About

The Gray Lab research priorities are focused on addressing questions related to environmental toxicology, primarily using physiological and ecological approaches to examine the impacts of legacy and emerging contaminants (PAHs, POPs, microplastics, nanoplastics, and pharmaceuticals) from various environmental matrices.

Research topics

• Ecology
• Biology
• Environmental science
• Environmental chemistry
• Chemistry
• Remote sensing
• Oceanography
• Fishery
• Microbiology
• Environmental engineering
• Animal science
• Geology

Selected publications

• Spatial and temporal variability of microplastic abundance in estuarine intertidal sediments: Implications for sampling frequency

  The Science of The Total Environment · 2022 · 50 citations

  Senior authorCorresponding
  • Environmental science
  • Oceanography
  • Ecology

  Microplastics (<5 mm) are well documented across shorelines worldwide; however, high variability in microplastic abundance is often observed within and among field studies. The majority of microplastic surveys to date consist of single sampling events that do not consider spatiotemporal variability as a potential confounding factor in the interpretation of their results. Therefore, these surveys may not accurately capture or reflect levels of microplastic contamination in the environment. Here, we provide the first investigation of small-scale spatial and temporal variability of microplastic abundance, distribution, and composition in the intertidal zone of an urbanized US estuary to better understand the short-term, daily spatiotemporal variability of microplastics in dynamic coastal environments. Intertidal sediment was collected from both the low and high intertidal zones of a sandy estuarine beach located in South Carolina, southeastern US every 1 to 2 days at low tide over 17 days (12 sampling events; total n = 72). Study-wide, microplastic abundance ranged from 44 to 912 microplastics/m2 and consisted primarily of polyethylene, nylon, polyester, and tire (or tyre) wear particles. High temporal variability was observed, with microplastic abundance differing significantly among sampling events (p = 0.00025), as well as among some consecutive tidal cycles occurring within 12 h of each other (p = 0.007). By contrast, low spatial variability was observed throughout the study with no significant differences in microplastic abundance detected between the low and high intertidal zones (p = 0.76). Of the environmental factors investigated, wind direction on the day of sampling had the greatest effect on temporal microplastic variability. Our results demonstrate that there can be significant temporal variability of microplastic abundance in estuarine intertidal sediments and are important for informing the methods and interpretation of future microplastic surveys in dynamic coastal environments worldwide.

  DOI

• Are nitrogen and carbon cycle processes impacted by common stream antibiotics? A comparative assessment of single vs. mixture exposures

  PLoS ONE · 2022 · 17 citations

  1st authorCorresponding
  • Environmental chemistry
  • Biology
  • Environmental science

  A variety of antibiotics are ubiquitous in all freshwater ecosystems that receive wastewater. A wide variety of antibiotics have been developed to kill problematic bacteria and fungi through targeted application, and their use has contributed significantly to public health and livestock management. Unfortunately, a substantial fraction of the antibiotics applied to humans, pets and livestock end up in wastewater, and ultimately many of these chemicals enter freshwater ecosystems. The effect of adding chemicals that are intentionally designed to kill microbes, on freshwater microbial communities remains poorly understood. There are reasons to be concerned, as microbes play an essential role in nutrient uptake, carbon fixation and denitrification in freshwater ecosystems. Chemicals that reduce or alter freshwater microbial communities might reduce their capacity to degrade the excess nutrients and organic matter that characterize wastewater. We performed a laboratory experiment in which we exposed microbial community from unexposed stream sediments to three commonly detected antibiotics found in urban wastewater and urban streams (sulfamethoxazole, danofloxacin, and erythromycin). We assessed how the form and concentration of inorganic nitrogen, microbial carbon, and nitrogen cycling processes changed in response to environmentally relevant doses (10 μg/L) of each of these antibiotics individually and in combination. We expected to find that all antibiotics suppressed rates of microbial mineralization and nitrogen transformations and we anticipated that this suppression of microbial activity would be greatest in the combined treatment. Contrary to our expectations we measured few significant changes in microbially mediated functions in response to our experimental antibiotic dosing. We found no difference in functional gene abundance of key nitrogen cycling genes nosZ, mcrA, nirK, and amoA genes, and we measured no treatment effects on NO3- uptake or N2O, N2, CH4, CO2 production over the course of our seven-day experiment. In the mixture treatment, we measured significant increases in NH4+ concentrations over the first 24 hours of the experiment, which were indistinguishable from controls within six hours. Our results suggest remarkable community resistance to pressure antibiotic exposure poses on naïve stream sediments.

  DOI

• Accumulation and depuration of microplastic fibers, fragments, and tire particles in the eastern oyster, Crassostrea virginica: A toxicokinetic approach

  Environmental Pollution · 2022 · 53 citations

  Senior authorCorresponding
  • Chemistry
  • Animal science
  • Environmental chemistry
  DOI

Frequent coauthors

• Bryan Pham

  65 shared

• S.G. Dalal

  Clínica Ruiz

  65 shared

• Kum Ja Lee

  Loma Linda University Medical Center

  65 shared

• Mojtaba Akhtari

  Loma Linda University Medical Center

  65 shared

• Daniel Park

  University College London

  64 shared

• John E. Weinstein

  12 shared

• Megan Gaesser

  4 shared

• Bonnie Ertel

  4 shared

Labs

• Gray LabPI

Education

• PhD, Biology

  University of North Carolina at Greensboro

  2020

• Master of Arts, Biology

  The Citadel, Graduate College

  2014

• Bachelor of Science , Health, Exercise, and Sports Science

  The Citadel, Military College of South Carolina

  2013

Awards & honors

• NSF CAREER Award (2025)
• Outstanding Research Award, Department of Biological Science…
• Society of Environmental Toxicology and Chemistry- President…
• Virginia Tech Institute for Society, Culture and Environment…
• Outstanding Service Award, Department of Biological Sciences…

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