Time variation in transfer amounts of mercury by a river system near an artisanal and small-scale gold mining area in West Java, Indonesia

To evaluate the impact of mercury released into a river system by artisanal and small-scale gold mining (ASGM) activity in West Java, Indonesia, the temporal variations in elemental mercury, mercury ions, dissolved total mercury and particulate mercury concentrations in river water were observed in March 2015 (rainy season) and August 2015 (dry season) at a fixed observation point, and the migrated amount of mercury was estimated. Variations for other metals, total organic carbon (TOC), and total nitrogen (TN) contents were also measured. There have been few reports in which the amount of mercury transferred from ASGM activities is quantitatively estimated, and this study provides important data for evaluating the environmental impact of mercury released by ASGM activities. The concentration of filtered total mercury and the particulate mercury concentration observed in the dry season were 161 ± 167 μg L−1 and 142 ± 93 μg L−1, respectively, and these values were significantly higher than the values of 24.5 ± 23.9 μg L−1 and 53.7 ± 44 μg L−1 for filtered total mercury and particulate mercury, respectively, observed in the rainy season. On the other hand, the river flow in the rainy and dry seasons was 2.6 × 104 ± 5×103 m3 h−1 and 8.2 × 103 ± 8×102 m3 h−1, respectively, and an apparent increase in the amount of water in the rainy season was observed. The transfer amounts in the rainy and dry seasons obtained from these results were 6.2 × 102 ± 6.7 × 102 g h−1 and 1.6 × 103 ± 1.6 × 103 g h−1, respectively, for filtered total mercury and 1.3 × 103 ± 1.3 × 103 g h−1 and 1.1 × 103 ± 7×102 g h−1, respectively, for particulate mercury. The temporal variations in these values exhibited a wide range, indicating the effects of weather conditions and of the mining process.