Boon Siong Wee

Adhesion of Dust Particles to Common Indoor Surfaces in an Air-Conditioned Environment

Adhesion between dust particles and indoor surfaces can lead to negative effects on human health by triggering allergic and asthmatic reactions. In this study, adhesion forces of indoor office dust and activated carbon (AC, as model soot) particles to four common indoor materials (Al, Cu, PVC, and glass) were measured by colloidal probe atomic force microscopy. Chemical analysis of office dust shows it is largely made up of oxygenated hydrophilic organic carbon material. Both metal surfaces experienced weaker dust and AC adhesion than PVC or glass by up to 2–12 times lower primarily due to the presence of attractive electrostatic forces in the latter two (non-conducting) surfaces. Dust and AC adhesion were also highly sensitive to surface roughness, with an inverse relationship between adhesion force and roughness due to the reduction in contact area between the particle and a rougher material surface. Capillary forces play only a minor or negligible role in dust and AC surface adhesion. Adhesion models utilizing a purely van der Waals approach such as the simple Hamaker model and modified Rumpfs model are insufficient to determine the actual particle-surface contact radii and requires the accounting of non-van der Waals forces to adhesion. Copyright 2014 American Association for Aerosol Research

A NAA collaborative study in white rice performed in seven Asian countries

Since 2000, collaborative studies for applying NAA have been performed through the Forum for Nuclear Cooperation in Asia (FNCA) sponsored by the Japanese Government. White rice is a main food for Asians and thus was selected as a common target sample for a collaborative study in 2008. Seven Asian countries including China, Indonesia, Japan, Korea, Malaysia, Philippines and Thailand, are greatly concerned about the composition of arsenic, heavy metals, and essential trace elements and took part in this study. Rice samples were purchased and prepared by following a protocol that had been proposed for this study. Samples were analyzed by their own NAA systems. In each country, more than 10 elements were examined and the results were compared. These data will be very useful in the monitoring of the levels of food contamination and to evaluate the nutritional status for people living in Asia.

Biomonitoring of Trace Elements Using Epiphytic Lichens Collected in a Suburban Area of Selangor, Malaysia

Lichen samples (Dirinaria sp. and Parmotrema sp.) were collected in a suburban area of Selangor. Their chemical compositions were determined using the instrumental neutron activation analysis (INAA) and 21 elements (Al, As, Ce, Co, Cr, Cs, Eu, Fe, Hf, Hg, K, La, Mn, Na, Rb, Sc, Se, Sm, Th, V and Zn) were reported. Most of the concentrations found in the lichens were similar to those of baseline data from unpolluted areas. Regression analysis found that the elements Al, As, Ce, Cr, Eu, Fe, Hf, La, Mn, Na, Sm, and Th showed statistically significant correlations (p < 0.05) with Sc, which suggests that they were associated with crustal materials. Other elements Co, Cs, Hg, K, Rb, Se, V and Zn showed weak correlations with Sc implied that they were possibly contributed by anthropogenic sources. The enrichment factors of the elements Hg and Se were found to be high signifying that they may be originated from long-range transport from sources. The elements V and Zn were slightly enriched in the lichen samples, which could be due to some anthropogenic inputs. From correlation with Sc and enrichment factors, some constrain on potential elemental pollutants namely Hg, Se, V and Zn that could be due to anthropogenic pollutants could be identified. The use of lichens as biomonitor for trace elements has been able to indicate possible natural and anthropogenic inputs, which could provide information on air pollution in the study area.