Trace metal contamination of waters, sediments, and organisms of the Swan Lake area of Galveston Bay

Abstract

Swan Lake is a sub-bay of the Galveston Bay system. The area received runoff from a tin smelter via the Wah Chang Ditch which ran through it in the past but the ditch is now cut off by a hurricane protection levee. An industrial waste disposal facility (Gulf Coast Waste Disposal Authority) is located north of the Wah Chang Ditch. Consequently there have been concerns about possible metal contamination in this area. I determined trace metal concentrations in water, sediments, and organisms (oyster, mussel, snail, crab, fish, shrimp, and spartina) in the area. Sediments and organisms were analyzed for total Ag, Al, As, Cd, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sn, and Zn. Water samples were analyzed for Cd, Cu, Fe, Mn, and Sn. The variabilities and geographic trends in sediment trace metals indicated that waste disposal and airborne inputs from facilities located at the Tex Tin site were likely sources for metal pollution found in the sediments. Sediments in the study area showed elevated trace metals relative to Galveston Bay and other Texas bay sediments. Three different samplings of the Wah Chang Ditch showed no temporal patterns in metal distribution in the sediments. Lead especially was uniformly high on the three different trips, respectively averaging 1250 (Trip 1), 893 (Trip H), and 1350 ppm (Trip V). Metal enrichments at depth in the sediment column indicated that the Swan Lake area has recently received less input of metal contaminated sediment than in the past. Anthropogenic inputs did not greatly influence the natural concentrations of Fe, Al, and Ni in sediments either in the past or at present. Most organisms showed very small spatial variations. However, the oysters in Swan Lake are enriched in most metals relative to Galveston Bay and other U. S. Gulf of Mexico oysters. The mussels in this study do not reflect the unusually elevated environmental metal concentration in the sediments from which they were taken. Iron and Pb concentrations in oysters seemed to be directly related to sediment concentrations at each location. Oysters show higher concentrations in most metals than those in mussels. The Zn level was II 3 times higher in oysters. For organisms collected from the Swan Lake area trace metal concentrations were generally in the order oysters > snail > crab > shrimp > fish. Metal concentrations in Wah Chang Ditch water were very elevated relative to those of the Brazos River and Galveston Bay and closely reflect those in sediments of the Wah Chang Ditch.