Post on 06-Jan-2018
description
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?