Table 38 continued. 



a Statistically significantly different from controls (alpha=0.05). 



D Significantly different from controls (alpha=0.05) and mean value 80% or less of the control re- 

 sponse. 



Spatial Extent of Toxicity. Using test results of <80% of control responses as a critical value, the 

 spatial extent of toxicity was estimated. Approximately 25% of the study area exhibited toxic samples 

 in the bivalve survival tests, 30% was toxic in the bivalve embryo development tests, 38% was toxic in 

 the amphipod tests, and approximately 39% of the area was toxic to microbial bioluminescence. Ap- 

 proximately 5.7% of the area was toxic in all four of these tests. These estimates are similar to the 

 estimate of the spatial extent of sediment toxicity to amphipod survival (21%) for the entire Virginian 

 province of EMAP, which includes the present study area (Schimmel et al., 1994). However, the 

 estimated spatial extent of toxicity to amphipods within the Newark Bay region of the study area (85%) 

 was much higher than that for the remainder of the study area or the Virginian province. 



These calculations of the spatial extent of toxicity must be viewed as rough estimates, since a number 

 of factors could have contributed to bias in the analyses. Although the Phase 1 survey area was strati- 

 fied a priori, the selection of the boundaries for each stratum could have affected the results. Since 

 many of the sampling sites were selected with some knowledge of the site from previous studies, there 

 may have been some bias in the site selection. Each station within a site was chosen by the vessel 

 operator with no attempt to sample near known sources; nevertheless, there could have been bias in the 

 station selections. The coordinates for each sampling station were not selected with a probabalistic, 

 random method (Schimmel et al., 1994). On the other hand, there was no attempt to bias the site and 

 station selections to over- or under estimate the toxicity of the area. 



During Phase 2 of the survey, the samples were chosen randomly with a probabalistic, random-strati- 

 fied sampling design similar to that used by the EMAP. As a consequence, the estimate of the spatial 

 extent of toxicity (85%) within the Newark Bay area should be more accurate than that calculated for 

 the entire survey area. 



Spatial Patterns in Toxicity. The area-wide patterns in toxicity, as determined by the four test end- 

 points measured in Phase 1, collectively, are illustrated for the station means in Figure 46 and for the 

 site means in Figure 47. Stations and sites were depicted as toxic when at least one of the four test end- 

 points indicated a statistically significant elevation in toxicity relative to the controls. These two fig- 



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