Cl-] is high, O2 can be used

Signal 1 (1 ppb)/

Background

N2 =1.0

RPq = 0.50

O2 = 0.75

RPq = 0.55

NH3 = 0.65

RPq = 0.60

7%H2/He = 1.0

RPq = 0.70

52Cr 6.4 4 7 1

75As 51 25 290 200

75As16O --- 340 2 --- ---

78Se 35 18 9 1.5

Normal Mode Bkg 52Cr 2,377,440 5,507,800 5,155,460 5,725,700

DRC Mode Bkg 52Cr 1,480 cps 6,320 cps 4,070 cps 4,653,150

1 in mobile phase + 5% MeOH

2 ~ 90% conversion of As to AsO (AFT=200V must be optimized)

For removal of interferences, several reaction gases were examined for the Dynamic Reaction Cell on the ICP-MS. Looking at 

the signal to background ratios in the mobile phase blank and blank spiked with 1 ppb of arsenic, selenium, and chromium, it 

was found that the use of N2 as the reaction gas gave the best compromise conditions for all three elements. Other reaction 

gases can be employed depending on the data quality needs. For example, if the best detection limits are required for chromium, 

ammonia would be the best choice of reaction gas.
15

Slide 12

Detection Capabilities – N2 Gas

 Calibrated at 1, 2, 5, 10 ppb

 Ran 100, 200, 500 ppt 

standards

 Look at accuracy of result 

at low levels

 As PQL ~ 50 ppt

 Se PQL ~ 50 ppt 

 Cr PQL ~ 100 ppt CrVI

 Best using NH3 gas

This slide shows low-level standards for each species using nitrogen as the reaction gas. The instrument was calibrated at 1, 2, 

5, and 10 ppb and standards at 100, 200, and 500 ppt were analyzed. The Practical Quantitation Limit was established as the 

spike level where recovery was within 20 percent of the prepared value. So under these conditions using nitrogen as the 

reaction gas, the As and Se PQLs were 50 ppt and the Cr PQL was 100 ppt (for both species of each element).
16

Slide 13

Calibration and Issues

 1,000 mg/L stocks diluted 

separately to 10 ppb in mobile 

phase (pH=7.6)

 As+3, As+5, Cr+3, Cr+6, Se+4, Se+6 

(Source:Spex Certiprep, VHG, 

Inorganic Ventures)

 Allowed to sit ~30 min for Cr+3-

EDTA complex to form

 Determine retention times

 Evaluate standard stability and 

contamination issues

 Acps for As+3 / As+5 2%

 Acps for Cr+3 / Cr+6 1%

 Acps for Se+4 / Se+6 4%

 Se+6 contains ~10% Se+4

 Issue for multicomponent 

calibrations

National Scientific PP vials and PKI black/Teflon caps

Calibration was performed with standards prepared from commercially available stock solutions for each species. Three different 

vendors have been used (Spex, Inorganic Ventures, and VHG Labs). Care should be taken to ensure the standards do not 

contain significant amounts of the other species. Analysis of each species separately will determine the retention time on the 

column and allow evaluation of contamination from other species. Note that ideally the areas counts per second for species of 

the same element should be similar (within 1-2 percent).
17

Slide 14

Vial Contamination

Vial and cap type

As III 

(ppb)

As V 

(ppb)

Se IV 

(ppb)

Se VI 

(ppb)

Cr III 

(ppb)

 Cr VI 

(ppb)

Unrinsed Clear Glass w/PKI cap nd 9-20 nd nd nd nd

Rinsed Clear Glass w/PKI cap nd 6-10 nd nd nd nd

Washed Clear Glass w/PKI cap nd 0.1-0.4 nd nd nd nd

Amber Glass w/PKI cap nd 0.3-0.7 nd nd 0.2-0.6 nd

Rinsed Amber Glass w/PKI cap nd 0.1-0.2 nd nd nd nd

Washed Amber Glass w/PKI cap nd 0.04-0.07 nd nd nd nd

PKI PP no cap nd 0.1-0.3 nd nd nd nd

N-Sci PP no cap nd 0.01-0.03 nd nd 0.1? nd

N-Sci PP w/PKI cap nd 0.02-0.04 nd nd nd nd

Rinsed N-Sci PP w/PKI cap nd 0.03-0.06 nd nd nd nd

Washed N-Sci PP w/PKI cap nd 0.01-0.03 nd nd nd nd

Rinsed N-Sci PP w/TargetDP cap nd 0.02-0.06 nd nd nd nd

Future testing of National Scientific glass vials planned as they are 

reportedly low in As contamination

When performing speciation analyses everything the samples touch must be checked for possible contamination or residues that 

