Research Areas
Overview
We address public health research questions through molecular-level analyses of chemical contaminants and biomarkers. A primary component of this research is the development of advanced analytical methods. Often these compounds are analyzed in complex sample matrices at low abundance; therefore, most methods in our laboratory utilize chromatography and mass spectrometry for chemical identification and quantification.
We work across a variety of public and environmental health related fields, including microplastic pollution, environmental tobacco product waste, pollution in the US-Mexico border region, pesticide contamination, bioaccumulative contaminants in marine wildlife, offshore DDT+ pollution in the southern California Bight, evaluation of wastewater treatment systems, and thirdhand tobacco smoke pollution. Example research areas are described below.
For a full list of past projects, please see the publications of Dr. Hoh and Dr. Dodder.
Contaminant Fate, Transport, and Human Exposure Assessments
Quantitative mass spectrometry methods are used to study the behavior of specific environmental contaminants and their associated biomarkers. Our laboratory develops targeted GC/MS and LC/MS/MS analytical methods for tobacco smoke components and related biomarkers (e.g., nicotine, tobacco specific nitrosamines, and cotinine), pesticides and related biomarkers, persistent organic pollutants (e.g., PCBs, organochlorine pesticides, and flame retardants), and other contaminants of known and emerging concern. Contaminant fate and transport is investigated in macro and micro (outdoor and indoor) environments. Human exposure is assessed through biomonitoring methods (e.g. urine) and simple wearable devices such as silicone wristband passive samplers.
Example Projects
- Examining the efficiency of contaminated soil/sediment remediation through analysis of PAHs.
- Pesticide exposure among agricultural communities.
- Secondhand smoke and e-vape exposure assessment using silicone wristbands.
Example Literature
- Environmental Tobacco Smoke as a Source of Polycyclic Aromatic Hydrocarbons in Settled Household Dust
- Integrated Framework for Identifying Toxic Transformation Products in Complex Environmental Mixtures
- Nicotine levels in silicone wristband samplers worn by children exposed to secondhand smoke and electronic cigarette vapor are highly correlated with child's urinary cotinine
Microplastic Pollution
Plastics discarded in the environment progressively fragment into microplastic particles. Most research to date has focused on non-fiber, non-rubber microplastics, such as microbeads and fragments derived from rigid plastics, and has primarily examined effects attributable to the particles themselves rather than to chemicals released from the material. Our current research addresses a complementary aspect of microplastic pollution: tire-wear particles, textile fibers, and cigarette filters. Cigarette filters are composed of cellulose acetate microfibers. Tire-wear particles and cigarette filter microfibers may pose greater hazards than the base polymer itself because embedded additives and sorbed contaminants can be mobilized through physical fragmentation, aqueous leaching, and sunlight-driven photochemical degradation. The roles of leaching and photodegradation on contaminant mobilization and fate are being investigated.
Example Projects
- Evaluate the aqueous mobilization of chemicals from microfibers, tire wear particles, and cigarette filter fibers under different environmental conditions.
- Elucidate mechanisms of aquatic toxicity produced by leaching chemicals from the new and aged microplastics.
Example Literature
- Ingested plastic transfers hazardous chemicals to fish and induces hepatic stress
- Classify plastic waste as hazardous
- Micron-size tire tread particles leach organic compounds at higher rates than centimeter-size particles: Compound identification and profile comparison
- Behavior of compounds leached from tire tread particles under simulated sunlight exposure
Environmental Impacts of Tobacco Product Waste and Cannabis Farming
Discarded cigarette butts are among the most prevalent litter found at ocean beaches and in inland waterways. In addition, the growing popularity and improper disposal of electronic nicotine delivery devices (ENDS) is an emerging source of tobacco product waste. However, the environmental and health impacts of these tobacco waste products have not been evaluated. Cigarette tobacco and smoke contain numerous toxic chemicals, and cigarette filters are made of non-biodegradable plastic that traps cigarette smoke particulates and less volatile chemicals. Therefore, harmful chemicals may leach from the filters and unburnt tobacco in cigarette butts.
Cannabis cultivation may have local environmental impacts due to the use of pesticides and fertilizer, and from plant residue.
Example Projects
- Identification of tobacco product waste contaminants and evaluation of their bioaccumulation and toxicity.
- Evaluate impacts of urban stormwater runoff on water quality.
