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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?