Leaching of Alternative Chemical Treated Wood

&Aquatic Toxicity of

Alternative Chemical Treated Wood Leachates

Update: July 9, 2001

“Chemical and Toxicity Characterization of Pressure Treated

Wood Leachate.”

• Kristin Stook

• Master of Engineering Thesis

Rationale

• Research in previous years found that alternative wood preservatives had advantages over CCA with respect to disposal issues and human toxicity issues

• Aquatic toxicity of alternatives raised as an issue

Objectives

• Conduct a side-by-side comparison of CCA-treated wood and alternative chemical-treated wood with respect to chemical leaching and aquatic toxicity of leachates

• Gather basic data that can be used as part of overall assessment of preserved wood types

Status

Chemical Analysis

Aquatic ToxicityAnalysis

Interpretation&

Recommendations

Leaching of Alternative Chemical Treated Wood

Update: July 9, 2001

Wood Preservatives

• CCA- chromated copper arsenate

• ACQ- alkaline copper quaternary

• CBA- copper boron azole

• CC- copper citrate

• CDDC- copper dimethyldithiocarbamate

Wood Preservative

Inorganic Organic

CCAChromium, Copper, Arsenic

N/A

ACQ Copper, Boron DDAC

CBA Copper, Boron Tebuconazole

CC Copper Citrate

CDDC Copper CDDC

Wood Preservative Components

Sample Preparation

Wood Preservation

• Wood was selected based on certain criteria

• One (2’) section of each piece of untreated dimensional lumber was sent for treatment

• ½ to UM and ½ to UF

Size Reduction

• Cut wood using a 10’’ miter saw

• Ground using a pulverizer

Leaching Tests

• SPLP- Synthetic Precipitation Leaching Procedure

• TCLP- Toxicity Characteristic Leaching Procedure

• Synthetic seawater (Instant Ocean)

• DI water

Analytical Procedures

Wood Wood PreservativePreservative InorganicInorganic OrganicOrganic

CCA ICP-AES N/A

ACQ ICP-AES Two-Phase Titration

CBA ICP-AES GC/MS

CDDC ICP-AES Spectrophotometer

CC ICP-AES IC

Chemical LeachingResults

Start with CCA-Treated Wood

0

2

4

6

8

10

ARSE

NIC

CONC

ENTR

ATIO

N (m

g/L)

CCA-1 CCA-2

Arsenic Concentrations Found in CCA-treated Wood Leachates

DI TCLP SPLP SW

TC= 5 mg/L

Copper Concentrations Found in CCA-treated Wood Leachates

0

2

4

6

8

10

12

Cop

per C

once

ntra

tion

(mg/

L)

CCA-1 CCA-2

SPLPDI TCLP SW

Chromium Concentrations Found in CCA-treated Wood Leachates

0

1

2

3

4

CH

RO

MIU

M C

ON

CE

NT

RA

TIO

N (

mg

/L)

CCA DI CCA-R DIUNTREATED DI CCA TCLP CCA-R TCLP UNTREATED TCLPCCA SPLP CCA-R SPLPUNTREATED SPLP CCA SWCCA-R SW UNTREATED SW

SPLPDI TCLP SW

Difference in Leaching Tests for Alternative Chemical

Treated Wood

Copper Boron Azole

0

10

20

30

40

50

60

CBA DI CBA TCLP CBA SPLP CBA SW

Cop

per

Con

cent

ratio

n (m

g/L)

General Observations about Leaching Tests

• For copper, TCLP and saltwater extract the most (DI and SPLP are equivalent)

• TCLP extracts the most chromium

• Arsenic leaching approximately equal for TCLP, SPLP and DI

• Organic chemicals for the most part leach independent of leaching fluid

Compare Copper Leachability

0

10

20

30

40

50

60

70

Copper (mg/l)

CCA CDDC CB ACQ CC

Comparison of Copper Leachability(concentration in mg/l)

SPLP

0

5

10

15

20

25

30

35

40

MassCopper

Leaching(%)

CCA CDDC CBA ACQ CC

Comparison of Copper Leachability(mass leaching in %)

SPLP

0

5

10

15

20

25

30

35

40

MassMetal

Leaching(%)

CCA CDDC CBA ACQ CC

Comparison of Total Metal Leachability(mass leaching in %)

SPLP

Observations

• CCA treated wood leaching similar to previous tests (SPLP, TCLP)

• Copper concentrations greater in alternative treated wood leachates

• The mass percentage of copper that leaches is higher

• The mass percentage of organic components that leach is chemical specific

Remaining Work

• Boron analysis

• Interpretation

Aquatic Toxicity of Alternative Chemical Treated

Wood Leachates

Update: July 9, 2001

Aquatic Toxicity Assays

Why conduct?

Chemical leaching data can not account for other factors that affect aquatic toxicity, such as complexation, binding, interaction, etc…

MetPLATETM

• Metal bioavailability• Short term acute

toxicity assay• 96-well microplate• CPRG- enzyme• Absorbance

measured at 570 nm

Microtox

• General toxicity assay

• Uses the decrease in the bioluminescence of the marine organism Vibrio fisherii to measure aquatic toxicity

Selenastrum capricornutum

• Chronic toxicity assay

• 96-hr test• Relative inhibition of

the leachates is measured based on a negative control

Ceriodaphnia dubia

• 48 hour acute bioassay

• Samples analyzed in triplicate with 5 dilutions

• Ten neonates per sample

• Count the number of live/dead neonates

Toxicity Expressions

• EC50- mg/L or percent

• LC50- mg/L or percent

• IC50- mg/L or percent

How Do Toxicity Tests Compare?

• Let’s look at results on CDDC on SPLP leachate

0.001

0.01

0.1

1

10

EC50/IC50(%)

Daphnia

Algae

Met

plate

Mic

roto

x

Comparison of Toxicity Tests(SPLP Leaching of CDDC)

C.daphnia

0.00%

0.05%

0.10%

0.15%

0.20%

0.25%

EC50

(%)

CCA-1 CCA-2 ACQ CC CDDC CBASPLP

S.capricornutum

0.00%

0.01%

0.02%

0.03%

0.04%

0.05%

0.06%

0.07%

0.08%

EC50

(%)

CCA-1 CCA-2 ACQ CC CDDC CBASPLP

Copper as a Surrogate

• Literature suggests that the copper leached from CCA is the primary toxicant to aquatic organisms

• Does this apply to the alternative wood preservatives as well?

Leachate EC50s (C.dubia) vs. Copper Concentrations

0.001

0.01

0.1

1

1 10 100 1000

Copper (mg/l)

EC

50 (%

)

R2 = 0.869

C.dubia Copper/Leachate Comparison

0.001

0.01

0.1

1

1 10 100 1000

Copper Concentration (mg/L)

EC

50 (%

)

EC50 Cu = 2.4 ug/l

EC50 Cu = 11 ug/l

General Observations

• Alternative chemical treated wood chemicals exhibit a greater degree of aquatic toxicity

• Most sensitive tests are algae and daphnia, followed by Metplate and Microtox

Next Steps

• Conduct hormonally active chemical assay

• Determine the relative contribution of copper and the co-biocides to aquatic toxicity

• Make recommendations on how to use the data in the decision-making process

Questions?