Research Highlight: Mapping and Monitoring Toxicants using Carbon Nanotube Sensors
By Maggie He
MIT Superfund Research Program scientists and engineers are studying N-nitrosodimethylamine (NDMA) and polycyclic aromatic hydrocarbons (PAHs), chemicals that can be harmful to the environment and also to our health. Both NDMA and PAHs undergo secondary chemical reactions to produce alkylating agents that damage DNA, and consequently they have the potential to cause cancer. NDMA arises in the environment as a result of reactions among legacy contaminants that were released to the environment by previous industrial processes. It is also a contaminant with emerging importance, since it is produced by chlorination of water and by carbon capture. As a result, the contamination of NDMA in drinking water is a significant health concern. PAHs are intrinsic products of combustion. The chemical structure of PAHs varies in their polycyclic skeleton as well as their exocyclic functional groups. PAHs and their breakdown products by atmospheric oxidation have different levels of carcinogenicity.
NDMA and PAHs are conventionally detected and monitored by in-lab analysis using high-performance liquid chromatography (HPLC) and gas chromatography (GC) coupled to mass spectrometry (MS). Although these analyses can detect environmentally relevant concentrations, they are slow, expensive, require sample preparation/pre-concentration, and necessitate sophisticated, expensive, and bulky instrumentation. Additionally, laborious analyses with extensive field sampling and transport cannot provide real-time monitoring of contamination levels. Considering the limitations of conventional analyses, portable sensors with the capability of real-time monitoring that can be distributed to contaminated sites for an extended period are needed. In addition to portable sensors, online and positional tracking of contaminants will modernize our technologies and improve human health by enabling steps for minimizing exposure.
Carbon nanotube sensors are ideal active elements that enable portable deployment in the field. They require little power, are inexpensive, and provide real-time response to analytes. Carbon nanotubes derive much of their behavior from their one-dimension (1-D), tube-shaped nanomaterial structures. These unique nanomaterials have very high surface area and outstanding electrical and mechanical properties essential to sensor applications. Most importantly, the properties of carbon nanotubes can be tailored by functionalization, wherein chemical groups can be anchored to the material’s surface, to impart sensitivity and selectivity to specific analytes.
Carbon nanotubes are readily incorporated into chemiresistive sensor chips and passive radio frequency identification (RFID) tags (Figure 1). Chemiresistive sensors are readable by a direct electrical connection and RFID tags can be wirelessly powered and read by a smartphone’s near-field communication (NFC). The response of these sensors can provide quantitative information about the analyte’s concentration.
At the MIT-SRP Center, graduate student Shao-Xiong Luo and postdoctoral fellow Maggie He from the Swager laboratory are developing portable carbon nanotube sensors for the mapping and monitoring of carcinogenic NDMA and PAHs in air and water. The team is currently developing methods for the functionalization of carbon nanotubes, incorporating selectors to tailor the carbon nanotubes to selectively interact with NDMA and PAHs and fabricating sensors with these materials to test device performance.
The team anticipates realization of portable sensors that can be used in the field to detect these toxicants in the Mystic River Watershed near three Massachusetts Superfund sites in the near future. Densely distributing sensors at contaminated sites will allow SRP to dynamically and efficiently track contamination levels. The collected spatiotemporal data on the actual concentration of NDMA and PAHs will be shared with the public, so that communities there can make well-informed actions to minimize harmful exposure, and will also be shared with the EPA in order to optimize efforts for site remediation.
Zhu, R.; Desroches, M.; Yoon, B.; Swager, T. M. Wireless Oxygen Sensors Enabled by Fe(II)-Polymer Wrapped Carbon Nanotubes. ACS Sensors 2017, 2 (7), 1044–1050.
Trainee Spotlight: Hélène Angot
Dr. Hélène Angot is a postdoctoral associate at MIT in Professor Noelle Selin’s group. She investigates the atmospheric sources and fate of toxic global pollutants through observational and modeling tools. Toxic pollutants are emitted into air worldwide by multiple natural and anthropogenic sources. The atmosphere provides both a route of exposure (via inhalation) and a means for the long-range transport and transformation (e.g., oxidation) of pollutants in the environment. Through a modeling approach, Dr. Angot aims to draw the link between global emissions and local impact on Maine tribal areas.
Currently, Dr. Angot contributes to Project 2 of the MIT Superfund Research Program, aimed at modeling the atmospheric transport and fate of carcinogenic polycyclic aromatic hydrocarbons (PAHs) and their degradation products (oxy- and nitro-PAHs). These compounds are present in Superfund and other contaminated sites, such as the Loring Air Force Base near Limestone, ME, making an understanding of their lifecycle especially relevant to the MIT SRP Center. While degradation products can be more toxic and harmful than their primary precursors, their atmospheric reactivity and fate is poorly understood. A fully coupled scheme is currently under development within the global chemical transport model GEOS-Chem. The ultimate outputs are model estimates of PAHs and degradation products' atmospheric levels, which are crucial for improving estimates of potential exposures and public health impact. This work is done in close collaboration with Prof. Mathew Evans’ group at the University of York’s Chemistry Department (UK) and Prof. Jesse Kroll’s group at MIT.
