Small-Scale Gold Mining and the State in the Philippines
Contested Extractivism, Society and the State
Elevated mercury (Hg) concentrations have been found in the Ambalanga Catchment, Benguet, where small-scale gold mining (SSM) is the main source of livelihood. To determine the distribution of total mercury (THg) and methylmercury (MeHg), and the possible physical controls on Hg methylation in the watershed, stream sediment sampling in the eight subbasins of the Ambalanga Catchment was conducted on two periods: low-flow (LF) stage in November 2001 and high-flow (HF) stage in July 2003. Results
... July 2003. Results revealed high THg concentrations in three subbasins (Acupan, Dalicno, and Sangilo) in the 2001 period and six subbasins (Acupan, Dalicno, Sangilo, Surong, Gold Creek, and Upper Ambalanga) in 2003. The increase in contaminated subbasins is attributed to the increase in river discharge which resulted in increased erosion of contaminated sediments. Significantly high concentrations of MeHg were found in two subbasins (Acupan and Lucbuban) in 2001 and four subbasins (Acupan, Dalicno, Sangilo, and Upper Ambalanga) in 2003. The high MeHg may be driven by the enhancement of the methylation process in areas with large amounts of fine-grained sediments that accumulated in lower hydrologic gradient (and ensuing increased organic activity) close to and at some distance downstream from the point sources. 1056 at the point source (BAT1-E at 3,600 ng/g), followed downstream by consistently decreasing concentrations. Channel morphology also plays a significant role. Stamenkovic et al. (2004) and Flanders et al. (2010) reported that both pond/wetland and channel margins/sites exhibited high potential for Hg methylation, for higher rates would be expected at sites with slower water or lower hydrologic gradient. In many instances, sediment samples collected below the water line were taken in sites with slow flow. It is where gentle to relatively flat river slopes can be expected where water flow tends to slow down. This therefore serves as a temporary sink for Hg and organic matter conducive to methylation activity.