About

Patricia Holden is a professor at the UC Santa Barbara Bren School of Environmental Science & Management. Her background is in civil and environmental engineering and soil microbiology, with her education including a PhD in Soil Microbiology from UC Berkeley, an MEng in Civil & Environmental Engineering from UC Berkeley, an MS in Civil Engineering from Purdue University, and a BS in Civil Engineering from the University of Tennessee. Her research focuses on environmental microbiology, microbial ecology, water quality, soil microbiology and processes, biodegradation, wastewater, and pathogens in the environment. She has a research group that includes postdoctoral researchers and PhD candidates working on topics such as biogeochemistry, soil microbial ecology, nutrient cycles, and climate change.

Research topics

• Biology
• Medicine
• Chemistry
• Engineering
• Environmental science
• Pathology
• Virology
• Waste management
• Biochemistry
• Biophysics
• Business
• Microbiology
• Environmental planning
• Environmental health
• Environmental engineering

Selected publications

• Aquatic Toxicological Assessment of Solid Pyrolysis Product (SPP) from Synthetic Textile Feedstock Relative to Biochar, Carbon Black, and Activated Carbon

  Environmental Science & Technology · 2026-04-03

  articleSenior authorCorresponding

  Pyrolysis as a waste conversion process appears relatively feedstock-agnostic, yielding carbonaceous solid pyrolysis products (SPPs) plus condensable gases. Ground SPPs may substitute for or improve upon other carbon commodity particles, yet the environmental hazards of textile-derived SPPs have not been characterized. Here, we produced SPP particles from textile waste feedstock and from wood (biochar) using a pyrolysis process that could scale to waste management. We used electron microscopy, spectroscopy, gas adsorption, and standardized biochar analyses to characterize the chemical, morphological, and surface functionalization properties of the products. Base food-web aquatic toxicity of particle suspensions, relative to industrial carbon black and powdered activated carbon (AC), was assessed for particle concentrations up to 500 mg L–1, using marine bacterial (Aliivibrio fischeri) bioluminescence, freshwater protozoan (Tetrahymena thermophila) viability, growth and particle uptake, and freshwater microalgal (Raphidocelis subcapitata) growth. Although exposure was confirmed, for example, by protozoan ingestion of SPPs, there were no inhibitory effects of textile SPP on bacterial bioluminescence, protozoal viability or growth, or microalgal growth; textile SPP leachates appeared stimulatory to microalgae. These results suggest that SPPs from synthetic textile feedstocks may be biologically compatible with aquatic ecosystems, whereas AC induced dose-dependent reactive oxygen species (ROS) production in abiotic conditions and inhibited A. fischeri bioluminescence. This study provides critical new data on the aquatic biocompatibility of textile SPPs, supporting the circular economy by exploring the environmental safety of the conversion of mixed, synthetic textile waste.

  PublisherDOI

• Environmental impact of open burning of polyester and cotton textile waste: a comparative analysis

  Environmental Science and Pollution Research · 2026-03-08

  articleOpen access

  Abstract Open burning of waste (OBW), particularly textile waste, is a growing but under-researched global issue with critical environmental and public health implications. This study examines the scale and impact of open burning of textile waste (OBTW), focusing on polyester and cotton materials commonly found in post-consumer and industrial waste streams. While high-income countries strictly regulate open burning, it remains prevalent in low- and middle-income countries due to limited waste infrastructure and poor waste management, contributing to severe air pollution and greenhouse gas (GHG) emissions. Our analysis estimates that between 10 and 20 Mt (medium 15 Mt) of textile waste is burned annually across 137 countries, with polyester burning alone contributing 8.3 to 24.6 Mt of fossil carbon dioxide (CO 2 ) emissions. The South Asia region accounts for 37% of these emissions, highlighting regional disparities in waste impacts. Open burning also releases hazardous pollutants such as particulate matter (PM 2.5 , PM 10 ), polycyclic aromatic hydrocarbons (PAHs), and toxic heavy metals (THMs), disproportionately affecting vulnerable populations. Although natural fibers like cotton emit less CO 2 , their combustion can still produce high levels of carbon monoxide (CO) under specific conditions. A sensitivity analysis shows that uncertainty in polyester emissions is driven mainly by the textile fraction in MSW and polyester emission factors, whereas uncertainty in cotton emissions is primarily influenced by the assumed cotton fiber share within the textile waste stream. This demonstrates that current emission inventories may misestimate impacts unless improved textile composition data and fiber-specific emission factors become available. This study underscores the urgent need for improved data, targeted research on pollutant behavior during textile combustion, and the development of waste management strategies to reduce the environmental and health burdens of open-burning practices.

