11:15 AM - 11:30 AM
[HQR05-09] Changes in heavy metal concentrations and their origins during the Anthropocene in Urauchi Bay, Kochi, Japan
Keywords:Anthropocene, Inlet bay, heavy metal pollution, lead isotope, environmental changes
The proposed geological epoch known as the Anthropocene (Crutzen, 2002) signifies a period where the Earth's environment has been impacted by human activities. Sediments in inlet preserve as detailed records of environmental changes caused by human activity, allowing for the continuous analysis of eras before and after the Anthropocene. Uranouchi Bay located in the central part of Kochi is an inlet characterized by a narrow mouth and an elongated shape spanning 12 km east to west, where fish farming is currently thriving. This presentation aims to elucidate the changes in heavy metal concentrations and their origin during the Anthropocene recorded in the sediment of Uranouchi Bay.
Using sediment core collected from the inner part of Uranouchi Bay (U-1: water depth 9.7 meters), we conducted analyses using XRF core scanners (ITRAX) and ICP-MS to assess changes in heavy metal concentrations, using MC-ICP-MS to identify the origins of heavy metals based on lead isotopic ratios. Dating was estimated using radioactive isotopes (210Pb, 137Cs). From 1954 (25 cm) to 1964 (20 cm), heavy metals exhibited a rapid increase in concentration compared to earlier periods.
We compared the results of the non-destructive, high-precision, high-resolution measurements from XRF core scanners (ITRAX) and ICP-MS analyses. While both analyses showed similar overall increasing trends, the determination of the depth at which heavy metal concentrations began to increase was done through ICP-MS analysis, revealing the onset of anthropogenic heavy metals increases around 1954. In the ICP-MS analysis, it is evident that there is a difference in that the pre-treatment involved extracting and measuring heavy metals adhering to the surface of sediment grains.
From the mixing diagram of the overall lead isotopic ratios (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 207Pb/206Pb, 208Pb/206Pb) and Al/Pb, it was determined that the sources of lead in Uranouchi Bay shifted from an older era with low lead content and high lead isotopic ratios (end member 1) to two sources after the 1950s: one with high lead content and low lead isotopic ratios (end member 2). Plotting these results on a diagram summarizing lead isotopic ratios from river sediment collected from the southwest Japan forearc (Saito et al, 2020) showed end member 1 aligning with the nearby plot position of the Niyodo River, while end member 2 lacked corresponding data, suggesting a high likelihood of anthropogenic introduction. Lead ores from China (Hsu and Sabatini, 2019) and Australia (Huston and Champion, 2023), both major lead-producing countries, exhibit similar characteristics to end member 2 of lead in Uranouchi Bay samples (higher 207Pb/204Pb ratio compared to 206Pb/204Pb), indicating a high probability of lead originating from imported ores from these countries being the source of end member 2 anthropogenic lead emissions.
Using sediment core collected from the inner part of Uranouchi Bay (U-1: water depth 9.7 meters), we conducted analyses using XRF core scanners (ITRAX) and ICP-MS to assess changes in heavy metal concentrations, using MC-ICP-MS to identify the origins of heavy metals based on lead isotopic ratios. Dating was estimated using radioactive isotopes (210Pb, 137Cs). From 1954 (25 cm) to 1964 (20 cm), heavy metals exhibited a rapid increase in concentration compared to earlier periods.
We compared the results of the non-destructive, high-precision, high-resolution measurements from XRF core scanners (ITRAX) and ICP-MS analyses. While both analyses showed similar overall increasing trends, the determination of the depth at which heavy metal concentrations began to increase was done through ICP-MS analysis, revealing the onset of anthropogenic heavy metals increases around 1954. In the ICP-MS analysis, it is evident that there is a difference in that the pre-treatment involved extracting and measuring heavy metals adhering to the surface of sediment grains.
From the mixing diagram of the overall lead isotopic ratios (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 207Pb/206Pb, 208Pb/206Pb) and Al/Pb, it was determined that the sources of lead in Uranouchi Bay shifted from an older era with low lead content and high lead isotopic ratios (end member 1) to two sources after the 1950s: one with high lead content and low lead isotopic ratios (end member 2). Plotting these results on a diagram summarizing lead isotopic ratios from river sediment collected from the southwest Japan forearc (Saito et al, 2020) showed end member 1 aligning with the nearby plot position of the Niyodo River, while end member 2 lacked corresponding data, suggesting a high likelihood of anthropogenic introduction. Lead ores from China (Hsu and Sabatini, 2019) and Australia (Huston and Champion, 2023), both major lead-producing countries, exhibit similar characteristics to end member 2 of lead in Uranouchi Bay samples (higher 207Pb/204Pb ratio compared to 206Pb/204Pb), indicating a high probability of lead originating from imported ores from these countries being the source of end member 2 anthropogenic lead emissions.