Long-Range Atmospheric Mercury Transport from Across East Asia to a Suburban Coastal Area in Southern Vietnam.

Exports of atmospheric mercury (Hg) from continental East Asia, a major Hg emitter in the globe, have been reported by several studies in neighboring countries such as Japan and Korea. Nonetheless, studies concerning this topic in Southeast Asia (SEA) countries are still limited. Accordingly, gaseous elemental mercury (GEM) has been measured from Can Thanh High School (CTHS), a suburban coastal site in southern Vietnam to study its characterization and discover the evidence of Hg trans-boundary transport from regional sources (e.g., East Asia). Data collected in July, August, and October 2022 were used in this study, and the overall GEM concentration was 1.61 ± 0.32 ng m-3. The GEM levels were higher in October than in July and August, potentially due to the discrepancy in air mass transport patterns induced by tropical monsoon and source origins of Hg. MERRA-2, backward trajectories, and CALIPSO images revealed the trans-boundary air pollution from continental East Asia to southern Vietnam, evidenced by significantly elevated (> 30%) atmospheric Hg concentrations as well as other air pollutants when the plume arrived at CTHS. Furthermore, our results also imply that atmospheric Hg exported from East Asia could influence large areas in SEA, suggesting the need for more studies in various SEA countries in the upcoming future. This study illustrated the influence of regional Hg emissions on local atmospheric Hg pollution and provided data to improve knowledge of the Hg biogeochemical cycle in SEA.

Pollution characteristics, associated risks, and possible sources of heavy metals in road dust collected from different areas of a metropolis in Vietnam.

Road dust samples were collected from different areas in Ho Chi Minh City (HCMC)-the largest city in Vietnam to explore pollution characteristics, ecological and human health risks, and sources of heavy metals (HMs). Results revealed the level of HMs found in the samples from residential and industrial zones of HCMC in the order of Mn > Zn > Cu > Cr > Pb > Ni > Co > As > Cd, Zn > Mn > Cu > Cr > Pb > Ni > Co > As > Cd. Due to the high enrichment of Cu, Zn in residential areas and Cu, Pb, Zn in industrial areas, the HM contamination in these areas remained moderate to severe. The findings also revealed a rising trend in the level of HMs in road dust from the east to the west of HCMC, and a heavy metal contamination hotspot in the west. In addition, industrial areas were more contaminated with HMs, posing greater associated risks than residential areas. Children living in urban areas of HCMC were found to be exposed to unacceptable health risks. Meanwhile, adults living in industrial areas face intolerable cancer risk. Among the nine HMs, Cd, Pb, and Cu posed the greatest ecological risk, while Cr and As were the main culprits behind health risks. HMs in road dust might derive from non-exhaust vehicular emissions, crustal materials, and industrial activities. The results suggested that industrial areas to the west of HCMC should focus more on reducing and controlling severe pollution of HMs.

Atmospheric particulate-bound mercury (PBM10) in a Southeast Asia megacity: Sources and health risk assessment.

Particulate-bound mercury (PBM) is a global environmental concern owing to its large dry deposition velocities and scavenging coefficients, both of which drive Hg into terrestrial and marine ecosystems. PBM observation studies have been widely conducted over East Asia, but comparable studies in Peninsular Southeast Asia (PSEA) remain scarce. This is the first study reporting PBM concentrations for Ho Chi Minh City (HCMC), the biggest metropolitan area in Vietnam. A total of 222 samples were collected in 2018 and contained an average PBM10 (particulate matter - PM with diameter ≤10 µm) concentration and Hg mass fraction (i.e. PBM/PM) of 67.3 ± 45.9 pg m-3 and 1.18 ± 1.12 µg g-1, respectively. Although PBM concentration was lower than those reported in Chinese megacities, the Hg mass fraction was similar to those in China, suggesting strong enrichment from anthropogenic Hg emissions in HCMC. Traffic-induced particulate emission and deposition processes were major factors governing PBM temporal variation at our site. In addition, the prevailing southwest monsoon winds brought air masses that passed through industrial areas and were associated with a higher Hg mass fraction. Statistically significant positive correlations (R2 = 0.11-0.52, p < 0.01) were observed for PBM with PM and the Hg mass fraction, indicating similar PM and Hg sources or oxidized Hg adsorption onto PM via gas-particle partitioning. Moreover, PCA results revealed a higher contribution of primary sources than secondary sources to PBM concentration variability in HCMC. A health risk assessment indicated that the PBM concentrations at HCMC posed minimal non-carcinogenic risks (HI < 1) for children and adults, but dermal contact may act as an important exposure route since lightweight clothing is common among residents. This PBM dataset over PSEA, a region with high atmospheric Hg emissions, provides a valuable resource for the Hg scientific community to improve our understanding of Hg biogeochemical cycle.

Multiscale Temporal Variations of Atmospheric Mercury Distinguished by the Hilbert-Huang Transform Analysis Reveals Multiple El Niño-Southern Oscillation Links.

