Cadmium Bioavailability and Accumulation in the Presence of Humic Acid to the Zebra Mussel, Dreissena polymorpha

Abstract

Metal speciation in aquatic systems is mainly determined by the type and concentration of ligands present in solution. A very important group of complexing agents is dissolved organic matter (DOM), e.g., humic and fulvic acids. According to the free-ion activity model, only the free metal ion is available to biota. Nevertheless, DOM has been reported to decrease or increase metal uptake, leading to uncertainty concerning the bioavailability of metal-DOM complexes. In this work the effect of Aldrich humic acid on cadmium accumulation by the zebra mussel, Dreissena polymorpha, was studied under laboratory conditions. Mussels, collected in a drinking water reservoir, were exposed to varying environmentally relevant concentrations of cadmium in the presence and absence of humic acid. Cadmium concentrations in the mussel tissues were analyzed, and measurements with a cadmium-ion-selective electrode were made to determine the free cadmium ion activity in the exposure waters. The uptake of humic acid by the zebra mussels was measured by the decrease of the total organic carbon (TOC) concentration in the water over time. The free cadmium ion activity in the water decreased from 51.6% to 19.9% of the total cadmium concentration in the presence of humic acid. This decrease by a factor of 2.6 resulted in a decrease in the cadmium uptake rate in the soft tissue of zebra mussels from 12.9 to 7.9 nmol/g dry wt/day, which corresponds to a decrease by a factor of 1.6. This implies that cadmium uptake rates were higher than predicted by the free-ion activity model and indicates that cadmium-humic acid complexes are partly available to zebra mussels.

Modeling the effect of water chemistry on the bioaccumulation of waterborne cadmium in zebra mussels

“…The effects of DOM on Cd bioaccumulation in D. polymorpha observed in the present study are consistent with apparently contradictory results obtained by Voets et al [10] and Roditi et al [14]. Voets et al [10] found that the presence of approximately 55 mg/L (i.e., $23 mgDOC/L) of Aldrich humic acid in the medium prevented Cd accumulation, whereas Roditi et al [14] showed that a small amount of DOC (concentrations of DOC derived from algae ranged from 1.96 to 3.28 mg/L) enhanced metal uptake.…”

“…It was also demonstrated that Zn had a protective effect on Cd toxicity [8,9]. The protective effect of dissolved organic matter (DOM) has been reported by different studies [10,11], because it modifies Cd speciation. However, some exceptions were also reported, in particular for some bivalves like Mytilus edulis or Dreissena polymorpha [12][13][14].…”

Trophic position of zebra mussel veligers and their use of dissolved organic carbon

“…Nevertheless, the uptake of some allochthonous materials by veligers cannot be ruled out. Adult zebra mussels are known to take up humic acids in addition to algal lysates (Voets et al 2004), but the d 13 C of humics is likely to reflect their terrestrial origins and the nonterrestrial signature of zebra mussel veligers in the St. Lawrence River implies that this is not a primary source in their diet.…”

Effects of settling organic matter on the bioaccumulation of cadmium and BDE-99 by Baltic Sea benthic invertebrates

“…When truly dissolved, uptake of Cd can be a result of diffusion through respiratory surfaces and the epidermis, whereas when it is associated with dissolved (DOM) and particulate (POM) organic matter, the exposure is presumably higher through the diet (Wang and Fisher, 1999;Lee et al, 2000). However, when associated with DOM, the bioavailability of Cd may be limited (Voets et al, 2004). The speciation and bioavailability of metals also varies with chemical conditions in the sediment, such as pH (Heijerick et al, 2003), salinity and redox potential.…”