DISCUSSION 



Few studies have measured the concentrations of PCDDs 

 and PCDFs in sediments, especially marine sediments. This is 

 mainly because of the level of difficulty associated with the 

 chemical analyses and the lack of appropriate instrumentation. 

 The instrumentation utilized (preferably high resolution gas 

 chromatography-mass spectrometry) must be sensitive enough to 

 measure picogram quantities of compounds in the sample extracts 

 and be able to definitively identify the compounds to the 

 specific congener. This is particularly difficult, because 

 chlorinated compounds from several chemical classes (biphenyls, 

 biphenylenes, naphthalenes and diphenyl ethers) are found in 

 environmental samples and show very similar fragmentation 

 patterns. Many of these compounds such as polychlorinated 

 biphenyls (PCBs) are found in concentrations considerably higher 

 than those of the PCDDs and PCDFs. For example the 

 concentration of PCBs as Aroclor 1254 in the BRH Original 

 Composite IS about 7000 ng/g (Munns et al.. In preparation). 

 This IS about 350 times the total PCDD concentration and 1000 

 times the PCDF levels measured in that sediment in the present 

 study (Table 4) . 



There are 75 possible congeners of PCDDs and 135 

 potential PCDF compounds. Generally, not all of these compounds 

 are found in environmental samples with the possible exception 

 of fly ash (Karasek and Hutzinger, 1986) . However, sediments can 

 contain numerous PCDDs and PCDFs in measurable quantities. Table 

 4 shows that as many as 16 different PCDD and 41 PCDF peaks were 

 found in measurable quantities in some of the samples. This 

 means that many different compounds were present. More compounds 

 than this were possibly present because some of the compounds 

 coelute as a single peak (Table 4) . 



Measurable concentrations of PCDDs and PCDFs were 

 detected in all four of the BRH sediment samples and the 

 Reference station sample (Table 4). The sum or total 

 concentrations of all of the measured PCDDs were highest and 

 similar m the BRH Original Composite, BRH Wetland, and BRH 

 Upland samples. The 2 00 East sample contained lower levels and 

 the lowest total PCDD concentration was found at the South 

 Reference site. 



The same trend was also observed for the total PCDF 

 concentrations. The levels were highest and similar in the BRH 

 Original Composite, BRH Wetland and BRH Upland samples. The 200 

 East sample had a lower total PCDF concentration and the lowest 

 level was measured in the South Reference sample; however, there 



