Variations in the source, metal content and bioreactivity of technogenic aerosols: a case study from Port Talbot, Wales, UK

https://doi.org/10.1016/j.scitotenv.2004.04.019Get rights and content

Abstract

Atmospheric aerosol samples were collected during different prevailing wind directions from a site located close to a busy motorway, a major steelworks, and the town of Port Talbot (Wales, UK). A high-volume collector was used (1100 l/min), enabling relatively large amounts of particulate matter (PM10–2.5 and PM2.5) samples to be obtained on a polyurethane foam [PUF, H2N–C(O)O–CH2CH3] substrate over periods of 2–7 days. Four samples were chosen to exemplify different particle mixtures: SE- and NE-derived samples for particles moving along and across the motorway, a NW-derived sample from the town, and a mixed SW/SE-derived sample containing a mixture of particles from both steelworks and motorway. The latter sample showed the highest average collection rate (0.9 mg/h, 13 μg/m3) and included a prominent pollution episode when rainy winds were blowing from the direction of the steelworks. Both NW and SE samples were collected under dry conditions and show the same collection rate (0.7 mg/h, 10 μg/m3), whereas the NE sample was collected during wetter weather and shows the lowest rate (0.3 mg/h, 5 μg/m3). Scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis system (EDX) analyses show all samples are dominated by elemental and organic carbon compounds (EOCC) and nitrates, with lesser amounts of sulphates, felsic silicates, chlorides and metals. ICP–MS analyses show the SW/SE sample to be richest in metals, especially Fe, Zn, Ni, and Mn, these being attributed to an origin from the steelworks. The SE sample, blown along the motorway corridor, shows enhanced levels of Pb, V, Ti, As, and Ce, these metals being interpreted as defining a traffic-related chemical fingerprint. The NW sample shows a very low metal content. DNA plasmid assay data on the samples show TM50 values varying from 66 to 175 μg/ml for the adjusted whole sample and 89 to 203 μg/ml for the soluble fraction. The SW/SE-mixed metalliferous sample is the most bioreactive (both whole and soluble) and the soluble fraction of the metal-depleted NW sample is the least bioreactive. The metal content of the aerosol samples, especially soluble metals such as Zn, is suggested to be the primary component responsible for oxidative damage of the DNA, and therefore most implicated in any health effects arising from the inhalation of these particulate cocktails.

Introduction

The link between the amount of respirable particulates and the increase in human mortality and morbidity is now well established, with, for example, an increase of 0.5% in daily mortality having been recorded for each 10 μg/m3 increase in particulate matter (PM10; Brunekreef and Holgate, 2002). Simple correlations between particulate mass and health effects however obscure the complexity of the fact that the air we breathe contains a complex mixture of different chemical elements and compounds from different sources. In populated areas, many of these particles will have a technogenic origin, derived in particular from road traffic and industrial sources. Some of the chemical components in these technogenic aerosols, such as metals and, especially, their soluble fraction, have attracted particular attention for their potential health effects (e.g., Adamson et al., 1999, Adamson et al., 2000, Dye et al., 2001, Ghio and Devlin, 2001). Some aerosol-linked health problems, however, may be due less to specific components than to a “cocktail effect” of different mixtures derived from one or more major sources. Thus, it becomes incumbent upon researchers collecting PM samples to identify the different components present at any given site and to apportion likely sources before possible health effect studies on the aerosols are conducted (e.g., Moreno et al., 2003).

The chemical composition of the PM “air particulate cocktail” (APC) that will enter the lungs will depend on the relative importance of major aerosol contributions, such as traffic, silicate dust, sea salt, sulphates and industrial metal condensates, as well as on the prevailing weather conditions, especially wind speed and direction (Sharan, 1996). With regard to the latter, wind speed and hourly fine PM concentrations have been negatively correlated in both winter and summer, whereas wind speed and coarser particle concentration are positively linked in summer and are negatively correlated in winter Wrobel et al., 2000, Ragosta et al., 2002. The amount of total suspended particles is also closely related to temperature and rainfall, with high temperatures favouring the resuspension of airborne particles and with precipitation inducing a loss of particle mass in the air (Ragosta et al., 2002). Thus, at any given time and place, the amount of PM and its chemical make-up can vary enormously.

The study presented here considers the variations in APC that can occur at a site where the nonanthropogenic PM background from rural and marine sources is strongly contaminated by industrial, urban, and traffic emissions. Aerosol mixtures collected from this site under different weather conditions are then examined for their potential bioreactivity using a plasmid DNA scission assay method.

Section snippets

Site location and meteorology

The site chosen for the study is in the grounds of a small hospital lying between a motorway and a major steelworks at the eastern edge of the coastal town of Port Talbot in South Wales (Fig. 1). More specifically, Groeswen hospital lies just 100 m southwest of the extremely busy London to South Wales M4 motorway, 100 m north of an urban access road to Port Talbot, 800 m northeast of the steel-producing factory, and around 2500 m from the sea. The traffic flow in the immediate surrounding area

Aerosol loading

A total of 69.11 mg of PM10–2.5 and 127.06 mg of PM2.5 were obtained during the four collecting periods over a total of 15 days (Table 1), with the highest aerosol loading per hour being in the mixed steelworks and motorway (SW/SE) sample (0.90 mg/h, 13 μg/m3 in 3 days). Samples from both the SE (motorway) and NW (Port Talbot) quadrants had the same average amount of sample (0.68 mg/h, 10 μg/m3 in 3 and 2 days, respectively), whereas the sample collected from the NE quadrant had the lowest

SE sample: rural motorway corridor

The sample collected while the winds were blowing from the SE is derived primarily from the dust blowing along (and at low angles across) the busy M4 motorway under dry conditions. The motorway runs SE from the site for around 9 km, crossing essentially rural countryside, and there are no “hotspot” pollution point sources nearby. The sample was collected over a 73-h period, during which 49 mg of the sample was obtained at an average rate of 0.7 mg/h (10 μg/m3) and with most (73%) of the sample

Conclusions

The field measurements conducted at the Port Talbot site reveal the kinds of variation in chemistry and bioreactivity of ambient aerosol mixtures that can be expected from sites sourcing different anthropogenic aerosols. The SE “rural motorway corridor” sample is presumably typical of aerosol mixtures present alongside UK motorways outside town or industrial settings when a dry wind is blowing along, or at low angles to, the road. It contrasts with the NW-derived “town” sample in which the

Acknowledgements

The authors would like to thank Martin Hooper, Tony King (Neath Port Talbot County Borough Council and Groeswen Hospital in Port Talbot), Andrew Whittaker and Iain McDonald (Cardiff University) for their help during collection and analysis of the samples, as well as two anonymous referees for their useful comments in improving the text. Finally, we gratefully acknowledge the UK Meteorological Office and DEFRA for providing weather and PMIO mass data during the collection periods for research

Cited by (0)

View full text