might negatively impact the stability of the species being determined. In this table, several types of HPLC vials were checked for 

contamination. It was found that the clear glass vials used previously for chromium speciation were unsuitable for use when 

arsenic was also being measured because of high levels of arsenic contamination. In addition, amber glass vials used for 

arsenic speciation were unsuitable for use when chromium was being determined. Vial blanks should always be tested with 

every run or change in supplier. Species stability should also be checked with each vial type. Some releasing agents in plastics 

or washing procedures can cause species instability.
18

Slide 15

Quality Control

 Analytical spikes performed on each sample!

 Allows evaluation of matrix effects on analysis

 Data can be flagged or corrected for spike recovery

 Chromatogram of 25 ppb each As, Se, Cr species

We have found that including an analytical spike on EVERY sample gives us a lot of information about the effects of the sample 

matrix on the individual species and allows us to assess the quality of the analytical data. Based on the spike results the sample 

results can either be flagged or corrected for spike recovery. This chromatogram shows a 25 ppb standard with all six species 

being analyzed: As(III), As(V), Se(IV), Se(VI), Cr(III) and Cr(VI). Notice the good peak shapes and separation of all species. 
19

Slide 16

Matrix Effects on Separation

 M-176 water reduces some Cr(VI) to Cr(III)

 http://bqs.usgs.gov/srs/

 Cr(III)-EDTA peak is smaller than expected, another Cr peak at early 

RT...

These two chromatograms are from a USGS reference water sample M-176 (available at http://bqs.usgs.gov/srs/) which has 

routine levels of major cations and anions and should not contain As, Se, or Cr in significant levels. The upper chromatogram 

shows M-176 alone has a small amount, 0.5 ppb, of As(V) present. However when this sample is spiked at 25 ppb (the same 

level as the previous slide), we see that the Cr(VI) is somewhat smaller than expected (maroon line) compared to the standard 

(green line). In addition the Cr(III) is significantly smaller and there is another broad chromium peak appearing earlier in the 

chromatogram. This could indicate that the levels of major cations are competing for the EDTA in the Cr(III)-EDTA complex and 

causing it to fall apart. For this sample, the chromium speciation values would be unreliable based on the spike results.
20

Slide 17

Matrix Effects on Separation

 M-172 water matrix spiked with all species

 Shows As(III) to As(V) conversion

 Shows Se(VI) peak is splitting

The analytical spike on another USGS reference water sample , M-172, shows that the As(III) is possibly being converted to 

As(V) and there may be some matrix-induced signal enhancement since both peaks read significantly higher than the expected 

25 ppb. Note: an internal standard is not being used to correct for signal drift. Also the Se(VI) peak appears to be spread out 

and separating into 2 Se(VI) peaks. In this case the peak detection parameters might need to be adjusted to integrate the both 

peaks from Se(VI) – if we are sure they are both from Se(VI). For this sample, the arsenic and selenium data should be flagged 

as possibly containing significant error. In general, the analytical spike values on all the sample results we will discuss today 

were within 20 percent of the expected value.
21

Slide 18

Stability

 All species stable in mobile 

phase (pH 7.6) for ~24 hours 

at 20  ̊C

 Can extend to 48 hours at 1-

10  ̊C

 Se not stable after 48 hours

 Freezing appears to be 

detrimental for all species

 Not flash frozen

 1-2 mL total volume

 Stability varies with matrix –

another reason for spikes on 

each sample

Cr Stability at 1C

0.85

0.9

0.95

1

1.05

1.1

1.15

T=0 T=24 T=48 T=120

Elapsed Time (Hours)

Normalized Intensity

Cr(III)

Cr(VI)

Cr Stability at 20 C

0.85

0.9

0.95

1

1.05

1.1

1.15

T=0 T=24 T=48 T=120

Elapsed Time (Hours)

