Lee Hoon Lim

Short-term variation in the concentration of selected ions within individual tropical rainstorms

Rainwater was collected at the campus of the University of Brunei Darussalam in Bandar Seri Begawan, Brunei Darussalam, using a funnel-in-bottle sampler. Polypropylene bottles were changed at intervals during rainstorm events. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5°C for subsequent chemical analysis. Analyses for Na, Mg, Ca, Zn and Fe were carried out by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES); Cu and Mn were analysed by graphite furnace atomic absorption spectroscopy (GFAAS); K was analysed using flame atomic emission spectroscopy (FAES); and Cl−, NO3− and SO42− were analysed by ion chromatography (IC). Concentration versus time profiles are reported for three rainstorm events. All ions exhibited a decrease in concentration during the rainstorm. The first sample contained the highest concentration of ions, consistent with a “first-flush” effect. The contribution of the initial stages of the shower to the total quantity of ion deposited during the entire rainstorm is quite overwhelming; in many cases 20 to 30% of the mass was deposited in less than 5% of rainstorm duration. On the other hand, the pH and conductivity variation during rainstorms did not exhibit a consistent pattern.

A rain acidity study in Brunei Darussalam

Fifty-three bulk deposition samples were collected at the campus of the University of Brunei Darussalam between April and November 1994 using a funnel-in bottle sampler. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5 °C for subsequent chemical analysis. Analyses for Cl−, NO3− and SO42− were carried out by means of ion chromatography, while Na+, K+, Ca2+ and Mg2+ were determined by atomic spectroscopy. The recorded pH values were in the range of 4.35 to 6.59. Seventy-seven percent of the samples had pH values below 5.6, demonstrating the occurrence of acidic deposition. The range, mean and standard deviation of measured concentrations are reported. There was very little difference between measurements in filtered and unfiltered samples. Correlation coefficients between pairs of parameters are reported and discussed.

Phytoextraction potential of water fern (Azolla pinnata) in the removal of a hazardous dye, methyl violet 2B: Artificial neural network modelling

ABSTRACT This study investigated the potential of Azolla pinnata (AP) in the removal of toxic methyl violet 2B (MV) dye wastewater using the phytoextraction approach with the inclusion of an Artificial Neural Network (ANN) modelling. Parameters examined included the effects of dye concentration, pH and plant dosage. The highest removal efficiency was 93% which was achieved at a plant dosage of 0.8 g (dye volume = 200 mL, initial pH = 6.0, initial dye concentration = 10 mg L−1). A significant decrease in relative frond number (RFN), a growth rate estimator, observed at a dye concentration of 20 mg L−1 MV indicated some toxicity, which coincided with the plant pigments studies where the chlorophyll a content was lower than the control. There were little differences in the plant pigment contents between the control and those in the presence of dye (5 to 15 mg L−1) indicating the tolerance of AP to MV at lower concentrations. A three-layer ANN model was optimized (6 neurons in the hidden layer) and successfully predicted the phytoextraction of MV (R = 0.9989, RMSE = 0.0098). In conclusion, AP proved to be a suitable plant that could be used for the phytoextraction of MV while the ANN modelling has shown to be a reliable method for the modelling of phytoextraction of MV using AP.

Heavy Metals in Paddy Soils of Brunei Darussalam and Their Relationship with Selected Soil Properties

In Brunei Darussalam, available information of heavy metals in agricultural soils is sparse and hence a baseline study was carried out on soils in rice growing areas. In this study, trace elements as well as common soil characteristics were determined from twenty six of major rice fields such as Wasan, Limau Manis, Selapon and Lot Senkuang. Al, Fe, Mn and Cd were high in these areas however; Cu, Zn, Cr, Co, Ni and Pb were below safety limit of soil while Mn and Cd were above the permissible limit according to the WHO/CCME/European Union guidelines. The variations in metal concentrations in these samples are highly correlated to the acidic condition, organic matter and CEC of the paddy soils. The distributions of Al, Fe, Cu, Mn, Cd, Cr, Co, Pb were high at low pH. Cu, Zn, Cd, Ni and Pb showed positive correlation with organic matter while the quantities of Al, Fe, Mn, Cr and Co were negatively correlated. Correlation analyses showed that the Cd, Zn and Ni were associated with CEC while most of the metals were related to Al and Fe. The soils of the studied areas are extremely acidic with pH 3.0-4.6, and low in cations, CEC and available P, while having a high OM content. Low content of P was due to high amount of Al and Fe in these areas.