Are efforts against lead contamination working?

July 10, 2016 - 06:00

Efforts to reduce industrial emissions of lead have been ongoing for several decades. However, some of the lead comes from natural sources, so how can scientists tell if the efforts are worth while?

The global scale of lead (Pb) contamination from industrial sources has been well documented; lead from human activity, mainly from combustion of leaded gasoline, has been detected in remote sites including samples of Arctic and Antarctic surface ice and ocean deep waters.

However, decreases in environmental Pb-contamination following the near-global phase-out of leaded automobile gasoline, beginning in the 1970s, have since been observed.

"Consequently, a reasonable expectation is that industrial Pb-concentrations have also measurably decreased in the Southern Ocean following the virtual elimination of leaded gasoline in the Southern Hemisphere," Kuria Ndungu, a Research Scientist at The Norwegian Institute for Water Research, says.

Mainly natural sources
The Amundsen Sea continental shelf spans about 315000 square kilometers and extends approximately 300 kilometers in an east-west direction. (Map: Polargeo/Wikimedia commons.)

In a recent study, published in the current issue of Environmental Science & Technology journal, Ndungu and American colleagues tested this hypothesis in the Amundsen Sea, a shelf region of West Antarctica in the Southern Ocean.

"We chose this region because the effects of global climate change in West Antarctica are especially pronounced: Glaciers that drain into the Amundsen Sea Embayment are among the world’s fastest dischargers of ice into the ocean," Ndungu says.

The scientists measured levels of Pb in seawater and sediments.

Kuria Ndungu. (Photo: NIVA/Ndungu)

"The results of our study show that about 60− 95% of the lead at our sites, at the time of sampling, is natural in source: that is, derived from the weathering of Antarctic continental rocks," says Ndungu.

Less lead in the future

"As climate change continues to drive ocean circulation changes, we hypothesize that the overall flow of lead in the Amundsen Sea will decrease, as industrial atmospheric lead emissions continue to decline."

The scientists conclude that lead budgets for this region are projected to change over the next few decades.

"We also hypothesize that a greater proportion of that the flow of lead will be natural Pb from sedimentary sources and basal meltwater, which is thousands of years old, due to changes in ocean circulation. As a result, Pb budgets for this region, and for the greater Southern Ocean, are projected to change over the next few decades as a result of both reductions in atmospheric emissions of industrial lead and increases in atmospheric emissions of industrial CO2," Ndungu says.