title: Aspects of the chemistry of lead in multiphase soil model systems and the environment

authors: Raksasataya, Mathya

abstract: Synthetic model soils were used to evaluate redistribution of Pb in both the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Programme) (1993) and the commonly-applied procedure of Tessier et al. (1979). Redistribution of Pb in both schemes was found to be substantial, sufficient to render meaningless any attempts to quantify the original phase associations of Pb in cases where these are not known. In the model systems, the manganese oxide (hausmannite) and humic acid phases were found to be responsible for most of this redistribution in both schemes. Despite the fact that both schemes allow severe Pb redistribution to occur, differences are apparent in the manner in which this occurs. Whereas Tessier et al.’s procedure in all cases yielded the highest recovery of Pb at the reducing step, the three-stage BCR procedure released the most Pb at the oxidizing step, in both cases irrespective of where it originated. These differences are attributable to a combination of high temperature (96 °C) and the presence of 25% v/v acetic acid in Tessier et al.’s reducing step. These conditions were found to reduce the sorptive capacity of humic acid by more than 50%, in addition to retaining more of the Pb in solution by complexation with acetate ions.

Extensive redistribution in the three-stage BCR procedure was also observed in systems where natural soils were mixed with Pb-spiked synthetic phases. In keeping with the results relating to synthetic soil models, the organic matter and Fe/ Mn oxide fractions of the natural soils appear to dominate the redistribution of Pb during the extraction. 

Two approaches were tested in terms of their ability to counteract the redistribution of Pb. Each approach was applied to the first extraction step of the BCR scheme, which underwent a range of modifications. These involved the use of 6 distinct solid sequestering materials, and 5 dissolved complexing agents. The most promising of all the approaches are those which involve the two soluble structurally-distinct complexing agents cryptand 2.2.2 (a macrobicyclic ligand) and nitrilotriacetic acid (NT A). The addition of each ligand generally improved the percentages of Pb recovered from the multi-phase model soils, with Pb originally spiked on calcite. However, the effectiveness of the cryptand and NTA at inhibiting redistribution (at concentrations of 9 x 10⁻³ and 1 x 10⁻⁴ M, respectively) was dependent on the percentages (by weight) of the hausmannite and humic acid in each model system. In the presence of no more than 2% hausmannite, both cryptand and NTA could satisfactorily recover about 60% of the Pb, provided that the percentages of humic acid in the systems were not higher than 10% and 5%, respectively.

The preliminary criteria for selecting a potentially useful soluble complexing agent suggested by the results of this study are that the ligand possess (a) a high stability constant for the ion involved, and (b) a semi-encapsulated metal binding site (which appears to inhibit direct surface extraction from occurring). It is desirable in the case of Pb to decrease the extraction time of the first step in the BCR scheme to minimize opportunity for redistribution. 

The modified extraction solution using the cryptand successfully recovered Pb from a mixture of Pb-spiked calcite and a “clean” natural soil. However, when applied to contaminated roadside soil and dust samples (in the absence of a spiked phase), the modified extraction solution did not significantly alter the recovery pattern of Pb, relative to the conventional extraction solution. This result may reflect the natural distribution of Pb in these samples. 

Four parks in the City of Hamilton were selected as monitoring sites for assessment of levels of Pb in roadside soil and street dust during the removal of leaded-petrol from the New Zealand market. Samples were collected every 2 - 3 months during November 1995 to September 1996. The mean concentrations of Pb in top 2 cm kerbside soil from all the parks reveal a slight downward trend (statistically significant in three parks) whereas those of the fine and coarse fractions of kerbside dust were oscillating.

text: Aspects of the chemistry of lead in multiphase soil model systems and the environment Synthetic model soils were used to evaluate redistribution of Pb in both the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Programme) (1993) and the commonly-applied procedure of Tessier et al. (1979). Redistribution of Pb in both schemes was found to be substantial, sufficient to render meaningless any attempts to quantify the original phase associations of Pb in cases where these are not known. In the model systems, the manganese oxide (hausmannite) and humic acid phases were found to be responsible for most of this redistribution in both schemes. Despite the fact that both schemes allow severe Pb redistribution to occur, differences are apparent in the manner in which this occurs. Whereas Tessier et al.’s procedure in all cases yielded the highest recovery of Pb at the reducing step, the three-stage BCR procedure released the most Pb at the oxidizing step, in both cases irrespective of where it originated. These differences are attributable to a combination of high temperature (96 °C) and the presence of 25% v/v acetic acid in Tessier et al.’s reducing step. These conditions were found to reduce the sorptive capacity of humic acid by more than 50%, in addition to retaining more of the Pb in solution by complexation with acetate ions.

Extensive redistribution in the three-stage BCR procedure was also observed in systems where natural soils were mixed with Pb-spiked synthetic phases. In keeping with the results relating to synthetic soil models, the organic matter and Fe/ Mn oxide fractions of the natural soils appear to dominate the redistribution of Pb during the extraction. 

Two approaches were tested in terms of their ability to counteract the redistribution of Pb. Each approach was applied to the first extraction step of the BCR scheme, which underwent a range of modifications. These involved the use of 6 distinct solid sequestering materials, and 5 dissolved complexing agents. The most promising of all the approaches are those which involve the two soluble structurally-distinct complexing agents cryptand 2.2.2 (a macrobicyclic ligand) and nitrilotriacetic acid (NT A). The addition of each ligand generally improved the percentages of Pb recovered from the multi-phase model soils, with Pb originally spiked on calcite. However, the effectiveness of the cryptand and NTA at inhibiting redistribution (at concentrations of 9 x 10⁻³ and 1 x 10⁻⁴ M, respectively) was dependent on the percentages (by weight) of the hausmannite and humic acid in each model system. In the presence of no more than 2% hausmannite, both cryptand and NTA could satisfactorily recover about 60% of the Pb, provided that the percentages of humic acid in the systems were not higher than 10% and 5%, respectively.