In addition to PAHs, Dr. Angot also studies atmospheric mercury (Hg) transport and transformation. Upon deposition to ecosystems, Hg converts to highly toxic methylmercury (MeHg) and bioaccumulates in aquatic systems. Tribal communities are therefore particularly affected by Hg contamination due to their traditional dependence on subsistence fishing. The United Nations Minamata Convention on Hg entered into force last summer. Under this Convention and as a co-benefit on greenhouse gases mitigation policies, global Hg emissions are expected to decrease. Dr. Angot is investigating benefits attributable to this policy in terms of future local Hg deposition and fish contamination. In a scenario of delayed global action, benefits will decrease due to increasing legacy emissions (i.e., recycling of previously deposited Hg). These results underline the importance of near-term action for limiting the Hg burden of future generations.
MIT Superfund Friday Forum
Three Superfund Friday Forum Seminars have been held since the MIT SRP began. The inaugural Superfund Friday Forum, on October 6, 2017, began with an introduction by Director Prof. Bevin Engelward, who provided an overview of the program, as well as descriptions of the relevant Superfund sites and contaminants of interest. Program Co-Director Prof. John Essigmann then presented the main research seminar. He discussed the history of industrial activity in the Mystic River Watershed in Massachusetts and described the former Loring Air Force Base in Maine. His presentation provided new members of the MIT SRP with a concise description of our community partners and the motivation for our research. Prof. Essigmann also presented the foundational work upon which Project 3 is based, which is focused on identification of high-resolution mutational signatures induced by chemical exposure.
The second Superfund Friday Forum was presented on November 17, 2017 by Prof. Akram Alshawabkeh, Director of the Puerto Rico Testsite for Exploring Contamination Threats (PROTECT) Superfund Research Center based at Northeastern University. Prof. Alshawabkeh presented an overview of the PROTECT program, providing an inspirational model of effective environmental research. This seminar helped contextualize the goals of their environmental and toxicological research with examples of research progress and implementation in Puerto Rico.
At the most recent Superfund Friday Forum, Prof. Benjamin Kocar of MIT’s Civil and Environmental Engineering Department presented an overview soil research being done in his laboratory. The Kocar group integrates geology, chemistry, and biology to study the transport of contaminants, nutrients and gases in aqueous and soil systems.
Taken together, the MIT Superfund Friday Forum Series is off to a great start with talks providing valuable context and inspiration.
Northeast Regional SRP Meeting in Woods Hole
Thirteen members of the MIT Superfund Research Program team attended the Northeast SRP meeting in Woods Hole on March 26-27, organized by Boston University’s SRP. This meeting was an excellent opportunity to strengthen connections with other Superfund Research Centers, inspiring future efforts and fostering collaborations. Program Director Prof. Bevin Engelward gave a presentation that summarized the context and goals of the MIT SRP, which was a helpful venue for introducing the new MIT SRP to NE SRP Center members. Along with Prof. Engelward, Program Co-Director John Essigmann and CEC Director Kathy Vandiver served as mentors at the trainee luncheon. Nine trainees presented posters, and Project 1 postdoc Hélène Angot’s poster, titled “Toxic Pollutants: from Worldwide Atmospheric Emissions to Impacts on Maine Tribal Areas,” was awarded second place.
Inaugural MIT Superfund Research Program Poster Session
The MIT Superfund Research Program teamed up with the MIT Center for Environmental Health Sciences (CEHS) to offer their first joint poster session on April 10th. Nine SRP trainees showcased their research. For the SRP awards, James Rowe won first place, Maggie He and Lennon Luo shared second place, and Ishwar Kohale won third place. The first place winner was given the opportunity to attend either the National or the Northeast Annual Superfund Meeting. For the CEHS awards, Superfund trainee Dr. Hélène Angot won first place in the postdoctoral category for her poster, “Toxic Pollutants: from Worldwide Atmospheric Emissions to Impacts on Maine Tribal Areas.”
Superfund trainees’ posters and coauthors are listed below (trainees’ names are underlined).
Hélène Angot, Noelle E. Selin, Peter Ivatt, Nicholas Hoffman, Amanda Giang, Mat Evans. “Toxic Pollutants: From Worldwide Atmospheric Emissions To Impacts On Maine Tribal Areas.”
Jessica C. Beard, Timothy M. Swager. “Fluorescence-Based Detection of NDMA and Polycyclic Aromatic Hydrocarbons.”
