Do fish oil supplements contain mercury?

"Last year, researchers at Boston’s Massachusetts
General Hospital measured the mercury
levels in five fish oil preparations and found
negligible amounts in all five. They concluded
that mercury is found primarily in the fish
tissue and is removed in the process of making
fish oil. ConsumerLab.com reported no
detectable levels of mercury in 20 fish oil
supplements. Consumer Reports tested 16
top-selling fish-oil supplements and found
that they contained no significant amounts
of mercury, polychlorinated biphenyls (PCBs),
or dioxins."

Robb-Nicholson C. By the way, doctor. The stories about mercury and other toxins in fish have me worried that my fish oil supplements may be contaminated. Have there been any studies of these toxins in fish oil capsules?. [Journal Article] Harvard Women's Health Watch. 12(1):8, 2004 Sep