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