Heavy metal pollution and nutrient deficiency problems in the abandoned Bagacay mine in Samar island

The National Policy Agenda on the Revitalization of Mining in the Philippines in 2004 gives top priority to the remediation and rehabilitation of abandoned mining sites all over the country. Consequently, the Department of Environment and Natural Resources (DENR) has identified remediation and rehabilitation of several abandoned mining sites as one of its top priorities (MGB-MESD 2006). Among all abandoned mining sites throughout the country needing urgent rehabilitation, the Bagacay Mine ranks first (MGB-MESD 2006).

Bagacay Mine, located at the border of a nature reserve in the western part of Samar Island, was formerly worked for the recovery of pyrite (FeS2) and copper (Cu) for nearly 50 years until its abandonment in 1992. It exhibits many environmental problems such as heavy metal pollution of soil and water and the formation of Acid Mine Drainage. Recent efforts to rehabilitate the area by re-vegetating it with introduced trees species such as mahogany (Swietenia macrophylla), mangium (Acacia mangium) and ipil-ipil (Leucaena leucocephala) as well as some grass species like tiger grass (Thysanolaena maxima) were a total failure.

An environmental assessment by the Mines and Geosciences Bureau (MGB-MESD, 2006) revealed very high levels of heavy metals in sediments (and soils) collected from various parts of the abandoned mining site. For the upstream sediments (soil and sediments deposited by various tributaries unaffected by mining activities), the levels of heavy metals (in mg/kg) were: Fe (5,900 to 96,000), Cu (9 to 2,216), Zn (<1 to 516) and Pb (22 to 694). The midstream materials which included rock and soil materials from the main pit and waste dumps, silt and sediments in the pit, and tailings from the tailing dams were more polluted and showed the following concentrations (mg/kg): Fe (36,400 to 487,500), Cu (220 to 50,100), Zn (100 to 187,700), Pb (8 to 2,341), As (6 to 5,969) and Hg (1 to 13). For the downstream sediments (from the Taft River), the heavy metals concentrations in mg/kg were: Fe (104,300 to 373,500), Cu (466 to 5,279), Zn (2,314 to 7,138), Pb (44 to 354), As (352 to 693) and Hg (2 to 5).

Some native plant species are starting to grow in clumps even in the most polluted portions of the abandoned site. Edralin (2008) collected soil samples around each clump of the native plants as well as plant tissues for chemical analysis. Findings revealed that the soil in the spots where the plants are starting to grow still have very low fertility status and are extremely acidic aside from containing excessive levels of the heavy metals. The study showed that the native plants that start to grow in the area have low nutrient (N and P) requirement and are able to tolerate the polluted condition either by not absorbing (avoiding) the heavy metals or by absorbing high levels of the metals (the study considered only Cu and Pb). The concentration of Cu in the plants such as Saccharum spontaneum L. and Neonauclea formicaria (Elm.) Merr. was positively correlated with the soil OM content. Two fern species Pityrogramma calomelanos (L.) Link and Lycopodium cernuum L. showed the highest concentrations of Cu in their tissues with values that fall within the toxic range for plants. Also, the highest concentration of Pb was shown by Lycopodium cernuun L. and Dicranopteris linearis (Burm.) Underw. with some of their Pb values also falling within the plant toxicity range.

References

Doyle C, Wicks C, Frank N 2007. Mining in the Philippines Concerns and Conflicts. Fact Finding Mission to the Philippines Report. Society of St. Columban, Widney Manor Rd., Knowle, Solihull B93 9AM, West Midlands, UK

Edralin Don Immanuel A. 2008. Copper, lead, nitrogen and phosphorus levels in soils and plants in the abandoned Bagacay mine in Western Samar. MSc thesis in tropical ecology, Visayas State University, Baybay, Leyte, Philippines.

Kabata-Pendias A 2004. Soil-plant transfers of trace element- an environmental issue.
Geoderma 122: 143-149

Mines and Geosciences Bureau - Mining Environment and Safety Division (MGB-MESD) 2006). Environmental Assessment of Abandoned Bagacay Mine Relative to the Proposed Interim Remediation Measures of the World Bank Supported Project. North Avenue, Diliman, Quezon City.