Three monitoring methods, including manual monitoring methods based on active and passive samplings and an automatic active monitoring method, for atmospheric mercury (Hg) concentrations are recommended in the guidance on monitoring Hg based on Article 22 of the Minamata Convention on Mercury, which entered into force in 2017. However, among these methods, the dataset obtained by manual monitoring based on active sampling and automatic active monitoring has not yet been verified. Parallel observations using these two methods were conducted in one month for each season from May 2021 to February 2022 at urban and rural sites in Japan. The main objective of this study was to evaluate the comparability of the observations obtained using the two methods. Because the sampling duration of the manual monitoring method based on active sampling using the Japanese monitoring network was 24 h, the data on the daily mean concentrations of atmospheric Hg obtained by both methods were compared, and their consistency was evaluated using t-test, correlation analysis, and Bland–Altman analysis.The observation values obtained by the two methods were consistent (correlation coefficients=0.99 or higher) in all seasons, despite the large seasonal variation in meteorological conditions, and the unpaired t-test indicated that there were no differences between them in each season. Moreover, the Bland–Altman analysis showed that more than 96% of the data points were found to be within the 95% limit of agreement. Therefore, the manual monitoring method based on active sampling used in this study was in better agreement with the automatic active monitoring method. These results indicate that the data obtained by both methods are comparable. Additionally, manual monitoring based on active sampling can be used to build mercury monitoring networks at a lower cost than automatic active monitoring. Overall, the data obtained by both methods were proven to be beneficial for the effectiveness evaluation of the Minamata Convention.

Volcanic and geothermal activities are one of the major emission sources of mercury (Hg), emitting 500 tons y^− 1 into the atmosphere, and it is known that there are three main forms of Hg released to the atmosphere from these activities: gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM). In this study, the concentrations of GEM, GOM and PBM_2.5 (PBM in particles less than 2.5 μm) were continuously observed for 2 years at Sensuikyo Station, located 2.5 km northeast from Nakadake No. 1 Crater of Mt. Aso. The observed mean concentrations of GEM, GOM, and PBM_2.5 in the entire period were 1.64, 0.021 and 0.021 ng m^− 3, while maximum concentrations were 9.04, 2.45 and 3.20 ng m^− 3, respectively. The concentrations increased significantly when the volcanic activity was high and when the wind blew from the crater. Under high volcanic activity, the mean concentrations of GEM, GOM and PBM_2.5 were 1.3, 4.1, and 15.3 times higher than those during calm conditions. Changes in GOM and PBM_2.5 concentrations between active and calm conditions were significantly higher than those of GEM. The amplitude of volcanic tremors is usually used as a reference indicator of the volcanic activity. GOM and PBM_2.5 concentrations became higher before the volcanic tremor amplitude increased. However, the reliability of atmospheric GOM measurements in volcanic regions with high levels of acidic gases is still debatable. Therefore, PBM_2.5 concentrations can be used as one of the indicators to assess the activity of Mount Aso volcano. Graphical Abstract

Artisanal and small-scale gold mining (ASGM) releases mercury into tropical freshwater systems, yet integrated assessments of Southeast Asian oxbow lakes remain scarce. We quantified total mercury (THg) in water, sediment, and fish from Lake Hanjalutung, an ASGM-affected oxbow lake in Central Kalimantan, Indonesia. Water and sediment were sampled at five river and lake stations in the dry (July 2025) and rainy (November 2025) seasons, and thirteen fish of five species were obtained from a lake net-cage unit in the rainy season. THg was measured by cold-vapor and thermal-decomposition atomic absorption spectrometry. Water THg was higher in the dry season (26.13–42.66 ng/L) than in the rainy season (8.20–24.05 ng/L). Geoaccumulation index (I_geo) values were higher in the lake interior (1.65–2.01) than in the river channels (0.53–1.46), consistent with Hg retention in the lake. Fish THg ranged from 0.16 to 1.51 mg/kg dw. Bioaccumulation factors (BAF; fish/water) ranged from 5.3 × 10³ to 39.2 × 10³ L/kg, and biota–sediment accumulation factors (BSAF; fish/sediment) exceeded unity for all species. Both indices correlated positively with body length, although this association largely reflected interspecific differences. Maximum allowable weekly intake (MAWI) estimates indicate a potential exposure risk. Intake estimated from regional data exceeded the MAWI for Wallago leeri by 9- to 12-fold for one-year-old children and approximately 8-fold for pregnant women. Preferential consumption of lower-Hg species, such as Pristolepis grootii, may increase allowable intake approximately 3.5-fold, a preliminary finding requiring confirmation.

Artisanal and small-scale gold mining (ASGM) has driven mercury contamination in tropical freshwater systems, yet integrated assessments of Southeast Asian oxbow lakes remain rare. This study quantified total mercury (THg) concentrations in water, sediment, and fish from Lake Hanjalutung, an ASGM-affected oxbow lake in Central Kalimantan, Indonesia. Water THg was higher in the dry season (26.13–42.66 ng/L) than the rainy season (8.20–24.05 ng/L), whereas lake interior sediment was more enriched during the rainy season. Geoaccumulation index (I_geo) values increased from the river channels to the lake interior (1.7–2.0, moderately to heavily contaminated), confirming that the lake acts as a mercury sink. Fish THg concentrations ranged from 0.16 to 1.51 mg/kg dw. Bioaccumulation factors (BAF) ranged from 5.3 × 10³ to 39.0 × 10³ L/kg, and biota-sediment accumulation factors (BSAF) exceeded unity for all species, with both indices increasing significantly with body length, indicating body size as the primary driver of bioaccumulation. Maximum allowable weekly intake (MAWI) analysis showed that estimated regional consumption exceeded safe thresholds for all receptor groups, by 9- to 12-fold for one-year-old children and approximately 8-fold for pregnant women consuming W. leeri. Substituting with P. grootii consistently increased allowable intake by 3.5-fold, offering a practical, species-based risk reduction strategy for communities dependent on freshwater fish for protein.

Air-sea mercury (Hg) exchange is an important process in the natural Hg cycle. Hg evasion from oceans accounts for approximately 40% of the global Hg emissions into the atmosphere, which was estimated to be 8,000 t yr-1. In this study, we determined Hg fluxes through dissolved gaseous Hg (DGM) measurements using a manual method along a 47ºN transect of the North Pacific Ocean and Alaska Bay in the summer of 2017, and conducted continuous monitoring using a gas-liquid equilibrator system in sea areas between 30ºN and 50ºN in the western North Pacific Ocean during the summer of 2022 and 2023. Atmospheric gaseous elemental Hg (GEM) was also continuously observed. The average GEM concentrations in 2017 and 2023 were 1.54 ± 0.22 and 1.25 ± 0.27 ng m-3, respectively, similar to the background levels of the Northern Hemisphere. In contrast, GEM concentrations in 2022 reached approximately 2.00 ng m-3. The GEM and DGM concentrations and Hg fluxes gradually increased from north to south. The Hg fluxes were nearly zero in the region around 45°N. Hg evasion fluxes were greater between 30-35°N because of higher DGM concentrations. In addition, atmospheric GEM and seawater DGM concentrations were positively correlated with surface seawater temperature (SST). From these results, the boundary line of the SST between Hg evasion and invasion in the study areas was estimated at approximately 5 ℃, using a 1.50-ng m-3 GEM background concentration for the Northern Hemisphere.