Normalized Intensity

Cr(III)

Cr(VI)

Cr Stability at -20 C

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

T=0 T=24 T=48 T=120

Elapsed Time (Hours)

Normalized Intensity

Cr(III)

Cr(VI)

For speciation, stability testing is critically important. The sample collection and storage conditions (for example, light vs. dark, temperature, 

preservative, sample matrix, etc.) can drastically affect the stability of the species you are trying to measure. Our tests showed that our 

standards were stable in the mobile phase for only 24 hours at room temperature. If refrigerating or using a Peltier-cooled autosampler, 

stability could be extended to 48 hours by keeping the standards at 1-10 °C. Our testing showed that after 48 hours both selenium species 

were not stable. In addition, freezing in a normal freezer (as compared to liquid nitrogen flash freezing) appeared to be detrimental for ALL 

species. The stability will also vary with the sample matrix and the presence of known oxidizing or reducing agents in the sample. All the 

samples tested were kept in the dark or shielded from the light unless being aliquoted, this is extremely important for As as it has been 

documented sunlight can oxidize As+3 to As+5 quite rapidly.
22

Slide 19

Stability Must Be Checked

 Matrix and/or temperature can influence!

 48 hours after spiking

 All analyses done same day as leaching

Since the sample matrix can drastically influence species stability we found that performing analytical spikes on a separate 

aliquot of each sample as they are being diluted for analysis is critical in assessing matrix effects on the results. The top 

chromatogram shows that in the M-172 reference water, Cr(VI) is significantly converted to Cr(III) after 48 hours and that freezing 

the sample actually increases the amount of Cr(VI) reduced. Subsequently, all of our speciation analyses are coordinated to 

begin immediately after samples are collected or leached to minimize storage effects on the sample results. Storage prior to 

analysis is at 4-10 °C.
23

Slide 20

So back to our results. The DI and simulated lung fluid leaches performed on ash and soil samples with elevated arsenic and 

chromium levels show that as the ash samples from residential areas (GV Ash 01 and Harris 07 Ash) contact de-ionized water 

and the simulated lung fluid, chromium is released and the predominant form of chromium present is hexavalent chromium, 

Cr(VI). This is not surprising given the oxidizing conditions in a fire and the high pH values associated with the ash samples. 

Moreover, the lung fluid leach resulted in significantly more chromium being extracted from the ash and again, the predominant 

form of this is hexavalent chromium. Air monitoring data are needed in order to compare the concentrations of Cr(VI) found in 

μg/g ash to the OSHA PEL of 5 μg/m3 . 

2007 CA Fires – Total Cr vs. Cr(VI)

 More Cr is leached out in lung fluid leach

 Ash samples liberate much higher Cr values

 Significant portion of it is Cr(VI)

 OSHA PEL (8 Hr) Cr(VI) = 5 μg/m3

Chromium Measured in Leachates

0

20

40

60

80

100

120

Harris 06

Ash

GV Soil 01 GV Ash 01 Harris 07

Ash

Concentration in Leachate 

(μg/L)

DI Leach Total Cr (5 min)

DI Leach Cr(VI) (5 min)

Lung Fluid Total Cr (24 Hr)

Lung Fluid Cr(VI) (24 Hr)

GV = Grass Valley

Chromium Measured in Leachates

0

20

40

60

80

100

120

Harris 06

Ash

GV Soil 01 GV Ash 01 Harris 07

Ash

Concentration in Leachate 

(μg/L)

DI Leach Total Cr (5 min)

DI Leach Cr(VI) (5 min)

Lung Fluid Total Cr (24 Hr)

Lung Fluid Cr(VI) (24 Hr)

GV = Grass Valley

2.7 μg/g

3.2 μg/g
24

Slide 21

2007 CA Fires – Total As vs. As(V)

 Se < 2 ppb (all forms)

For arsenic, again we see some amount of arsenic is extracted in the DI water leach and some of it is present as As(V). 

