Time activity modelling of domestic exposures to radon

Radon gas occurs naturally in the environment with a variable distribution. In some areas radon concentrates sufficiently within the built environment that it is considered as a public health risk. It is possible, successfully, to reduce radon levels in the built environment, and it has been shown that such remediation programmes can be justified in terms of the costs and benefits accruing. However, the estimated dose received by people in their homes depends on the time spent indoors. The research presented here uses data derived from time activity surveys in Northamptonshire, together with radon data from a representative home, to model potential exposures for different population sub-groups. Average home occupancy ranged from 14.8h (probable error 2.5h) for students to 17.7 (3.1) h for adults; schoolchildren spent an average of 14.9 (1.2) h at home. Over a quarter of adults, however, were in the home for 22 h on more. These differences in occupancy patterns lead to substantial differences in radon exposure. In a home with an average hourly ground floor radon concentration of 467 Bqm(-3), modelled hourly average exposures ranged from ca. 250 Bqm(-3) for students and school children, to over 340 Bqm(-3), for women based at home. Modelled exposures show a non-linear association with total time spent at home, suggesting that exposure estimates based on linear models may provide misleading estimates of health risks from radon and the potential benefits of radon remediation. Highest hourly exposures are likely to be experienced by people with highly occupancy, living in single-storey, ground floor accommodation (for example, the elderly the infirm and non-working young mothers). Since these may be least aware of radon risks, and least able to take up remediation measures, they should be specifically targeted for radon monitoring and for assistance in remediation schemes.     

14C and delta13C characteristics of organic matter and carbonate in saltmarsh sediments from south west Scotland

The distribution of contaminant radionuclides from the Sellafield nuclear fuel reprocessing plant was used to establish chronologies for three saltmarsh sediment cores from south west Scotland. delta(13)C and (14)C analyses indicated that the cores provided a useful archive record of variations in input of organic matter and carbonate. The results imply that prior to major releases of contaminant (14)C from Sellafield, the (14)C specific activity of organic matter in Irish Sea offshore sediments was about 24 Bq kg(-1) C, while that of the carbonate component was below the limit of detection. These results provide baseline data for modelling the uptake of contaminant (14)C by the Irish Sea sediment system. The study confirmed that small(13)C analyses provide a sensitive means of apportioning the origin of saltmarsh organic matter between C(3) terrigenous plants, C(4) terrigenous plants and suspended particulate marine organic matter. For the <2 mm fraction of sediment, a clear pattern of decreasing marine organic input was observed in response to increasing elevation of the marsh surface as a result of sediment accumulation. Bulk sediment, including detrital vegetation, had a dominant input from terrigenous plants. The combined use of delta(13)C and (14)C data revealed that organic matter in the marine organic component of the <2 mm fraction of contemporary surface sediments of the saltmarshes is dominated by recycled old organic material.     

Performance Assessment of Rain Gardens1

Abstract: The most widely used approach for evaluating the performance of stormwater best management practices (BMPs) such as rain gardens is monitoring, but this approach can involve a long time period to observe a sufficient number and variety of storm events, a high level of effort, and unavoidable uncertainty. In this paper, we describe the development and evaluation of three approaches for performance assessment of rain gardens: visual inspection, infiltration rate testing, and synthetic drawdown testing. Twelve rain gardens in Minnesota underwent visual inspection, with four determined to be nonfunctional based on one or more of the following criteria: (1) presence of ponded water, (2) presence of hydric soils, (3) presence of emergent (wetland) vegetation, and (4) failing vegetation. It is believed that these rain gardens failed due to a lack of maintenance. For the remaining eight rain gardens, an infiltrometer was used to determine the saturated hydraulic conductivity (K_sat) of the soil surface at several locations throughout each basin in what is termed infiltration rate testing. The median K_sat values for the rain gardens ranged from 3 to 72 cm/h. Synthetic drawdown testing was performed on three rain gardens by filling the basins with water to capacity where possible and recording water level over time. The observed drain times for two of those rain gardens were in good agreement with predictions based on the median of the infiltrometer measurements. The observed drain time for the third rain garden was much greater than predicted due to the presence of a restrictive soil layer beneath the topsoil. The assessment approaches developed in this research should prove useful for determining whether the construction of the rain garden was performed properly, a rain garden is functioning properly, and for developing maintenance tasks and schedules.     

Effects of Traffic Management and Transport Mode on the Exposure of Schoolchildren to Carbon Monoxide

The exposure to CO of schoolchildren was assessed in the town of Northampton, UK, both by direct measurement and by GIS-based activity modelling. Personal measurement of CO showed that exposures when travelling by car were significantly greater than those when walking, although journey times by car were shorter. However, journey exposures had little effect on maximum 8h mean CO exposures. CO concentration fields in the study area were modelled from current traffic flows, and those expected under different traffic management scenarios. These fields were then used, in combination with children's home and school location, and their activity profiles, to simulate frequency distributions of exposure for different transport modes and traffic management scenarios. The results show a large variability in the effect of traffic management interventions, depending on the child's home and school location.     

Effects of travel mode on exposures to particulate air pollution

Monitoring was carried out of particulate concentrations whilst simultaneously walking and driving 48 routes in London, UK. Monitoring was undertaken during May and June 2005. Route lengths ranged from 601 to 1351 m, and most routes were travelled in both directions. Individual journey times ranged from 1.5 to 15 min by car (average 3.7 min) and 7.3 to 30 min (average 12.8 min) whilst walking; car trips were therefore repeated up to 5 times for each single walking trip and the results averaged for the route. Car trips were made with windows closed and the ventilation system on a moderate setting. Results show that mean exposures while walking are greatly in excess of those while driving, by a factor 4.7 for the coarse particle mass (PM10-PM2.5), 2.2 for the fine particle mass (PM2.5-PM1), 1.9 for the very fine particle mass (相似文献   

Improving suspended sediment measurements by automatic samplers

Suspended solids either as total suspended solids (TSS) or suspended sediment concentration (SSC) is an integral particulate water quality parameter that is important in assessing particle-bound contaminants. At present, nearly all stormwater runoff quality monitoring is performed with automatic samplers in which the sampling intake is typically installed at the bottom of a storm sewer or channel. This method of sampling often results in a less accurate measurement of suspended sediment and associated pollutants due to the vertical variation in particle concentration caused by particle settling. In this study, the inaccuracies associated with sampling by conventional intakes for automatic samplers have been verified by testing with known suspended sediment concentrations and known particle sizes ranging from approximately 20 μm to 355 μm under various flow rates. Experimental results show that, for samples collected at a typical automatic sampler intake position, the ratio of sampled to feed suspended sediment concentration is up to 6600% without an intake strainer and up to 300% with a strainer. When the sampling intake is modified with multiple sampling tubes and fitted with a wing to provide lift (winged arm sampler intake), the accuracy of sampling improves substantially. With this modification, the differences between sampled and feed suspended sediment concentration were more consistent and the sampled to feed concentration ratio was accurate to within 10% for particle sizes up to 250 μm.