Leaching of Alternative Chemical Treated Wood

andAquatic Toxicity of

Alternative Chemical Treated Wood Leachates

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

Leaching of Alternative Chemical Treated Wood

Wood Preservatives

• CCA- chromated copper arsenate• ACQ- alkaline copper quaternary• CBA- copper boron azole• CC- copper citrate• CDDC- copper dimethyldithiocarbamate

Wood Preservative Inorganic Organic

CCA Chromium, 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

CHR

OM

IUM

CO

NCE

NTRA

TIO

N (m

g/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

Leaching Tests Results 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

4050

60

70

Copper (mg/l)

CCA CDDC CBA ACQ CC

Comparison of Copper Leachability

(concentration in mg/l)

SPLP

05

10152025303540

MassCopper

Leaching(%)

CCA CDDC CBA ACQ CC

Comparison of Copper Leachability(mass leaching in %)

SPLP

05

10152025303540

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

Aquatic Toxicity of Alternative Chemical Treated

Wood Leachates

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(%)

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%E

C50

(%)

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

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

Interpretation

• Results show that alternative treated wood products are expected to leach more copper to aquatic systems

• Since copper is a potent aquatic biocide, this raises a concern

Interpretation

• However, several additional factors will impact the true impact on an aquatic system:– Dilution– Sedimentation– Binding/Complexation

• How do you account for these factors?

Predict Aquatic Concentrations

• Piling in unidirectional flow

Brooks conceptualization of a Pile in unidirectional flow

=15 degrees

Current

Piling of radius Rp

Dilution Zone

Point at which water column predictions are made

Transient (D) along which predictions are made

Copper Leaching from Pressure Treated Wood

0

2

4

6

8

10

12

14

1 2 4 7 10 14 18 21

No. of Days

Cu

Con

cent

ratio

n in

mg/

L

CBA

ACQ

CCA

Relative Risk

• Results from previous work indicates risk from CCA-treated wood is greater with respect to human toxicity and waste management

• Results from this work indicates that risk from alternative-treated wood is greater with respect to aquatic toxicity

Relative Risk

• Relative risk factors were calculated for different risk pathways by comparing measured concentrations to known benchmarks

Recommendations

• Further evaluation of co-biocides needed

• Impacts of alternatives in aquatic systems should be evaluated in field studies

Questions?