However, in the simulated lung fluid leachates, significantly more arsenic is extracted and the predominant form is As(V). For 

selenium, for all samples Se in all forms was less than 2 ppb in all extracts. 
25

Slide 22

2009 Jesusita Fire - Arsenic

 DI Water Leach

 Most As present in oxidized 

As(V) form

Jesusita Fire Results - Arsenic

0

2

4

6

8

JSA09-03 Ash JSA09-15 Ash JSA09-7 Soil

ppb in DI water extract

As(III)

As(V)

Total As 

Similar leaching experiments were carried out with soil and ash samples from the 2009 Jesusita fire. In the DI water leach, low 

levels of arsenic were extracted and the predominant form was again As(V). The sum of the measure As(III) and As(V) values 

matches well with the total arsenic values measured using traditional ICP-MS analysis.
26

Slide 23

2009 Jesusita Fire - Chromium

 DI Water Leach

 Most Cr present was in more toxic 

Cr(VI) form

Jesusita Fire Results - Chromium

0

10

20

30

40

50

60

JSA09-05 Ash JSA09-06 Ash JSA09-08 Ash JSA09-7 Soil JSA09-07 Ash

10X

ppb in DI water extract

Cr(III)

Cr(VI) 

Total Cr 

In the case of chromium from the Jesusita fire, a significant level of chromium was leached out of some samples and again the

predominant form was Cr(VI). One residential sample (JSA09-07) had 10 times the amount of the rest of the samples. It should 

be noted that in California the total chromium limit in drinking water is 50 μg/L while the Federal limit remains at 100 μg/L. In 

August 2009, the California Office of Environmental Health Hazard Assessment issued a draft Public Health Goal (PHG) for 

Cr(VI) of 0.06 μg/L. The California Department of Health Services is currently working on a Maximum Contaminant Limit for 

Cr(VI) based on this PHG. See http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Chromium6.aspx for current status and 

information.
27

Slide 24

2009 Station Fire - Chromium

0

200

400

600

800

1000

ppb in DI water extract

13A Out Bldg Ash 12A Res. Ash 10A Res. Ash

Station Fire - Chromium in Residential Ashes

Total Cr

Cr(III)

Cr(VI)

 Chromium in burned residential 

areas high and predominately 

Cr(VI) in DI water leach

A few samples from the 2009 Station Fire showed significant levels of total chromium (150-850 ppb) present in the 5 minute DI 

water leach. Again, our speciation analysis indicates that the predominant form of chromium present is hexavalent chromium. 
28

Slide 25

2009 Station Fire - Chromium

 DI Water Leach

 Lower Cr values than 

residential samples

0

2

4

6

8

10

12

14

ppb in DI water 

extract

26R Red

Ash

28A Ash

Oak Forest

26A Black

Ash Tree

20A Arroyo

Seco Ash

26A

Oak/pine

Ash

Station Fire - Chromium in Non-Residential Ashes

Cr(VI)

Cr(III)

Total Cr

In samples from nonresidential areas in the Station Fire the total levels of chromium extracted in the DI water leach were

significantly less than seen from the residential samples. Since chromium is used in many textiles, wood preservatives, and 

other household items, finding higher levels of chromium in residential areas is not surprising. Again, the speciation analysis 

indicates the predominant form of chromium present in the leachates is hexavalent chromium. 
29

Slide 26

Conclusions

 Analytical method can be used to determine inorganic 

forms of As, Se, and Cr in a variety of matrices

 Soils and ashes from residential areas have higher 

Cr(VI) levels than wildland areas

 Predominant form of Cr found in fire-impacted soil and 

ash samples is Cr(VI)

 Alkaline pH resulting from contact of ash with water and 

water-based fluids may have a stabilizing effect on Cr(VI)

 Potential human health impact from high pH and for 

exposure to Cr(VI)-containing ash and soils by firstresponders and clean-up crews

 Particularly for inhaled ash particles that are high in Cr

 Air monitoring tests for Cr(VI) suggested during fire 

clean-up/recovery operations to assess health effects

In summary, our speciation method can determine the inorganic forms of As, Se, and Cr in a variety of matrices.

Leach studies on ash and soil from fire-impacted areas indicates that the predominant form of chromium found is the hexavalent 

form. This is of importance to first responders, clean-up crews, and homeowners who may have physical contact or breathe in 

these ash and soil particles. Since hexavalent chromium is a known lung carcinogen, we need more studies and air-monitoring 

testing in order to fully evaluate the potential effects on human health from exposure to these fire-impacted ashes and soils.