population can have a range of metal concentrations up to an order of 
magnitude, thus obscuring differences between techniques that may be small 
but real. Comparison of clam homogenate values, however, will render obvious 
differences of less than 25% which would be arduous or impossible to discern 
using natural populations. 
CONCLUSIONS 
We have shown that a satisfactorily homogeneous reference material can be 
prepared with a minimum of specialized equipment. The material has a low 
relative standard deviation for the 10 metals Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, V, 
and Zn. For reasons that are not always clear, the other metals analyzed Al, Ca, 
Co, and Ti have higher relative standard deviations. The material is useful as a 
benchmark reference material so that analyses at different times can be shown 
to be intercomparable. Thus, legal defensibility of time series studies of 
pollution sites can be greatly enhanced. The material is also ideal for methods 
development and intercalibrations because of its very low relative standard 
deviation. Therefore, with cooperation from a cafeteria kitchen, it becomes a 
relatively simple task to prepare such a reference material when a certified 
standard from a recognized supplier such as NBS is not available. 
ACKNOWLEDGEMENTS 
We gratefully acknowledge the statistical consulting of Drs. J. Callahan and 
J. Heltshe of the University of Rhode Island, and the assistance of Dr. R. Payne 
and Messrs. B. Reynolds, D. D’Alessio, F. Storti, E. Truesdell, and C. Young of 
this lab. 
REFERENCES 
1. Eisler, R. 1973. Annotated Bibliography on Biological Effects of Metals in 
Aquatic Environments, 287 pp. Washington, D.C.: U.S. Government Printing 
Office (U.S. Environmental Protection Agency, Rep. No. R3-73-007). 
2. Eisler, R. and M. Wapner. 1975. Second Annotated Bibliography on 
Biological Effects of Metals in Aquatic Environments, 400 pp. Springfield, 
Virginia: National Technical Information Service. (U.S. Environmental 
Protection Agency Rep. No. 600/3-75-008). 
3. Pesch, G., B. Reynolds, and P. Rogerson. 1977. Trace Metals in Scallops 
from Within and Around Two Ocean Disposal Sites. Mar. Pollut. Bull. <5 p. 
224. 
4. Anonymous. 1975. Catalog of NBS Standard Reference Materials. NBS 
Special Publication 260. p. 32. 
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