  PublisherOA PDFDOI

• Assessment of Tobacco Product Waste Pollution in an Urban Reserve Via a Comprehensive Chemical Analysis for Contaminants

  SSRN Electronic Journal · 2025-01-01

  preprintOpen access
  PublisherDOI

• Detergent-mediated reduction of fiber fragment emissions during conventional machine laundering of textiles and garments

  Cleaner Materials · 2025-03-01 · 1 citations

  articleOpen accessSenior authorCorresponding

  • Detergents were studied for fiber fragments (FFs) emitted during textile washing. • FF masses were lower with a novel “low shed”, versus conventional, detergent. • The low shed detergent performed similarly across multiple textiles and facilities. • Similar FF reductions occurred for complete garment laundering (wash and dry) • Adopting a low shed detergent could widely, and immediately, reduce FFs. Synthetic textile fiber fragments (sFFs) shed via laundering including washing and drying—historically, but perhaps less accurately, known as synthetic microfibers—are microplastics contaminating environmental biota, ecosystems, and human food supplies. Reducing sFF emissions is of global concern, but there are few source reduction options. sFF emissions vary by fixed factors such as the type of garment edge treatment, the type of fiber or fabric (e.g. staple vs. filament, or surface treatment such as fleece), washing machine type, water conditions, and drying conditions. However, detergent effects are less studied and, while using any detergent—especially powder—may increase sFF emissions, the concept of liquid detergents formulated to reduce sFF emissions remains unexplored. Here, we report a novel “low shed” detergent’s comparative effects on sFF mass emissions, from two studies. First, four institutions washed each of four fabric types using either a conventional detergent or a novel (low shed) detergent, finding that the latter decreased sFF mass emissions despite institutional—operational and methodological—differences. The masses of sFFs per mass of textiles averaged, for each of four institutions, 0.08 ± 0.06, 0.07 ± 0.07, 0.05 ± 0.04, and 0.08 ± 0.04 g/kg when using the novel detergent, versus 0.23 ± 0.13, 0.16 ± 0.11, 0.14 ± 0.05, and 0.11 ± 0.05 g/kg for the conventional detergent. Despite multiple fixed differences in washing conditions across the institutions, the sFF shedding amounts significantly differed according to detergent. Second, for studies at one institution, textile fiber fragment (FF) mass emissions from laundering whole garments comprised of mixed synthetic and cotton fibers were also comparatively decreased with the low shed detergent during washing, wherein the novel detergent resulted in significantly less FF (0.37 g/kg) than the conventional detergent (0.50 g/kg; Wilcoxon test, p = 0.02, n = 8). Although whole garment FF masses captured from the machine dryer (lint trap plus dryer exhaust) did not vary by antecedent detergent (0.50 and 0.49 g/kg, using the novel versus conventional detergent, respectively), the overall garment laundering process across washing and drying emitted relatively decreased FF masses with the low shed detergent (0.87 g/kg) compared to the conventional detergent (0.99 g/kg, p = 0.02). Taken together, the results of this study demonstrated that detergent type could be an important factor in determining the release of sFFs and FFs during laundering, with a possible way to reduce the release being intentional detergent formulation.

