Impact of bromide exposure on natural organochlorine loss from coastal wetland soils in the Winyah Bay, South Carolina

Abstract

Naturally formed halogenated organic compounds are common in terrestrial and marine environments and play an important role in the halogen cycle. Among these halogenated compounds, chlorinated organic compounds are the most common halogenated species in all soils and freshwater sediments. This study evaluated how a previously observed phenomenon of bromination of organic matter in coastal soils due to salt-water intrusion impacts the stability and fate of natural organochlorine (org-Cl) in coastal wetland soils. The reacted solid and liquid samples were analyzed using X-ray spectroscopy (in cm and at micron scales for solids) and ion chromatography. We find that introduction of Br⁻ species and their subsequent reactions with organic carbon are associated with an average of 39% loss of org-Cl species from leaf litter and soil. The losses are more prominent in org-Cl hotspots of leaf litter, and both aliphatic and aromatic organochlorine compounds are lost from all samples at high Br⁻ concentrations. The combination of solid and aqueous phase analysis suggests that org-Cl loss is most likely largely associated with volatilization of org-Cl. Release of labile org-Cl compounds has detrimental environmental implications for both ecosystem toxicity, and stratospheric ozone. The reactions similar to those observed here can also have implications for the reactions of xenobiotic chlorinated compounds in soils.