Seaweed is very efficient at absorbing and concentrating minerals and various elements, including metals, from seawater.   Metals such as copper, iron, and zinc are considered essential minerals because they’re needed for health, but others such as arsenic, cadmium, lead, and mercury, known as heavy metals because of their high atomic mass, are toxic at high levels.  However, even essential minerals can be toxic if ingested at too high levels or out of balance with other minerals.
Metals occur naturally in the ocean due to weathering of the earth’s crust.  Unfortunately, over the past century anthropogenic (manmade) sources have elevated the levels of some heavy metals in the oceans.  These are widely distributed in all the world's oceans. This is why ‘where and how’ sea vegetables are harvested matters.  Some parts of the ocean contain more heavy metals and other contaminants than others, maybe because they receive industrial effluent or are located near a large metropolis.
The northern Gulf of Maine, where most of our sea vegetables are sourced, has very little industrial activity and no major metropolis. Northern Maine is covered by a vast 3.5-million-acre forest known as the North Maine Woods, and with a population density of less than 25 people per square mile it’s the least populated region east of the Mississippi.  Organic certification further ensures our sea vegetables are harvested away from marinas, aquaculture pens, and other sources of contamination, and that they’re handled and processed without the use of chemicals.  As a final precaution, every year 3rd party labs analyze samples of our seaweed for heavy metals and other contaminants.  We post the results on our website for customers to see; we’re one of the few seaweed companies anywhere with this practice.