Lynn W

Philip M. Gschwend

Professor of Civil and Environmental Engineering
Ph.D 1979, W.H.O.I.
Room 48-415
Phone: (617) 253-1638
Email: pmgschwe@mit.edu

The overarching goal of our research is to develop means to predict the fates of organic chemicals in natural and engineered environments. To that end, we pursue studies of processes controlling compound fates. We emphasize studies of the sorption of organic chemicals, including interactions with colloidal phases. We also emphasize field studies seeking to quantify the distributions of organic compounds so that we can deduce the importance of individual transport or transformation processes.

Fate of Semivolatile Organic Compounds Discharged to Surface Drainage Systems from Superfund Sites
Xenobiotic Organic Compound Cycling in Coastal Waters
Manipulating Subsurface Colloids to Enhance Cleanup of DOE Waste Sites

Fate of Semivolatile Organic Compounds Discharged to Surface Drainage Systems from Superfund Sites (NIEHS)

We seek to predict the transport of organic compounds via drainage systems away from Superfund sites. Our approach involves collecting sediment and water samples from a drainage area adjacent to a large Superfund site and then analyzing these materials for the organic compounds present. We also monitor the temporal changes in their occurrence throughout the year. Coupled with measures of flows, we calculate the inputs and outflows of specific chemicals from particular regions of the drainage. To the extent that chemical outputs do not match inputs, we hypothesize feasible sources and sinks which might explain the discrepancy and then test proposed mechanisms via controlled laboratory observations.

In order to assess organic chemicals in coastal marine environments, we must (1) be able to characterize the processes controlling their chemical speciation. and (2) be able to evaluate the rates of processes affecting particles in coastal seawater. The first objective requires us to examine the distribution of contaminants like PCBs and PAHs among dissolved, colloidal, and settling particle phases. Moreover, we seek to find properties of the sorbates, sorbents, and solutions from which these "phase" distributions can be estimated a priori. The second objective requires us to assess quantitatively the fluxes of solids from the water column to the sediment beds below.

Our approaches for examining the phase distributions of organic contaminants in coastal seawaters has involved (a) time-resolved fluorescence quenching and small concentrations of spiked fluorophores to observe the importance of colloidal phases for binding such organic chemicals, and (b) measurements of a very special sorbent, soot, which appears to play a very significant role in the speciation of combustion-derived pollutants like PAHs.

Our approaches for examining the settling of particles involve using both water-column and sediment-bed measurements. By measuring U238-Th234 disequilibria in the water column, we extract settling rate constants for the suspended solids at any particular site and time. Our second approach to verify these water column deductions involves use of Pb210-dated sediment cores to evaluate the import fluxes of the same chemicals into the bed. Comparisons of these two independent measures is used to demonstrate the effectiveness of the U238-Th234 disequilibrium approach.

Xenobiotic Organic Compound Cycling in Coastal Waters (ONR)

Manipulating Subsurface Colloids to Enhance Cleanup of DOE Waste Sites (DOE)

Our research is aimed at (a) developing improved understandings of the processes involved in holding colloids immobile in subsurface media, and (b) exploring the prospects for mobilizing such colloids to enhance cleanups. These colloids are important because they are the chief sorbent media for many contaminants of concern.

Using aquifer materials from a Southeastern Coastal Plain site, we explore the mechanisms which control the releases of attached colloids into the groundwater flow. We use electron microscopy observations of the intimate particle:particle juxtapositions in the solids. Next, by flushing these aquifer sands with various aqueous solutions, we have found that the bulk of the attached colloids appear to be (a) bound to one another via intermediary amorphous iron oxyhydroxides, and (b) attracted to the other colloids by juxtapositions of oppositely charged phases.

In our continuing efforts, we have returned to the field site, where the aquifer solids were initially collected, and tested the possibility of mobilizing colloids in the ground. Our efforts have proven successful as measured by the presence of turbidity in suitably altered flushing solutions (and the absence of turbidity in control tests.) We are now completing measurements of the ancillary parameters necessary to interpret the field tests.

Selected Publications

Gustafsson, ?, F. Haghseta, C. Chan, J.K. MacFarlane, and P.M. Gschwend. Quantification of the dilute sedimentary "soot-phase": Implications for PAH speciation and bioavailability. Environ. Sci. Technol. 31, 203-209, 1997.
Gustafsson, ? and P.M. Gschwend. Aquatic colloids: Concepts, definitions, and current challenges. Limnol. Oceanogr. 42, 519-528, 1997.
Gustafsson, ?, P.M. Gschwend, and K.O. Buesseler. Using 234Th disequilibria to estimate the vertical removal rates of polycyclic aromatic hydrocarbons from the surface ocean. Marine Chemistry, 57 , 11-23, 1997.
Gustaffson, ?, P.M. Gschwend, and K.O. Buesseler. Settling removal rates of PCBs into the Northwestern Atlantic derived from 238U-234Th disequilibria. Environ. Sci. Technol. 31, 3544-3550, 1997.
Holm閚, B.A. and P.M. Gschwend. Estimating sorption rates of hydrophobic organic compounds in iron oxide- and aluminosilicate clay-coated aquifer sands. Environ. Sci. Technol. 31, 105-113, 1997.
Luthy, R.G., G.R. Aiken, M.L. Brusseau, S.D. Cunningham, P.M. Gschwend, J.J. Pignatello, M. Reinhard, S.J. Traina, W.W. Weber Jr., and J. C. Westall. Sequestration of hydrophobic organic contaminants by geosorbents. Environ. Sci. Technol. 31, 3341-3347, 1997.
Swartz, C.H., A.L. Ulery, and P.M. Gschwend. An AEM-TEM study of nanometer-scale associations in an aquifer sand: Implications for colloid mobilization. Geochim. Cosmochim. Acta 61 , 707-718, 1997.