I read the Sciences News article " Breast milk: A leading source of PCB's ".
This is a summary of the article by Svati Patandin, et al. 'American Journal
of Public Health', October.
The research did compare Dutch babies who were breastfeed and formula feed and
their levels of PCB's.  The results the breastfeed children had higher levels
but this is what is very important the final sentence:
" The solution, she and her coauthors argue, is not to forgo breast-feeding
but to lower PCB concentrations in the food chain so mothers accumulate less
in their milk. "
I hope this helps, I was happy with their conclusion.
Ann Perry RN IBCLC