Transcript A Comparative Study of the Leaching and Toxicity of

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
Interpretation
&
Recommendations
Aquatic Toxicity
Analysis
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 Components
Wood
Preservative
Inorganic
Organic
CCA
Chromium,
Copper, Arsenic
N/A
ACQ
Copper, Boron
DDAC
CBA
Copper, Boron
Tebuconazole
CC
Copper
Citrate
CDDC
Copper
CDDC
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
Preservative
CCA
ICP-AES
N/A
ACQ
ICP-AES
Two-Phase Titration
CBA
ICP-AES
GC/MS
CDDC
ICP-AES
Spectrophotometer
CC
ICP-AES
IC
Inorganic
Organic
Chemical Leaching
Results
Start with CCA-Treated Wood
ARSENIC CONCENTRATION (mg/L)
Arsenic Concentrations Found in
CCA-treated Wood Leachates
10
CCA-1
8
6
TC= 5 mg/L
4
2
0
CCA-2
DI
TCLP
SPLP
SW
Copper Concentrations Found in
CCA-treated Wood Leachates
12
Copper Concentration (mg/L)
CCA-1
CCA-2
10
8
6
4
2
0
DI
TCLP
SPLP
SW
CHROMIUM CONCENTRATION (mg/L)
Chromium Concentrations Found in
CCA-treated Wood Leachates
4
3
CCA DI
UNTREATED DI
CCA-R TCLP
CCA SPLP
UNTREATED SPLP
CCA-R SW
CCA-R DI
CCA TCLP
UNTREATED TCLP
CCA-R SPLP
CCA SW
UNTREATED SW
2
1
0
DI
TCLP
SPLP
SW
Difference in Leaching Tests
for Alternative Chemical
Treated Wood
Copper Concentration (mg/L)
Copper Boron Azole
60
50
40
30
20
10
0
CBA DI
CBA TCLP CBA SPLP CBA SW
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
Comparison of Copper Leachability
(concentration in mg/l)
70
60
50
Copper 40
(mg/l) 30
20
10
0
CCA
SPLP
CDDC
CB
ACQ
CC
Comparison of Copper Leachability
(mass leaching in %)
40
35
30
Mass 25
Copper
20
Leaching
15
(%)
10
5
0
CCA
SPLP
CDDC
CBA
ACQ
CC
Comparison of Total Metal Leachability
(mass leaching in %)
40
35
30
Mass 25
Metal
20
Leaching
15
(%)
10
5
0
CCA
SPLP
CDDC
CBA
ACQ
CC
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
Comparison of Toxicity Tests
(SPLP Leaching of CDDC)
10
1
0.1
0.01
ot
ox
M
ic
r
e
pl
at
M
et
Al
ga
e
ap
hn
ia
0.001
D
EC50/
IC50
(%)
C.daphnia
0.25%
EC50 (%)
0.20%
0.15%
0.10%
0.05%
0.00%
SPLP
CCA-1 CCA-2 ACQ CC CDDC CBA
S.capricornutum
0.08%
0.07%
EC50 (%)
0.06%
0.05%
0.04%
0.03%
0.02%
0.01%
0.00%
SPLP
CCA-1
CCA-2
ACQ
CC
CDDC
CBA
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
1
2
EC50 (% )
R = 0.869
0.1
0.01
0.001
1
10
100
Copper (mg/l)
1000
C.dubia Copper/Leachate
Comparison
EC50 (%)
1
EC50 Cu = 11 ug/l
0.1
0.01
EC50 Cu = 2.4 ug/l
0.001
1
10
100
Copper Concentration (mg/L)
1000
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?