Natalie Barkdull and Dr. Gregory Carling, Geology Department

Introduction

Artisanal and small scale gold mining (ASGM) accounts for almost half of anthropogenic mercury (Hg) emissions worldwide and causes widespread water pollution. Gold extraction by Hg amalgamation releases Hg-laden sediment and water into local watersheds where anaerobic organisms can convert inorganic Hg into organic methylmercury (MeHg), the most toxic form of Hg. In Indonesia, many studies identify harmful levels of Hg in fish, sediment, soil, crops, and human hair affected by ASGM; however, no study to our knowledge has examined total Hg and MeHg concentrations and transport downstream from processing sites. We evaluated Hg contamination in four Central Java gold mining areas by collecting water samples along river transects.

Methodology

This study evaluated four contaminated mining areas in Central Java, Indonesia with the help of Indonesian geology professors at UPN in Yogyakarta (Fig. 1). Before sampling, we surveyed mining locations, mining techniques, topography, and streamflow. We collected water samples in the dry season (June-July) along river transects to characterize chemistry upstream and downstream of gold-processing zones (Fig. 1). “Clean Hands – Dirty Hands” protocols (USEPA Method 1669) were used during all steps of sampling. At each sampling site, filtered samples (<.45 μm) were taken for Hg, trace elements, major cations, dissolved organic carbon (DOC), and major anions. Unfiltered samples were collected for Hg, and water isotopes. Additionally, water turbidity and alkalinity measurements were taken in-situ on unfiltered samples. A multi-meter YSI water probe was used to collect data about water temperature, dissolved oxygen (DO), conductivity, pH, and oxidation reduction potential (ORP). Samples were refrigerated and flown back to BYU for laboratory analysis. Total and methylated forms of Hg were measured by use of a Brooks Rand Mercury Analyzer according to EPA method 1631. Additional chemical analysis will be carried out at BYU in the coming months.

Results

Preliminary results indicate elevated total Hg concentrations downstream of ASGM sites exceeding 250 ng/L (Fig. 1). Adjacent to ore processing sites, concentrations exceed 25000 ng/L (Fig. 1). We found the highest Hg concentrations in Boto Village and Cihonje Village, and the lowest at Kokap and Kebonsari. We also measured the highest water turbidity adjacent ASGM processing sites. We did not account for seasonal changes in flow or temporal variability from sporadic contaminant release because of time constraints. Relationships between sites may vary during the rainy season due to increased streamflow and runoff. Hg concentrations only represent a “snapshot” of water chemistry. At this time, only total Hg analysis (filtered and unfiltered) is complete, however we will conduct additional tests in coming months to assess total water chemistry of the 4 contaminated areas.

Discussion

Despite ongoing testing, several important conclusions about ASGM activities in Java can be made. The scale of ASGM operations varies drastically by site; The Kokap area only operated 50 amalgamators with relatively low Hg concentrations, while Cihonje Village operated over 5000 amalgamators with Hg concentrations exceeding 250 ng/L. However, high Hg concentrations (exceeding 1500 ng/L) were also measured in Boto Village, which only operated 40 amalgamators. Therefore, the number of amalgamators doesn’t directly predict high Hg concentrations. We also measured a high ratio of unfiltered to filtered Hg at the most polluted sites (Fig. 1). High turbidity measurements at these sites support that the most polluted water carries a large sediment load. Downstream, water quality improved as turbidity and Hg concentrations decreased. This indicates settling of Hg laden sediment and colloidal particles. We hypothesize increased river flow in the wet season will mobilize Hg sediment from river channels and banks near processing sites and contribute higher Hg concentrations. Furthermore, we observed Hg-laden mine tailings cascade downhill into rice fields and vegetable farms at all sites. Studies in the San Francisco Bay Delta show that rice fields promote MeHg formation and rice grains readily incorporate MeHg. We will investigate the risk of MeHg formation in Indonesian rice fields during future study.

Conclusions

Although lab analysis is ongoing, preliminary total Hg measurements suggest ASGM activities in Central Java contribute significant Hg pollution and pose health risks to local residents. Future work will examine Hg concentrations in the wet season and the impact of rice fields on MeHg formation.

Figure 1. (right)

Total mercury (THg) concentrations during the dry season (June-July) in rivers at four artisanal and small scale gold mining locations (ASGM) across Central Java, Indonesia. At each site, filtered and unfiltered samples were collected and analyzed for Hg concentrations. Concentrations were highest adjacent to mining and processing sites, while lowest downstream. The fraction of filtered (<.45 μm) vs unfiltered Hg displayed to show dissolved and particulate Hg concentrations at each site.