Department of Civil and Environmental Engineering
Stanford University
Terman Engineering Center, Room M-52
Stanford, CA 94305-4020
Telephone: (650) 723-3921
Fax: (650) 725-8662
Email: luthy@stanford.edu
Research Interests
Research Focus
The research of my group focuses on environmental engineering and water quality, including physicochemical processes with application to sustainable practices. Broadly, this work addresses the fate of hydrophobic organic compounds and interdisciplinary approaches to understand the behavior and bioavailability of organic contaminants and the application of these approaches to environmental quality criteria and new cleanup practices, and implications for water reuse and ecological regeneration.
We study the behavior of so-called emerging contaminants, like perfluorochemicals and compounds in consumer products, as well as legacy contaminants such as polychlorinated biphenyls [PCBs], polycyclic aromatic hydrocarbons [PAHs], and DDT.
We are working on the PCB problem in rivers and estuaries, including San Francisco Bay. PCBs accumulate in fish and cause consumption advisories for resident fish like striped bass in San Francisco Bay. We study interactions among contaminants, sediments, and benthic biota to understand the bioavailability of organic contaminants and gain insights on approaches to control contaminant bioavailability and improve water and sediment quality. Bioavailability depends on how strongly compounds like PCBs or DDT are bound to soil or sediment and our recent work suggests that adding sorbent carbonaceous material to sediment is a new technology for in situ sediment treatment that avoids all the difficult problems resulting from dredging.
Recent advances in understanding the environmental transport and fate of PCBs, PAHs and DDT provide stronger scientific and technological underpinnings for managing problems with these organic chemicals. However, how we apply this understanding to emerging contaminants is a challenge for the future. Emerging contaminants like perfluorinated organics, pharmaceuticals, and fragrances are receiving increased attention because of their widespread use and potential harmful effects. But we lack good models and adequate biological and physicochemical understanding of how these compounds are transformed and interact with biota. Addressing these problems requires interdisciplinary collaborations among environmental engineers, environmental geologists, biologists, chemists and chemical engineers, and toxicologists, for example.
Recent Projects
Field Testing of Activated Carbon Mixing and In situ Stabilization of PCBs in Sediment
Sponsor: Department of Defense, Environmental Security Technology Certification Program.
Partners: US Army Engineer Research and Development Center, University of Maryland Baltimore County, US Navy, Aquatic Environments Inc., Compass Environmental Inc.
Problem Statement. Contaminated sediments pose challenging cleanup and management problems. Currently the standard approach to addressing contaminated marine “mud flat” sediments is the expensive and sometimes ineffective and controversial ex situ process of dredging and off-site disposal. Finding acceptable and cost-effective in situ technologies for contaminated sediment management may increase public acceptance of local management of sediment contamination as well as significantly reduce expenditures on environmental restoration.
Technical objectives. The project seeks to demonstrate and validate an innovative treatment for in situ stabilization of PCBs in sediment under field conditions at Hunters Point Naval Shipyard. We are assessing the effectiveness of activated carbon (AC) sorbent mixed with sediment as a cost-effective, in situ, non-removal, management strategy for reducing the bioavailability of hydrophobic organic contaminants such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs).
Measurement and Modeling of Ecosystem Risk and Recovery for In Situ Treatment of Contaminated Sediments
Sponsor: US Department of Defense, Strategic Environmental Research and Development Program
Partners: US Geological Survey
Background: Many Department of Defense (DoD) and US EPA Superfund sites are contaminated with polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), which are persistent, bioaccumulative, and toxic, and pose major ecological problems. An ESTCP-funded in situ sediment treatment study is underway to reduce bioavailable PCBs at Hunters Point Naval Shipyard Parcel F (San Francisco Bay, CA). There is a need to monitor ecosystem health before and after treatment to assess the efficacy of treatment and ensure that the remediation activity does not harm the native ecosystem. Conventional ecosystem health determinants, such as benthic organism bioassays and community surveys, are time-consuming and expensive. There are currently no fast, inexpensive field methods to predict bio-uptake of contaminants and explain post-treatment ecological effects.
Objectives: The goal of the project is to develop a comprehensive strategy to assess the ecological recovery of a contaminated site after in situ treatment. The main objectives of this strategy are to incorporate rapid, inexpensive assessment tools to measure contaminant concentrations in the sediment pore water, to use a biodynamic modeling approach to predict contaminant burden at the base of the food web, and to develop a general model to predict the ecological characteristics of recovery. The three objectives are tied together in that biodynamic modeling predictions of contaminant uptake, which depend on contaminant pore water concentrations measured with the rapid assessment tools, are employed in the general ecosystem recovery model. Using this comprehensive approach, we will assess the ecological recovery at Hunters Point after in situ remediation by activated carbon amendment.
