Research

Our primary research interests are in the areas of environmental justice, water quality, climate change and environmental and human health.  My major Research Activities (RA) currently:

RA 1: Climate, water and health. 

My research under this theme involves climate sensitive diseases and human health effects due to extreme weather events among vulnerable populations. 

After joining Tulane, my research involved studying the occurrence of Naegleria fowleri in potable water supplied by private wells. This was funded by the Louisiana Water Resources Research Institute, USGS. Naegleria fowleri, also known as “the brain-eating amoeba”, is a free living amoebae found naturally in hot springs and warm surface waters. N. fowleri can cause primary meningoencephalitis (PAM), most often leading to death within 4 to 6 days if inhaled or forced into the nasal passages when swimming or diving. It is naturally found in soil and warm water and has a three stage life cycle. N. fowleri exists in soil in a cystic form and excysts to a flagellate stage when in contact with warm water and a source of food (bacteria). The flagellate stage feeds on bacteria at the air- water interface in hot springs, surface water, and other water systems that may remain still for prolonged periods. In 2011, two people died of PAM caused by N. fowleri in DeSoto Parish and St. Bernard Parish, Louisiana. Both cases involved the use of a neti-pot. In 2013, there was second death in St. Bernard Parish (4-year old boy) caused by PAM and confirmed to be N. fowleri infection. Testing conducted in 2013 by Louisiana Department of Health and Hospitals (DHH)/CDC in both St. Bernard and DeSoto found this amoeba in the treated distribution system water supply. To date, a total of 7 Louisiana’s public water systems have tested positive for N. fowleri (Louisiana DHH). 

I’m also PI in another grant ‘Impact of Saltwater Intrusion on Groundwater microbiome’ funded by Louisiana Board of Regents.  The goal  of  this  study  is  to gain  baseline  knowledge  of  the  impact  of  saltwater  intrusion  on  the  groundwater microbiome  of  private wells in  Louisiana.  Over 500,000  people  depend  on  private wells  for  their  drinking water in the State of Louisiana.  In addition, guidance for both utilities and the general public is needed  to determine how to reduce exposure to contaminants in groundwater sources in Louisiana.  Data from this study  will  provide  information  to  state  and  federal  agencies  that  can  be  used  to  develop  guidance  for  protection  of  groundwater supplies.  The results  from this research project may provide valuable insights regarding microbial  and viral communities in ground water impacted by saltwater intrusion.  Additionally, since groundwater  is used  as  a  drinking  water  source  in  Louisiana,  it  will  also  aid  in  future  research  projects,  such  as  evaluation  and  development  of  small  disinfection  technologies  for  the  control  and  treatment    of  contaminants.    The  hypothesis  is  that  saltwater  intrusion  alters  the  structure  and  function  of  the  groundwater  microbiome  and  viriome. The objectives are (1) use next‐generation sequencing to determine the impact of saltwater intrusion on  microbial communities;  (2) assess how bacteriophages are shaping the bacterial diversity and density in private  wells; (3) identify well owners’ perceptions of groundwater quality associated with saltwater intrusion and water  shortages; and (4) develop an educational workshop focusing on well water safety for private well owners.

RA 2: Harmful Algal Blooms 

My research also addresses critical issues of harmful algal blooms in coastal Louisiana and northern Gulf of Mexico and water quality. In summer of 2019, the State of Mississippi had to close all its public beaches for swimming and fishing due to blooms of blue-green cyanobacteria  linked with the extensive 2019 openings of the Bonnet Carré spillway). This event has been estimated to have caused more than $100 million dollar in damages to Mississippi alone, including fisheries, natural resources and tourism. The years 2018 and 2019 were the first time the spillway was opened in 2 consecutive years and 2019, during a historic Mississippi River flood, was the first year the spillway was opened twice in a year, for a total of 123 days open, according to the U.S. Army Corps of Engineers. The unprecedented duration of freshwater input into Lake Pontchartrain during the warm summer months sparked concerns over Lake Borgne Mississippi Sound. Toxic cyanobacteria blooms did develop and caused numerous closures of swimming beaches in Louisiana and Mississippi. Increased rainfall in the central US likely means that these freshwater diversions into Lake Borgne and Mississippi Sound are likely to increase in the future. The overall goal of this project is to improve understanding and predictive capability of Cyanobacteria Harmful Algal Blooms (CyanoHABs) by enhancing UAS, satellite remote sensing and satellite-assisted forecasting of CyanoHABs particularly in Lake Borgne and Mississippi Sound using the Artificial Intelligence (AI) technology. 