Atmospheric mercury (Hg) cycling is sensitive to climate-driven changes, but links with various teleconnections remain unestablished. Here, we revealed the El Niño-Southern Oscillation (ENSO) influence on gaseous elemental mercury (GEM) concentrations recorded at a background station in East Asia using the Hilbert-Huang transform (HHT). The timing and magnitude of GEM intrinsic variations were clearly distinguished by ensemble empirical mode decomposition (EEMD), revealing the amplitude of the GEM concentration interannual variability (IAV) is greater than that for diurnal and seasonal variability. We show that changes in the annual cycle of GEM were modulated by significant IAVs at time scales of 2-7 years, highlighted by a robust GEM IAV-ENSO relationship of the associated intrinsic mode functions. With confirmation that ENSO modulates the GEM annual cycle, we then found that weaker GEM annual cycles may have resulted from El Niño-accelerated Hg evasion from the ocean. Furthermore, the relationship between ENSO and GEM is sensitive to extreme events (i.e., 2015-2016 El Niño), resulting in perturbation of the long-term trend and atmospheric Hg cycling. Future climate change will likely increase the number of extreme El Niño events and, hence, could alter atmospheric Hg cycling and influence the effectiveness evaluation of the Minamata Convention on Mercury.

Design of a Spark Big Data Framework for PM2.5 Air Pollution Forecasting.

In recent years, with rapid economic development, air pollution has become extremely serious, causing many negative effects on health, environment and medical costs. PM2.5 is one of the main components of air pollution. Therefore, it is necessary to know the PM2.5 air quality in advance for health. Many studies on air quality are based on the government's official air quality monitoring stations, which cannot be widely deployed due to high cost constraints. Furthermore, the update frequency of government monitoring stations is once an hour, and it is hard to capture short-term PM2.5 concentration peaks with little warning. Nevertheless, dealing with short-term data with many stations, the volume of data is huge and is calculated, analyzed and predicted in a complex way. This alleviates the high computational requirements of the original predictor, thus making Spark suitable for the considered problem. This study proposes a PM2.5 instant prediction architecture based on the Spark big data framework to handle the huge data from the LASS community. The Spark big data framework proposed in this study is divided into three modules. It collects real time PM2.5 data and performs ensemble learning through three machine learning algorithms (Linear Regression, Random Forest, Gradient Boosting Decision Tree) to predict the PM2.5 concentration value in the next 30 to 180 min with accompanying visualization graph. The experimental results show that our proposed Spark big data ensemble prediction model in next 30-min prediction has the best performance (R2 up to 0.96), and the ensemble model has better performance than any single machine learning model. Taiwan has been suffering from a situation of relatively poor air pollution quality for a long time. Air pollutant monitoring data from LASS community can provide a wide broader monitoring, however the data is large and difficult to integrate or analyze. The proposed Spark big data framework system can provide short-term PM2.5 forecasts and help the decision-maker to take proper action immediately.

Contamination, source attribution, and potential health risks of heavy metals in street dust of a metropolitan area in Southern Vietnam.

This study investigates distribution, pollution indices, and potential risk assessment for human health and ecology of eight heavy metals in twenty-five street dust samples collected from metropolitan area-Ho Chi Minh City, Vietnam. Results showed that Zn was of the highest concentration (466.4 ± 236.5 mg/kg), followed by Mn (393.9 ± 93.2 mg/kg), Cu (153.7 ± 64.7 mg/kg), Cr (102.4 ± 50.5 mg/kg), Pb (49.6 ± 21.4 mg/kg), Ni (36.2 ± 15.4 mg/kg), Co (7.9 ± 1.9 mg/kg), and Cd (0.5 ± 0.5 mg/kg). The principal component analysis revealed that three sources of heavy metals measured in street dust include vehicular activities (32.38%), mixed source of vehicular and residential activities (26.72%), and mixture of industrial and natural sources (20.23%). The geo-accumulation index values showed levels of non-pollution to moderately pollution for Mn and Co; moderately pollution for Ni; moderately to strongly pollution for Cd, Cr, and Pb; and strongly pollution for Cu and Zn. The potential ecological risk values of all sampling sites were close to the high-risk category. Zn (28.9%), Cu (25.4%), and Mn (24.4%) dominantly contributed to the ecological risk. For non-carcinogenic risk, the hazard quotient values for both children and adults were within a safety level. For carcinogenic risk, the TCRChildren was about 3 times higher than TCRAdults, but still within a tolerable limit (1 × 10-6 to 1 × 10-4) of cancer risk. Cr was a major contribution to potential risks in humans. Such studies on heavy metal in street dust are crucial but are still limited in Vietnam/or metropolitan area in Southeast Asia. Therefore, this study can fill the information gap about heavy metal contaminated street dust in a metropolitan area of Vietnam.

Temporal changes in atmospheric mercury concentrations at a background mountain site downwind of the East Asia continent in 2006-2016.

