Arch. Environ. Contam. Toxicol. 27, 54-59 (1994) ARCHIVES OF Environmental Contamination a n d Toxicology © 1994 Sprimger-Verlag New York Inc. Trace Metals in Sediments and Potential Availability to Anadara granosa I. Mat, M. J. Maah, A. Johari Centre for Foundation Studies in Science, University of Malaya, 59100 Kuala Lumpur, Malaysia Received: 9 September 1993/Revised: 18 January 1994 Abstract. Trace metals in the sediments non-residual fraction and their relative abundance in various sedimentary components from the culture bed ofAnadara granosa were investigated. High levels of Cd (40%), Ni (40%), and Pb (43%) were associated with the sediment exchangeable phase (EP). The sediment moderately re- ducible phase (MRP) was more predominant than the easily reduc- ible phase (ERP) and the organic sulphide phase (OSP) in the sorption of available trace metals. However, this area was not considered to be heavily impacted by trace metal pollution. Since there was no significant concentration gradients observed in sedi- ments and bivalves collected from all stations, trace metal enrich- ment factors were determined. A. granosa collected from this area was enriched by Zn, Cu, Pb, Ni, Cd, and Ni. the humic fraction of the organic matter assumes a greater role in the sorption of Cu, Pb, and Zn in sediments of low iron content (Luoma and Bryan 1981). The availability of trace metals to aquatic organisms, on the other hand, are commonly correlated with the loosely bound rather than the total metal concentrations in sediments (Luoma 1983; Diks and Allen 1983). Therefore, the partitioning of trace metals in various geochemical phases should be considered explicitly before establishing the extent of trace metals availability to benthic dwelling organisms. The present paper is intended to establish the relative distribution of certain toxicologically significance trace metals in various sedimentary components with particular interest in the potential availability of these metals to the economically important bivalve, Anadara granosa. The distribution and relative abundance of trace metals in sedi- ment geochemical phases are of paramount importance when the potential biological impact of trace metals to benthic dwell- ing organisms is to be ascertained. It is not unlikely, therefore, that the strength of association between metals and sediment geochemical phases would be among the factors in determining the potential availability of trace metals to benthic organisms (Jenne and Luoma 1977). Trace metals that are loosely associated with the sediment geochemical phases (exchangeable phase and carbonate phase) are assumed to be easily bioavailable whereas those that are associated with sulphides and organic matter are relatively sta- ble and not directly bioavailable, especially under anaerobic conditions (Arakel and Hongjun 1992). Also, it has been em- phasized that oxides of Fe and Mn and the organic matter in sediments assume an important role in the sorption of (loosely referred as any form of association between metals and sedi- mentary components at molecular levels) of trace metals avail- able in aquatic environment (Tessier et al. 1985; Young and Harvey 1992). Therefore, depending on their relative abun- dance, they may compete between each other in accommodat- ing binding sites for the sorption of trace metals (Young and Harvey 1992). This contention is supported by the finding that Correspondence to: I. Mat Materials and Methods Sample Collections The culture-bed ofA. granosa from the mudflat of Lekir in the state of Perak, Peninsular Malaysia (Figure 1) was selected. This area is among the gazetted sites for the intensive semi-culture of the commercially important bivalve, A. granosa, initiated by the Fishery Department of Malaysia. Therefore, it is assumed that this area is not to be heavily contaminated anthropogenically. Fourteen sampling stations (1 km apart) were designated. Sample collections in all stations were made between the mean high water neap tide and mean low water neap tide. Surficial sediments (arbitrarily taken as the upper 5 cm) were collected by using acid cleaned plastic corers (3 cm diameter) and transfered into acid cleaned plastic canis- ters. The atmosphere above the sediment samples was not purged. The effect of oxygen during the extraction process is considered to be minimal (Rule and Alden 1992). Bivalves of 36 - 4 mm shell length were also collected manually from same stations where the sediment samples were previously collected. Ten to 15 bivalves were obtained from each station. They were cleaned and depurated for 24 h before transporting them to the laboratory. Sediments and bivalves were kept frozen prior to analyses. Sediment Analyses Sediment samples were scrutinized for visible debris and oven dried at 101°C for 8 h. Sediment subsamples of 2 g (<210 Ixm) from each