Influences of natural colloids on metal bioavailability to two marine

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Original languageEnglish
Pages (from-to)4571-4576
Journal / PublicationEnvironmental Science and Technology
Volume34
Issue number21
Online published26 Sep 2000
Publication statusPublished - 1 Nov 2000
Externally publishedYes

Abstract

We examined the bioavailability of colloid-bound metals [Cd, Cr(III), and Zn] to two marine bivalves (mussel Perna viridis and clam Ruditapes philippinarum) from subtropical and tropical waters. Natural colloids (between 1 nm and 0.2 μm) were isolated by cross-flow ultrafiltration. Bivalves were then exposed to radiolabeled colloids, and the uptake of colloid-bound metals was compared with the uptake of metals associated with the low molecular weight fraction (LMW, <1 kDa). In general, the bioavailability of colloid-bound Zn to mussels was significantly inhibited as compared to that of the LMW-bound Zn. Its uptake decreased with increasing colloidal organic carbon (COC) concentration. There was no major difference in Cd bioavailability between the LMW and the colloidal treatments, primarily because most of the radiolabeled colloidal Cd remained in the truly dissolved phase during the uptake period. In contrast, the bioavailability of colloid-bound Cr was enhanced in the mussels. In clams, bioavailability of metals was not significantly influenced by colloidal binding, although Zn uptake was slightly enhanced when it was associated with the LMW fraction. The measured dry weight concentration factor (DCF) in bivalve tissue was the highest for Zn, followed by Cd and Cr. Furthermore, DCF was higher in the mussels (20-340) than in the clams (10-35). Colloid-bound metals were mostly accumulated in mussel digestive gland and remaining soft tissue (64-87%), whereas a large fraction (36-73%) of metals was found on the shell of the clams. Coagulation of radioactive tagged colloidal organic matter was insignificant (<9%) for metals in the absence of large suspended particles, indicating that coagulation effects on metal uptake were minimal under our experimental conditions. Thus, our study demonstrated that colloid-bound metals were bioavailable to both the mussels and the clams, but the influences of colloidal binding on metal uptake varied among metals and between the two bivalves.