Increasing Trends of Legacy and Emerging Organic Contaminants in a Dated Sediment Core From East-Africa

Temporal trends of industrial organic contaminants can show how environmental burdens respond to changes in production, regulation, and other anthropogenic and environmental factors. Numerous studies have documented such trends from the Northern Hemisphere, while there is very limited data in the literature from sub-Saharan Africa. We hypothesized that the temporal trends of legacy and contemporary industrial contaminants in sub-Saharan Africa could greatly differ from the regions in which many of these chemicals were initially produced and more extensively used. For this purpose, a dated sediment core covering six decades from a floodplain system in urban Dar es Salaam, Tanzania, was analysed. The samples were analysed for selected legacy persistent organic pollutants (POPs) [polychlorinated biphenyls (PCBs) and polybrominated biphenyl ethers (PBDEs)] and chemicals of emerging concern (CECs) [alternative brominated flame retardants (aBFRs), chlorinated paraffins (CPs), and dechloranes]. All groups of chemicals showed a steep increase in concentrations towards the uppermost sediment layers reflecting the more recent years. Concentrations of the individual compound groups in surface sediment were found in the order CPs >> aBFRs ∼ ∑25PBDEs > dechloranes ∼ ∑32PCBs. Time trends for the individual compounds and compound groups differed, with ∑32PCBs showing presence in sediments since at least the early 1960s, while some CECs first occurred in sediments corresponding to the last decade. Investigations into potential drivers for the observed trends showed that socioeconomic factors related to growth in population, economy, and waste generation have contributed to increasing concentrations of PBDEs, aBFRs, CPs, and Dechlorane Plus. Further monitoring of temporal trends of industrial organic contaminants in urban areas in the Global South is recommended.

The generation and evolutionary study of novel aptamers for environmental contaminants

<p>The contamination of waterways by environmental pollutants is of growing global concern. The bio-accumulative properties of these contaminants suggest long-term impacts on many species, even those not directly exposed. There is ample evidence of the presence of environmental contaminants within biological fluids of humans, but their effects on health are largely unknown. Understanding the extent of this problem is hampered by labour-intensive extraction techniques that require expensive instrumentation and highly specialised technical expertise. Due to the prohibitive nature of routine analysis, the occurrence of many of these compounds in New Zealand waterways is unknown. Thus, a robust, portable and sensitive biosensor is urgently needed to guide regulatory agencies worldwide. Aptamers are single-stranded nucleic acid molecules that can bind to a specific target molecule with high affinity. Whilst the use of aptamers presents a novel technology to monitor small molecule environmental contaminants, the generation of high affinity aptamers has been limited. The objectives of this PhD study were to: (1) measure key emerging organic contaminants (EOC’s) in a selection of New Zealand waterways covering different land-use types; (2) generate and characterise aptamers that bind three key EOC’s, namely glyphosate, nonylphenol and oxybenzone, and; (3) explore the evolutionary pathways that random nucleotide libraries follow when generating aptamers to a small molecule under different stringencies. A novel bioinformatics pipeline for the analysis of high throughput (HT) SELEX data from multiple selection strategies has been developed and implemented. The conventional method of gas chromatography mass spectrometry (GC-MS) was used to analyse water samples from waterways in the North Island of New Zealand. Technical nonylphenol equivalents and oxybenzone were detected above the minimum detection limit (7.5 ng/L and 0.5 ng/L respectively) at all sampled sites. Concentrations of nonylphenol exceeding environmental guidelines were detected in the Waiwhetu Stream, a small stream within an industrial area in Lower Hutt. The pesticide terbuthylazine was detected at all sampled sites with particular high concentrations in the Waiwhetu and Porirua Stream. Carbendazim (a fungicide) and hexazinone (a herbicide) were also highly prevalent being detected at 87.5% and 75% of sites respectively. Glyphosate was detected at 800 ng/L in both the Waiwhetu Stream and the Porirua Stream. In general, contaminant load was much higher in urban areas than rural or forested areas. These results indicate that EOCs are present in NZ waterways and are likely to be having an impact on aquatic species. The selection of aptamers to three key EOC’s was completed using standard (glyphosate and nonylphenol) and high-throughput (HT) (oxybenzone) SELEX methodologies. DNA aptamers for glyphosate and oxybenzone were successfully generated and characterised. The GLY04 (glyphosate) and OXY-ED7-C1 (oxybenzone) aptamers were characterised using micro-scale thermophoresis and exhibited a Kd of 158 and 107.5 nM, respectively. This is the first report of a glyphosate-binding aptamer in the literature. Attempts to generate a DNA aptamer for nonylphenol were unsuccessful. Whilst five aptamer candidates were generated through 20 rounds of selection, they did not show any evidence of binding to the target molecule. A HT-SELEX approach was utilised to study the effect of different selection parameters on the same starting library during the generation of an oxybenzone aptamer. Six strategies, compared to a standard protocol, were assessed including mutation via error-prone PCR, increased washing volume, increased detergent concentration, higher incubation temperature and negative selection and counter selection. Within each strategy, the frequency and enrichment of candidates at each SELEX round was determined using a novel bioinformatics pipeline. On average, higher frequency candidates were present at the end of SELEX within strategies using higher stringency. Higher enrichment was also observed in the strategy using the most stringent conditions. In summary, this PhD study presents a number of novel findings. The wide-scale presence of key EOC’s in New Zealand waterways was determined. The generation of aptamers that bind to glyphosate and oxybenzone with a nanomolar affinity reveals that aptamers can be generated to such small molecules. This study also resulted in the development of a novel bioinformatics pipeline for HT-SELEX analysis that resulted in a number of recommendations on the design of such experiments. The findings presented herein highlight the possibilities and pitfalls of selecting future aptamers for EOC’s and for implementing HT-SELEX experiments.</p>

