Leaching of Alternative Chemical Treated Wood and Aquatic 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 InorganicOrganic CCA Chromium, Copper, Arsenic N/A ACQCopper, BoronDDAC CBACopper, BoronTebuconazole CCCopperCitrate CDDCCopperCDDC 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 Preservative InorganicOrganic CCAICP-AESN/A ACQICP-AESTwo-Phase Titration CBAICP-AESGC/MS CDDCICP-AESSpectrophotometer CCICP-AESIC

Chemical Leaching Results

Start with CCA-Treated Wood

Arsenic Concentrations Found in CCA-treated Wood Leachates DITCLPSPLPSW TC= 5 mg/L

Copper Concentrations Found in CCA-treated Wood Leachates SPLPDITCLPSW

Chromium Concentrations Found in CCA-treated Wood Leachates SPLPDITCLPSW

Leaching Tests Results for Alternative Chemical Treated Wood

Copper Boron Azole

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) SPLP

Comparison of Copper Leachability (mass leaching in %) SPLP

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…

MetPLATE TM 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 EC 50 - mg/L or percent LC 50 - mg/L or percent IC 50 - 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)

SPLP

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 EC 50 s (C.dubia) vs. Copper Concentrations

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 R p Dilution Zone Point at which water column predictions are made Transient (D) along which predictions are made

Copper Leaching from Pressure Treated Wood 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?