Atmospheric mercury (Hg) has been monitored at the Lulin Atmospheric Background Station (LABS) in Taiwan since April 2006 and is still continuing. Here we reported the trend in gaseous elemental Hg (GEM) concentrations at LABS between April 2006 and December 2016, before the Minamata Convention on Mercury entered into force in 2017. Previous research indicated nighttime (0-8 am) data collected at LABS are better representative of regional influence. Therefore, only nighttime GEM data were used for trend analysis. A significant decreasing trend in GEM at a rate of -1.5% yr-1 (-0.022 ng m-3 yr-1, p < 0.01) was found, comparable to the decreasing trends observed in Europe, North America, South Africa, and over the North Atlantic Ocean. Five major GEM source regions to the LABS were identified, including northern Indochina Peninsula, China, Northeast Asia, the Pacific Ocean, and South China Sea. Significant decreasing trends in GEM were found for air masses coming from northern Indochina Peninsula (-0.042 ng m-3 yr-1, -2.6% yr-1, p < 0.01), China (-0.041 ng m-3 yr-1, -2.4% yr-1, p < 0.01), Northeast Asia (-0.031 ng m-3 yr-1, -2.0% yr-1, p < 0.05), and the Pacific Ocean (-0.022 ng m-3 yr-1, -1.7% yr-1, p < 0.05). Decreasing GEM trend (-0.020 ng m-3 yr-1, -1.5% yr-1), but insignificant (p > 0.05), was also found for air masses coming from South China Sea. The decreasing trends observed with air from the Pacific Ocean and South China Sea indicated declining background GEM concentrations in Northern Hemisphere. Decrease in GEM concentrations at the LABS was in agreement with the reduction in atmospheric Hg export from the East Asia continent caused by changes in Hg emission quantity and speciation, and temporal and spatial distribution in emission sources that have been suggested by recent research. Additionally, changes in the frequency distribution of air mass origins and transport paths may also contribute to the changes in GEM concentrations at LABS.

A New Monitoring Effort for Asia: The Asia Pacific Mercury Monitoring Network (APMMN).

The Asia Pacific Mercury Monitoring Network (APMMN) cooperatively measures mercury in precipitation in a network of sites operating in Asia and the Western Pacific region. The network addresses significant data gaps in a region where mercury emission estimates are the highest globally, and available measurement data are limited. The reduction of mercury emissions under the Minamata Convention on Mercury also justifies the need for continent-wide and consistent observations that can help determine the magnitude of the problem and assess the efficacy of reductions over time. The APMMN's primary objectives are to monitor wet deposition and atmospheric concentrations of mercury and assist partners in developing their own monitoring capabilities. Network planning began in 2012 with wet deposition sampling starting in 2014. Currently, eight network sites measure mercury in precipitation following standardized procedures adapted from the National Atmospheric Deposition Program. The network also has a common regional analytical laboratory (Taiwan), and quality assurance and data flagging procedures, which ensure the network makes scientifically valid and consistent measurements. Results from our ongoing analytical and field quality assurance measurements show minimal contamination in the network and accurate analytical analyses. We are continuing to monitor a potential concentration and precipitation volume bias under certain conditions. The average mercury concentration in precipitation was 11.3 (+9.6) ng L-1 for 139 network samples in 2018. Concentrations for individual sites vary widely. Low averages compare to the low concentrations observed on the U.S. West Coast; while other sites have average concentrations similar to the high values reported from many urban areas in China. Future APMMN goals are to (1) foster new network partnerships, (2) continue to collect, quality assure, and distribute results on the APMMN website, (3) provide training and share best monitoring practices, and (4) establish a gaseous concentration network for estimating dry deposition.

Sensitivity of a tropical micro-crustacean (Daphnia lumholtzi) to trace metals tested in natural water of the Mekong River.

Metal contamination is one of the major issues to the environment worldwide, yet it is poorly known how exposure to metals affects tropical species. We assessed the sensitivity of a tropical micro-crustacean Daphnia lumholtzi to three trace metals: copper (Cu), zinc (Zn) and nickel (Ni). Both, acute and chronic toxicity tests were conducted with metals dissolved in in situ water collected from two sites in the lower part of the Mekong River. In the acute toxicity test, D. lumholtzi neonates were exposed to Cu (3-30µgL-1), Zn (50-540µgL-1) or Ni (46-2356µgL-1) for 48h. The values of median lethal concentrations (48h-LC50) were 11.57-16.67µg Cu L-1, 179.3-280.9µg Zn L-1, and 1026-1516µg Ni L-1. In the chronic toxicity test, animals were exposed to Cu (3 and 4µgL-1), Zn (50 and 56µgL-1), and Ni (six concentrations from 5 to 302µgL-1) for 21days. The concentrations of 4µg Cu L-1 and 6µg Ni L-1 enhanced the body length of D. lumholtzi but 46µg Ni L-1 and 50µg Zn L-1 resulted in a strong mortality, reduced the body length, postponed the maturation, and lowered the fecundity. The results tentatively suggest that D. lumholtzi showed a higher sensitivity to metals than related species in the temperate region. The results underscore the importance of including the local species in ecological risk assessment in important tropical ecosystems such as the Mekong River to arrive at a better conservational and management plan and regulatory policy to protect freshwater biodiversity from metal contamination.