Wednesday, April 29, 2020

Toxic Stone Age Fish

One doesn't expect to find an article about the archaeology of food in Forbes magazine.  But there was one last week, and it's a doozy.  It's about how archaeology shows that fish eaten by Stone Age people 9,500 years ago contained high levels of heavy metals.  The Forbes article may be found here.

According to the Forbes article, several studies have come to the conclusion that Stone Age fish and marine mammals contained elevated levels of elements such as lead, mercury, and cadmium.  The research involved analyzing bones from archaeological sites near the North American coast and in the Norwegian Arctic.  The actual study report on the Norwegian Arctic may be found at Science Direct here (note: the actual report is paywalled; only the abstract is available for free).

The current theory is that at the beginning of the last Ice Age, large quantities of water were trapped as ice near the North and South Poles and inland ice shields.  During the Last Glacial Maximum about 20,000 years ago, ocean levels were more than 900 feet/300 meters lower, exposing the large portions of the continental shelf--and allowing heavy metals from the exposed rock to be released into the soil.  Then, between 14,000 and 6,000 years ago, the seas rose once more--and the heavy metals were released into the sea water, where they found their way into the bodies of cod and harp seals (the animals whose bones were studied), and probably also into the bodies of the early humans who ate them.  The abstract of the Norwegian study characterizes the heavy metal levels of these food animals during the Stone Age thus:
Stable isotope and elemental analyses of the Atlantic cod (Gadus morhua) and harp seal (Phoca groenlandica) bone component of the marine food that dominated the Younger Stone Age (c. 6.1–3.5 ka BP) diet in Varanger, Arctic northern Norway, indicate, at times, climate change induced highly elevated levels of the heavy metals cadmium (Cd) and lead (Pb), and elevated levels of mercury (Hg). On average, the levels of cadmium and lead contamination in cod were up to 22 and 3–4 times, respectively, higher than today's recommended limits in soft tissue. The corresponding figures for seal were 15 and 3–4 times, respectively. The levels of Hg were generally below today's recommended limit in soft tissue, but still of considerable magnitude, almost similar to the measured values in modern fish in the Arctic.
Climate change--and its effects on life, and food--is not new to Earth. The only real difference is that now homo sapiens sapiens may be able to try to do something about it.


  1. I had no idea fish could become contaminated with heavy metals via natural processes, I'd always thought this was purely related to pollution from human activities.

    1. So did I, and probably so did many people. That's why I wanted to draw a little attention to this article.