Application of a biofilm formed by a mixture of yeasts isolated in Vietnam to degrade aromatic hydrocarbon polluted wastewater collected from petroleum storage.

In this study, three good biofilm-forming yeast strains, including Candida viswanathii TH1, Candida tropicalis TH4 and Trichosporon asahii B1, were isolated from oil-contaminated water and sediment samples collected in coastal zones of Vietnam. These strains were registered in the GenBank database with the accession numbers JX129175, JX129176 and KC139404 for strain TH1, TH4 and B1, respectively. The biofilm formed by a mixture of these organisms degraded 90, 85, 82 and 67% of phenol, naphthalene, anthracene and pyrene, respectively, after a 7-day incubation period using an initial concentration of 600 ppm phenol and 200 ppm of each of the other compounds. In addition, this biofilm completely degraded these aromatic compounds, which were from wastewater collected from petroleum tanks in Do Xa, Hanoi after 14 days of incubation based on gas chromatography mass spectrometry analysis. To the best of our knowledge, reports on polycyclic aromatic hydrocarbon and phenol degradation by biofilm-forming yeasts are limited. The results obtained indicate that the biofilm formed by multiple yeast strains may considerably increase the degradation efficiency of aromatic hydrocarbon compounds, and may lead to a new approach for eliminating petroleum oil-contaminated water in Vietnam.

Study of ranking of bio-indices using benthic macroinvertebrates for Lower Dongnai River System, Vietnam.

It has been demonstrated by research that the most successful assessment methods have been based on the benthic macroinvertebrate communities. A lot of bio-indices have been applied to evaluate the water quality widely. However, most of them have got the rankings for the water quality assessment. In this study, based on the monitoring results of the benthic macroinvertebrate and the environmental parameters in the Lower Dongnai River System during three-year periods (2007 - 2009), the linear correlations among the most popular bio-indices and each environmental parameter were considered. These environmental variables having the most closed correlation with the biological indices were DO (dissolved oxygen), WQI (water quality index) and total nitrogen. From the analysis, the ranking of bio-indices using benthic macroinvertebrate for the Lower Dongnai River System were established. The findings proved that the ranking of bio-indices for water quality assessment can be used to evaluate the water quality for the Lower Dongnai River System.

Antibiotic contaminants in coastal wetlands from Vietnamese shrimp farming.

BACKGROUND AND PURPOSE: Shrimp culture has been expanded rapidly in recent years in coastal wetland zone of Vietnam due to favorable natural conditions. However, this industry has caused several negative impacts to the environment. One of the critical issues is the excessive application of antibiotics including human medicines. These chemicals could be released from shrimp ponds and then accumulated and contaminated of the ecosystem. This review article discusses a whole range of findings that address various aspects of the usage, occurrence and potentially environmental risks of antibiotics released from shrimp farming, with emphasis on the South Vietnam coastal wetland. METHODS: The published information on the usage and occurrence of antibiotics in Vietnamese shrimp farming has been reviewed. A global comparison was also carried out. This follows by a brief overview of the transport and fate of these antibiotics in the environment. RESULTS: Several antibiotics commonly used in Vietnamese shrimp culture have been detected in wastewater and sediment of the ponds, as well as in surrounding coastal wetlands, resulting in the existence of antibiotic-resistant bacteria. However, their transport and fate could not be clearly defined. CONCLUSIONS: The well-documented accumulation of antibiotics in mud and sediments in Vietnamese coastal wetlands potentially poses serious risks for the local wetland ecosystems. Thus, research on the transport and fate of antibiotics' residues from the ponds into the surrounding environment is urgently needed.