A rsenic Speciation Based on Molecular Weight : Equilibrium D ialysis Sheena Powell Szuri, BS Florida International University TAG Meeting January 10, 2003

Purpose of Study Arsenic (As) leaching from CCA structures is a problem Arsenic (As) leaching from CCA structures is a problem As can form complexes with compounds of different molecular weight (an indication of particle size) As can form complexes with compounds of different molecular weight (an indication of particle size) Dissolved organic matter (DOM), Fe, Mn, Ca, Al Dissolved organic matter (DOM), Fe, Mn, Ca, Al Size of complexes of As affect bioavailability & mobility through soil Size of complexes of As affect bioavailability & mobility through soil Photo: Ken Helle for the St. Petersburg Times

Method Development Equilibrium Dialysis Equilibrium Dialysis Facile separation of compounds based on molecular weight/size Facile separation of compounds based on molecular weight/size Inductively-Coupled Plasma Mass Spectrometry (ICP/MS) Inductively-Coupled Plasma Mass Spectrometry (ICP/MS) Hydride-Generation Atomic Fluorescence Spectroscopy (HG/AFS) Hydride-Generation Atomic Fluorescence Spectroscopy (HG/AFS)

Equilibrium Dialysis

The Dialysis Membranes Material: Material: cellulose ester cellulose ester polyvinylidene fluoride (PVDF) polyvinylidene fluoride (PVDF) nitrocellulose nitrocellulose Wet or Dry Wet or Dry Treatment Treatment Clamps Clamps Pore Size Pore Size 0.5kD 0.5kD 3.5kD 3.5kD 12kD 12kD

Experimental Design

Control Study Determine best equilibrium time for 3 membrane sizes (0.5kD, 3.5kD, 12kD) Time 1 Time 2 Time 3 As W + As Equilibrium W As W + As

Arsenic Concentration 0.5kD Inside Outside Equilibrium >3 days

Arsenic Concentration 3.5 kD Inside Outside Equilibrium <1 day

Arsenic Concentration 12kD Inside Outside Equilibrium <1 day

Leachate Study Determine concentration of As in different molecular weight fractions Determine concentration of As in different molecular weight fractions Sample collection Sample collection A Construction and Demolition (C&D) landfill A Construction and Demolition (C&D) landfill A Municipal Solid Waste (MSW) landfill A Municipal Solid Waste (MSW) landfill L KCl L KCl + L

HG-AFS ICP-MS C&D Leachate I I II I I OO O O O O

MSW Leachate HG-AFS ICP-MS I I I I I I O OOO O O

Conclusions Equilibrium dialysis - fast, simple, effective Equilibrium dialysis - fast, simple, effective As bound to molecules less than 3.5kD (also less than 12kD) As bound to molecules less than 3.5kD (also less than 12kD) Future studies: Future studies: Acquire additional leachate samples Acquire additional leachate samples Examine influence of matrix elements (DOM, Fe, Mn, Ca, Al) Examine influence of matrix elements (DOM, Fe, Mn, Ca, Al) Examine influence of physicochemical parameters (pH, Eh, salinity) Examine influence of physicochemical parameters (pH, Eh, salinity) Need to investigate leachates with 0.5kD membrane Need to investigate leachates with 0.5kD membrane

Sheena Powell Szuri, BS Florida International University TAG Meeting January 10, 2003 Questions?