While the Gulf of Mexico Coast produces two-thirds of the nation’s oysters with Louisiana alone producing about 47 percent of U.S. landings according to NOAA data, the oyster production has always been operated in a precarious state, vulnerable to various man-made and natural contamination threats, such as harmful algal blooms, and oil spills. A critical issue facing the oyster monitoring programs in the implementation of the regulations is the lack of predictive model-based decision-support tools for achieving the shift of oyster management. I saw that this represented a unique opportunity to collaborate with Dr. Zhiqiang Deng, Professor of Water Resources Engineering at the Louisiana State University. Our goal was to address the critical issue and thereby assist the oyster industry and government agencies to achieve the paradigm shift of oyster management from primarily reacting to contamination events after they have occurred to preventing the problems, promoting sustainable development of oysters and their habitats in the Gulf of Mexico.  

RA 3: Pathogens and Water Reuse 

Another area in terms of laboratory research that I am currently pursuing is investigating the relative abundance of enteric viruses and antibiotic resistance genes in defacto, indirect and direct potable reuse.

The US faces immediate challenges regarding the sustainability of freshwater supplies for urban and agricultural needs. In some locations, treated wastewater is the only remaining water resource that has not be completely utilized. Potable use of freshwater supplies that are influenced by municipal wastewater effluent is actually commonplace. Many US communities including New Orleans, Louisiana utilize drinking water source that is comprised in part of wastewater from upstream communities, also known as de facto potable water reuse. This is largely unregulated, often inefficient and yields water of questionable quality (1). In contrast, burgeoning human population combined with rapidly increasing urbanization has created unique water quality and quantity challenges in the semi-arid Southwest. Water-stressed areas such as Tucson, AZ, Orange County, Las Vegas must augment their drinking water source with alternative waters to satisfy projected demands. Indirect potable reuse is easily the most attractive alternative, and this water reuse follows infiltration or injection of treated wastewater and temporary underground storage. Treated wastewater may also be discharged and/or blended into surface water upstream of advanced drinking treatment facilities, as is the case in the DC-Maryland-Virginia region along the Potomac River and Occoquan reservoir. Indirect potable reuse water quality benefits that have not been effectively quantified, especially with managed aquifer recharge (MAR). While most systems depend on environmental buffers to blend high- purity reuse water with native waters, at least three US communities (Cloudcroft, NM, Big Springs TX, and Wichita Falls, TX) are developing direct potable reuse without a natural buffer. In addition, California Senate Bill 918 became law in 2010, and required the Department of Public Health to investigate the feasibility of developing criteria for direct potable reuse in the State of California to mitigate severe drought. Although potable water reuse systems provide a sustainable water supply, the primary obstacle to implementation has been public and scientific concerns regarding unregulated or unknown viruses. Our specific objectives are:

Objective 1 – Conduct a field survey in to investigate the relative abundance and diversity of viruses in defacto versus indirect potable reuse.

Objective 2– Use bioinformatics to analyze the deep sequencing data in the context of metadata to characterize the viriome associated with these water systems.

Objective 3 – Identify appropriate viral indicators specific to potable reuse characteristics and geographical regions, as well as a universal indicator, to monitor treatment efficacy.

