Persistent organochlorine pollutants in different bivalve species from central Vietnamese coasts: Concentrations, profiles, and biota-sediment accumulation factors.

Concentrations of typical persistent organochlorine pollutants (POCPs) like organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in five bivalve species collected from central Vietnamese coasts were determined to provide insights into spatial distribution and bioaccumulation characteristics of these substances. Concentrations of pollutants decreased in the order: PCBs (median 14.6; range 1.39-74.1), dichlorodiphenyltrichloroethane and its metabolites DDTs (2.92; 0.282-70.7), hexachlorocyclohexanes HCHs (2.46; 0.081-30.1), and endosulfan compounds ENDs (1.67; 0.041-36.6) ng/g wet weight. Considerable levels of legacy POCPs in the biota are likely attributed to illegal and/or unintentional sources. Concentrations and accumulation profiles of POCPs in biota samples were affected by species- and site-specific factors. The biota-sediment accumulation factors predicted enrichment potentials of OCPs (notably ENDs and DDTs) from sediment to biota in some certain areas.

Assessment of some water quality parameters in the Red River downstream, Vietnam by combining field monitoring and remote sensing method.

The Red River is the largest river in northern Vietnam, and it serves as the main water source for production and human activities in the Red River Delta region. Cities and provinces located in the Red River Delta, for example, Hanoi, Nam Dinh, and Ha Nam, have experienced rapid economic growth with various large urban, industrial zones, and agricultural areas. As a result of urbanization and industrialization, surface water in this region has been contaminated by multiple anthropogenic sources. In this study, in addition to water quality assessment using WQI, we used the reflectance values of visible and near-infrared bands and in situ data to build a regression model for several water quality parameters. Among ten parameters examined, two parameters, including total suspended solids (TSS) and turbidity, were used to construct regression correlation models using the Sentinel-2 multispectral images. Our results can contribute useful information for comprehensive monitoring, evaluation, and management scheme of water quality in the Red River Delta. The application of this method can overcome the limitation of actual observation results that only reflect local contamination status and require a lot of sampling and laboratory efforts.

Field evaluation of diffusive gradients in thin-film passive samplers for wastewater-based epidemiology.

There is a need for a simple water sampling technique to enable routine monitoring of community drug consumption through wastewater-based epidemiology (WBE). This study investigates the potential use of diffusive gradients in thin films to sample organic compounds (o-DGT) for WBE. Three types of resin gels (HLB, XAD 18, and XDA-1) within o-DGT samplers each were deployed in triplicate at the inlets of two sewage treatment plants of Southern Asian cities. The target compounds included 15 illicit drugs and 18 antibiotics. A comprehensive evaluation was undertaken regarding each resin's ability to accumulate the target compounds and accuracy by comparing active samples. The organic compounds accumulated on each resin gel were characterised at the molecular level using Fourier transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS). The results showed that the HLB resin performed better than the XAD 18 and XDA-1 resins. Based on calculations using the HLB-DGT data, methamphetamine and heroin were the two most popular illicit drugs consumed among the studied populations, and were followed by ketamine and codeine, which agreed well with the authoritative reports and reference data. The total drug consumption in Hanoi was one order of magnitude higher than that in Guangzhou, thus implying a probably more serious drug situation in the former. Overall, the findings of this study demonstrate that o-DGT passive samplers are a promising tool for WBE studies, particularly at WWTPs or in urban streams where an automatic sampler for taking composite water samples is absent.

Contamination status and temporal trends of persistent toxic substances in sediment cores from coastal areas of central Vietnam.

Residue concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) were measured in sediment core samples from two estuary areas of central Vietnam to elucidate recent status and temporal trends of pollution based on the depth profiles. Concentrations of PCBs, PBDEs, and endosulfan compounds were generally higher than those of the remaining OCPs. Peak concentrations of OCPs were found in the sediment layers corresponding to the late 1950s to the early 1980s, implying the intensive application of these insecticides in Vietnam during such periods. Although the highest PCB concentrations were measured in sediment layers dated in the 1970s, increasing PCB residues observed in the shallower layers may be related to the strong industrialization and urbanization in Vietnam. BDE-209 exhibited increasing concentrations and proportions to total PBDEs towards shallower depths, suggesting substantial use and on-going releases of deca-BDE products in recent years.

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.

Distribution, accumulation profile, and risk assessment of polybrominated diphenyl ethers in sediment from lake and river systems in Hanoi Metropolitan Area, Vietnam.

Concentrations of seven polybrominated diphenyl ethers (PBDEs) congeners were determined in surface sediments collected from several rivers and lakes in Hanoi, the capital city of Vietnam, to understand the status of background contamination, accumulation pattern, sources, and toxic implications for benthic organisms. Total PBDE concentrations in all sediment samples ranged from 0.03 to 17.5 ng/g dry weight (mean 1.33 ng/g dry wt). The most predominant congeners were BDE-47 and BDE-99, which comprised 30 and 25 % of total PBDE concentrations, respectively. Results from statistical analysis indicated that the potential sources of PBDEs of sediments in Hanoi may come from penta-BDE and octa-BDE mixtures. Risk quotients of PBDEs in sediments were also calculated for a benthic species, ranged from 2.12 × 10-6 - 1.60 × 10-2, and were markedly lower than threshold value for occurrence of any ecotoxicological risk. This study provides some of the most comprehensive data on the occurrence of PBDEs in sediments from lake and river systems in Vietnam.

Distribution and depth profiles of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and polychlorinated biphenyls in sediment collected from offshore waters of Central Vietnam.

Concentrations of PCBs and OCPs were measured in 35 surface sediment samples collected from offshore waters of Central Vietnam. The mean concentrations of PCBs, HCHs, and DDTs in surface sediments were 86.5, 37.0, and 44.5pgg(-1), respectively. Additionally, nine PCDDs, eleven PCDFs, and twelve dl-PCBs were also examined in 19 sediment core samples collected from five locations. Concentration of PCDDs, PCDFs, and dl-PCBs ranged from 200 to 460, 0.39 to 2.9, and 1.6 to 22pgg(-1), respectively. OCDD was detected at the highest concentration, ranged from 100 to 300pgg(-1). Generally, the concentrations of PCDD/Fs at shallower depths were higher, meanwhile the depth profiles of dl-PCBs in sediment cores were different than the depth profiles of PCDD/Fs. The results suggest that the pollution of PCBs might be from many different sources leading to the variation between depths.