and precision. Changes made in 1980 and 1981 resulted from an increased 

 appreciation of using "clean" technique to avoid contamination of samples 

 during collection, processing, and analysis. 



The viewpoint that "clean" technique is necessary for accurate 

 determination of metal concentrations, especially in seawater, is quite 

 correct and cannot be overemphasized (e.g., Moody and Lindstrom, 1977; 

 Brulane et al., 1979). For example, the relationship between technique 

 and results is strikingly evident in the values for soluble Cu in Giants Neck 

 seawater (Table 2). Although there is no reason to assume that metal 

 concentrations should change with time, mean values in 1980 and 1981 were 

 five to eight times less than in 1972. 



SUMMARY OF RESULTS 



In the decade of seawater sampling at MNPS and nearby areas, the 

 outstanding result is the overall decrease in reported concentrations of 

 Cu, Fe, and Zn. This trend, however, reflects increasing analytic 

 sophistication and not actual decreases in concentration (see above) . It 

 is revealing that values continued to decrease subsequent to the start of 

 Unit 2 operation in 1975. Therefore, only values determined from 1979 

 onward provide reliable estimates. (There are obvious exceptions; for 

 example, Zn concentrations in 1981 were extraordinarily high and indicate 

 contamination) . There were no apparent long-term changes in Cr and Pb in 

 seawater from 1971-1981, simply because these metals have been at or below 

 detection limits. (N.B. Analyses of Pb are particularly prone to 

 contamination and without extra-scrupulous technique, concentrations are 

 likely to be overestimated (Patterson and Settle, 1979)). 



