Methodology

There are three basic steps required to measure contaminants, grain size, and carbon  in sediments:

Grain Size

After acidification and treatment with hydrogen peroxide, the samples were sieved to separate the sand (>63 µm) fraction.  The remaining fractions were measured for silt and clay on an Elzone 180 XY Particle Size Analyzer.  All data are reported as % of the total sample.

Organic Carbon
 
    Salt Ponds:
Total organic carbon (TOC) measurements were done by loss-on-ignition with a 12 hour dewatering step (110ºC) and a one hour ignition step (550ºC).  A factor of 0.44 was used to convert organic matter to organic carbon.  A representative subset of samples was measured on a carbon-hydrogen-nitrogen (CHN) analyzer for verification.  Samples with >70% sand were excluded from the analysis.

    Narragansett Bay and Massachusetts Rivers:  
Total carbon was measured by CHN analyzer. 

Trace Metals

Extraction
    Total digestion technique: 
This technique was used for trace metal determination for all of the Salt Ponds samples, and for the Narragansett Bay Follow-up study (including Massachsuetts river sites).  0.2g of freeze dried sediment was digested with concentrated hydrochloric, nitric, and hydrofluoric acids in a heated sonicator bath. It was neutralized after 48 hours with boric acid, and brought to volume with deionized water.

    Partial digestion technique: 
This method was used for trace metal determination for all of the Narragansett Bay Project dataset, as well as a subset of the Narragansett Bay Follow-up dataset.  2N nitric acid was added to 2g of freeze dried sediment, and samples were placed in a constant temperature water bath at 50ºC for 50 hours.  After the digestion was complete, samples were centrifuged at 2500 RPM for 10 minutes. The supernatant was decanted and stored until analysis. 

Analysis
    Salt Ponds:
The samples were analyzed for Cu and Pb using a Perkin Elmer 4100 ZL graphite furnace atomic absorption spectrometer with Zeeman correction.  The samples were analyzed for Hg using an automated mercury analyzer.