  PublisherDOI

• Bacterial community analysis of recreational beach waters reveals human fecal contamination and pathogenicity across varying field conditions

  Water Research · 2025-04-22 · 1 citations

  articleOpen accessSenior authorCorresponding

  Assessing human fecal contamination of recreational beach waters is a public health challenge owing to multiple sources and environmental conditions affecting indicator, pathogen, and source marker relationships. Human fecal-associated markers, such as HF183, accurately indicate human waste, but reliance on individual markers risks false negative diagnoses, owing to marker source loading variations and attenuation. Bacterial community analysis is a data-dense approach that could improve the accuracy of human waste detection, but relatedness to actual human health hazards under complex coastal water conditions is unproven. Here, two Malibu and one Pacific Palisades, CA recreational beaches differing in urbanization and sewerage were studied over two years across varying seasonal rainfall, and beach berm, conditions. Fecal indicator bacteria (FIB), HF183, and human norovirus concentrations were quantified and related to bacterial community 16S rRNA gene sequences which were further analyzed for putative human pathogens and sewage proportions. All lower watersheds harbored human fecal sources, and surf zone contamination was enhanced by rainfall runoff with berm breaching, which intensified with urbanization. Notably, for sequenced surf zone waters sampled across all weather conditions (n = 36), sequence-based putative pathogen proportions correlated with qPCR HF183 concentrations (w/ and w/o PMA treatment; p = 0.0) and with human norovirus G1concentrations (p = 0.04) which also correlated with HF183 sequence abundance in bacterial communities (p = 0.02). Although human fecal sources appeared to vary seasonally and a range of physical conditions influenced surf zone fecal contamination, human fecal contamination and associated health hazard were reliably evidenced by bacterial community analysis in this study.

  PublisherDOI

• Nano-La ₂ O ₃ undermines honeybee cognition by invading the brain and accelerating neuronal apoptosis

  Environmental Science Nano · 2025-01-01 · 1 citations

  articleOpen access

  Nano-La 2 O 3 invades honeybee brains and increases neuronal apoptosis, resulting in impaired olfactory reward learning and memory.

  PublisherOA PDFDOI

• Metagenomics analysis yields assembled genomes from prokaryotic anaerobes with polymer‐degrading potential

  Biotechnology Progress · 2024-06-17 · 1 citations

  articleOpen access

  Anaerobic microbial communities are often highly degradative, such as those found in the herbivore rumen and large-scale anaerobic digesters. Since the microbial communities in these systems degrade recalcitrant organic polymers, we hypothesize that some microbes in anaerobic environments may be involved in man-made plastic association, deformation, or even breakdown. While efforts have been put toward characterizing microbial communities, many microbes remain unidentified until they can be sufficiently cultivated to generate enough genetic material to assemble high-quality metagenome assemblies and reference genomes. In this study, microbial consortia from goat fecal pellets and anaerobic digester sludge were cultivated for over 6 weeks to assemble metagenomes from novel anaerobic taxa with potential degradative activity. To select for microbes with potential plastic-degrading abilities, plastic strips were included in culture, though the presence of plastic did not appear to enrich for particularly degradative consortia, yet it did select for novel species that otherwise may not have been characterized. Whole-genome shotgun sequencing enabled assembly of 72 prokaryotic metagenome-assembled genomes (MAGs) with >90% completion, <5% contamination, and an N50 >10,000 bp; 17 of these MAGs are classified as novel species given their lack of similarity to publicly available genomes and MAGs. These 72 MAGs vary in predicted carbohydrate-degrading abilities, with genes predicted to encode fewer than 10 or up to nearly 400 carbohydrate-active enzymes. Overall, this enrichment strategy enables characterization of less abundant MAGs in a community, and the MAGs identified here can be further mined to advance understanding of degradative anaerobic microbial consortia.

