Short title: Mapping radon variation between and within geological units ABSTRACT Previously, the potential for high radon levels in UK houses has been mapped either on the basis of grouping the results of radon measurements in houses by grid squares or by geological units. In both cases, lognormal modelling of the distribution of radon concentrations was applied to allow the estimated proportion of houses above the UK radon Action Level to be mapped. This paper describes a method of combining the grid square and geological mapping methods to give more accurate maps than either method can provide separately. The land area is first divided up using a combination of bedrock and superficial geological characteristics derived from digital geological map data. Each different combination of geological characteristics may appear at the land surface in many discontinuous locations across the country. HPA has a database of over 430,000 houses in which long-term measurements of radon concentration have been made, and whose locations are accurately known. Each of these measurements is allocated to the appropriate bedrock-superficial geological combination underlying it. Taking each geological combination in turn, the spatial variation of radon potential is mapped, treating the combination as if it was continuous over the land area. All of the maps of radon potential within different geological combinations are then combined to produce a map of variation in radon potential over the whole land surface. IntroductionExposure to radon indoors is the largest contributor to the radiation exposure of the population. It is also a highly variable contributor, the average indoor radon concentration varying by more than an order of magnitude between different areas. In order to prevent members of the public receiving high exposures to radon, it is necessary to identify those areas most at risk of high levels. This allows surveys of radon in existing houses to be directed to those areas where high radon levels are most likely to be found, and also allows building regulations in those areas to be altered to prevent new houses having high radon levels.Maps of indoor radon levels are a convenient method of identifying the areas at risk. Such maps cannot be used to predict the radon level in an individual building, because radon levels can vary widely between apparently identical buildings located on the same geological unit. Maps can, however, give estimates of the mean radon levels in buildings by area. In addition, maps showing the geographical variation in the probability that new or existing buildings will exceed a radon reference level are particularly useful for directing action to prevent excessive exposures to radon. The more accurate the maps are, both in outlining the areas and in estimating the magnitudes, the better authorities and individuals can take appropriate decisions and target funding.Indirect indicators of indoor radon are sometimes used to derive maps of radon prone areas (e.g. Kemski et al 2001; Mikšová and Barnet ...

Endemic goitre has been reported in the climatic Wet Zone of south-west Sri Lanka for the past 50 years, but rarely occurs in the northern Dry Zone. Despite government sponsored iodised salt programmes, endemic goitre is still prevalent. In recent years, it has been suggested that Se deficiency may be an important factor in the onset of goitre and other iodine deficiency disorders (IDD). Prior to the present study,

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The Tundulu and Kangankunde carbonatite complexes in the Chilwa Alkaline Province, Malawi, contain late-stage, apatite-rich lithologies termed quartz-apatite rocks. Apatite in these rocks can reach up to 90 modal% and displays a distinctive texture of turbid cores and euhedral rims. Previous studies of the paragenesis and rare earth element (REE) content of the apatite suggest that heavy REE (HREE)enrichment occurred during the late-stages of crystallization. This is a highly unusual occurrence in intrusions that are otherwise light REE (LREE) enriched. In this contribution, the paragenesis and formation of the quartz-apatite rocks from each intrusion is investigated and re-evaluated, supported by new electron microprobe (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data to better understand the mechanism of HREE enrichment. In contrast to the previous work at Tundulu, we recognize three separate stages of apatite formation, comprising an "original" euhedral apatite, "turbid" apatite, and "overgrowths" of euhedral late apatite. The crystallization of synchysite-(Ce) is interpreted to have occurred subsequent to all phases of apatite crystallization. The REE concentrations and distributions in the different minerals vary, but generally higher REE contents are found in later-stage apatite generations. These generations are also more LREE-enriched, relative to apatite that formed earlier. A similar pattern of increasing LREE-enrichment and increased REE concentrations toward later stages of the paragenetic sequence is observed at Kangankunde, where two generations of apatite are observed, the second showing higher REE concentrations, and relatively higher LREE contents. The changing REE distribution in the apatite, from early to late in the paragenetic sequence, is interpreted to be caused by a combination of dissolution-reprecipitation of the original apatite and the preferential transport of the LREE complexes by F-and Cl-bearing hydrothermal fluids. Successive pulses of these fluids transport the LREE out of the original apatite, preferentially re-precipitating it on the rim. Some LREE remained in solution, precipitating later in the paragenetic sequence, as synchysite-(Ce). The presence of F is supported by the F content of the apatites, and presence of REEfluorcarbonates. Cl is not detected in the apatite structure, but the role of Cl is suggested from comparison with apatite dissolution experiments, where CaCl 2 or NaCl cause the reprecipitation of apatite without associated monazite. This study implies that, despite the typically LREE enriched nature of carbonatites, significant degrees of hydrothermal alteration can lead to certain phases becoming residually enriched in the HREE. Although at Tundulu the LREE-bearing products are re-precipitated relatively close to the REE source, it is possible that extensive hydrothermal activity in other carbonatite complexes could lead to significant, late-stage fractionation of the REE and the formation of HREE minerals.

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Rice paddy fields in the Naboc area, near Monkayo on the island of Mindanao, Philippines, have been irrigated four times a year over the last decade using Naboc River water contaminated with kg of fish (220 µg MeHg) and 100g of mussels (50 µg MeHg) from the Naboc River, would total 285 µg MeHg (equivalent to 4.75 µg/kg bw for a 60 kg adult), which is nearly three times the JECFA PTWI of 1.6 µg/kg bw. This will significantly contribute to the population mercury exposure and might explain why 38% of the local inhabitants were classified as Hg intoxicated during a mercury toxicity assessment (Drasch et al., 2001).

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