As and Cr Speciation of New & Weathered CCA-Treated Wood
Purpose Basic As and Cr Chemistry Solvent-Extraction Leaching Experiments (Cr & As) As Analysis of GW at Florida C&D Landfills As Leaching from Lysimeters Outline
Quantify As & Cr species in leachates from CCA-treated wood As & Cr toxicity varies with each specie As & Cr mobility varies with each specie Estimate the impact of As & Cr leaching from in-service & disposed CCA-treated wood on groundwater Purpose & Motivation of Study
As Speciation Arsenic As(III) As(V)MMAADMAA Inorganic Organic Valence Inorganic Arsine (g)
Arsenic As(III) As(V)MMAADMAA Inorganic Organic Valence Inorganic Arsine (g) As Speciation Toxicity & Mobility
Arsenic As(III) As(V)MMAADMAA Inorganic Organic Valence Inorganic Arsine (g) As Speciation Toxicity & Mobility
Cr Speciation Chromium Cr(VI)Cr(III) Inorganic Valence Inorganic Cr Speciation Toxicity & Mobility
Analytical Methods for Speciation As: HPLC-ICP-MS or HPLC-HG-AFS Cr: IC for Cr(VI) Total Cr by ICP-AES Cr(III) by difference
Solvent Extraction Study
CCA-treated wood subjected to leaching solvent, rotated for 18 2 hrs & filtered. Filtrate analyzed for As & Cr species New CCA-treated wood TCLP SPLP DI Water Rainwater Untreated 0.25 pcf 0.6 pcf 2.5 pcf Weathered CCA-treated wood Playground Utility pole Fence C&D waste Solvent-Extraction of CCA-Treated Wood pH 1,2,3. etc..
pH Experiment - New Wood (0.32 pcf) As(V) was the only specie detected Highest concentration at extreme pH Environmental pH range ~ 5mg/L Total As (As(V)) – HPLC-HG-AFS Total As – ICP-AES Environmental pH
pH Experiment - Weathered Wood (0.41 pcf) As(III) & As(V) detected, As(III) up to pH 9.5 Environmental pH range – Total As increase Total As > 5 mg/L pH Arsenic Concentration (mg/L) Environmental pH As(III) As(V) Total As - HPLC-HG-AFS Total As – ICP-AES
J (46.01) L (27.54) H (24.57) K (20.37) G (13.03) I (9.12) D (5.90)C (5.63) B (4.06) E (3.86) F (3.62) A (1.49) M (24.05) N (6.26)Q (5.79)O (5.28) R (5.47) S (3.16)P (1.96) V (1.86) T (1.41) SPLP Arsenic Concentration (mg/L) As(III) As(V) Total As Retention (kg/m 3 ) New Weathered SPLP New & Weathered Wood (Simulated Rain Water)
Leachate As Conc. vs CCA Retention kg/m 3 New Weathered Total As Conc. (mg/L) Total As Conc. (mg/L) SPLP Rainwater TCLP DI Water Seawater
Environmental pH pH Experiment - New Wood (0.32 pcf) Cr(III) predominates Cr(VI) observed at high pH values
Unburned wood Cr as Cr(III) No Cr(VI) observed SPLP New & Weathered Wood (Simulated Rain Water)
Ashing results in converstion of Cr(III) to Cr(VI) Cr in ash leachate exists as Cr(VI) Ash – SPLP and TCLP
Ash Results for Chromium Low Retention Level Wood Leaches More Cr
As & Cr species leaching pH dependent At environmental pH range (6-10) - As ~ 5mg/L - Cr ~ 1 mg/L More As leaching from weathered wood than new wood As(III) As Leaching in rainwater, TCLP, SPLP comparable. Seawater less. Incineration results in the conversion of some Cr(III) to Cr(VI). Greater conversion for lower retention levels. Summary
? ? Questions ?