Dialysis minipeeper for measuring pore‐water metal concentrations in laboratory sediment toxicity and bioavailability tests

Abstract

AbstractWhave modifieda classical peeper (dialysiscell)design to create minipeepers that are ofconvenient sze for direct pore‐water sampling in laboratory sediment toxicity and bioavailability tests. A series of experiments placing peepers in nickel and zinc solutions, two size fractions of nickel‐spiked sand, and two field‐collected, nickel‐spiked sediments, were conducted to evaluate peeper efficacy in measuring overlying water and pore‐water metal concentrations. In water‐only experiments, concentrations in the peeper cells were not significantly different from those in the surrounding solution by 48 and 96 h for nickel and zinc, respectively. Peeper cells in the sand experiments equilibrated with the surrounding pore water in ≤120 h. In both trials with natural sediment, peeper equilibrium occurred in ≤48 h. Nickel flux into the peeper cells during the first hour of experimentation showed that the rate of equilibration was initially related to media porosity. In fine sand and natural sediment, equilibration was influenced not only by nickel diffusion into the peeper cells, but also by a decrease in concentrations of nickel in pore water due to sediment sorption and diffusion into overlying water. This shortened the time required to reach equilibrium by reducing the difference between the peeper cell and the surrounding pore‐water solution. Overall, minipeepers equilibrated with the surrounding pore water or overlying water within a time period sufficiently short to allow for the use of minipeepers in routine sediment toxicity and metal bioavailablity experiments. Sampling precision using minipeepers was comparable (CV = 10.8 %) to that obtained by conventional sediment centrifugation and filtration (CV = 10.5 %).