THE ESTUARINE CLAM RANGIA-CUNEATA AS A BIOMONITOR OF DIOXINS AND FURANS IN THE NECHES RIVER, TAYLOR BAYOU, AND FENCE LAKE, TEXAS

Polychlorinated dibenzopara-dioxins (PCDDs) and dibenzofurans (PCDFs) were measured in the tissues of the estuarine clam Rangia cuneata at f our sites in the Neches River that had been subjected to paper mill ef fluent and at two remote sites. One of the river samplings was taken b efore dioxin control measures and another 2 yr after the control measu res began. Measurable concentrations of PCDD/Fs were present at all si tes, but higher concentrations were present at the Neches River sites. Whole tissue concentrations of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) and all PCDD congeners for the two collections were not signif icantly different (p > 0.05), but lipid-normalized concentrations for the two collections were significantly different (p < 0.05). Highest c oncentrations of PCDDs at sites located 8 km and 16 km upriver from th e paper mill effluent outfall indicated that the materials were transp orted upriver by saltwater intrusion and/or that nonpoint sources exis ted upriver. The presences of PCDD/Fs in clam tissues from the remote sites also indicated that other sources of these materials existed. Ev en under extreme physiological conditions (spent reproductive phase, l ow lipid contents, water temperature 10 degrees C; ripe reproductive p hase, high lipids, water temperature 32 degrees C) Rangia cuneata was an effective biomonitor to determine the distribution of PCDD/Fs at sp ecific sites.