I realize that's what the article says, but I'm skeptical. I think they meant a total of 9 kg.
The type of silicone used in implants is 0.968 to 1.29 grams per cubic centimeter. That means that a 9,000 gram (or 9 kg) implant would be 6796 to 9297 cubic centimeters.
That's 384.3 to 567.3 cubic inches, or 1.66 to 2.45 gallons.
I can't imagine 2 gallons of silicone in each breast. I'm having a hard enough time envisioning 1 gallon in each.
A lot of us are. But we will keep trying. ;^)