To develop an easy and reliable method for detecting pesticides and their residues in the Mekong Delta, a GC‐MS analytical method was developed and validated according to European guidelines (SANTE/11945/2015) for the determination of residues of three pesticides (quinalphos, trifluralin and dichlorvos) in water. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.002 and 0.007 μg/L, respectively, for quinalphos and trifluralin, and 0.016 and 0.053 μg/L, respectively, for dichlorvos and quinalphos. The repeatability, the within‐laboratory reproducibility as well as the trueness met the European criteria. The recovery rate ranged between 72% (for dichlorvos and quinalphos) and 82% (for trifluralin). The developed method was then applied for the analysis of 33 water samples, collected in April 2013, at the beginning of the rainy season in the Mekong Delta in Vietnam. Thirteen samples were from rice field, 10 were collected from cat fish ponds and from red tilapia cages. Results showed that only 9% of total water samples analysed contained residues of pesticides, but only in water from rice fish systems. From the 13 samples taken in these systems, quinalphos was detected in three samples. The other two pesticides were not detected. A comparison between analytical results obtained from GC‐MS and an alternative method, that is GC‐ECD indicated that GC‐ECD is less sensitive than GC‐MS, with LOQ ranging from 0.37 to 1.18 (depending on the pesticide). However, for samples with concentrations above these LOQ, no significant difference was observed between the results obtained from the two analytical methodologies.

The study aimed to investigate the effect of rosemary (Rosmarinus officinalis) extract on the quality changes of fishballs from knife fish (Chitala chitala) and striped catfish byproduct (Pangasianodon hypophthalmus) during frozen storage. Fishballs were supplemented with rosemary extracts at two concentrations of 13 mg/kg and 156 mg/kg. The control treatment was the sample without extract. The products were steamed, vacuum packed in PA bags and stored at a temperature from -18oC to -20oC. Sampling was done at 0, 30, 60, 90, 120, 150 and 180 days of storage period for analysis of pH, Total volatile base nitrogen (TVB-N), total viable bacteria count (TVC), pathogenic bacteria, sensory properties, peroxide value (PV), Thiobarbituric acid reactive substances (TBARs). Results showed that Escherichia coli and Salmonella spp. were absent in the fishballs, reflecting the safety of products for consumers. Adding rosemary extract at 156 mg/kg in fishballs displayed more effectiveness in inhibiting the formation of lipid oxidation and microbial growth when compared to the control sample during the frozen storage. Based on the results of physicochemical and sensory quality, the supplementation of rosemary extracts showed a significant promise for improving the quality of fishballs. Fishballs from knife fish and striped catfish by-products could be maintained their sensory properties and prolonged their shelf-life up to 180 days of frozen storage.

In order to determine the distribution and enable the elimination of quinalphos, a popular active pesticide compound used in the Mekong Delta, an experiment was set up in a rice-fish integration system in Can Tho City, Vietnam. Fish was stocked into the field when the rice was two-months old. Quinalphos was applied twice in doses of 42.5 g per 1000 m². Water, fish and sediment samples were collected at time intervals and analyzed by a Gas Chromatography Electron Capture Detector system. The results show that quinalphos residues in fish muscles were much higher than those of the water and the bioconcentration factor (logBCF) was above 2 for the fish. The half-life of first and second quinalphos applications were 12.2 and 11.1 days for sediment, 2.5 and 1.1 days for silver barb, 1.9 and 1.3 days for common carp, and 1.1 and 1.0 days for water, respectively.