UPTAKE OF CHLORDANE BY A DEPOSIT-FEEDING BIVALVE - DOES THE DEPTH OF SEDIMENT CONTAMINATION MAKE A DIFFERENCE

Intertidal sediment was treated with technical chlordane (11 ppb) and combined with untreated natural sediment in small containers to produc e a range of contaminant depth profiles (viz., top 2 cm [only] treated , all except the top 2 cm treated, all treated, all untreated). Adult specimens of Macomona liliana (a tellinid bivalve) were placed in some of the containers. All of the containers were immersed in seawater an d exposed to an artificial semidiurnal tidal regime over 5 d. Approxim ately 24 to 36% of the applied chlordane was lost from the sediments, presumably dissolved in the recirculating seawater. Losses of chloroda ne were generally greater when shellfish were present, possibly throug h transport to the sediment surface and subsequent solubilization in s eawater. Macomona liliana accumulated the greatest concentration of ch lordane (5,728 ppb lipid) from sediments having a uniform concentratio n of chlordane (7 ppb at the end of the experiment), whereas those in containers with either the top 2 cm treated or all but the top 2 cm tr eated, accumulated 3,617 and 2,756 ppb lipid, respectively. The shellf ish body burden accounted for only a small proportion (less-than-or-eq ual-to 1%) of the total chlordane in each of the containers. Chlordane depth profiles were not as well defined in the sediments having Macom ona liliana, as those that did not. These results indicate that Macomo na liliana can assimilate organochlorines bound to sediments at depths below 2 cm, most probably by ingestion. Animals constantly exposed to contaminated sediment accumulated more than those able to feed altern ately on contaminated and uncontaminated sediments. The ability of Mac omona liliana to accumulate and depurate contaminants throughout the s ediment profile may increase the chances of more sensitive species bei ng exposed to harmful concentrations.