- Analyze pesticides in ambient waters downstream of cannabis farms.
Example Literature
- Assessing Toxicity and in Vitro Bioactivity of Smoked Cigarette Leachate Using Cell-Based Assays and Chemical Analysis
- Leached Compounds from Smoked Cigarettes and Their Potential for Bioaccumulation in Rainbow Trout (Oncorhynchus mykiss)
- Influence of tobacco product wastes in a protected coastal reserve adjacent to urbanization
- Cannabis and the Environment: What Science Tells Us and What We Still Need to Know
Bioaccumulative Contaminants in Sentinel Species
Biomagnifying contaminants originating from the California coast will accumulate in high trophic level marine mammals, and other coastal animals, at levels that may induce a biological impact. These species also serve as spatial and temporal trend indicators of historical and emerging contaminants. Using non-targeted mass spectrometry, we developed an approach for the detection of a broad range of organic compounds in fish oil, marine mammal blubber, and avian species.
Example Projects
- Enhanced cataloging by non-targeted mass spectrometry of bioaccumulative chemicals in stranded marine mammals to assess health impacts.
- Assessing potential endocrine disrupting chemicals in the critically endangered California condor.
Example Literature
- Nontargeted Biomonitoring of Halogenated Organic Compounds in Two Ecotypes of Bottlenose Dolphins (Tursiops truncatus) from the Southern California Bight
- Newly Identified DDT-Related Compounds Accumulating in Southern California Bottlenose Dolphins
- Apex marine predators and ocean health: Proactive screening of halogenated organic contaminants reveals ecosystem indicator species
- Assessing Marine Endocrine-Disrupting Chemicals in the Critically Endangered California Condor: Implications for Reintroduction to Coastal Environments
Thirdhand Tobacco Smoke Exposure
Tobacco smoke can be a major contributor to indoor air pollution. When dust and surfaces remain contaminated long after active smoking has ceased, it is referred to as "thirdhand" smoke. We investigate human exposure to thirdhand smoke under various indoor settings such as homes, cars, and commercial businesses, and compare thirdhand smoke profiles to smoking behavior. Drs. Hoh and Dodder are active members of the thirdhand smoke consortium. Our studies have contributed to understanding the health impacts of thirdhand smoke, leading to the California requirement that home sellers disclose the presence of known thirdhand smoke contamination to potential buyers (Assembly Bill 455).
Example Projects
- Persistent thirdhand smoke toxicants in indoor environments.
- Thirdhand smoke pollution and remediation in low-income housing.
- Contribution of thirdhand smoke to overall tobacco smoke exposure in a pediatric population.
- Effects of thirdhand smoke exposure on the microbiome of children.
Example Literature
- When smokers move out and nonsmokers move in: Residential thirdhand smoke pollution and exposure
- Thirdhand smoke and exposure in California hotels: non-smoking rooms fail to protect non-smoking hotel guests from tobacco smoke exposure
- Prevalence and Income-Related Disparities in Thirdhand Smoke Exposure to Children
Non-Targeted Contaminant Discovery
There is concern that unrecognized or novel contaminants are either contributing to current health impacts or may pose an elevated risk in the future. Non-targeted mass spectrometry approaches provide a comprehensive contaminant profile that can be used to investigate differences among sample groups, evaluate remediation efficiency, identify unknown compounds, and suggest new chemicals for further risk assessment. Custom software is developed to process the non-targeted data sets. We are continuously working to further the development of non-targeted analytical approaches and their applications to environmental monitoring, food safety, and exposure assessments, and hazard assessments.
Example Projects
- Evaluation of contaminant removal in decentralized water reuse systems.
- Identify unexpected organic contaminants following advanced oxidation water treatment processes.
- Nontargeted analysis of sediment and water in San Francisco Bay.
Example Literature
- Nontargeted Comprehensive Two-Dimensional Gas Chromatography/Time-of-Flight Mass Spectrometry Method and Software for Inventorying Persistent and Bioaccumulative Contaminants in Marine Environments
- Organic contaminants in human breast milk identified by non-targeted analysis
- Novel chemical contaminants associated with thirdhand smoke in settled house dust
- Comparison of Trace Organic Chemical Removal Efficiencies between Aerobic and Anaerobic Membrane Bioreactors Treating Municipal Wastewater