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oa Litnet Akademies : 'n Joernaal vir die Geesteswetenskappe, Natuurwetenskappe, Regte en Godsdienswetenskappe - Die risikoprofiel van Pb en Cr in stedelike padstof : natuurwetenskappe

 

Abstract

Verstedeliking en die gepaardgaande groeiende ekologiese voetspoor wat dit agterlaat, is 'n wesenlike probleem wêreldwyd. Dit is dan ook alombekend dat lugbesoedeling as gevolg van verstedeliking en industriële groei nie net eksponensieel toegeneem het oor die afgelope twee dekades nie, maar ook beduidend verskillend is van dit wat mens in die platteland sou aantref. Een van die bydraende faktore tot lugbesoedeling is die herverspreiding van padstof in die lug as gevolg van padverkeer en ander faktore. Dit is spesifiek die mikrongrootte-fraksie wat kommerwekkende afmetings aanneem. Aangesien padstof ryk is aan organiese en anorganiese verbindings wat veral in die fyner fraksies gekonsentreer is, is dit 'n bron van verskeie karsinogeniese en toksiese verbindings met wisselende biobeskikbaarhede en hou dus vir mens en dier gesondheidsgevare in. Verskeie wetenskaplike artikels handel oor die konsentrasies van spoorelemente, toksiese metale en metalloïede in padstof (Hooker en Nathanail 2006), maar daar is weinig oor die molekulêre en strukturele karakter van die verbindings te vinde. In vitro- en diertoksikologiese studies toon juis aan dat die chemiese samestelling van ingeademde deeltjies 'n uiters belangrike rol speel in die toksikologiese, genotoksiese en karsinogeniese meganismes in die liggaam, en dat die komponent-spesifieke toksiese effekte nog nie behoorlik verstaan word nie. Oorgangsmetale wat aan die stofdeeltjies in die lug bind, kan in die liggaam (en veral die longe) lei tot die vervaardiging van reaktiewe suurstofspesies, wat 'n wesenlike kommer is onder die meer kwesbare bevolkingsgroepe, soos kinders, oumense en terminaalsiek pasiënte. Dit is dus duidelik dat die chemiese karakterisering van die fyn fraksie van padsedimente van belang is wat volksgesondheid betref. Tydens 'n vroeëre studie is padsediment in 'n stedelike omgewing in die Verenigde Koninkryk versamel en gedeeltelik gekarakteriseer (Barrett e.a., 2010). Dieselfde monsters, wat ook in verskeie deeltjiegroottes gefraksioneer is, is verder met behulp van X-straal-fluoressensie-spektrometrie (XSFS) en induktief-gekoppelde-plasma-massaspektrometrie (IGP-MS) geanaliseer om die elementele samestelling kwantitatief te bepaal. Deur gebruik te maak van rekenaarbeheerde elektrontastende X-straal-mikroanalise (RB-EXMA) is individuele deeltjies geanaliseer (200 deeltjies per deeltjiegrootte) sodat hulle molekulêre struktuur afgelei kon word van die elementele verwantskappe. Hierdie bevindings is vergelyk met mikro-Raman-spektroskopie- (mRS-) resultate. Die fyn fraksie (<38 µm) het die hoogste Pb- (238 dpm) en Cr- (171 dpm) konsentrasies getoon. Die RB-EXMA-data het aangetoon dat >50% van die Cr-ryke deeltjies verwantskappe met Pb toon. Die mRS-data toon dan ook inderdaad dat die Cr hoofsaaklik teenwoordig is in die Cr(VI)-oksidasie-toestand en meestal as loodchromaat voorkom. Beide Pb- en Cr-konsentrasies neem toe soos die deeltjiegrootte afneem (279 (<38 mm) - 13 dpm (&lt;1mm); 171 (<38 mm) - 91 dpm (<1mm) onderskeidelik). Bo en behalwe die teenwoordigheid van kommerwekkend hoë konsentrasies oksiderende spesies soos Cu, Fe en Mn is die karsinogeniese en toksiese potensiaal van die fyn fraksie, wat as gevolg van verpoeiering en herverspreiding inadembaar is, baie duidelik. In vitro-toetse van hierdie padstoffraksies toon dat die Cr en Pb geredelik gemobiliseer word in kunsmatige longvloeistof en dat tot soveel as 54% Cr en 97% Pb vrygestel word.


Exponential urbanisation and industrial growth occur on a global scale and result in an ecological burden, of which one important part is pollution. It is well known that the extent of air pollution has escalated over the past two decades in several parts of the world, despite mitigating measures and legislation. Current research points to the fact that air pollution in urban and industrial areas is substantially different from that found in rural areas. Road dust (RD) contributes up to 35% of airborne particulate matter due to resuspension thereof, and poses a health concern due to carcinogenic and toxic components potentially present in the micron-sized fractions. Although literature does report on the concentrations of trace, toxic metals and metalloids present in RD (Hooker and Nathanail 2006), the molecular make-up of particulates generated due to the resuspension of the RD is not well documented. In vitro and animal toxicological studies have confirmed that the chemical composition of inhaled particles plays a major role in its toxic, genotoxic and carcinogenic mechanisms, but the component-specific toxic effects are still not understood. Transition metals binding to air particle matter can result in reactive oxygen species in the human body (particularly in the lungs), and this is a significant risk, especially for vulnerable population groups like elderly people, children and terminally ill patients. The characterisation of the molecular composition of the fine fraction is evidently of importance for public health. During an earlier study, road dust from an inner-city environment in the UK was collected and partially characterised (Barrett e.a. 2010). These same-size fractions were analysed for their elemental concentrations, using X-ray Fluorescence Spectrometry (XRFS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). In addition, single-particle analysis was performed on the different fractions by means of Computer Controlled Electron Probe X-ray Micro Analysis (CC-EPXMA) and their molecular structure probed by studying elemental associations. These findings were correlated with Micro Raman Spectroscopy (MRS) results. It was found that the fine fraction (<38 µm) had the highest Pb (238 ppm) and Cr (171 ppm) concentrations. The CC-EPXMA data showed >50% association of Cr-rich particles with Pb and the MRS data showed that the Cr was mostly present as lead chromate and therefore in the Cr(VI) oxidation state. Concentrations of both Pb and Cr decreased substantially (279 (<38 mm) - 13 ppm (&lt;1mm); 171 (<38 mm) - 91 ppm (<1mm) respectively) in the larger fractions. Apart from rather alarmingly high concentrations of oxidative stressors (Cu, Fe, Mn), the carcinogenic and toxic potential of the inhalable fraction is evident. Preliminary bioaccessibility data indicated that both Cr and Pb are readily mobilised in artificial lisosomal liquid and up to 54% of Cr and 97% of Pb was released.

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/content/litnet/9/3/EJC129836
2012-12-01
2016-12-06
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