Summary of Technology: Two rapid assessment tools will be used to measure PCB sediment pore water concentrations: polyethylene sampling devices (PEDs) and a PCB immunoassay. The tools will be tested in the laboratory and validated in the field, and the results will be correlated with those obtained using conventional methods. Once correlated, the rapid, cost-effective measurement tools will allow for greater data resolution while monitoring ecosystem recovery. The measured sediment pore water PCB concentrations will also serve as inputs to a biodynamic model, which will be used to predict contaminant uptake by native benthic organisms. This approach uses measured uptake, elimination, and metabolism rates and allows for predictive modeling under a variety of conditions. Building upon the biodynamic modeling for individual species, a general model will be constructed to predict the ecological characteristics of recovery at a contaminated site post-treatment. In contrast to the conventional benthic community survey method, which is time-consuming and non-transferable, this modeling approach requires only basic information about taxa-specific biodynamics, which only need to be established once for each species, combined with data on the species available for community recruitment.
Biodynamic Modeling of Perfluorochemical Bioaccumulation to Assess the Use of Recycled Wastewater for Urban Stream Flow Augmentation and Habitat Regeneration
Background and Problem Statement: Access to clean water is a major challenge of the 21st century, particularly in light of anticipated urban population growth. To address the increasing demand for water, many municipalities are advocating the use of recycled water for non-human consumption applications. Recycled water, which has been treated in wastewater treatment plants (WWTPs) to remove the vast majority of chemicals and pathogens, can be used for irrigation, cooling, commercial laundries, and a wide variety of other applications. As a state with limited water resources, California has over 360 locations using recycled water. A recently proposed use for recycled water in the city of San Jose, CA, is stream flow augmentation for habitat restoration. The Santa Clara Valley Water District (SCVWD) plans to use recycled water to augment stream flow in Upper Silver and Coyote Creeks during the low-flow summer season. These two urban creeks provide important river habitat and aesthetic and recreational value for residents of San Jose.
While recycled water is treated to the highest standards possible for non-human consumption, traditional WWTP processes may not remove all trace organic pollutants. One such class of pollutants is perfluorinated chemicals (PFCs), which are used in a variety of industrial and household products (e.g., fire-fighting foams and textile and paper coatings) and have been detected in wildlife and in humans around the globe. Research conducted in the Luthy lab and by others indicates that WWTPs are likely the dominant sources of PFCs to the urban environment. PFCs are persistent, bioaccumulative, and may be toxic to humans; perfluorooctanoic acid (PFOA) has been labeled a likely human carcinogen in a draft EPA risk assessment.8
Current research in the Reinhard lab indicates that trace amounts of PFCs appear sporadically in surface water samples from Upper Silver and Coyote Creeks; however, they consistently measure PFCs at concentrations an order of magnitude higher in the San Jose recycled water proposed for use in the flow augmentation of these creeks. To ensure that this habitat restoration project does not introduce new problems to the ecosystem it is designed to restore and to address questions about PFC fluxes in the environment, more information is needed concerning the uptake and elimination of these chemicals in organisms at the base of the food web. Biodynamic modeling, in which contaminant bioaccumulation is described as a mass balance of uptake (from water and food particles) and elimination, has been successfully applied in the Luthy lab to predict body burdens of polychlorinated biphenyls (PCBs) in a freshwater clam, Corbicula fluminea, and a marine clam, Macoma balthica.9 Such a modeling approach applied to PFCs may offer a better understanding of the mechanisms of bioaccumulation for these chemicals.
Project Description: The goal of the proposed project is to assess the ecological impacts of stream flow augmentation with recycled water in terms of contaminant accumulation at the base of the food web. To achieve this goal, we will use a biodynamic modeling approach coupled with field studies to understand the mechanisms of bioaccumulation of PFCs using a freshwater clam, C. fluminea, as a model organism. Our specific objectives are to:
The scope of this project will likely expand and involve collaborators from other laboratories and programs, including biology.
