Trace metal concentrations, except mercury and silicon, were analyzed by atomic 

 absorption spectrophotometry using graphite furnace or flame (Table 3). Mercury was 

 analyzed by cold vapor atomic absorption, and silicon was analyzed colorimetrically using an 

 ultraviolet spectrophotometer. 



Sediment texture. Sediment texture (grain size) was determined as the percentage (based on 

 dry weight) of gravel, sand, silt, and clay. Coarse and fine fractions initially were 

 separated by wet-sieving. The silt-clay fraction was analyzed by collecting, desiccating, and 

 weighing aqueous aliquots at timed intervals after thorough mixing of the fraction. The sand 

 and gravel fraction, after being dried, was sieved through a 2-mm screen and the weight of 

 gravel and sand subtractions were determined. 



Total organic carbon and total inorganic carbon. Total organic carbon (TOC) and total 

 inorganic carbon (TIC) in sediments were analyzed by a modification of United States 

 Environmental Protection Agency (EPA) Method 415.5 (Organic Carbon, Total) and Section 4.8 

 of the O.I. Corporation Model 700 TOC Analyzer Operating Procedures and Service Manual, 

 which describes the analysis of TIC and TOC on the same aliquot of the sample. 



All samples were thawed, allowed to warm to room temperature, and wet-homogenized 

 by stirring. Aliquots with a wet weight of approximately 0.02 g were weighed into 

 precombusted ampules with 1 mL of Milli-Q™ water. TIC was determined by sealing each 

 ampule on the TOC analyzer (0.1. Corporation Model 700). Two mL of 5 percent phosphoric 

 acid was injected into the ampules. The carbon dioxide generated was purged with nitrogen 

 to an infrared detector. The resulting millivolt (mV) reading was converted to micrograms 

 TIC. 



TOC was analyzed by removing the ampules from the analyzer and purging with oxygen. 

 One mL of potassium persulfate solution (5 percent K2S20g) was added immediately before 



the ampules were sealed. Samples were digested by heating the ampules in an autoclave. 

 Ampules were then attached to the TOC analyzer ampule-breaking assemblage. Carbon (as 

 carbon dioxide) was purged from the ampule using nitrogen and detected as above. The 

 resulting values were recorded as ug organic carbon. 



15 



