Comprehensive two-dimensional chromatographic techniques for ultra-trace quantitative analysis of chlorinated dioxins in South Africa

Abstract

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are toxic environmental pollutants formed as by-products of industrial and thermal processes. They are chlorinated compounds that have similar structures and chemical properties that were included in the original United Nations Environment Programme’s ‘dirty dozen’ and now form part of the Stockholm Convention (SC) on Persistent Organic Pollutants (POPs). As a signatory to the Stockholm Convention, South Africa has the obligation to undertake appropriate research, monitoring, and cooperation pertaining to POPs, and more particularly, PCDD/Fs. Currently there is no established PCDD/F laboratory in South Africa capable of these demanding measurements and alternative approaches must be considered that are more affordable, more robust and more user friendly for a developing economy. PCDD/Fs are highly toxic, causing a myriad of negative human health effects such as chloracne, carcinogenicity, hepatotoxicity, teratogenicity, endocrine disruption and alterations in neural development. The toxicity of PCDD/Fs is mediated through the aryl hydrocarbon receptor (AhR). PCDD/Fs bind to the AhR and elicit an AhR-mediated biochemical and toxic response. The in-depth information available on the mechanism of toxicity also allows for PCDD/Fs to be analysed using the AhR receptor mediated response in genetically modified cell lines. This led to the development of a bio-analytical screening technique using in vitro H4IIE-luc reporter gene bio-assay for AhR active compounds for the initial screening of PCDD/Fs in soil and sediment. The intension in this study was to develop an integrated approach to the analysis of PCDD/Fs in the South African environment, considering the associated cost as well as the available instrumentation, expertise and relevance within a developing economy. Historically, the quantitative confirmatory analysis of these compounds has been achieved by targeted analysis using gas chromatography coupled with high-resolution magnetic sector mass spectrometry instruments (GC-HRMS), the accepted benchmark technology used for determining the level of trace organic environmental contaminants such as PCDD/Fs. However, these methods are time consuming and expensive. Advances in technology have led to comprehensive two-dimensional gas chromatography - time-of-flight mass spectrometry (GC×GC-TOFMS) methodology that can be used for the analysis of PCDD/Fs in samples with different matrices. This approach is well suited for application in developing economies where access to GC-HRMS and highly skilled personnel is limited. This thesis describes the bio-analytical technique and the method development and analysis of the seventeen toxic PCDD/F congeners using GC×GC-TOFMS methodology. The technique provides the selectivity (added peak capacity of GC×GC) and the sensitivity (focusing effect of the modulator) needed to meet the requirements as mandated for analysis in US EPA Method 1613B. Extracted samples analysed on a GC-HRMS instrument, were re-analyzed using the low-resolution GC×GC-TOFMS instrument and the results confirmed using a high resolution TOF mass spectrometer (HRT). The quantitative results obtained compare well with those obtained using GC-HRMS. Because GC×GC-TOFMS is not a target compound analytical technique (as is GC-HRMS), it is possible to obtain information on numerous other classes of organic pollutants present in the samples in one analytical run, although this information can be sample clean-up dependant. Preliminary validation of the GC×GC-TOFMS method is investigated using a certified reference material and real South African soil samples. The South African soil samples studied showed extremely high levels of PAHs, aliphatic hydrocarbons and sulphur. The organic content and matrix interference of South African soil samples (and the NIST standard reference material sediment; SRM 1944) provided significant challenges for the validation study. This study has shown that GC×GC-TOFMS provides a quick, convenient screen for numerous pollutant classes which may be present in environmental samples. Retrospective data mining of archived data (extraction dependant) is possible and has provided key information on other chlorinated and brominated contaminants present in South African waste, soil and sediment samples. NMISA now has a viable GC×GC-TOFMS dioxin analytical method for low level (ultra-trace) quantitative screening of chlorinated compounds that can be offered to South African analytical laboratories for routine dioxin analysis. The work is relevant scientifically and is a definitive contribution to the growing compilation of GC×GC methodology, providing efficient methods for this demanding environmental application.