Mark Hahn has been working on aquatic toxicology for many years. It is a relatively small list of us in the USA who do this kind of work, so I wasn’t all that surprised that he has done work both with my master’s advisor at Duke University (Rich DiGuilio) and my PhD advisor at Oregon State University (Larry Curtis) – both terrific mentors. This trio has done a tremendous amount of work on how pollutants affect fish, focusing on the PAHs and PCBs and their effects on AhR (a receptor) and oxidative stress. One of the breakthroughs in this area is the discovery that some fish (killifish) have developed resistance to PCB exposure because of certain P450 enzyme profiles – Rick and Mark worked on this, and Mark now uses CRISPR to knock out certain genes to see how that affects toxicity on zebrafish. Really cool.
Mark entered the world of microplastics through his two mentees. One is Jordan Pitt, at the very tail end of her PhD. Jordan is interested in how plastics accumulate and move inside fish – and specifically the tiny nanoplastics. She is tracking their movement into muscle tissue (the stuff of fish fillets and sandwiches), and across the blood-brain barrier (the supposedly impenetrable fortress of the brain). In some of her work, she didn’t see as much uptake as she expected, and is now trying to figure out if using metal doping instead of fluorescence would lead to better detection at low levels. She is not using Nile Red dye, but counts each particle and performs Raman on each little one – she spends every Friday with the beloved Raman spectroscope. FTIR only works for larger particles, and as a nano-researcher, Jordan is “extremely jealous” of those who focus on larger FTIR-friendly microplastics. When I visited, Jordan was using a confocal microscope to see which dye works best to image the blood-brain barrier. She likes the green one, the lowest molecular weight one, because it shows the greatest level of diffusion (or leakage), which makes sense from a physiological perspective.
Bryan James, Mark’s other current mentee, took an entirely different path to microplastics. He has his PhD already and is trained in biomedical materials. He wondered if the plastics used to deliver medications and/or the wear-and-tear of replaced hips would have any human health consequences. And then one of the great nurdle spills happened off the coast of Sri Lanka in May of 2021. A ship with 1680 tonnes of nurdles (tiny plastic pellets used to make larger plastic stuff) caught fire and sank (read more here). Bryan got involved through Christopher Reddy, as they wanted to know if burnt plastics would likely be more, or less, toxic than unburnt plastics (read more here). As if knowing the effects of the various sizes, shapes and compositions of microplastics themselves isn’t hard enough – now we need to add the level of burntness to the list of variables! Bryan also looks at the relative toxicity of Ziploc bags versus single-use bags (Ziplocs are worse, so reuse them please), and of the photo-degraded microplastics are more toxic than the more recently released microplastics. He describes this as a “transcriptomics fishing expedition” as we don’t really know what those products are and how they might affect gene expression, but it looks like the areas affected include focal adhesions and the extracellular matrix.
Mark also grew up in Rochester, NY and knows Ithaca well. He even knows Ithaca College, having collaborated a bit with Ian Woods on zebrafish genetics. We toured his labs and one of two researchers said, “You are from Ithaca, right? I grew up on Stone Quarry Road, right next to the Ithaca College Natural Lands.” I can relate. It is a small world, really.
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