Metal contaminated sediments can be toxic to aquatic organisms and are common in human-dominated ecosystems, which results in metals being a leading cause of ecosystem impairment. Bioavailability of metals is influenced by their affinity for dissolved and solid-phase ligands, including iron (Fe) oxyhydroxides, which have been hypothesized to reduce metal toxicity in sediments. The authors examined the adsorption kinetics of copper (Cu) and nickel (Ni) with goethite (α-FeOOH) and characterized the influences of solute metal concentration, pH, ionic strength, and humate concentration on steady-state partitioning of the metals with goethite under conditions representative of natural aquatic environments. Copper and Ni readily adsorbed to goethite, and steady-state partitioning was achieved within 2 h. Although ionic strength had no effect on metal partitioning, adsorption of Cu and Ni to goethite was enhanced by alkaline pH and reduced by competition with humate. Because distribution coefficient (KD ) values for Cu and Ni from the present study are comparable to values measured in natural systems, the authors hypothesize that goethite may contribute significantly to the adsorption of both Ni and Cu to particles in the environment. The authors suggest that incorporating binding by Fe oxides in metal bioavailability models should be a priority for improving risk assessment of metal-contaminated oxic sediments.
Accurate determinations of trace levels of mercury (Hg) in water require scrupulously clean sampling equipment and storage bottles. To avoid Hg contamination during storage, it has been presumed that water samples must be stored in either glass or Teflon bottles cleaned with a rigorous method, such as submersion in hot acid. These cleaning procedures are hazardous, and use of Teflon bottles can be cost prohibitive for major oceanographic programs. We investigated the suitability of alternative cleaning procedures and bottle materials for storage of seawater containing sub‐picomolar levels of Hg. We found that a simple technique with detergent, dilute acid, and bromine monochloride removes Hg from all bottle materials tested, which included FEP Teflon, glass, polycarbonate (PC), low‐density polyethylene (LDPE), and fluorinated polyethylene (FLPE). The technique is effective for bottles that are either new or used previously for trace‐level oceanographic samples (total Hg < 10 pM). Stability of seawater Hg levels differed dramatically among storage bottle materials during a 74‐ week test. Hg in seawater stored in LDPE, FLPE, and FEP bottles increased within 15 weeks of storage at room temperature. In contrast, Hg levels in seawater stored in PC bottles were increased modestly only after 74 weeks of storage and those in glass bottles were unchanged throughout the test. We recommend future use of this new cleaning method and encourage greater use of glass and PC bottles for storage of waters containing low levels of Hg.
