Analysis of gaseous polycyclic aromatic hydrocarbon emissions from cooking devices in selected rural and urban kitchens in Bomet and Narok counties of Kenya.

Traditional combustion devices and fuels such as charcoal, wood and biomass, are widely utilised in rural and urban households in Africa. Incomplete combustion can generate air pollutants which are of human toxicological importance, including polycyclic aromatic hydrocarbons (PAHs). In this study, portable multi-channel polydimethylsiloxane rubber traps were used to sample gas phase emissions from cooking devices used in urban and rural households in Bomet and Narok counties of Kenya. A wide range of total PAH concentrations was found in samples collected (0.82 - 173.69 µg/m3), which could be attributed to the differences in fuel type, combustion device, climate, and nature of households. Wood combustion using the 3-stone device had the highest average total PAH concentration of ~71 µg/m3. Narok had higher indoor total gas phase PAH concentrations averaging 35.88 µg/m3 in urban and 70.84 µg/m3 in rural households, compared to Bomet county (2.91 µg/m3 in urban and 9.09 µg/m3 in rural households). Ambient total gas phase PAH concentrations were more similar (Narok: 1.26 - 6.28 µg/m3 and Bomet: 2.44 - 6.30 µg/m3). Although the 3-stone device and burning of wood accounted for higher PAH emissions, the charcoal burning jiko stove produced the highest toxic equivalence quotient. Monitoring of PAHs emitted by these cooking devices and fuels is critical to public health and sustainable pollution mitigation.

Distribution patterns of arsenic species in a lichen biomonitor.

As stand-alone approaches, chromatographic separations of arsenic in lichen using HPLC-ICP-MS or the use of sequential extractions have historically been shown to have low analyte recoveries and poor analyte selectivity respectively. This study modifies the first step of a sequential extraction with a chromatographic separation of five arsenic species using HPLC-ICP-MS, followed by a three-step sequential extraction and analysis with ICP-MS. The method was applied to lichens from a rural and urban site to demonstrate the applicability thereof, and the sum of arsenic concentrations from the extraction steps were compared to the total arsenic concentrations. Short term species stability of the As species in the lichen matrix was also evaluated over 1 month in the water-extractable fraction, where As species concentrations changed week by week, providing insight into biotransformation mechanisms. In the modified extraction step, dimethylarsinic acid (DMA) and arsenobetaine and an unknown As species (AsB + U1) were statistically (p < 0.05) higher in the urban site than the rural site. Analyte recoveries using the combined method were higher than other studies reported in literature, with percentage recoveries of 104% and 111% of As in the urban and rural sites respectively. Arsenic concentrations were found in the following order of abundance at both sites: oxidizable > reducible > water-extractable > residual. Concentrations of total As in the oxidizable and non-bioavailable fraction were statistically lower (p < 0.05) in the rural site than in the urban site. Based upon the information gained from this study, we could draw concise conclusions regarding the source apportionment, timing and the magnitude of the pollution event.

Comparison of sample preparation procedures on metal(loid) fractionation patterns in lichens.

The effects of different sample preparation strategies and storage on metal(loid) fractionation trends in plant material is largely underresearched. In this study, a bulk sample of lichen Parmotrema austrosinense (Zahlbr.) Hale was analysed for its total extractable metal(loid) content by ICP-MS, and was determined to be adequately homogenous (<5% RSD) for most elements. Several subsets of this sample were prepared utilising a range of sample preservation techniques and subjected to a modified sequential extraction procedure or to total metal extraction. Both experiments were repeated after 1-month storage at 4 °C. Cryogenic freezing gave the best reproducibility for total extractable elemental concentrations between months, indicating this to be the most suitable method of sample preparation in such studies. The combined extraction efficiencies were >82% for As, Cu, Mn, Pb, Sr and Zn but poor for other elements, where sample preparation strategies 'no sample preparation' and 'dried in a desiccator' had the best extraction recoveries. Cryogenic freezing procedures had a significantly (p < 0.05) negative effect on metal extractability, and is therefore inappropriate for sequential extraction procedures in lichens. Biotransformation over a period of a month is suspected for most elements, with the exception of Sr and Zn, where changes in the fractionation patterns were statistically significant (p < 0.05), indicating the need for minimal delay in sample cleaning and preservation when species fractionation patterns are of interest. This study also shows that the assumption that species stability can be ensured through cryopreservation and freeze drying techniques needs to be revisited.

Fluorescence detection of pesticides using quantum dot materials - A review.

High pesticide use, especially in agriculture, can lead to environmental pollution and potentially adverse health effects. As result, pesticide residues end up in different media, including water and food products, which may serve as direct routes for human exposure. There is thus a continuous drive to develop analytical methods for screening and quantification of these compounds in the different environmental media in which they may occur. Development of quantum dot (QD) based sensors for monitoring pesticides has gained momentum in recent years. QD materials have excellent and unique optical properties and have high fluorescence quantum yields compared to other fluorophores. They have thus been used in numerous studies for the development of probes for organic pollutants. In this paper we specifically review their application as fluorescence probes for pesticide detection in different media including water and in fruits and vegetables. The low detection limits reported demonstrate the potential use of these methods as alternatives to expensive and time-consuming conventional techniques. We also highlight potential limitations that these probes may present when it comes to routine application. Finally we discuss possible future improvements to enhance the selectivity and robustness of these sensors. We note that there is still a need for researchers to develop standardized QD based sensors which could lead to their commercialization and routine application.

Monitoring of atmospheric gaseous and particulate polycyclic aromatic hydrocarbons in South African platinum mines utilising portable denuder sampling with analysis by thermal desorption-comprehensive gas chromatography-mass spectrometry.

Concentrations of diesel particulate matter and polycyclic aromatic hydrocarbons (PAHs) in platinum mine environments are likely to be higher than in ambient air due to the use of diesel machinery in confined environments. Airborne PAHs may be present in gaseous or particle phases each of which has different human health impacts due to their ultimate fate in the body. Here we report on the simultaneous sampling of both phases of airborne PAHs for the first time in underground platinum mines in South Africa, which was made possible by employing small, portable denuder sampling devices consisting of two polydimethylsiloxane (PDMS) multi-channel traps connected in series separated by a quartz fibre filter, which only require small, battery operated portable personal sampling pumps for air sampling. Thermal desorption coupled with comprehensive gas chromatography-mass spectrometry (TD-GC×GC-TofMS) was used to analyse denuder samples taken in three different platinum mines. The samples from a range of underground environments revealed that PAHs were predominantly found in the gas phase with naphthalene and mono-methylated naphthalene derivatives being detected at the highest concentrations ranging from 0.01 to 18 µg m(-3). The particle bound PAHs were found in the highest concentrations at the idling load haul dump vehicle exhausts with a dominance of fluoranthene and pyrene. Particle associated PAH concentrations ranged from 0.47 to 260 ng m(-3) and included benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene. This work highlights the need to characterise both phases in order to assess occupational exposure to PAHs in this challenging sampling environment.