Physico-chemical properties and transboundary transport of PM2.5 in Bien Hoa City, Dong Nai Province, Southeastern Vietnam.

Air pollution is one of the most concerning environmental issues, wherein PM2.5 concentration plays an important role. This study monitored and evaluated the PM2.5 concentration trends in Bien Hoa City, Dong Nai Province, Vietnam. Twenty 24-h PM2.5 samples were continuously collected during the rainy (15 Oct. to 25 Oct. 2021) and dry (19 Mar. to 29 Mar. 2022) seasons. The PM2.5 samples were analyzed by scanning electron microscopy to determine the surface pattern and size distributions were analyzed using ImageJ software. The water-soluble fractions of 15 trace metal(oid)s concentrations (Al, Cu, Ni, K, Ca, Co, Mn, Cr, As, Zn, Pb, Cd, Na, Fe, and Mg) bound to PM2.5 were analyzed by inductively coupled plasma-mass spectrometry. The results showed that the 24-h fine fraction PM2.5 concentrations were 24.1 ± 12.2 µg/m3 and 63.0 ± 18.7 µg/m3 in the rainy and dry seasons, respectively. The results indicate that the size distributions of the particles of 2.0-2.5 µm are minor, and the majority are ultrafine particles with aerodynamic diameter ≤ 1.0 µm. Overall, the mass concentration level of the water-soluble fraction of trace metal(oid)s in PM2.5 in the rainy season was higher than that in the dry season. Among these, Ca, K, and Na were the most abundant earth crustal elements in PM2.5 in the rainy and dry seasons, accounting for 85% and 41.2% of the total trace element concentrations, respectively. The major sources of PM2.5 are local and regional sources of thermal power plants, industrial parks, and waterborne transportation (domestic rivers and marine). The activities undertaken to remove Agent Orange (e.g., soil excavation, transportation, and rotary kiln incinerators) at the Bien Hoa airbase area also cause increases in the PM2.5 level in the atmosphere of Bien Hoa City.

Ambient air monitoring around the dioxin remediation site in Da Nang, Vietnam, using passive air samplers.

The concentrations and temporal variations of polychlorodibenzo-p-dioxins and polychlorodibenzofurans (PCDDs/PCDFs) in ambient air between March 2013 and February 2017 were investigated by passive air samplers containing polyurethane foam (PUF) disks in the dioxin remediation area using in-pile thermal desorption (IPTD) technology at Da Nang airport, Vietnam. The PCDD/PCDF concentrations in ambient air at each site depended on the location of the emission sources and the wind direction, the dioxin contamination level of excavated materials, the periods of excavation and transport, and the operation of the IPTD treatment system. The PCDD/PCDF concentrations were the highest in the former Agent Orange mixing and loading area (AOMLA), which was the closest to the IPTD system, with total toxic equivalent (TEQ) values ranging from 0.437 to 15.3 pg/PUF/day. The total TEQ concentrations in the Sen Lake area ranged from 0.138 to 2.41 pg/PUF/day. The lowest concentration of PCDDs/PCDFs occurred in the northern perimeter area, with total TEQ values ranging from 0.164 to 0.972 pg/PUF/day. The decreasing trend of the PCDD/PCDF concentrations in ambient air was confirmed over time at all three monitoring sites, among which there was a strong decrease in the former AOMLA after February 2015. Residents living near the Da Nang airport were at a low risk of being exposed to PCDDs/PCDFs through inhalation during remediation project implementation, while residents living close to the former AOMLA faced elevated risks with an average daily dose of PCDDs/PCDFs through inhalation ranging from 0.017 to 0.82 pg TEQ/kg body weight/day.

Distributions and seasonal variations of organochlorine pesticides, polychlorinated biphenyls, and polybrominated diphenyl ethers in surface sediment from coastal areas of central Vietnam.

Concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) were determined in surface sediment from five estuaries of central coasts of Vietnam to understand the spatial distributions and seasonal variations. The contamination pattern was in the order: PCBs (9.72-3730 ng g-1 dry wt.) > PBDEs (11.8-311 ng g-1 dry wt.) > DDTs (0.462-26.7 ng g-1 dry wt.) > HCHs (0.491-22.6 ng g-1 dry wt.) > endosulfan compounds (0.196-19.4 ng g-1 dry wt.). DDTs and HCHs showed a little geographical variation, whereas PCBs and PBDEs exhibited clearer spatial distribution trend. Elevated concentrations of PCBs and PBDEs were detected in some sites in Nghe An and Quang Binh Province, which could be related to the human activities such as tourism, transportation, and domestic consumption. Seasonal variations of DDTs and HCHs were observed, showing higher residues in rainy seasons.