Leaching of Alternative Chemical Treated Wood and Aquatic Toxicity

1. Leaching of Alternative Chemical Treated WoodandAquatic Toxicity of Alternative Chemical Treated Wood Leachates

2. 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

3. 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

4. Leaching of Alternative Chemical Treated Wood

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

6. Wood Preservative Components

7. Sample Preparation

8. 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

9. Size Reduction • Cut wood using a 10’’ miter saw • Ground using a pulverizer

10. Leaching Tests • SPLP- Synthetic Precipitation Leaching Procedure • TCLP- Toxicity Characteristic Leaching Procedure • Synthetic seawater (Instant Ocean) • DI water

11. Analytical Procedures

12. Chemical LeachingResults

13. Start with CCA-Treated Wood

14. Arsenic Concentrations Found in CCA-treated Wood Leachates TC= 5 mg/L DI TCLP SPLP SW

15. DI TCLP SPLP SW Copper Concentrations Found in CCA-treated Wood Leachates

16. DI TCLP SPLP SW Chromium Concentrations Found in CCA-treated Wood Leachates

17. Leaching Tests Results for Alternative Chemical Treated Wood

18. Copper Boron Azole

19. 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

20. Compare Copper Leachability

21. Comparison of Copper Leachability(concentration in mg/l) SPLP

22. Comparison of Copper Leachability(mass leaching in %) SPLP

23. Comparison of Total Metal Leachability(mass leaching in %) SPLP

24. 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

25. Aquatic Toxicity of Alternative Chemical Treated Wood Leachates

26. Aquatic Toxicity Assays Why conduct? Chemical leaching data can not account for other factors that affect aquatic toxicity, such as complexation, binding, interaction, etc…

27. MetPLATETM • Metal bioavailability • Short term acute toxicity assay • 96-well microplate • CPRG- enzyme • Absorbance measured at 570 nm

28. Microtox • General toxicity assay • Uses the decrease in the bioluminescence of the marine organism Vibrio fisherii to measure aquatic toxicity

29. Selenastrum capricornutum • Chronic toxicity assay • 96-hr test • Relative inhibition of the leachates is measured based on a negative control

30. 48 hour acute bioassay Samples analyzed in triplicate with 5 dilutions Ten neonates per sample Count the number of live/dead neonates Ceriodaphnia dubia

31. Toxicity Expressions • EC50- mg/L or percent • LC50- mg/L or percent • IC50- mg/L or percent

32. How Do Toxicity Tests Compare? • Let’s look at results on CDDC on SPLP leachate

33. Comparison of Toxicity Tests(SPLP Leaching of CDDC)

34. SPLP

35. SPLP

36. 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?

37. Leachate EC50s (C.dubia) vs. Copper Concentrations

38. 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

39. 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

40. 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?

41. Predict Aquatic Concentrations • Piling in unidirectional flow Brooks conceptualization of a Pile in unidirectional flow Point at which water column predictions are made =15 degrees Transient (D) along which predictions are made Dilution Zone Current Piling of radius Rp

42. Copper Leaching from Pressure Treated Wood CBA ACQ CCA

43. 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

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

45. Recommendations • Further evaluation of co-biocides needed • Impacts of alternatives in aquatic systems should be evaluated in field studies

46. Questions?