0 5 10 15 0 500 1,000 1,500 2,000 2,500 0 50 100 150 200 250 300 350 Total PCBs (ppm) Cs-137 (pCi/kg) Zn (ppm)
Figure 26.6. Total PCBs (A), 137Cs (B), and Zn (C) plotted against approximate year of deposition for two sediment cores from the Kingston area (site 6; Fig. 26.1). Model II assigns sedimentation rates of 0.9 to 1.9 cm yr-1 to the core at mile point 91.8 and 0.85 to 4.0 cm yr-1 to the core at mile point 88.6. Application of this model produces excellent agreement of the total PCB, 137Cs andZn chronologies, although some minor discrepancies still exist for other tracers. (Source: Chillrud, 1996)
in several samples from the period of overlap and showed that data from the two cores could be combined in a single extended chronology. This approach was confirmed by trace metal analyses on sections of a third core from this site collected in 1996. Chronologies of Cu, Pb, Zn, Ag, and Cd showed almost perfect agreement with those developed from the 1988 core. The results also indicate that chronologies of metal loadings to Jamaica Bay derived from dated sediment core depth profiles are not significantly affected by pore water mobility of these elements in the anoxic sediments found at the site (Chillrud, unpublished data).
In the mid-tidal Hudson (site 6; Fig. 26.1) cores collected in 1979 and 1986 provided contaminant chronologies extending back several decades (Bopp and Simpson, 1989). With dating based on 137Cs and PCB level time horizons, chronologies developed from the two cores showed excellent agreement (Fig. 26.6; Chillrud, 1996). Analysis of surficial sediment with detectable levels of 7Be collected in
1995 provided the recent trace metal data reported for this site (Figs. 26.3-26.5).
Cores collected from a cove on the Upper Hudson (site 1; Fig. 26.1) in 1983 (Fig. 26.2C) and 1991 (Fig. 26.2D) had near ideal profiles of 137Cs activity with depth. Trace metal chronologies showed excellent agreement and reflected the importance of Hercules/Ciba-Geigy inputs (Chillrud et al., 2003). These and several other cores from the same cove provided detailed information on the history of PCB inputs to the Upper Hudson from the GE capacitor plants several miles upstream (Brown et al., 1984; Bush et al., 1987; Bopp and Simpson, 1989; TAMS, 1996; McNulty, 1997).
Paired, well-dated cores collected years apart at the same site also provide an excellent means of studying in situ processes such as transformations of organic contaminants. Samples from two co-located cores can be paired on the basis of time of deposition. The paired samples would have similar initial contaminant compositions and concentrations and would have experienced similar depositional and microbial environments. Differences in contaminant compositionbetweenpaired samples can be interpreted as the result of transformations that occurred during the period between the dates of core collection - an in situ incubation period. This approach was first applied to the microbial reductive dechlorination of PCBs in the mid-tidal Hudson cores from site 6 (Fig. 26.6; Chill-rud, 1996) collected seven years apart, in 1979 and 1986. Only minor changes in composition consistent with reductive dechlorination were reported. This study was expanded to include congener-specific PCB analysis and the Upper Hudson cores from site 1 (Figs. 26.2C & D; McNulty, 1997) where PCB concentrations were much higher and in situ PCB dechlorination had been discovered (Brown et al., 1984). For the paired cores from site 1, the in situ incubation period was eight years (1983 to 1991). The observed dechlorination pathways were consistent with those widely reported in laboratory studies (Bedard and Quensen, 1995), but the overall rate and extent of in situ dechlorination at site 1 were significantly less than had been reported in a number of much shorter laboratory incubation experiments. At site 3, the congener-specific PCB analyses revealed minor compositional changes consistent with initial stages of microbial dechlorination (McNulty, 1997) and earlier observations.
The co-located core technique has been recently applied to another class of contaminants, alkylphe-nol ethoxylate (APEO) metabolites. APEOs are surfactants found in many detergents. The metabolites are of concern because they are persistent in the environment and are endocrine disruptors (Servos, 1999). Jamaica Bay has received significant inputs of APEOs associated with discharges ofmu-nicipal wastewater. Analyses of sections from the cores collected there in 1988 and 1996 have been used to determine the input history of APEOs and to study the pathways and rates of APEO metabolism (Ferguson et al., 2003).
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