Occurrence of persistent toxic substances in soils, sediments, fishes and human breast milk in southern Vietnam

Global contamination and toxic effects of persistent toxic substances (PTSs) have been an emerging environmental issue and have received considerable attention during the past four decades. The rapid agricultural and industrial growths as well as the expansion of urban areas in Hochiminh City and Mekong River Delta, two of the most densely populated areas in the world with about 26 million peoples, result in the widespread contamination of PTSs in southern Vietnam. Due to adverse effects to human health and environment, more attention has been paid to PTSs in Vietnam since the early 1990s. However, these works mainly focused on PTSs in water, soil and sediment media. PTSs in animals, birds and human (blood, adipose tissue, breast milk, etc.) have drawn less attention due to high cost of research and the need of sophisticated analytical techniques. With the support of Swiss Agency for Development and Cooperation (SDC) project in the frame of a collaboration between Vietnam and Switzerland, we have carried out the research named "Persistent Toxic Substances in southern Vietnam; Development analytical methods, bioaccumulation and modeling". Our research has established suitable analytical methods, which is able to analyze simultaneously PCBs, PBDEs, OCls pesticides and especially, mirex and toxaphene, which are analyzed for the first time in Vietnam, in various matrices such as soil/sediment, fish and human breast milk samples by HRGC/LRMS. The sampling sites (including Hochiminh City, Dongnai – Baria Vungtau province and Mekong Delta) have been selected based on previous studies in Vietnam and collected documents from Vietnam Environment Administration and POPs Project of Vietnamese government. Twenty-one PCB congeners, twelve PBDE congeners and twenty-six organochlorine pesticides were chosen for research due to their high toxicities. Soil, sediment, fish tissue, and human breast milk were selected as the matrices to examine the PTSs residue. The obtained results showed that PTSs levels of soil and sediment samples in southern Vietnam are not so high, e.g. DDTs and PCBs levels are lower than those in previous studies in Vietnam. Endosulfans were found in almost all sites suggesting the widespread contamination due to their large usage in agriculture. Toxaphene was only found in soil close to agrichemical warehouse at high level indicating potential source of toxaphene from the pesticide stockpiles. PBDEs were detected in most of the samples but at the low levels, which shows a possibly atmospheric deposition source. Other PTSs were detected at low levels (< 5 ng/g dry wt.) or below LOD of the analytical method. PTSs concentrations in wild fish samples from Saigon and Tien Rivers are lower than those determined in previous studies in Vietnam and in the world. However, unlike DDTs, PCBs showed a slow decreasing in fish samples and this suggests a continuous contamination. Besides, due to large usage in agricultural activities, endosulfans were also found in almost all wild fish samples from Saigon and Tien River (23.9 and 8.3 ng/g lipid wt., respectively). Other PTSs were detected at low levels (< 5 ng/g dry wt.) or below LOD of the analytical method. PTSs levels in human breast milk of HCMC residents are lower than those in previous study (except PCBs and CHLs). The higher PCB residues observed in human breast milk from HCMC suggest continuously high exposure to PCBs via the food chain to human. In this study, PTSs levels in human breast milk of primiparous mother higher than those in multiparous mothers. This trend well agrees with previous study in Hanoi and HCMC. By using statistic methods for obtained results (cluster analysis and PCA), we have shown the similarity of PTSs profiles pattern between landfill soil, TN-SG River sediments and Saigon River fish samples. Logically, we might suggest that there is a transfer of PTSs compounds from landfill and TN-SG River to fish samples collected from Saigon river. Our results clearly demonstrate that municipal and industrial waste from landfill and urban activities of HCMC could be considered as PTSs pollution sources. The results of the present study have contributed to the improvement of PTSs research capability of Vietnam. This research also efficiently supports and serves the projects of monitoring, studying and evaluating impacts of PTSs on South Vietnam ecosystem during the implementation of NIP under Stockholm Convention.

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