P. A. Keitch

Corona ions from powerlines and increased exposure to pollutant aerosols

PURPOSE To investigate corona ions emitted from high-voltage powerlines and assess their effects on exposure to environmental pollutant aerosols. MATERIALS AND METHODS The charge density of ions in air required to produce a given change in the observed DC field at ground level was calculated. A DC field mill meter was used to map the DC fields near 132, 275 and 400 kV powerlines. RESULTS The Earths natural DC field of around approximately 100 Vm(-1) was significantly modified near powerlines in 8 out of 14 cases. Typically, downwind of the powerlines the field direction was reversed giving values to -340 V m(-1). In one case, the effect extended more than 500 m from a 275 kV line. DISCUSSION These results can be analysed in terms of the charge density present. This analysis suggests that typically 2000 excess negative charges per cm3 are required to match the measured DC fields. Such space charge will result in unipolar aerosol charging in excess of the normal bipolar steady state charge distribution of pollutant aerosols. This may lead to increased lung deposition on inhalation.

Increased exposure to pollutant aerosols under high voltage power lines

PURPOSE To assess increased exposure to airborne pollutants near power lines by investigating theoretically and experimentally the behaviour of 222Rn decay product marker aerosols in the 50 Hz electric field under power lines. MATERIALS AND METHODS The behaviour of aerosols in outdoor air including those carrying 222Rn decay products was modelled theoretically in the presence of an AC field. TASTRAK alpha-particle spectroscopy was used to characterize 218Po and 214Po aerosols outdoors. Sampling points were chosen along a line at right angles up to 200 m from a number of high voltage power (transmission) lines. Each sampling point comprised an arrangement of mutually orthogonal TASTRAK detectors. Exposures were carried out at different power line locations in various weather conditions. RESULTS The model predicts a two- to three-fold increase in deposition of aerosols on spherical surfaces mimicking the human head under high voltage power lines. Experimental measurements using detectors mounted on grounded metal spheres showed an enhanced deposition of both 218Po and 214Po aerosols. Enhanced 218Po deposition on 400 kV lines ranged from 1.96+/-0.15 to 2.86+/-0.32. Enhanced 214Po deposition on 275 kV and 132 kV lines were 1.43+/-0.07 and 1.11+/-0.21, respectively, where the latter value was not significant. CONCLUSIONS The observations demonstrate a mode of increased exposure to pollutant aerosols under high voltage power lines by increased deposition on the body. The total (indoor + outdoor) 218Po and 214Po dose to the basal layer of facial skin is estimated to be increased by between 1.2 and 2.0 for 10% of time spent outdoors under high voltage power lines.

Fat Cells in Red Bone Marrow of Human Rib: Their Size and Spatial Distribution with Respect to the Radon-derived Dose to the Haemopoietic Tissue

Samples of human rib were collected at autopsy and 20 were selected for marrow fat cell measurement, representing an age range of 16-96 years. The mean diameter of fat cells in red bone marrow of human rib was found to increase from around 48 microns at ages 16-29 years to around 65 microns at ages 82-96 years. There was a greater number of fat cells of smaller size range in younger ages compared with that in older ones. The maximum size of fat cells was found to be 102 microns. Calculated radon-derived doses to haemopoietic tissue ranged from 60 to 162 microSv y-1 at average UK exposures of 20 Bq m-3. It was concluded that the bone marrow fat fraction is the important parameter as far as alpha-radiation dose from radon in fat is concerned. This updates the theoretical estimates of dose carried out by Richardson et al. (1991).

Modification of atmospheric DC fields by space charge from high-voltage power lines

Abstract Corona ion discharge is responsible for a flux of small ions emanating from an overhead power line capable of modifying the ambient electrical environment. The ensuing space charge can be detected as a change in magnitude of the earths natural DC electric field at ground level. DC field mill meters were used to measure the vertical component of electric fields upwind and downwind of 132 and 400 kV power lines. Evidence of space charge blowing downwind of power lines was observed in 21 out of 22 cases. Time series measurements recorded in the downwind direction were highly variable with fields of higher magnitude compared to those recorded upwind. Model DC field profiles were used to estimate a lower limit to the space charge density at body height arising from power lines. The average lower limit was ∼3000 cm −3 excess unipolar charges. The result suggests that between 10% and 60% of outdoor aerosols gain excess charge by the attachment of corona ions. Downwind of a 400 kV line in Somerset that was prone to excessive corona discharge, the estimated mean lower limit excess unipolar space charge density was ∼6000 cm −3 , suggesting that up to 100% of aerosols gain excess charge by the attachment of corona ions. Investigations into the time variation of DC electric fields around motorways and the natural diurnal variation of the earths DC field were also undertaken and compared to the power line data. The results show that the power line time series are clearly distinguishable from typical examples of both types of field variation, demonstrating the relatively highly charged atmospheres that generally exist around high-voltage power lines. The results are of potential public health concern, because they suggest a degree of aerosol charging that may result in a non-trivial increase in lung deposition of inhaled pollutant aerosols.

