ABSTRACT

This study aimed to investigate geosmin and 2-methylisoborneol (MIB)-producing cyanobacteria and actinomycetes as sources of earthy-musty odours in Phayao Lake, northern Thailand. Known earthy-musty odour producers, Lyngbya sp., Phormidium sp., Anabaena sp. and Oscillatoria sp., were found as the dominant genera of cyanobacteria in the lake water.  Odour-producing Streptomyces spp. were also found to be significantly present in the lake sediment where majority of Streptomyces spp. (63%) isolated were geosmin-producers. The significant density of actinomycetes, particularly Streptomyces, suggests that they played as important contributor to the production of geosmin and MIB in the lake.

Understanding the phytoplankton in aquaculture ponds is critical for proper pond management. Despite the importance, the relationships between phytoplankton composition, cultured fish type, season, and nutrients were not well understood. This study statistically investigated these relationships in aquaculture ponds. Data collected at 21 tilapia and 13 catfish ponds in September 2009 (wet season), December 2009 (cold season), and March 2010 (hot season) in northern Thailand were used for the analysis. The statistical analysis showed that PO4-P and NH4-N concentrations in catfish ponds were significantly higher than in tilapia ponds (p < 0.05, Wilcoxon test). The cyanobacterial abundance in catfish ponds was significantly greater than in tilapia ponds (p < 0.05, Wilcoxon test). In the hot season (March), green algae were abundant (p < 0.05), while cyanobacteria were depleted (p < 0.05). Multiple linear regression model was applied to determine important factors for statistically explaining cyanobacterial abundance. The result indicated that the best model selected by AICc included season and pond type as factors influencing cyanobacterial abundance but not nutrients. However, since the effect of nutrients was included in the difference in nutrient concentration due to the difference in fish species in the ponds, it was speculated that nutrients were insignificant as explanatory variables. Furthermore, it was hypothesized that cyanobacterial abundance was reduced in March (hot season) because the predation of cyanobacteria by tilapia may be encouraged at high temperature.

Geosmin is one of the major causative compounds of earthy-musty odor and taste (off-flavor) in drinking water (lakes) and in farmed fish. In this study, the sorption of cyclodextrin polymers (CDPs) towards geosmin in aqueous solution was investigated. Sorption kinetics, the effect of solution pH and contact time on the sorption capability of α-, β-and γ-cyclodextrin polymers was discussed. Results disclosed that the sorption of geosmin by the CDPs followed the Ho and McKay kinetic mechanism with the liquid film diffusion as the rate-determining step. Both β-CDP and γ-CDP exhibit high removal efficiencies of 93.4% and 96%, respectively, within 240 minutes at 25˚C and pH 7, whilst α-CDP was not effective, removing only 40% geosmin, at an initial concentration of 5 µg•L −1 and 5 g•L −1 of CDP dose. The cyclodextrin polymers can adapt to a wide range of pH from 3.0 to 11.0 for geosmin adsorption with pH 7.0 as optimum. Results indicate that these sorbents demonstrate significant potential in reducing the concentration of geosmin in water that presents taint problems in both drinking water and fish.

Microplastic contamination in the aquatic environment is a worldwide problem endangering aquatic organisms and human health. However, few reports were published in the Philippines especially in different edible fishery products. Hence, an investigation to report its prevalence in edible fishery products, especially in a fishery-dependent country, is necessary. This study was conducted to detect, characterize, and quantify microplastics from cultured Green mussel Perna viridis in Bacoor Bay, Cavite, Philippines. Samples (n=63) were collected from the inner, middle, and outer parts of Bacoor Bay. Isolation and characterization were conducted using wet peroxide oxidation-assisted density separation and stereomicroscopy, respectively. Results show a low concentration of microplastics from P. viridis cultured in Bacoor Bay. The highest microplastic count was observed from the inner bay (0.41 particle/gwet weight) followed by the middle bay (0.40 particle/gwet weight), then the outer bay (0.27 particle/gwet weight). The majority of microplastics in all sites were fibers (61%), color red (29%), and were dominated with > 10 to 50 µm length. This study revealed that microplastic is prevalent in Bacoor bay. Further study on confirming the microplastic polymers from P. viridis cultured in Bacoor bay is recommended.