  PublisherOA PDFDOI

• Ecosystem service values support conservation and sustainable land development: Perspectives from four University of California campuses

  Ecological Engineering · 2024-08-29 · 4 citations

  articleOpen access

  Urban landscapes homogenize our world at global scales, contributing to “extinction of experience”, a progressive decline in human interactions with native greenspace that can disconnect people from the services it provides. College age adults report feeling disconnected from nature more than other demographics, making universities a logical place to explore interventions intended to restore a connection with nature. This study surveyed 1088 students and staff across four university campus communities in Southern California, USA and used multicriteria decision analysis to explore their landscape preferences and the implications of those preferences for combatting extinction of experience. Our results suggest that perspectives of, and preferences for, different greenspace forms vary significantly (i.e., they are not perceived as substitutable). Support for native ecosystems, particularly coastal sage scrub (top ranked landscape) was generally high, suggesting that disaffection with wild nature is not particularly widespread. Programs for replacing turf grass lawns (lowest ranked landscape) with native plants were also well supported, but support for stormwater bioswales was more moderate (and variable). This may reflect their relative newness, both on university campuses and in urban spaces more generally. Not all members of campus communities preferred the same landscapes; preferences differed with degree of pro-environmentalism and university status (undergraduate student, graduate student, staff). Even so, all respondents exhibited landscape preferences consistent with at least one approach for combatting extinction of experience, suggesting that ecologists, engineers and urban planners have a viable set of generalizable tools for reconnecting people with nature.

  PublisherOA PDFDOI

• Municipal Separate Storm Sewer System (Ms4) Dry Weather Flows and Potential Flow Sources as Assessed by Conventional and Advanced Bacterial Analyses

  SSRN Electronic Journal · 2023-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Municipal separate storm sewer system (MS4) dry weather flows and potential flow sources as assessed by conventional and advanced bacterial analyses

  Environmental Pollution · 2023-09-05 · 4 citations

  articleOpen accessSenior authorCorresponding

  Municipal separate storm sewer systems (MS4s) function in urbanized areas to convey flows during both wet weather (i.e., stormwater) and dry weather (i.e., urban runoff as well as subsurface sources of flow) to receiving waters. While urban stormwater is known to contain microbial and chemical pollutants, MS4 dry weather flows, or non-stormwater discharges (NSWDs), are much less studied, although they are also known to contain pollutants, especially when these flows include raw sewage. In addition, some natural NSWDs (e.g., from groundwater infiltrating MS4 pipes) are critical for aquatic habitat protection. Thus, it is important to distinguish NSWD sources to prevent non-natural flows while retaining natural waters (i.e., groundwater). Here, MS4 dry weather flows were assessed by analyzing water samples from MS4 outfalls across multiple watersheds and water provider service areas in south Orange County, CA; potential NSWD sources including sewage, recycled water, potable water, and groundwater were sampled and analyzed for their likely contributions to overall NSWDs. Geochemical and microbiological water quality indicators, as well as bacterial communities, differed across NSWDs, yet water quality within most locations did not vary significantly diurnally or by sampling date. Meanwhile, NSWD source waters had distinctly different bacterial taxa abundances and specific bacterial genera. Shared geochemical and microbial characteristics of certain sources and outfall flows suggested the contributions of sources to outfall flows. The average proportions by sources contributing to MS4 outfalls were further estimated by SourceTracker and FEAST, respectively. The results of this study highlight the use of multiple tools when assessing chemical and microbiological water quality to predict sources of NSWDs contributing to urban MS4 flows during dry weather. This information can be used to support management actions to reduce unnatural and high risk sources of dry weather drainage while preserving natural sources important to environmental health in downstream receiving waters.

  PublisherDOI

Recent grants

• Resource and Stress Interactions in Regulating Microbial Communities in a California Grassland Soil

  NSF · $400k · 2005–2010

Frequent coauthors

• John H. Priester

  University of California, Santa Barbara

  76 shared

• Randall E. Mielke

  55 shared

• Galen D. Stucky

  University of California, Santa Barbara

  52 shared

• Peter K. Stoimenov

  42 shared

• Christopher J. Ehrhardt

  41 shared

• Joshua P. Schimel

  38 shared

• Samuel M. Webb

  SLAC National Accelerator Laboratory

  38 shared

• Monika Mortimer

  China Jiliang University

  38 shared

Labs

• Patricia Holden's Research GroupPI

Education

• Ph.D., ESPM

  University of California Berkeley

  1995