The build up of toxins in our environment is definately something to be concerned about. The fact that they have sneaked their way into what should be the most natural food in the world should make us angry and motivated to tackle this pollution and the companies that produce it.
A very good book on this subject is The Story of Stuff for indepth discussion of this issue of environmental pollutants. She's also made a great little film about it for a quick overview.
Since 'Silent Spring' we've become aware that pollution isn't just the visible litter on the ground, its the chemicals we produce and coat our world in too, and these chemicals can get into the food chain and cause all sorts of problems.
The build up of these chemicals isn't the fault of breastfeeding. They are in all of our bodies, and it is sad that we're passing them onto our babies. But children will also be exposed to these same chemicals through cow's milk formula and through their environment and diet. Of course we should keep an eye on the concentrating effect of the food chain and breastfeeding. But its worth remembering that all the studies done which show that breastfeeding/breastmilk is beneficial are still true despite these toxins. So the net effect of breastfeeding is positive.
It certainly won't be putting me off, but its worth a reminder that its not just the planet that suffers through our polluting habits, its us too.