Tracking Environmental Lead Levels With Coral

In the absence of monitoring data, scientists have turned to corals to determine the level of lead circulating in the Indian Ocean.

AsianScientist (Jul 3, 2014) – Scientists have reconstructed the history of heavy metal lead (Pb) level in Singapore waters and the Indian Ocean.

While lead concentrations decreased in the North Atlantic Ocean by almost 10-fold after 1970’s with the regional phasing out of leaded gasoline consumption, the opposite has occurred in the surface of Indian Ocean. They have found that lead concentrations in the Indian Ocean and the Straits of Singapore rose from the mid-1970’s until early 2000’s. This lead concentration has declined since, but the current concentrations are now three times higher than that in the North Atlantic and North Pacific Oceans.

Monitoring lead in marine environments remains an analytically challenging task. High-fidelity data is produced from a only few inter-calibrated labs such as the one led by Professor Edward Boyle at the Massachusetts Institute of Technology (MIT) who contributed to the study.

In analysing their samples, the researchers were puzzled by an odd measurement: In samples taken off the coast of Singapore (Jong Island), they found an imprint of lead that they did not expect to find in this region of the world. While most countries around the Indian Ocean used leaded gasoline produced in Europe and the Middle East, the lead found near Singapore matches the kind once used in North American gasoline.

Prof. Boyle said, “It’s almost as if Singapore had gone off and imported a whole lot of lead from the United States. It doesn’t make any sense why they would do that, because there are more local sources that presumably would be cheaper, more economical.”

Dr. Intan Suci Nurhati from Singapore-MIT Alliance for Research and Technology (SMART) added, “We try to make sense of this mystery by regularly monitoring lead in seawater and aerosol. Lead in the air seems to be consistent with what we expect to find in the region, but our seawater sampling data lends support to the unexpected lead value that we see in coral.

“In this recently published paper, we conclude that leaded gasoline may not be the primary driver of lead deposited in Singapore waters; there are other sources to consider such as coal as well as complex sources and processes in the Straits of Singapore. Ultimately, we hope this data would help Singapore and stakeholders in our region in monitoring heavy metal pollution level and sources in our nearby oceans with respect to existing environmental regulations.”

The research team began collecting coral and water samples in Singapore in 2010, as well as gathering corals from the Indian Ocean through their collaborators. Upon bringing the coral samples back to the lab, the researchers analysed the corals for trace amounts of lead as well as lead isotopes which is a tool to pinpoint the source of lead. This is because lead ores from different mining sites have different lead isotope signatures.

Akin to trees, corals form annual layers that lock in information on lead in seawater during the formation of the layers, this process goes on throughout the lifetime of the corals which could live for decades. By ascertaining how much lead and what signature of lead isotope was deposited in a given annual layer, the researchers were able to reconstruct a history of lead level and sources in Singapore and the Indian Ocean over the past 60 years, which is the time when there was no monitoring data.

They found that lead levels began to increase in the mid-1970s, peaking in 2002 and 2003 before declining, a timeline consistent with the region’s pattern of industrialization and leaded gasoline use.

The article can be found at: Lee et al. (2014) Coral-based History of Lead and Lead Isotopes of the Surface Indian Ocean Since the Mid-20th Century.

——

Source: SMART; Photo: USFWS Pacific/Flickr/CC.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Asian Scientist Magazine is an award-winning science and technology magazine that highlights R&D news stories from Asia to a global audience. The magazine is published by Singapore-headquartered Wildtype Media Group.

Related Stories from Asian Scientist