Approximately 5 grams of sediment or soil was dried at 60°C for 72 hours. Approximately 0.1 grams of sample was analyzed for total mercury content using a Direct Mercury Analyzer 80 (DMA80; Milestone, Shelton, CT) using EPA Method 7473 as outlined by others (Basu et al., 2010 (link); Nam and Basu, 2011 ). All samples were batch processed and analyzed in triplicate, after each seasonal collection.
Accuracy (within 20% of expected values; mean recovery: 107%) and precision (within 7% relative standard deviation; mean RSD was 2%) were measured using standard reference materials including National Institute of Standards and Technology (NIST) San Joaquin Soil (NIST 2709), NIST Trace Elements in Soil (NIST 2586), and National Research Council (NRC) Canada Dogfish Liver (NRC DOLT-4). The theoretical method detection limit (TMDL; 3 times the standard deviation of the mean blank value) ranged from 0.01 to 0.67 ng mercury. Samples for which concentrations were below limit of detection are noted in the results section with the measured value being retained.
Accuracy (within 20% of expected values; mean recovery: 107%) and precision (within 7% relative standard deviation; mean RSD was 2%) were measured using standard reference materials including National Institute of Standards and Technology (NIST) San Joaquin Soil (NIST 2709), NIST Trace Elements in Soil (NIST 2586), and National Research Council (NRC) Canada Dogfish Liver (NRC DOLT-4). The theoretical method detection limit (TMDL; 3 times the standard deviation of the mean blank value) ranged from 0.01 to 0.67 ng mercury. Samples for which concentrations were below limit of detection are noted in the results section with the measured value being retained.