Perfluorochemical Biotransformation, Fate, and Availability in the Environment
Problem Statement: Found in such diverse products as pesticides, popcorn bags, and Prozac, fluorinated organic compounds are widely used in many commercial and industrial applications. Perfluorinated organic compounds, in which all carbon-hydrogen bonds are replaced with carbon-fluorine bonds, are both hydrophobic and oleophobic and are commonly used in carpet and textile coatings (e.g., ScotchGard) and surfactants (e.g., fire-fighting foams). Despite their many uses, little is known about the environmental behavior or persistence of perfluorinated compounds once they are released from industrial, commercial, and residential waste streams. However, these compounds have been detected in fish, birds, and marine mammals from around the globe, and have been widely detected in human blood. In light of these recent findings, 3M Company, one of the many perfluorinated organic compound chemical manufacturers, moved to discontinue its perfluorooctanesulfonyl fluoride (PSOF) and perfluorooctanoic acid (PFOA)-based product lines.
Objectives: This project aims to examine the biotransformation, fate, and availability of model fluorinated organic compounds in aquatic sediments. Sediment processes may play an important role in the movement of perfluorinated compounds from waste streams into the food chain. The importance of sediments in the fate of fluorinated compounds will be examined by determining the extent to which these compounds partition into and are transformed in sediments. Furthermore, by measuring the rates of biotransformation and sorption processes, examining the impact of partitioning on biotransformation and bioaccumulation, and identifying microbial populations responsible for observed transformations, substantial data will be collected and used to develop a scoping-level box-model of the ultimate environmental fate of these model compounds.
Musk Compound Fate in Effluent Discharges and Sediments
Problem Statement: Unlike many industrial chemicals, pharmaceuticals and personal care products (PCPs) have received relatively little attention with respect to their environmental behavior. Although the production of new products involves studies of human health effects, the impacts of the products once released to the environment are almost never considered. In contrast, new pesticides and industrial chemicals are now subject to regulations requiring substantial environmental testing before production can begin. PCPs are widely used in modern society and are then released to the environment at a rapid rate. As a result, even compounds that are not persistent could cause environmental impacts if their concentrations are maintained by the constant loading. There is also the possibility of cumulative effects of products with similar uses. Synthetic musk fragrances including nitromusks and polycyclic musks are PCPs of particular concern because their physico-chemical properties are similar to those of many persistent organic pollutants.
Objectives: Although synthetic musk compounds have been used as fragrances for over a century, little is known about their behavior in aquatic ecosystems. This work examines the location, sources, and impacts of these compounds in San Francisco Bay discharges and sediments. Because musks are known to be hydrophobic, they are likely to bind strongly to organic carbon in sediments. The behavior of other hydrophobic chemicals suggests that this compartment could play an important role in determining the fate and bioavailability of musks. However, the addition of the nitro groups as well as the potential for degradation to more polar metabolites makes the behavior of musks difficult to predict. This project is designed to address this uncertainty. This work entails the measurement of nitromusks and polycyclic musks in sediments and effluent discharges to determine if which musks are present and at what concentrations. Models will be constructed to describe the behavior of these compounds in discharges to San Francisco Bay.
Polycyclic Aromatic Hydrocarbons and Lampblack Residuals from Former Oil Gas Plants Sites
Prior to the distribution of natural gas, a manufactured gas was produced in California from gasifying crude oil. These operations resulted in lampblack solid residues found at many former oil-gas sites. This study evaluates lampblack-impacted field soils from four sites in California that formerly housed oil-gas process operations and assesses the properties of lampblack, the distribution polycyclic aromatic hydrocarbons (PAHs) between mineral, oil, and lampblack phases, and the associated effects on the partitioning of PAHs between lampblack and water. PAH analyses on density-separated components determined the distribution of PAHs among particle types. Microprobe two-step laser desorption/laser ionization mass spectrometry compared PAH fingerprints on solids; Fourier transform infrared microspectroscopy and nuclear magnetic resonance provided data on lampblack organic carbon type; and scanning electron microscopy with wavelength dispersive X-ray spectroscopy gave elemental microanalysis. Long-term aqueous equilibration measurements used an air bridge technique and were compared with centrifugation with alum flocculation. The significant findings of this study are: 1) oil-gas lampblack residuals comprise aromatic carbon with soot-like structure; 2) PAHs found in aged site soils are associated primarily with lampblack particles; 3) an aromatic oil phase is present within the lampblack samples; 4) PAH partitioning between lampblack and water depends on the relative importance of aromatic oil matter or lampblack carbon; and 5) whether oily matter or lampblack carbon governs PAH partitioning to water results in nearly two orders of magnitude difference in PAH aqueous concentrations. These findings improve mechanistic understanding of PAH sorption and solubility for aged lampblack residuals at former oil gas sites and should be useful for site-specific risk assessment and management.