A lead from the past
ENVIRONMENTALISTS who wish to revert to a non-polluted era may have to revise their glorious vision of an idyllic past before the industrial revolution. A recent analysis of lake sediments in Sweden reveals that lead pollution was a problem even 2,000 years ago (Nature, Vol 368, No 6469).
Ingemar Renberg of the department of environment health at the Universitiy of Umea and colleagues there and at the University of Agricultural Sciences in Umea, who undertook this analysis, examined sediment cores from several Swedish lakes. They extracted long cores of sediment -- between 1.5 and 4 metres -- from 19 lakes, while shallow cores were taken from the top 25 to 35 cm of the soil from 112 lakes.
Although the scientists are unable to say when exactly the lead concentrations began increasing, they reckon that this occurred some 2,600 years ago. Some 600 years later, the lead concentration in the sediment cores was some 5 times the pre-increase concentration, which averaged about 10 micrograms per gram of soil. They also noticed that there was a steep concentration peak some 1,000 years ago.
Because lead is not very mobile in the soil, and only small amounts of lead from the forests in lake catchment areas actually finds its way into the lakes, the scientists had assumed that the amount of lead found in the sediments reflected the amount of lead present in the atmosphere at the time of examination.