Copper and Cadmium Binding to Fish Gills: Modification by Dissolved Organic Carbon and Synthetic Ligands

Abstract

Adult fathead minnows (Pimephales promelas) were exposed to 17 g Cu∙L−1 or 6 g Cd∙L−1 for 2 to 3 h in synthetic softwater solutions at pH 6.2 containing either naturally-occurring, freeze-dried dissolved organic carbon (DOC) or synthetic ligands such as EDTA. After exposures, gills were assayed for bound Cu or Cd. As a first approximation, lake of origin or molecular size fraction of DOC did not influence Cu binding to gills, while DOC concentration did. DOC concentrations ≥4.8 mg∙L−1 prevented Cu from accumulating on fathead gills. At the relatively low concentrations used, neither Cu nor Cd interfered with binding of the other metal on gills, suggesting different gill binding sites. Cadmium accumulation on gills was more sensitive to increased concentrations of Ca and H+ than was Cu. Surprisingly, Cd bound to gills to the same or greater extent than did Cu: for synthetic ligands, Cd binds less well than Cu. This result corroborates previously published observations that Cd, unlike Cu, is taken up at gills through high affinity Ca channels. Accumulation of Cd on fish gills was never associated with 14C-labelled EDTA or 14C-citrate, indicating that free metal interacts with the gill while metal–ligand complexes usually do not.

Temporal assessment of copper speciation, bioavailability and toxicity in UK freshwaters using chemical equilibrium and biotic ligand models: Implications for compliance with copper environmental quality standards

“…This is in accordance with the commonly reported effects of these major cations on metal toxicity to aquatic organisms and probably reflect the competition between these ions and the free copper ion for binding on the cell surfaces (Playle et al, 1993;Campbell, 1995;Di Toro et al, 2001;De Schamphelaere and Janssen, 2002). Occupation of the sites by calcium and/or magnesium would result in normal membrane function, while occupation of the sites by copper would disrupt function as toxicity is considered to occur when a critical proportion of the sites are occupied by copper.…”

Effects of Acid Rock Drainage on Stocked Rainbow Trout (Oncorhynchus mykiss): An In-Situ, Caged Fish Experiment

“…Stream waters at Snake River study sites were calculated to be relatively soft (34-57 mg/L CaCO 3 ), limiting mitigation potential. Similarly, dissolved organic carbon (DOC) has been observed to reduce metal toxicity through the formation of organic/metal complexes that are less bioavailable to fish (Playle, Dixon, & Burnison, 1993). Year-round measurements of water quality parameters demonstrate routinely low DOC concentrations (< 2 mg/L) at both ARD-impacted sites in this study (Todd et al, 2005).…”

“…The higher the value of K M-Gill for a particular metal, the more tightly that metal will be bound to the gill. For filtered copper, a K Cu-Gill of 7.4 indicates that copper binds fairly strongly to gill tissue (Playle et al, 1993). This strong interaction between filtered copper ions and gill tissue is reflected in significant, site-specific differences in gill-bound Cu concentrations observed in this study (Figure 5a).…”

The effect of natural dissolved organic carbon on the acute toxicity of copper to larval freshwater mussels (glochidia)

“…Similarly, a significant increase in the survival of L. fasciola glochidia was observed when natural DOC was added to an acutely toxic Cu exposure. Negatively charged ligands such as DOC bind with positively charged cations such as Cu, reducing the amount of free Cu in solution and thus reduce the bioavailability of Cu [16]. The ameliorating effect of natural DOC on Cu toxicity in juvenile freshwater mussels (L. siliquoidea) was recently demonstrated by Wang et al [26].…”

“…Major ions, including Ca, Mg, and Na, compete with metal ions at the site of uptake [14,15]. Similarly, the presence of ligands, such as dissolved organic carbon (DOC), can bind with the metal ion and reduce its bioavailability [16]. Copper bioavailability is strongly influ enced by DOC.…”