Development of a Chemical Stain for Identifying Arsenic-Treated Wood

Amy Omae

August 18, 2005Medley, FL

Background

Identification methods for arsenic-treated wood Visual method Augmentation methods

XRF, LIBS, AA analysis

Arsenic test kits Arsine gas Wipe

Copper specific stains (PAN indicator) Alternative treated wood (ACQ, CBA, CC, CDDC)

EXPENSIVE

HAZARDOUS

DAYS OR WEEKS

INACCURATE

IDENTIFIES COPPER NOT ARSENIC

Background

Similarity of phosphate and arsenate

Colorimetric identification methods Ascorbic acid

Unable to prevent phosphate interference Vanadomolybdophosphoric acid

Unable to achieve a noticeable color Stannous chloride…

Phosphate Arsenate

Stannous Chloride Stain

Standard Methods, 1995 Intended for the detection of phosphate, PO4

3-

Colorimetric reaction BLUE

PO43- +12(NH4)2MoO4 +24H+ (NH4)3PO4•12MoO3 +21NH4

+ +12H2O

(NH4)3PO4•12MoO3 + Sn2+ (molybdenum blue) + Sn4+

Interference: Arsenate, AsO43-

Phosphate Arsenate

Stannous Chloride Stain

ModificationsReducing sensitivity to phosphate

1) Ammonium Molybdate

2) Stannous Chloride

Stannous Chloride Stain

ModificationsReducing sensitivity to phosphate

1) Ammonium Molybdate

2) Stannous ChlorideCombined Reagent

Stannous Chloride StainReagents Separated Reagents Combined

Ars

enat

eP

hosp

hate

Dissolution Method

20-mL sample vial10 mL distilled water9 drops combined reagent

8 parts ammonium molybdate 1 part stannous chloride

0.5 g sample (shredded wood or sawdust) Reaction time: 30-45 minutes Maximum intensity: ~5 hours

Dissolution Method

ACZA-treated wood Ammoniacal Copper Zinc Arsenate Western U.S. Maximum intensity: ~2 hours

(4.0 kg/m3)

Untreated CC CDDC CBA ACQ Borate CCA

Dissolution Method

NoneFaint B

lue

(0.025–0.070)Light B

lue

(0.071–0.220)Medium Blue(0.221–0.399)

Blue(0.400–1.149)

Intense Blue

(>1.150)

Untreated

4.0 kg/m3 CCA

0m 0s

15m 0s

22m 30s31m 40s39m 15s53m 30s1h 8m 0s

2h 30m 0s5h 30m 0s

λ = 690 nm

Dissolution Method

Field testRecycled wood

Sample

Result

Determined Chemical Treatment

Preservative

Reaction Time of Stannous Chloride StainPAN Indicator

(+/–)

Elements Detected by XRF Unit (Average, ppm)

Cr Cu As

A – <216.3 174.7 <10 Borate none

B – <205.3 <35.7 <9.3 Borate none

C + <284 <34 <10.3 Untreated none

D + <241.7 <51.3 <11.7 Untreated none

E + <261.3 10248 <9.7 Copper none

F + <253.3 1481 <18 Copper none

G + <236 6013 <10 ACQ none

H + 9194.3 5412.3 6431.7 CCA 17 min 24 sec

I + 2526.3 1418.7 1476.3 CCA 37 min 42 sec 

Dissolution Method

Shelf life (6 months; ends August 26, 2005) Reagents must be stored separately

0

5

10

15

20

25

30

35

40

45

50

55

60

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Shelf Life (weeks)

Reacti

on

Tim

e (

min

)

Other Application Methods

Interference withUntreated Wood

Whole wood application

Other Application Methods

Ash Masking color of ash

Wipes Simulate human hand Analyze wipe with dissolution method stannous chloride

stain New wood Effective; similar reaction time Weathered wood Effective; reaction time ~4 hours

UNTREATED 4.0 kg/m3 CCA 40 kg/m3 CCA

Future Objectives

Additional field testing on playgrounds MDL for phosphate and arsenate Adjust pH to reduce reaction time Prepare consumer instructions Submit technical report to:

Thank you!

Questions?