BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//IXAS: The International X-ray Absorption Society - ECPv6.15.15//NONSGML v1.0//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
X-ORIGINAL-URL:https://xrayabsorption.org
X-WR-CALDESC:Events for IXAS: The International X-ray Absorption Society
REFRESH-INTERVAL;VALUE=DURATION:PT1H
X-Robots-Tag:noindex
X-PUBLISHED-TTL:PT1H
BEGIN:VTIMEZONE
TZID:America/Los_Angeles
BEGIN:DAYLIGHT
TZOFFSETFROM:-0800
TZOFFSETTO:-0700
TZNAME:PDT
DTSTART:20190310T100000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0700
TZOFFSETTO:-0800
TZNAME:PST
DTSTART:20191103T090000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0800
TZOFFSETTO:-0700
TZNAME:PDT
DTSTART:20200308T100000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0700
TZOFFSETTO:-0800
TZNAME:PST
DTSTART:20201101T090000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:-0800
TZOFFSETTO:-0700
TZNAME:PDT
DTSTART:20210314T100000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0700
TZOFFSETTO:-0800
TZNAME:PST
DTSTART:20211107T090000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200611
DTEND;VALUE=DATE:20200612
DTSTAMP:20260718T122401
CREATED:20200514T015818Z
LAST-MODIFIED:20200617T021645Z
UID:384-1591833600-1591919999@xrayabsorption.org
SUMMARY:Alessandra Leri: XANES Spectroscopy to Illuminate Biogeochemical Cycling of Halogens in Environmental Systems
DESCRIPTION:The halogens chlorine and bromine have high electron affinities and exist in seawater mainly as chloride and bromide anions\, which have generally been considered unreactive in the environment. Using Cl and Br K-edge XANES spectroscopy\, we have measured high concentrations of organo-chlorine and -bromine in naturally degraded particulate organic matter (POM) from oceanic sediment traps. While organobromine speciation in marine POM is exclusively aromatic\, organochlorine is fractionated into aliphatic and aromatic particles that appear in a heterogeneous distribution. The major precursor of sediment trap material is phytoplankton biomass\, the detritus of which under-goes oxidative breakdown as part of the marine carbon cycle. We hypothesized that unsaturated lipid and protein moieties in phytoplankton detritus would be susceptible to halogenation through oxidative degradation mechanisms. Using model experiments\, we showed that algal particulates are readily chlorinated and brominated through various abiotic pathways\, including photochemical and Fenton-like reactions. These processes produce organohalogens in particulate algal detritus at levels exceeding 0.1% by mass. In contrast with the exclusively aromatic organobromine observed in natural marine POM\, the lab-based experiments generate aliphatic organobromine in algal particulates; however\, the aliphatic organobromine produced appears to be labile and susceptible to debromination on relatively short (3-week) timescales under highly oxidizing conditions. These findings have implications for the transformation and stabilization of marine organic carbon prior to sedimentary burial.\nWe have also measured high concentrations of non-volatile organochlorine and -bromine in several varieties of edible kelps. Such compounds are likely to contribute to organohalogen body burden in humans and other organisms.\n \nReferences: \n\nA. Leri\, M. Dunigan\, R. Wenrich\, and B. Ravel (2019). Particulate organohalogens in edible brown seaweeds. Food Chemistry 272\, 126. https://doi.org/10.1016/j.foodchem.2018.08.050\nA. Leri\, L. Mayer\, K. Thornton\, P. Northrup\, M. Dunigan\, K. Ness\, and A. Gellis (2015). A marine sink for chlorine in natural organic matter. Nature Geoscience 8\, 620. https://www.nature.com/articles/ngeo2481\nA. Leri\, L. Mayer\, K. Thornton\, and B. Ravel (2014). Bromination of marine particulate organic matter through oxidative mechanisms. Geochimica et Cosmochimica Acta 142\, 53. https://doi.org/10.1016/j.gca.2014.08.012\nA. Leri and B. Ravel (2014). Sample thickness and quantitative concentration measurements in Br K-edge XANES spectroscopy of organic materials. Journal of Synchrotron Radiation 21\, 623. https://doi.org/10.1107/S1600577514001283\n\n\n 
URL:https://xrayabsorption.org/events/journalclub-alessandra-leri/
CATEGORIES:XAFS Journal Club
END:VEVENT
END:VCALENDAR