A 60-year record of I in Taal Lake sediments (Philippines): Influence of human nuclear activities at low latitude regions.

The influence of human nuclear activities on environmental radioactivity is not well known at low latitude regions that are distant from nuclear test sites and nuclear facilities. A sediment core collected from Taal Lake in the central Philippines was analyzed for I and I to investigate this influence in a low-latitude terrestrial system. A baseline of I/I atomic ratios was established at (2.04-5.14) × 10 in the pre-nuclear era in this region. Controlled by the northeasterly equatorial trade winds, increased I/I ratios of (20.1-69.3) × 10 suggest that atmospheric nuclear weapons tests at the Pacific Proving Grounds in the central Pacific Ocean was the major source of I in the sediment during 1956-1962. The I/I ratios, up to 157.5 × 10 after 1964, indicate a strong influence by European nuclear fuel reprocessing plants. The East Asian Winter Monsoon is found to be the dominant driving force in the atmospheric dispersion of radioactive iodine (I) from the European nuclear fuel reprocessing plants to Southeast Asia, which is also important for dispersion of other airborne pollutants from the middle-high to low latitude regions. A significant I/I peak at 42.8 cm in the Taal Lake core appears to be the signal of the Chernobyl accident in 1986. In addition, volcanic activities are reflected in the iodine isotope profiles in the sediment core, suggesting the potential of using iodine isotopes as an indicator of volcanic eruptions.