The generation and evolutionary study of novel aptamers for environmental contaminants

<p>The contamination of waterways by environmental pollutants is of growing global concern. The bio-accumulative properties of these contaminants suggest long-term impacts on many species, even those not directly exposed. There is ample evidence of the presence of environmental contaminants within biological fluids of humans, but their effects on health are largely unknown. Understanding the extent of this problem is hampered by labour-intensive extraction techniques that require expensive instrumentation and highly specialised technical expertise. Due to the prohibitive nature of routine analysis, the occurrence of many of these compounds in New Zealand waterways is unknown. Thus, a robust, portable and sensitive biosensor is urgently needed to guide regulatory agencies worldwide. Aptamers are single-stranded nucleic acid molecules that can bind to a specific target molecule with high affinity. Whilst the use of aptamers presents a novel technology to monitor small molecule environmental contaminants, the generation of high affinity aptamers has been limited. The objectives of this PhD study were to: (1) measure key emerging organic contaminants (EOC’s) in a selection of New Zealand waterways covering different land-use types; (2) generate and characterise aptamers that bind three key EOC’s, namely glyphosate, nonylphenol and oxybenzone, and; (3) explore the evolutionary pathways that random nucleotide libraries follow when generating aptamers to a small molecule under different stringencies. A novel bioinformatics pipeline for the analysis of high throughput (HT) SELEX data from multiple selection strategies has been developed and implemented. The conventional method of gas chromatography mass spectrometry (GC-MS) was used to analyse water samples from waterways in the North Island of New Zealand. Technical nonylphenol equivalents and oxybenzone were detected above the minimum detection limit (7.5 ng/L and 0.5 ng/L respectively) at all sampled sites. Concentrations of nonylphenol exceeding environmental guidelines were detected in the Waiwhetu Stream, a small stream within an industrial area in Lower Hutt. The pesticide terbuthylazine was detected at all sampled sites with particular high concentrations in the Waiwhetu and Porirua Stream. Carbendazim (a fungicide) and hexazinone (a herbicide) were also highly prevalent being detected at 87.5% and 75% of sites respectively. Glyphosate was detected at 800 ng/L in both the Waiwhetu Stream and the Porirua Stream. In general, contaminant load was much higher in urban areas than rural or forested areas. These results indicate that EOCs are present in NZ waterways and are likely to be having an impact on aquatic species. The selection of aptamers to three key EOC’s was completed using standard (glyphosate and nonylphenol) and high-throughput (HT) (oxybenzone) SELEX methodologies. DNA aptamers for glyphosate and oxybenzone were successfully generated and characterised. The GLY04 (glyphosate) and OXY-ED7-C1 (oxybenzone) aptamers were characterised using micro-scale thermophoresis and exhibited a Kd of 158 and 107.5 nM, respectively. This is the first report of a glyphosate-binding aptamer in the literature. Attempts to generate a DNA aptamer for nonylphenol were unsuccessful. Whilst five aptamer candidates were generated through 20 rounds of selection, they did not show any evidence of binding to the target molecule. A HT-SELEX approach was utilised to study the effect of different selection parameters on the same starting library during the generation of an oxybenzone aptamer. Six strategies, compared to a standard protocol, were assessed including mutation via error-prone PCR, increased washing volume, increased detergent concentration, higher incubation temperature and negative selection and counter selection. Within each strategy, the frequency and enrichment of candidates at each SELEX round was determined using a novel bioinformatics pipeline. On average, higher frequency candidates were present at the end of SELEX within strategies using higher stringency. Higher enrichment was also observed in the strategy using the most stringent conditions. In summary, this PhD study presents a number of novel findings. The wide-scale presence of key EOC’s in New Zealand waterways was determined. The generation of aptamers that bind to glyphosate and oxybenzone with a nanomolar affinity reveals that aptamers can be generated to such small molecules. This study also resulted in the development of a novel bioinformatics pipeline for HT-SELEX analysis that resulted in a number of recommendations on the design of such experiments. The findings presented herein highlight the possibilities and pitfalls of selecting future aptamers for EOC’s and for implementing HT-SELEX experiments.</p>

Combined Nanofiltration and Thermocatalysis for the Simultaneous Degradation of Micropollutants, Fouling Mitigation and Water Purification

Due to progressive limitation of access to clean drinkable water, it is nowadays a priority to find an effective method of water purification from those emerging organic contaminants, which might have potentially harmful and irreversible effects on living organisms and environment. This manuscript reports the development of a new strategy for water purification, which combines a novel and recently developed Al2O3-doped silica nanofiltration membrane with a thermocatalytic perovskite, namely cerium-doped strontium ferrate (CSF). The thermocatalytic activity of CSF offers the opportunity to degrade organic pollutants with no light and without input of chemical oxidants, providing simplicity of operation. Moreover, our studies on real samples of secondary effluent from wastewater treatment showed that the thermocatalyst has the ability to degrade also part of the non-toxic organic matter, which allows for reducing the chemical oxygen demand of the retentate and mitigating membrane fouling during filtration. Therefore, the new technology is effective in the production of clean feed and permeate and has a potential to be used in degradation of micropollutants in water treatment.