Hveragerthi
Yes, but seaweeds also contain algins that bind heavy metals so they are effective in removing these heavy metals.
On the other hand most of the produce we eat contain lead from all the years of using leaded gasoline. Even though we do not do this anymore the lead that deposited in the soil is still there being picked up by the plants we eat. How many of California's farms are right next to major freeways?
And arsenic is used to preserve apples.
Cigarette smoke we have to breathe around smokers contains cadmium.
Many fish are loaded with mercury and other heavy metals.
When you are out in traffic you are inhaling particles of tires, exhaust, and the metals in the oil pushing past people's piston rings.
If you want to see something really scary get a California Fish and Game fishing guide and read all the fish that consumption has to be limited on because of all the metals, PCBs, etc. This includes fresh water sources.
Bottom line is that seaweeds are very beneficial and a lot safer than many of the everyday substances we are exposed to.