Arsenic and heavy metals contamination in small scale mining Selogiri Area, Wonogiri Regency, Central Java, Indonesia

HTUN, Tin May, Dr.Ir. I Wayan Warmada

2006 | Tesis | S2 Teknik Geologi

Daerah Selogiri terletak di Kabupaten Wonogiri, Jawa Tengah, Indonesia. Sudah ada aktifitas penambangan emas yang ekstensif di daerah Selogiri sejak sepuluh tahun yang lalu, menimbulkan pengaruh pada lingkungan. Penelitian ini membahas seluk-beluk geokimia lingkungan dari deposit mineral di daerah Selogiri serta aspek-aspek geologis, geokimia, fisik, dan toksikologis dari logam-logam yang dipilih seperti As, Pb, Zn, Hg dan Cd. Lima belas sedimen tailing yang dipilih dianalisa dengan menggunakan ICP- MS. Peta anomali yang menunjukkan distribusi elemen dibuat dengan menggunakan program GIS Are View 3.3. Konsentrasi utama elemen-elemen berat sebagian besar mengikuti yang terbanyak dari deposit bijih besi tambang Selogiri. Kandungan yang cukup tinggi dari Pb, Zn, Cd dan As digambarkan di sampel tailing yang terletak di tiga desa, yaitu Jendi, Nglenggong dan Keloran. Dua puluh tiga sampel air dianalisa dengan F-AAS (Flame Atomic Absorption Spectometry) dan NAA (Neutrons Active Analyis). Konsentrasi As, Pb dan Zn terbatas dan tidak penting. Mereka berubah-ubah menurut kompleksasi, dirangkaikan dengan sorpsi di atas partikulat (yang paling umum hydrous ferric atau hydrous aluminum oksida). Oleh karena itu, oksida Besi berperan dalam tindak- tanduk biogeokimia As dan analisa geokimia dari salah satu tailing tambang Selogiri menunjukkan bahwa kandungan Fe tertinggi adalah 22% dan kandungan As adalah 0.0385%. Jadi, ada nilai yang tinggi dari rasio Fe/As. Survei geokimia permulaan, untuk studi kontaminasi merkuri dari daerah Selogiri dilakukan di musim kemarau dan 82 untuk tanah, 30 untuk sedimen sungai (ukuran endapan, dari permukaan sungai). Daerah yang terkontaminasi Hg dipusatkan pada terusan sungai dan daerah lembah serta dekat tempat amalgamasi. Permukaan dan air tanah adalah media yang efektif untuk dilusi dan dispersi Hg. Jadi, ada langkah lebih jauh, mengikuti sedimen sungai dan pengambilan sampel air dilakukan di musim hujan, dan untuk membuat perbandingan antara hasil geokimia dari musim kemarau dan musim hujan. Sumber kontaminasi utama Hg adalah tempat amalgamasi dan kandungan Hg tinggi di sedimen sungai dekat dengan tempat amalgamasi di musim kemarau. Di musim hujan, karena Hg cair dalam air hujan, Hg yang didistribusikan di sedimen sungai nilainya menurun secara konstan dari sumber menuju hilir.

Selogiri Area is situated in the Wonogiri Regency, Central Java, Indonesia. There has been extensive gold mining activity in Selogiri area since ten years ago, resulting in impacts on the environment. This research discusses the specifics of environmental geochemistry of mineral deposits in Selogiri area and geological, geochemical, physical, and toxicological aspects of selected metals such as As, Pb, Zn, Hg, and Cd. The selected 15 tailing sediments were analyzed by using ICP-MS. Maps showing element distribution were created using the GIS program Arc View 3.3. For the compilation of potential risk maps, the regional distribution of the elements has been reclassified using as thresholds the Italian intervention criteria for residential/recreational and commercial/industrial land use. The main concentrations of heavy elements mainly follow hosting most of the ore deposits of Selogiri mine. Fairly high contents of Pb, Zn, Cd, and As are reflected in the tailing sampled located in the three villages named Jendi, Nglenggong, and Keloran around the Selogiri area. Potential risk maps have been compiled for four elements: Zn, Pb, Cd and As because the state of geochemical pollution is very serious for these four elements, which are the main elements contained in orebodies. Twenty three water samples were analyzed by F-AAS (Flame Atomic Absorption Spectrometry) and NAA (Neutrons Active Analysis). The concentration of As, Pb, and Zn are limited and below the analytical detection limit values. These are variable by aqueous complexation, coupled with sorption onto particulates (most commonly the hydrous ferric or hydrous aluminum oxides). Therefore, Iron oxides play a role in the biogeochemical behavior of As and the geochemical analysis of one of the tailing in Selogiri mine show that, the highest Fe content is 22% and As content is 0.0385%. So, there is high value of the Fe/As ratio. The preliminary geochemical survey, for the mercury contamination study from Selogiri area was conducted in dry season and 82 for soils, 30 for stream sediments (silt-sized, from the surface of the stream). Hg contaminated area are concentrated at stream channels and lowland areas and near amalgamation sites. The surface and ground water are effective media for Hg dilution and dispersion. So, there is a further step, follow-up stream sediments and water sampling were carried out in wet season, and in order to make the comparison between the geochemical results from dry and wet seasons. The main Hg contamination source is amalgamation sites and high Hg contents in stream sediments are close to the amalgamation sites in dry seasons. In wet season, because of Hg diluted in rain water, Hg distributed in stream sediments is constant decreasing values from the source to the downstream.

Kata Kunci : Kawasan Selogiri,Deposit Mineral,Logam, Selogiri; mining district; pollution; anomaly; maps