In terms of water reuse in agriculture, I’m also collaborating with Dr. John Brooks from USDA and Dr. Achyut Adhikari from the Louisiana State University-Ag Center. One of Louisiana’s and other delta and southeastern states greatest resources is water. However, recently both the abundance and quality of water has drastically declined due to prolonged droughts, an increase in demand for potable water to support a growing population and saltwater intrusion. In Louisiana, over 930 000 acres of cropland are irrigated with ground and surface waters (USDA Census, 2008). Ground water is the major source of water accounting for 67% of the total irrigated acreage (USDA Census, 2008). However ground water aquifer levels are declining rapidly as is the quality of the water (Louisiana Ground Water Resources Commission, 2012). As a result, the agricultural sector has an immediate urgency to develop and implement more sustainable water management practices that utilize high quality water. Water reuse through the treatment of surface and storm waters has emerged as a potential conservation practice that can provide high quality water for the irrigation of vegetables. We recently submitted a proposal entitled “An integrated approach to using storm water runoff for sustainable and safe vegetable production” to the USDA. This proposal is currently under review and aims to explore the possibility of using a model multiple barrier water chlorination irrigation system and advanced oxidation system to improve water and pepper fruit microbial quality. We have an interdisciplinary team and using an integrated approach we plan to provide science-based water management strategies to enhance water conservation and assist vegetable growers with producing high quality and safe food. 

RA 4: Environmental Justice and water quality

Also, my work at Tulane University has focused on environmental justice, water quality and microbial source tracking in collaboration with EPA Gulf of Mexico. Using molecular methods for source tracking can help to identify the source (human or non-human) of fecal contamination in irrigation, coastal and recreational waters. I was able to establish a MOU with the EPA Gulf of Mexico Program (GMP) on Oct 11, 2016. The purpose of this MOU is to explore possible collaborations and ways to increase cooperation between TU and GMP in areas of mutual interest, including but not limited to the GMP. The implementation of program activities in this MOU is intended to promote equal opportunity in higher education, contribute to the capacity of the GMP. We used a team approach to monitor water quality in New Orleans East. The team is made up of staff from the EPA’s Gulf of Mexico (GMP) Program, Lake Pontchartain Basin Foundation, New Orleans Sewerage and Water Board and Tulane University. Some aims include:

•   Disseminate water quality information to, local civic groups, LPBF and LA DEQ and the scientific/environmental community to aid in characterization and research studies

•    Analyze data to assess trends in the waterbodies. Sites showing poor water quality will be further investigated and BMPs implemented.

•    Improving water quality by working with a local champion to implement BMPs.

•    Meet GMP performance measures – water quality and Education

•    Work with inner city schools- EJ component

•    Help students with community hours (Water quality monitoring and developing/implementing BMPs)

The water system of New Orleans is a complex system of waterways, canals and stormwater drainage. Several of these canals and waterways are under Total Maximum Daily Load (TMDLs). Near Village de L’Est, a predominantly Vietnamese community in New Orleans East, a waterway is under a TMDL due to low Dissolved Oxygen levels. Low dissolved oxygen levels indicate poor stream health. These waters are surrounded by houses, churches and schools. We seek to determine the health of the water to guide the community in the best uses for the waterway, including suggestions on how to improve the water quality. Screening the canal for fecal contamination and analyzes the water quality physiochemical parameters (dissolved oxygen, temperature, salinity, conductance, specific conductance, turbidity, pH, total dissolved solids, nutrients, flow) and conduct the analysis for fecal indicator bacteria levels is needed to establish trends. In collaboration with the Mary-Queen Vietnam-CDC, the EPA’s Gulf of Mexico Program, the New Orleans Sewerage and Water Board, and the Lake Pontchartrain Basin Foundation (LPBF), my team monitored the water quality (on a bi-weekly basis) in New Orleans East. In addition, we plan to employ rapidly advancing technologies for DNA sequencing and computer-based analysis of sequences, which make it possible to characterize the taxonomic composition and function of biological communities in considerable detail. Also, DNA source tracking methods is applied to water samples collected from these canals. Compared with cultivation-based methods, the DNA source tracking method not only quantifies but also identifies pollution sources in surface water. The goal of this collaboration is to use advanced molecular methods including qPCR, ddPCR and metagenomics to identify the source of fecal contamination in New Orleans East and Lake Pontchartrain. Kinjal Shah, a Masters student joined the lab in January 2017 and she worked with Rachel Houge from the EPA GMP.