Christy Chao, Stephen Slocum, Harold Hemond, John M. Essigmann, Bevin P. Engelward. “Genotoxicity Testing For Airborne Environmental Contaminants.”
Maggie He, Shao-Xiong Luo, Timothy M. Swager. “Functionalized Carbon Nanotubes Sensors For Detecting Harmful Chemicals.”
Jennifer Kay, Joshua Corrigan, Bevin P. Engelward. “Evaluating Genetic Susceptibility To Cancer Following Exposures to Superfund Contaminants.”
Ishwar Kohale, Forest White. “Characterizing Signaling Dynamics in Response to Environmental Pollutants.”
Le Ngo, John Winters, Carol Swartz, Yang Su, Jing Ge, Aoli Xiong, Jongyoon Han, Leslie Recio, Leona Samson, Bevin P. Engelward. “High-Throughput Platform For Detection of DNA Adducts Induced By Metabolic Activation of Xenobiotics.”
James C. Rowe, Chris Lim, Martin Breitenlechner, Alexander Zaytsev, Jesse Kroll. “Characterization of Heterogeneous Oxidation Products of Polycyclic Aromatic Hydrocarbons Using Online Mass Spectrometry.”
MIT SRP Supports Citizen Science in Collaboration with Native Americans in Maine
Five years ago, Drs. Kathy Vandiver and Robert Croy, along with Prof. John Essigmann, reached out to Passamaquoddy Tribe located in the vicinity of Eastport Maine, who had asked for advice regarding news stories and publications warning of high arsenic levels in drinking water. The MIT group represented the Community Outreach, Education and Engagement Core of the Center for Environmental Health Sciences (CEHS). This initial contact led to a robust bi-directional interaction that serves as a platform upon which some of the Superfund community programs are based. Indeed, Superfund and CEHS now work closely together with the Sipayik Environmental Department of the Passamaquoddy Nation to address an ever widening suite of environmental questions and problems.
Throughout the past year, Dr. Kathy Vandiver (CEC Director), Prof. Harold Hemond (Project 1 Lead), Prof. John Essigmann (Program Co-Director and Project 3 Lead), have overseen and mentored two MIT Masters of Engineering students, Ms. Abby Harvey and Ms. Tchelet Segev (pictured). Their project is focused on testing drinking water for communities in Maine through Citizen Science participation, one of MIT SRP CEC’s specific aims. Specifically, residents of Eastport, Perry, and Pleasant Point, including many members of the Passamaquoddy Tribe, had expressed concern about their water quality, including variable color and taste. The municipal water supply for these towns is the Passamaquoddy Water District (PWD), which treats and distributes water from the Boyden Lake, a shallow nearby water body that is often used for recreational purposes.
Ms. Harvey and Ms. Segev had aimed to identify a project for their Masters thesis that would be of benefit to a community. Under the supervision of of Drs. Vandiver, Hemond, and Essigmann, Ms. Harvey and Segev launched a Citizen Science project in collaboration with the local Sipayik Environmental Department that serves the Passamaquoddy Tribe. This project provided an exciting opportunity for the MIT SRP to contribute and to learn from the experience, making this an effective pilot for future citizen science activities.
Ms. Harvey and Ms. Segev collected and analyzed the concentration of metals in household water samples. With guidance from Dr. Vandiver, the team held community meetings in Perry, Pleasant Point, and Eastport, ME (pictured) to listen to residents’ concerns, to describe the water-testing project, and to distribute Citizen Science sampling kits. Residents collected both standing and flushed water samples at their homes, with representation from both private well and municipal water supplies. The number of private wells tested was nearly double the participation of a US Geological Survey analysis between 2005-2009. Over 300 households submitted samples, an exceptional participation rate of more than 20% of homes in the area.
Approximately 1,000 samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for the concentrations of more than 10 different metals, including arsenic and lead. Select samples were shared with the Maine State Laboratory for parallel screening, and results showed excellent agreement. Additionally, household samples that scored high for metal content were re-analyzed for confirmation. Members of the Sipayik Environmental Department, Chris Johnson, Asha Ajmani (left), and Billy Longfellow (right) joined researchers at MIT for the ICP-MS analyses. The experience provided them with a professional development opportunity and enabled them to communicate the results more effectively with the local community. The MIT SRP benefitted greatly from participation by the Sipayik Environmental Department. Mr. Johnson, Ms. Ajmani, and Mr. Longfellow played key roles in organizing the program and engaging the communities in rural Maine.
Results from the sample analyses revealed that several households supplied by private wells had levels of arsenic exceeding EPA guidelines of 10 parts per billion (ppb). None of the households supplied by municipal water were found to have high levels of arsenic. For lead, several households’ standing water samples exceeded the EPA guideline (15 ppb). However, flushing the tap for at least two minutes lowered lead content to acceptable levels, indicating that the lead was introduced from household piping rather than the municipal water mains. Importantly, participants learned that running water before use could reduce their risk of lead exposure. All residents who had submitted samples were mailed a letter describing their household’s individual results, guidance for interpreting the results, and recommendations for reducing risk of exposure. The template of this letter can be found at the PEPH Resource Center.