Spatial distribution of naturally occurring 210Po and 226Ra in children's teeth

Deciduous and permanent teeth extracted from juveniles for orthodontic purposes have been analysed using alpha-sensitive plastic track detectors for the spatial distribution of total alpha-activity and naturally occurring 210Pb-supported 210Po and 226Ra. The distribution of these radionuclides is non-uniform, with 210Po being primarily associated with outer enamel and 226Ra with the pulp. The observations suggest that 210Pb/210Po concentrates at the interface of enamel with saliva or blood, by means of unidirectional ionic exchange with calcium. In contrast, 226Ra concentrates in the predentine band at the interface with pulp and with systemic blood circulation, where its uptake is permitted by the incomplete calcification in this band. Activity concentration was measured in 900 teeth. Total concentration on the outer enamel surface of deciduous teeth, permanent teeth from children < or = 10 years and permanent teeth from children > 10 years give respective mean values of 8.63 +/- 0.26, 5.76 +/- 0.48 and 7.00 +/- 0.15 Bq kg-1. 226Ra concentration on the corresponding longitudinal sections comprising pulp, dentine and annular enamel give respective mean values of 0.715 +/- 0.055, 0.418 +/- 0.083 and 0.514 +/- 0.029 Bq kg-1. Mean activity concentration in 32 foetal teeth was 2.05 +/- 0.31 Bq kg-1. The results form the basis of more detailed studies of (1) age-dependent uptake of alpha-radionuclides in teeth and their microdistribution, and (2) the geographical variation in activity concentration with respect to environmental factors such as domestic radon exposure.

Small-ion and nano-aerosol production during candle burning: Size distribution and concentration profile with time

The characteristics of small-ions and aerosols in the diameter range 0.4 nm to 1.1 μm, produced during burning of paraffin wax tea-light candles, were investigated using a custom-built aspiration condenser ion mobility spectrometer (ACIMS) and a sequential mobility particle sizer and counter (SMPS+C) system. Peaks in the number concentration were observed at diameters 10–30 nm and 100–300 nm, consistent with “normal” and “sooting” burn modes. In addition, a smaller mode in the size range 2.5–9 nm was observed, interpreted as a soot-precursor species. When a fan was placed behind the burning candle a “modified small-ion” signal was seen at sizes 1.1–2.0 nm. This was not observed without the fan present or when a lamp chimney was used. During burning, aerosol concentration was elevated and small-ion counts were low. However after extinction of the flame, this trend was reversed and the number of small-ions increased to levels higher than those observed prior to burning, remaining so for several hours.

Morphological features of the microdistribution of naturally occurring 210Pb/210Po and 226Ra in the teeth of children and juveniles

Purpose: To examine the microdistribution of natural α‐radioactivity in deciduous teeth of children and the permanent teeth of juveniles extracted for orthodontic purpose from across the UK. Materials and methods: The microdistribution of 210Pb‐supported 210Po and 226Ra in 708 deciduous and permanent teeth and 32 foetal teeth was measured on 1442 TASTRAK α‐particle track detectors. Results: Of the various findings, a number are of special interest. Around half of the 210Pb activity in the outer enamel of deciduous teeth appears to have been acquired in utero as a result of transplacental transfer. In deciduous and permanent teeth, 226Ra is concentrated mainly in the circumpulpal region, while the highest levels of 210Po are on the highly calcified outer enamel surface. Furthermore, activity concentrations recorded on this surface were ln‐normally distributed. Conclusions: 210Pb‐supported 210Po activity on the outer enamel surface of permanent teeth constitutes an assay of cumulative environmental exposure with which to assess exposure in bone, both in utero and in childhood. Such assessment can be used to study geographical variations in the α‐activity in teeth. More work is also required to determine the concentrations of both 210Po and 210Pb in the foetal skeleton.

Aspects of the geographical variations of naturally occurring 210Pb/210Po in permanent teeth of juveniles in the UK.

Purpose: To study geographical variations in the level of naturally occurring 210Pb‐supported 210Po in permanent teeth of juveniles in the UK. Materials and methods: Permanent teeth extracted from 278 juveniles for orthodontic purposes were obtained from 48 counties in the UK. 210Po activity concentration was measured on the outer enamel surface using TASTRAK α‐particle‐sensitive plastic track detectors. Results: Geometric mean±SE activity concentrations in teeth from urban, suburban and rural areas, excluding the high radon area of Devon, were 8.41 +0.25/−0.24, 7.76 +0.37/−0.35 and 7.20 +0.49/−0.46 Bq kg−1, respectively. Overall, there was no significant association between α‐activity on the outer enamel surface of permanent teeth and proximity to the major UK motorways. However, when the data were considered with respect to the prevailing south‐westerly wind on the western side of the UK, a statistically significant association with respect to donors living downwind (on the easterly side) of the motorways was found. This effect was greater for sections of the M5 and M6 motorways that traverse urban areas. 210Po levels in teeth were also associated with domestic radon concentration. This effect was comparable with that from traffic and urban pollution. Conclusions: Higher levels of 210Pb‐supported 210Po are seen in permanent teeth of juveniles near sources of increased exposure in the UK. Inhalation uptake is an important pathway of exposure, especially with respect to domestic radon exposure. The results might be important in assessing integrated exposure to 210Po in the skeleton and consequent high linear energy transfer dose to bone marrow.

A UK national survey of radon in domestic water supplies

Radon in domestic water supplies has been monitored by 504 schools throughout the UK. The results show that the levels of radon in drinking water are well below the threshold value of 100 Bq l-1, but vary significantly from county to county.