RA 5: Arsenic, Microbiome and Human Health 

Exposure to inorganic Arsenic (As) in drinking water is a global public health issue affecting an estimated 140 million people, primarily through consumption from contaminated wells (1). Inorganic As species (arsenite (As-III) and arsenate (As-V)) are the most toxic forms and primary sources of human exposure in drinking water. Exposure to high levels of inorganic As exposure and its carcinogenic and noncancerous effects have been well established. However, risk to certain cancers, cardiovascular diseases (CVD), respiratory conditions, and diabetes has also been linked to exposures below the EPA maximum contamination level of 10 ppb (µg/L) As in public water supplies (1). This research suggests there may be no safe threshold of As exposure without risk to health. It is now estimated that the human gut microbiome consists of approximately 100 trillion bacterial cells, a population approximately ten times greater than host cells in the human body. Changes to the relative abundances of beneficial or pathogenic microbiota can be a result of perturbation by arsenic exposure (1,2). Epidemiological studies have demonstrated a correlation between environmental or occupational arsenic exposure and a risk of CVD. The gut microbiome may modify disease risk associated with arsenic exposure (2). A recent study found a significant association of the family Aeromonadaceae and the genus Citrobacter with carotid intima-media thickness (cIMT), a surrogate marker of atherosclerosis., as well as a significant interaction between Citrobacter and water arsenic in Bangladesh cohort (2).

However, no epidemiologic studies have been conducted to identify the role of gut microbiome/virome in As toxicology and CVD risk in pregnant women. The goal of the proposed study “Maternal Health, Arsenic exposure, Gut microbiome/virome and Atherosclerosis (MAGA)” is to obtain a better understanding of exposure risks of As via drinking water and rice cereals in pregnancy (Aim  1), using biomarkers of recent (urine) and long-term (fingernail) exposures to As  and examine the relationship between arsenic exposure and atherosclerosis (Aim 2) and feces to characterize changes in bacterial/viral taxonomic composition and diversity during and post pregnancy (Aim 3). 

RA 6: Water, Sanitation and Hygiene 

One additional research project that I have initiated focuses on water quality, sanitation and hygiene in developing countries. Microbial contamination of drinking water is a major issue in many developing countries. 768 million people still lack access to safe water around the world. According to World Health Organization (WHO), water-related diseases are estimated to cause 1.8 million deaths each year, mostly in developing countries and have been the major cause of mortality and morbidity (WHO). The major earthquake (magnitude 7.8) occurred on April 25, 2015 in Nepal. An estimated 8670 fatalities and 2.8 million people were in immediate need of humanitarian assistance according to the government of Nepal. There were several aftershocks throughout the end of April followed by a major earthquake of 6.8 magnitude on May 12, 2015. On the other hand, due to inadequate, interrupted, or intermittent treatment, public health authorities in Nepal have repeatedly associated waterborne disease outbreaks with unsafe drinking water. Nepal is also one of the poorest countries in the world and people can’t afford water purification technologies such as the point-of-use (POU) filters which are effective on removing microbial pathogens. At present, their major drinking water source is jar water and tanker water, which source is unknown and might be contaminated. Specific objectives are to: 1) evaluate online sensors for the detection of opportunistic pathogens in potable water and biofilms supplied by intermittent water supply; 3) attempt to identify biotic and abiotic factors related to the survival of these pathogens in these water supplies; 4) develop a guidance document with Nepalese Ministry of Health for reducing risks from OPPPs exposure; and 5) develop models and a decision-support tool for best risk management practices. The project will provide information to local regulatory agencies that can be used to develop guidance for protection of drinking water supplies post-quake in Nepal.