In May, Ms. Harvey and Ms. Segev returned to Maine with Dr. Vandiver to present their findings at community meetings, which were reported on by the local Quoddy Tides newspaper. After learning about metal concentrations in their own household water via mail, participants attended meetings where town results were discussed. At the report back, presenters reviewed the purpose of the study and analyses performed and offered suggestions for reducing risk of exposure to metals in water. In addition, participants had the opportunity to confirm their understanding of their individual results.
For her Masters thesis, Ms. Harvey conducted a source analysis to determine the likely sources of metals in drinking water. Her study confirmed that arsenic comes from geologic sources whereas lead leaches into water from household piping. Ms. Segev’s Masters thesis included a health risk analysis. Her analysis gave rise to the prediction that 0.11 additional cancer cases in these towns could be attributed to arsenic in private well water.
This project served as an immensely informative pilot for launching future MIT SRP Citizen Science efforts. MIT SRP members gained invaluable experience working with federal, state, local, and tribal agencies to conduct testing of individuals’ drinking water. Collaborations with EPA Region 1 were particularly valuable. This project also fostered meaningful relationships between MIT SRP members and Native Americans in Maine, enabling future collaborations. With the skills, strategies, and relationships established in this project, the MIT SRP group continues to strengthen Citizen Science and community engagement projects.
MIT SRP Visits Malden High School STEM Classes
Malden is an Environmental Justice community located on the historically industrialized Malden River. The Malden River is part of the Mystic River Watershed, within which three Superfund sites are located. Despite recent remediation efforts along the Malden River, many Malden residents are unaware or skeptical of their river’s accessibility for recreation.
In recent years, Malden High School teachers teamed up with the MIT App Inventor Program to start classes in computing and engineering. Working together, they designed these classes to engage students in developing real solutions to problems that affect their local community. This year, the classes were asked to design apps and sensors that could be used along the Malden River. This project allowed students in both classes to engage in the same kinds of creative work that real computer scientists and engineers do in the workforce, and provided the opportunity for them to have to have a real impact in their community. As inspiration for the students’ projects, the App Inventor team invited members of the MIT Superfund Research Program to Malden High School to discuss their innovative research in sensor design and technology development to promote environmental health. MIT SRP community partner Friends of the Malden River also supported interactions with the high school students.
On April 5th, CEC leader Kathy Vandiver and RTC leader Jenny Kay brought trainees Irene Hu and Tchelet Segev to visit classes at Malden High School. Ms. Hu is a graduate student in Prof. Harry Hemond’s laboratory, and Ms. Segev is a Masters student working under the guidance of Drs. Harry Hemond, Kathy Vandiver and John Essigmann. To provide inspiration for the students’ final projects, Dr. Vandiver first presented a brief history of industry on the Malden River. In addition, Dr. Kay provided an overview of MIT SRP’s research program, which includes studying the presence, transport, and health effects of chemicals in waterways potentially contaminated with chemicals from previous industrial activities. Ms. Hu then described her research project, which is to design a sensor to measure flux of chemicals from sediment to water. Finally, Ms. Segev discussed her work in testing household water supplies for contamination. By sharing current, cutting-edge MIT research with direct relevance to the classes, the SRP team aimed to inspire the students to design useful apps and sensors for application along their local river.
In just a few weeks, the students designed a variety of apps and sensors to make the Malden River more welcoming, raise awareness, and get the community excited about their local river. The students shared their final projects with the public on May 22nd, where members of the MIT SRP and Friends of the Malden River were able to view and appreciate the students’ excellent products.
Scouting Out Sampling Locations Near Olin Chemical Superfund Site
The Olin Chemical Superfund site in Wilmington, MA is heavily contaminated with N-nitrosodimethylamine (NDMA), an emerging contaminant that is carcinogenic in animal models. As a first step, Program Director Prof. Bevin Engelward, Co-Director Prof. John Essigmann, RTC director Dr. Jenny Kay, and NDMA expert Prof. John Durant of Tufts University joined MIT Masters students Abby Harvey and Tchelet Segev to visit the Olin site in Wilmington and collect initial samples in the area.
While NDMA is known to contaminate the Olin site itself, less is understood about nitrosamine contamination in the surrounding environment. NDMA is miscible in water, creating high potential for transport to drinking water supplies. The chemical is sensitive to light, so potential sampling locations and conditions must be carefully researched and optimized. The team identified three locations within a mile of the Olin site and collected initial water samples from each. In the future, researchers will return to these sites in the dark hours of the early morning to collect light-protected water samples for measuring NDMA content.