was little difference between the total PCDF concentrations of 

 the 200 East and South Reference samples. 



The 2, 3,7,8-substituted congeners are considered to be 

 the most environmentally significant compounds (Kuehl et al., 

 1987) for both the PCDDs and PCDFs. This is because these 

 compounds are preferentially accumulated by organisms and are the 

 most toxic. The concentration of one 2,3,7,8 substituted 

 compound was measured for each level of chlorination for both 

 series of compounds. 



The compound, 2 , 3 , 7 , 8-tetra-CDD, is generally 

 considered to be the most toxic of all of the compounds measured 

 in this study (Safe et al., 1986). Only the BRH Wetland sample 

 contained a measurable concentration of this compound. The 

 measured 2 , 3 , 7, 8-tetra-CDD concentration in this sample was 0.043 

 ng/g (compared to the suggested criteria of 1 ng/g) . However, 

 since the detection limits for the BRH Original Composite and BRH 

 Upland samples were higher than this level (0.078 and 0.11 ng/g, 

 respectively) , these samples may have contained similar 

 concentrations of 2 , 3 , 7, 8-tetra-CDD. 



The detection limit achieved for a sample is dependent 

 on the level of interferences or the 'matrix' of the sample. 

 That is why the detection limits vary from sample to sample. For 

 less complex samples with lower levels of contamination, such as 

 the South Reference sample, lower detection limits are generally 

 achieved as was seen in this study. 



The ERL-D laboratory measured the concentrations of 

 numerous congeners in the BRH Original Composite including the 

 2 , 3 , 7, 8-substituted congeners measured here (Table 8). In 

 general, there is excellent agreement between the data from the 

 present study and the ERL-D results. The possible exception to 

 this is for 2 , 3, 7,8-tetra-CDF. The result reported in this study 

 is considerably higher than the ERL-D data. This difference is 

 probably due to incomplete resolution of the various tetra-CDFs 

 in the present study. 



Only two other studies could be found that report the 

 concentrations of PCDDs or PCDFs in estuarine or marine 

 sediments. Belton et al. (1985) reported the levels of 2,3,7,8- 

 tetra-CDD in the sediments of the Passaic River, New Jersey. 

 This area was sampled because very high concentrations of 

 2 , 3 , 7 , 8-tetra-CDD have been found in the soil around a chemical 

 plant that manufactured Agent Orange. It has been shown that 

 2 , 3, 7, 8-tetra-CDD is a major contaminant in Agent Orange. The 

 sediments of the Passaic River around this facility contained 

 2 , 3 , 7 , 8-tetra-CDD concentrations as high as 6.9 ng/g. Sediments 

 from other areas of the river had levels ranging from 0.13 to 1.2 

 ng/g. 



