title: Photorelease of microcystin-LR from resuspended sediments.
abstract: A series of ten photolysis experiments was conducted with sediments exposed to Microcystis sp. blooms to determine if sunlight is capable of mobilizing the biotoxin microcystin-LR (MC-LR) into the water column. There was a net photorelease of MC-LR in irradiated suspensions in all cases relative to dark controls, ranging from 0.4 to 192μgL-1g-1into the dissolved phase. This should be viewed as a minimum estimate of photorelease due to concurrent photodegradation of dissolved toxin. Dissolved MC-LR concentrations in a sediment suspension increased linearly in the aqueous phase during a six-hour irradiation with simulated sunlight suggesting that longer exposure times produce greater quantities of MC-LR. There was a significant positive correlation between photorelease of toxin and percent organic carbon of the resuspended material, implying that organic-rich sediments yield the greatest photorelease of MC-LR upon exposure to full spectrum sunlight. Samples exposed to photosynthetically active radiation (400nm-700nm) were responsible for less than 2% of the photorelease compared to full spectrum exposures. Model calculations indicate that photochemical processing of bloom impacted sediments could be responsible for as much as 100% of the average standing stock of MC-LR in a freshwater pond located in southeastern North Carolina, where surface water concentrations were also measured. Mass spectrometric analysis revealed a new peak in light exposed flasks that appears to be a photo-induced isomerized product of MC-LR. Photoproduction from resuspended sediments therefore represents a significant but previously unrecognized source of highly toxic MC-LR and photoproducts of unknown toxicity and fate to aquatic ecosystems.
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, NC 28403-3297, United States. Electronic address: kieberr@uncw.edu.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Kieber
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, NC 28403-3297, United States.
authors.forename: Lindsey M
authors.initials: LM
authors.lastname: Hartrey
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, NC 28403-3297, United States.
authors.forename: David
authors.initials: D
authors.lastname: Felix
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, NC 28403-3297, United States.
authors.forename: Coleman
authors.initials: C
authors.lastname: Corzine
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, NC 28403-3297, United States.
authors.forename: G Brooks
authors.initials: GB
authors.lastname: Avery
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, NC 28403-3297, United States.
authors.forename: Ralph N
authors.initials: RN
authors.lastname: Mead
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina Wilmington, Wilmington, NC 28403-3297, United States.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Skrabal
mesh_terms: D019015:Geologic Sediments / Q000382:microbiology*; D046931:Microcystis / Q000378:metabolism*; D010777:Photochemistry / Q000379:methods*; D013472:Sunlight
keywords: MC-LR; Photochemistry; Sediments; Sunlight