Effects of waterborne silver in a marine teleost, the gulf toadfish (Opsanus beta): Effects of feeding and chronic exposure on bioaccumulation and physiological responses

摘要

Marine teleosts drink seawater, and the digestive tract is a key organ of osmoregulation. The gastrointestinal tract therefore offers a second site for the potential uptake and toxicity of waterborne metals, but how these processes might interact with the digestive functions of the tract has not been investigated previously. We therefore compared the responses of adult gulf toadfish (Opsanus beta, collected from the wild) to a chronic 22 d exposure to waterborne Ag (nominally 200 mu g L-1 = 1.851.mu mol L-1), in the presence or absence of daily satiation feeding (shrimp). Ag exposure did not affect voluntary feeding rate. Feeding reduced the net whole body accumulation of Ag by >50%, with reductions in liver concentrations (high) and white muscle concentrations (relatively low) playing the largest quantitative roles. Feeding also protected against Ag buildup in the esophagus-stomach and kidney, and increased biliary and urinary Ag concentrations. The gill was the only tissue to show the opposite response. Although terminal plasma Na+, Cl-, and Mg2+ concentrations were unaffected, there were complex interactive effects on osmoregulatory functions of the gastro-intestinal tract, including drinking rate, gut fluid volumes, and intestinal base secretion rates. At the end of the exposure, the plasma clearance kinetics of an arterially injected tracer dose of Ag-110m were faster in toadfish that had been chronically exposed to waterborne Ag, and Ag-110m accumulation in their red blood cells was reduced. After 32 h, higher amounts of Ag-110m were found in bile and urine, but lower amounts in the intestine of the Ag-exposed toadfish; there were no other differences in tissue-specific distribution. The results suggest that feeding reduces waterborne Ag uptake through the digestive tract and alters physiological responses, while chronic exposure enhances regulatory functions. The time-dependent actions of the liver in Ag scavenging and detoxification are highlighted