Radon and its progenies have been ranked second of being responsible for lung cancer in humans. Hong Kong has four major groups of uranium-rich plutonic and volcanic rocks and is suffering from radon emanated therefrom. However, there is a lack of radon potential maps in Hong Kong to resolve the spatial distribution of radonprone areas. A ten-point radon potential system was developed in Germany (2005) to predict radon potential using both the in situ geogenic and geographic parameters under hierarchical ranking. Primarily, the ten-point system requires the desk study of the geological environment of sampling sites, which has an advantage of saving resources and manpower in extensive radon potential mapping over the traditional soil radon concentration sampling method. This paper presents a trial of radon potential mapping in Hong Kong to further verify the system. Despite some slight departures, the system demonstrates an acceptable correlation with soil radon concentrations (R 2 = 0.62-0.66) from 768 samples of mainly intermediate radon potential. Hong Kong has a mean soil radon concentrations of 58.9 kBqm -3 , while the radon potential from the ten-point system achieves an average of 4.93 out of 10 over the territory. The vicinity of fault zone showed high soil radon concentrations and potentials, which were conducive to uranium enrichment and rapid soil-gas diffusion near faults. High uranium-238 content in soil was found to cause high soil radon concentration with a large R 2 , 0.84. The Jurassic granite and volcanic crystal tuff cover more than 85 % of the whole Hong Kong area, and they show relatively high radon concentrations (Geometric mean 83 and 49 kBqm -3 , respectively) which are associated with their high uranium contents (Geometric mean 234 and 197 Bqkg -1 , respectively). While indoor radon concentration is an important factor for radon risk assessment, this study has not considered the correlation between indoor radon concentration and radon potential. The reason is that almost all buildings in Hong Kong are high-rise buildings where indoor radon concentrations are governed only by the radium content in the building materials and the ventilation conditions.

No abstract

<p>Aggregate formation and stabilization depends on the interaction of minerals and soil organic matter (SOM). So far, little is known about the interplay of individual organic matter qualities and soil texture within this process. We developed an experimental set-up to study early soil development and aggregate formation within a controlled lab environment. We designed artificial soil microcosms with different texture, mimicking natural soils, and added organic carbon (OC) derived from particulate organic matter (POM, milled hay litter), dissolved organic matter (DOM, solution derived from hay), and bacterial necromass (<em>Bacillus subtilis</em>). We performed a short-term incubation for 30 days under constant water tension and investigated microbial activity, soil structure development and OC allocation compared to a control that did not receive additional OC input. </p><p>OC input led to the formation of mostly large, water-stable macroaggregates (3000-630 µm) and some small microaggregates (<63 µm) in all microcosms as effect of microbial processing of the added OM. The addition and microbial decay of litter pieces led to physical occlusion of the particles into mainly large (3000-630 µm), OC-rich macroaggregates independent of the texture. The addition of DOM solution also induced the formation of large macroaggregates besides small microaggregates, although the OC input was much lower. Here, the aggregate formation was impaired by higher sand content in the mixtures. The addition of bacterial necromass led to the highest microbial activity, but relatively low aggregate formation, which might be a result of less physically active organic matter nuclei.</p><p>The results show that our experimental design allows to specifically investigate selected process complexes of soil structure formation defined by the addition of OM and soil texture.</p>