Grantee Research Project Results
1997 Progress Report: Sorption/Desorption Kinetics and Access to Transient Reactants Photochemically Generated from Natural Dissolved Organic Matter
EPA Grant Number: R825219Title: Sorption/Desorption Kinetics and Access to Transient Reactants Photochemically Generated from Natural Dissolved Organic Matter
Investigators: Burns, Susan E.
Institution: Western Michigan University
EPA Project Officer: Hahn, Intaek
Project Period: November 1, 1996 through October 30, 2001
Project Period Covered by this Report: November 1, 1996 through October 30, 1997
Project Amount: $461,023
RFA: Exploratory Research - Early Career Awards (1996) RFA Text | Recipients Lists
Research Category: Early Career Awards
Objective:
The research objectives are to 1) determine how the kinetics of sorption to and desorption from natural dissolved organic matter (DOM) vary with KDOC and chemical class, 2) determine how the kinetics of sorption/desorption affect the access chemicals have to transient reactants occurring inside and outside of DOM molecules, and 3) incorporate the effects of sorption/desorption kinetics into a photochemical model that is compatible with existing descriptions of photochemistry in natural waters (e.g., SOLAR).Progress Summary:
The kinetics of sorption to and desorption from DOM have been measured for a series of moderately hydrophobic PAHs and PCBs (Kow>103-105). The resulting rate constants for sorption to (ks) and desorption from DOM (kd) are higher than the values reported by Hassett and Millicic (1) for 2,2',5,5'-tetrachlorobiphenyl (PCB 47). For example, the measured value of kd for naphthalene is 3.24x10-3 min-1. while the corresponding value for PCB 47 is 7.1x10-4 min-1. Similarly, the value of ks for naphthalene is 1.58x10-3 L (mg DOC)-1 min-1 compared with 1.74x10-4 L (mg DOC)-1 min-1 for PCB 47. However, the PCBs investigated thus far all have lower KDOC values than PCB 47 (~104.86), suggesting that PCB sorption/desorption kinetics increase with decreasing KDOC. The range of KDOC values for the PAHs extends beyond that of PCB 47, suggesting that sorption/desorption kinetics for PAHs are higher, as a class, than PCBs.Values of kd measured thus far exceed 0.2 min-1, corresponding to maximum residence times in DOM of 5 minutes. In contrast, kd values for naphthalene and PCB 47 correspond to lifetimes in DOM of approximately 300 and 1400 minutes, respectively. Respective residence times for naphthalene and PCB 47 outside DOM are approximately 650 and 6000 minutes per unit DOC (mg/L).
These residence times begin to explain current and previous observations about the access organic contaminants have to reactivity originating inside and outside of DOM. In previous work, tests of access to intra- and extra-DOM reactivity employed systems in which the fraction of probe compound sorbed to DOM (fb) was either ?0.95 or #0.05, meaning the probe compound was either all in the intra-DOM phase or all in the extra-DOM phase. Under these conditions, slow DOM exchange kinetics would be expected to translate into access only to the reactivity of the resident phase, consistent with observation. In the current work, in addition to repeating these observations, compounds exhibiting faster DOM exchange kinetics are observed to have access to both intra- and extra-DOM reactivity.
1. Hassett, J.P.; Millicic, E. 1985 Environ. Sci. Technol. 19, 638.
2. Burns, S.E.; Hassett, J.P.; Rossi, M.V. 1997 Environ. Sci. Technol. 31, 1365.
3. Burns, S.E.; Hassett, J.P.; Rossi, M.V. 1996 Environ. Sci. Technol. 30, 2934.
Future Activities:
Measurements of sorption/desorption kinetics will be expanded to more hydrophobic PAHs and PCBs and will be extended to chlorobenzenes and chlorinated hydrocarbon pesticides. Measurements will also be extended to DOM from different sources. Tests of access to intra- and extra-DOM reactivity will be conducted using time resolved spectroscopic methods to relate actual reactivity with molecular probe-based measurements of reactivity. Finally, the combined kinetic and reactivity results will be integrated to allow the results to be used predictively.Journal Articles:
No journal articles submitted with this report: View all 6 publications for this projectSupplemental Keywords:
water column, rivers, lakes, UV radiation, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Geographic Area, Water, Restoration, Aquatic Ecosystem Restoration, Environmental Chemistry, Great Lakes, Ecology and Ecosystems, equilibrium partition coefficients, transient reactants, ecological impact, sorption kinetics, Aldrich humic acids, photochemical reactions, hydroxyl raadicals, degradation rates, aquatic ecosystems, dissolved organic matterProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.