RA 7:  Molecular Epidemiology of enteric viruses among children  in Nepal 

I am interested in global health and infectious diseases. I have established collaborations with top scientists from Nepal. We are working on understanding the epidemiology of enteric viruses and genotyping of Rotavirus, Norovirus and Sapovirus among children <5 years old in Nepal.

Rotavirus is the leading cause of severe childhood gastroenteritis, causing over 200,000 deaths per year and unfortunately, rotavirus vaccines are not effective in low income countries where the burden of rotavirus associated child mortality is highest. We propose to determine the epidemiology of Rotavirus and Norovirus among children enrolled in Kanti Children’s hospital post vaccination.This will be the first study in Nepal and the results will be invaluable to public health officials for improving the rotavirus vaccine efficacy.

RA 8:  PFAS Remediation

PFAS, known as "forever chemicals," have become a significant environmental concern due to their long-lasting presence leading to health and environmental problems. A 2018 Department of Defense assessment identified over 700 military sites with known or suspected PFAS discharges in the US. PFAS remediation methods commonly involve costly and impractical physical and chemical processes such as activated carbon adsorption, ion exchange, and advanced oxidation, often requiring high pressures and temperatures and leading to the generation of toxic waste. Biodegradation presents a promising and cost-effective alternative for large-scale, on-site PFAS remediation. Although there are currently no widely accepted and efficient biological methods for PFAS remediation, bioremediation remains a potential solution for addressing PFAS contamination in the future, offering improved efficiency and environmental sustainability.

The proposed research aims to explore an economically viable and eco-friendly approach that combines fungi and microbes with phytoremediation for PFAS contamination. When fungi and microbes are integrated into this method, it has the potential to provide an innovative and sustainable solution for PFAS-contaminated sites and offer a practical and sustainable means to restore affected areas. The main objective of this project is to develop a bioremediation method for PFAS-contaminated sites. The underlying hypothesis is that specific native plant species in Maryland can help control water movement, limit PFAS leaching, and break down PFAS directly through plant degradation or indirectly via microbial activity in the rhizosphere. Additionally, fungi enzymes may produce oxidized PFAS forms that reduce their toxicity and mobility, preventing contamination of groundwater.

RA 9:  AI/Machine Learning, WBE 

As part of the NIH funded grant, we are studying the potential of wastewater surveillance of SARS- CoV-2 in the US and low-income resource limited settings for mitigation and control of COVID-19. Therefore, the proposed study will facilitate a better understanding of persistence and disinfection of SARS-CoV-2 in wastewater. We are demonstrating environmental surveillance of SARS-CoV-2 in disadvantaged communities can be as an early warning tool for public health officials. The findings will also be invaluable to water resource recovery facilities for better management against potential exposure risk and ensuring worker health and safety.

Research Area 10: Environmental influences on health outcomes after extreme disasters like hurricanes

The natural world and human influences work together to create the devastation that follows a major disaster such as a hurricane.  Although many studies have examined broad patterns of effects on pregnancy outcomes after disasters, the causes of adverse outcomes are not always clear, as there are interrelated environmental pollutant exposures, psychological stressors, and lack of health care.  Without understanding which aspects of disaster exposure are the strongest contributors to adverse outcomes, it will not be possible to establish disaster responses that efficiently target the most important factors.  Our long-term goal is to create disaster response and mitigation programs that are effective in preventing the worst outcomes in pregnant women and their infants.  The overall objective of this application is to examine effects of environmental (harmful algal bloom, carbon monoxide) exposures and general disaster exposures (power outages, storm damage) with pregnancy-related outcomes.  Our central hypothesis is that severe exposure (defined by both magnitude and duration) to any of these factors will be associated with worse outcomes, while most people are resilient to minor exposure.  We are not aware of other research that has addressed red tide or carbon monoxide among pregnant women in the aftermath of a disaster, and ecological studies often examine very broad indicators of disaster exposure.  

Sherchan Lab, Environmental Health Sciences