Partitioning of Cd, Zn and Fe in the Tissues and Cytosols of Blood Cockles (Anadara granosa) from the Gulf of Thailand

Anadara granosa is a bivalve blood cockle occurring abundantly in tropical estuarine intertidal sediments. The accumulation of Cd, Zn and Fe and their partitioning at the sub-cellular level in the cytosol has been investigated in the gills, digestive gland, body and foot of A. granosa from seven estuaries in the Gulf of Thailand. Cadmium and Zn were bioaccumulated predominantly in the gills with smaller concentrations distributed equally throughout the other tissues. Iron was present at relatively low concentrations in gills but was higher, and more evenly distributed, in the digestive gland, body and foot. The concentrations of metallothionein-like protein (MTLP) were found to be in the range 1–11 mg g−1 (dry weight) with the highest values being in the digestive gland at all sites. Partitioning of the metals in the cytosols between low molecular weight (LMW) compounds, MTLP and high molecular weight compounds (HMW) indicated that 16–39% of total Cd, 6.5–15% of total Fe and < 6% of total Zn were bound with MTLP. However, 23–27% of total Zn was bound with the HMW fraction, ascribed potentially to its association with the blood pigment haemoglobin (Hb). The metal-handling strategy, involving Zn, is likely important to blood cockles in supporting their uptake of dissolved oxygen in under-saturated tropical waters