Importance of equilibration time in the partitioning and toxicity of zinc-spiked sediment bioassays

Chonnam National University, Gwangju, Gwangju, South Korea
Environmental Toxicology and Chemistry (Impact Factor: 3.23). 02/2004; 23(1):65-71. DOI: 10.1897/03-176
Source: PubMed


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.

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    • "In the case of metal-spiking, even with adequate pH control and long equilibration times, added metals may remain in highly bioavailable forms. Consequently the sediments often exhibit high porewater metal concentrations and fluxes (Lee et al., 2004; Simpson et al., 2004; Hutchins et al., 2007). Because of this, where spiked sediments are used in laboratory-based studies to assess metal bioaccumulation and toxicity, measurements of metal concentrations within sediment and water (porewater and overlying water) compartments before, during, and at the completion of tests are crucial to interpreting exposure pathways (Borgmann, 2000; Simpson and King, 2005). "
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