title: Importance of equilibration time in the partitioning and toxicity of zinc in spiked sediment bioassays.
abstract: The influences of spiked Zn concentrations (1-40 micromol/g) and equilibration time (approximately 95 d) on the partitioning of Zn between pore water (PW) and sediment were evaluated with estuarine sediments containing two levels (5 and 15 micromol/g) of acid volatile sulfides (AVS). Their influence on Zn bioavailability was also evaluated by a parallel, 10-d amphipod (Leptocheirus plumulosus) mortality test at 5, 20, and 85 d of equilibration. During the equilibration, AVS increased (up to twofold) with spiked Zn concentration ([Zn]), whereas Zn-simultaneously extracted metals ([SEM]; Zn with AVS) remained relatively constant. Concentrations of Zn in PW decreased most rapidly during the initial 30 d and by 11- to 23-fold during the whole 95-d equilibration period. The apparent partitioning coefficient (Kpw, ratio of [Zn] in SEM to PW) increased by 10- to 20-fold with time and decreased with spiked [Zn] in sediments. The decrease of PW [Zn] could be explained by a combination of changes in AVS and redistribution of Zn into more insoluble phases as the sediment aged. Amphipod mortality decreased significantly with the equilibration time, consistent with decrease in dissolved [Zn]. The median lethal concentration (LC50) value (33 microM) in the second bioassay, conducted after 20 d of equilibration, was twofold the LC50 in the initial bioassay at 5 d of equilibration, probably because of the change of dissolved Zn speciation. Sediment bioassay protocols employing a short equilibration time and high spiked metal concentrations could accentuate partitioning of metals to the dissolved phase and shift the pathway for metal exposure toward the dissolved phase.
authors.affiliation: NeoEnBiz Company, Seoul, Republic of Korea.
authors.forename: Jung-Suk
authors.initials: JS
authors.lastname: Lee
authors.forename: Byeong-Gweon
authors.initials: BG
authors.lastname: Lee
authors.forename: Samuel N
authors.initials: SN
authors.lastname: Luoma
authors.forename: Hoon
authors.initials: H
authors.lastname: Yoo
mesh_terms: D000327:Adsorption; D033304:Amphipoda; D000818:Animals; D001681:Biological Assay; D001682:Biological Availability; D019015:Geologic Sediments / Q000737:chemistry*; D007700:Kinetics; D007928:Lethal Dose 50; D015203:Reproducibility of Results; D013440:Sulfides / Q000737:chemistry; D014835:Volatilization; D014867:Water / Q000737:chemistry; D015032:Zinc / Q000737:chemistry* / Q000493:pharmacokinetics*
chemical_list: D013440:Sulfides; D014867:Water; D015032:Zinc