Streambed sediments and liver tissues of fish were analyzed for selected trace elements. Trace-element analyses were not done for ground water or surface water. Trace elements are present naturally in water and sediments at concentrations that depend on the type of rock where sediments originate (Hainly and others, 1994). Concentrations can be elevated above natural levels as a result of discharges from wastewater-treatment plants, industrial activity, or mining. Sediment samples from 21 sites were analyzed. Livers from bottom-feeding fish (white sucker) from 20 sites also were analyzed. Livers from bottom-feeding fish species (white sucker) and predator fish species (smallmouth bass) were collected at 3 of the 20 sites. Streambed sediments were analyzed for 27 trace elements; 24 were detected. Liver tissues of fish were analyzed for 22 trace elements; 18 were detected.
Livers were removed from fish and analyzed for trace elements. |
Human-health issues were not the focus of the trace-element studies. Because trace-element concentrations were determined only for fish livers and not for edible portions, no statements about suitability of fish for human consumption can be made. The U.S. Food and Drug Administration (FDA) action level for mercury is 1 part per million in the edible portion (fillets) of fish. Mercury concentrations in fish livers at four sites were close enough to the FDA action level to suggest a need for further study of mercury. Liver tissue from smallmouth bass in the Susquehanna River at Danville and the West Branch Susquehanna River at Lewisburg and white sucker in Codorus Creek and the Frankstown Branch Juniata River had mercury concentrations that ranged from 0.5 to 0.7 part per million.
Correlations were found between the concentrations in streambed sediments and the concentrations in livers of bottom-feeding fish for only 3 of 11 elements regarded as common contaminants. Arsenic, chromium, copper, lead, mercury, nickel, selenium, and zinc were not significantly correlated. Concentrations of cadmium, silver, and vanadium in livers from white sucker and the concentrations of these trace elements in streambed sediments were correlated. Although these associations do not imply direct cause and effect relations, they may indicate that these elements travel pathways through the aquatic system in a manner different from the other elements.
Trace-element concentrations in liver tissue from a predator species (smallmouth bass) and a bottom-feeding species (white sucker) were determined for samples from three sites. The liver tissue of smallmouth bass had higher concentrations of aluminum, cobalt, iron, mercury, selenium, strontium, and vanadium. The liver tissue of white sucker had higher concentrations of copper, manganese, and silver. These differences indicate that the two fish species may have different bioaccumulation mechanisms for these elements.
The bioavailability of trace elements in the sediments is not clearly understood but is known to depend on such local factors as concentration of dissolved solids and dissolved organics, pH, hardness, and sediment load, which also influence the prevailing chemical forms of trace elements in aquatic systems (Neilson, 1994). Therefore, the trace elements present in the streambed sediment may not have been bioavailable for uptake by fish. Moreover, the sediment samples may not have been collected in that part of the stream channel where the fish were most actively in contact with the streambed. These factors may help explain the lack of correlation between the concentrations detected in streambed sediments and the concentrations of the same element detected in the liver tissue of fish.
The highest concentrations of arsenic, beryllium, cadmium, cobalt, iron, manganese, nickel, selenium, and zinc in streambed sediment were at sites affected by mine drainage. Streambed sediment from the Susquehanna River at Danville had high to moderately high concentrations of all of these elements. Tributaries such as the West Branch of the Susquehanna River and Mahanoy Creek are affected by mine drainage and have the highest concentrations of beryllium, cadmium, cobalt, manganese, nickel, and zinc. The highest concentrations of lead were at sites on Codorus Creek and Quittapahilla Creek downstream from urban and industrial areas. Lead is also present in high concentrations in streambed sediment from Mahanoy Creek. Sediment from some sites in basins in the Piedmont Physiographic Province that have no industrial or mining activity also contained elevated concentrations of nickel, indicating that the bedrock in that area may be a natural source of nickel.
To better understand transport of trace elements to the Susquehanna River from a tributary affected by mine drainage, Study Unit personnel collected samples from Mahanoy Creek--including streambed sediment, water, coatings on rock surfaces, and liver tissue from white suckers-- and analyzed all these substances for trace elements (Breen and Gavin, 1995). Most trace elements being transported downstream were in the form of suspended particles or colloids. The coatings on rock surfaces contained high concentrations of trace elements, and the coatings could be dislodged from the rock surfaces during storms. Calculations showed that the transport of trace elements dislodged from rock surfaces during a storm would be small relative to the daily transport from suspended particles and colloids.
