[M-ZZ41] 環境汚染が進行する現代における環境、生物、人の調和を考える

[MZZ41-P01] Fate and transport of metals and metalloids in the mineralized Itogon subcatchment of the Agno River Watershed, Philippines

*Jenielyn Tuando Padrones¹、 Ylam Shalev dT Matba²、Kim Bryan N Cabrera²、Francis Ian P. Gonzalvo²、Kennethjer G. Alejo²、Juan Miguel R. Guotana²、Loucel E. Cui²、Sofia A. Alaira²、Decibel V. Faustino-Eslava²、 Nelly S. Aggangan³、Eric S. Andal ⁴、Marcela C. Lumbania⁴、Laura Quick⁵、Richard D. Williams⁵、Emma C. Biles⁶、Patrick Byrne⁶、Thomas J. Coulthard⁷、Karen A. Hudson-Edwards⁸、 Trevor Hoey⁹ (1.Institute of Renewable Natural Resources, College of Forestry and Natural Resources, University of the Philippines Los Banos, College, Laguna, Philippines、2.School of Environmental Science and Management, University of the Philippines, Los Baños, Laguna, Philippines、3.National Institute of Molecular Biology and Biotechnology, University of the Philippines, Los Baños, College, Laguna, Philippines、4.Itogon-Suyoc Resources, Inc., Itogon, Benguet, Philippines、5.School of Geographical and Earth Sciences,University of Glasgow, United Kingdom、6.School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, United Kingdom、7.Geography Department, University of Hull, United Kingdom、8.Environment and Sustainability Institute, Camborne School of Mines, University of Exeter、9.Brunel University London, Uxbridge, United Kingdom)

キーワード：metal contamination and pollution, Philippine tropical catchment, Ecological Risk Indices, Project PAMANA

The Agno River Watershed (ARW) has about 65 years of mining history since the first mine operated in 1957 extracting mostly Au, Cu, and Ag. Despite the scale and longevity of mining operations, establishing background environmental and ecological quality in this mine affected catchment is lacking particularly on the concentration, fate and transport of metal and metalloids contaminants. Project PAMANA or the “Philippine Mining at the National to Catchment Scale: From Legacy Impacts to Sustainable Futures' aims to address these issues to provide a holistic understanding of the legacy, present and future environmental, ecological and societal impacts of mining operations in the ARW. Several field campaigns from August 2021 to August 2022 were conducted to collect surface water, surface sediments, and representative plant species samples from numerous areas within the mineralized Itogon subcatchment of ARW. Surface water quality revealed that most sampling sites meet the standards of metals and metalloids except for Fe, Cu, Mn, As and Hg. Parameters such as temperature, dissolved oxygen (DO), chloride, nitrate, and ammonia contents were also measured. Most of the sites meet the standard set by the national government for temperature, DO, and chloride. However, a few areas with active mine operations exceed the standards for chloride, nitrate and ammonia.

For the sediment samples, rapid assessment was done using Portable X-Ray Fluorescence (P-XRF) analysis while representative samples were analyzed using Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES). In order to provide information on the contamination level, ecological risk indices based on the Taiwan sediment quality recommendations for metals and metalloids, and average shale value (ASV) for other elements were examined. Geospatial analysis of the P-XRF results revealed "hotspot" locations for several potentially ecotoxic elements, including Hg, Cu, Zn, and As. The results of the geospatial analysis were compared with ecological risk indicators such as the degree of contamination (Cf), geoaccumulation index (Igeo), pollutant load index (PLI), and potential ecological risk (PER) factor. To quantify the statistical relationships between the elements, principal component analysis (PCA) was used. The geospatial analysis' findings are supported by the index results, and the PCA analysis showed which elements were positively and negatively associated.

Preliminary results of the plant bioaccumulation of metals and metalloids in plants using ICP-OES within the selected active mining site in Itogon, Benguet showed that two (2) most abundant species of plants, namely Pedilanthus tithymaloides and Ageratina riparia were found to be enriched in As (bioaccumulation factor (BCF) > 1), and only the species of Pedilanthus tithymaloides obtained a bioaccumulation of Ni (BCF > 1). Results of the analysis showed the presence of ppm-level concentrations of metals and metalloids in the plants in descending order: As>Ni>Pb>Cu>Cd>Co>Zn>Cr>Fe. Arsenic (As) was the most abundant ecotoxic element for all the species while Fe was only found in Pedilanthus tithymaloides. This study provides important information that could be used for watershed management, intervention measures, metal recovery, and rehabilitation planning of mined-out areas.