The preliminary criteria for selecting a potentially useful soluble complexing agent suggested by the results of this study are that the ligand possess (a) a high stability constant for the ion involved, and (b) a semi-encapsulated metal binding site (which appears to inhibit direct surface extraction from occurring). It is desirable in the case of Pb to decrease the extraction time of the first step in the BCR scheme to minimize opportunity for redistribution. 

The modified extraction solution using the cryptand successfully recovered Pb from a mixture of Pb-spiked calcite and a “clean” natural soil. However, when applied to contaminated roadside soil and dust samples (in the absence of a spiked phase), the modified extraction solution did not significantly alter the recovery pattern of Pb, relative to the conventional extraction solution. This result may reflect the natural distribution of Pb in these samples. 

Four parks in the City of Hamilton were selected as monitoring sites for assessment of levels of Pb in roadside soil and street dust during the removal of leaded-petrol from the New Zealand market. Samples were collected every 2 - 3 months during November 1995 to September 1996. The mean concentrations of Pb in top 2 cm kerbside soil from all the parks reveal a slight downward trend (statistically significant in three parks) whereas those of the fine and coarse fractions of kerbside dust were oscillating.

year: 1998

title: Advanced adaptive classifier methods for data streams

authors: Gunasekara, Nuwan Amila

subjects: Stream learning

abstract: The exponential growth of the internet has resulted in an overwhelming influx of big data. However, traditional batch learning models face significant obstacles in effectively learning from these vast and constantly evolving data streams and generating up-to-date outcomes. To overcome these limitations, Stream Learning (SL) has emerged as a promising solution that enables continuous learning from evolving data streams and adapts to changes in input distributions.

This thesis focuses on the classification task of SL, specifically investigating streaming gradient-boosted trees and Neural Network (NN)s. Firstly, we introduce Streaming Gradient Boosted Trees (SGBT), a novel gradient-boosted method designed explicitly for SL classification. Next, we propose Continuously Adaptive Neural Networks for Data Streams (CAND), an architecture-agnostic NN approach for evolving data stream classification. Both SGBT and CAND outperform current state-of-the-art bagging and random forest-based SL methods, demonstrating their superiority in handling evolving data stream classification tasks.

Online Continual Learning (OCL) addresses the issue where NN learning from an evolving data stream forgets its past knowledge when confronted with a distribution shift. Online Domain Incremental Continual Learning (ODICL) is a specific variant of OCL where the input data distribution changes from one task to another. We propose two innovative methods: Online Domain Incremental Pool (ODIP) and Online Domain Incremental Networks (ODIN), for ODICL. The proposed methods leverage existing well-researched SL techniques described in Online Streaming Continual Learning (OSCL). ODIP and ODIN outperform current regularization methods without needing a replay buffer. ODIN achieves competitive results compared to replay-based methods. Both methods are ideal candidates for privacy-concerned ODICL scenarios, offering alternatives to regularization-based approaches.

Overall, this thesis explores advancements in SL classification and ODICL, presenting novel techniques that surpass existing approaches in their respective domains. These contributions have significant implications for addressing the challenges posed by evolving data streams in the era of big data.

text: Advanced adaptive classifier methods for data streams The exponential growth of the internet has resulted in an overwhelming influx of big data. However, traditional batch learning models face significant obstacles in effectively learning from these vast and constantly evolving data streams and generating up-to-date outcomes. To overcome these limitations, Stream Learning (SL) has emerged as a promising solution that enables continuous learning from evolving data streams and adapts to changes in input distributions.

This thesis focuses on the classification task of SL, specifically investigating streaming gradient-boosted trees and Neural Network (NN)s. Firstly, we introduce Streaming Gradient Boosted Trees (SGBT), a novel gradient-boosted method designed explicitly for SL classification. Next, we propose Continuously Adaptive Neural Networks for Data Streams (CAND), an architecture-agnostic NN approach for evolving data stream classification. Both SGBT and CAND outperform current state-of-the-art bagging and random forest-based SL methods, demonstrating their superiority in handling evolving data stream classification tasks.

Online Continual Learning (OCL) addresses the issue where NN learning from an evolving data stream forgets its past knowledge when confronted with a distribution shift. Online Domain Incremental Continual Learning (ODICL) is a specific variant of OCL where the input data distribution changes from one task to another. We propose two innovative methods: Online Domain Incremental Pool (ODIP) and Online Domain Incremental Networks (ODIN), for ODICL. The proposed methods leverage existing well-researched SL techniques described in Online Streaming Continual Learning (OSCL). ODIP and ODIN outperform current regularization methods without needing a replay buffer. ODIN achieves competitive results compared to replay-based methods. Both methods are ideal candidates for privacy-concerned ODICL scenarios, offering alternatives to regularization-based approaches.

Overall, this thesis explores advancements in SL classification and ODICL, presenting novel techniques that surpass existing approaches in their respective domains. These contributions have significant implications for addressing the challenges posed by evolving data streams in the era of big data.

year: 2023

title: The Role of Fatherhood in the Everyday Life of Young Māori Men

authors: Elkington, Angus Marangai Brons

subjects: maori men

abstract: Little research exists that explores the positive aspects of young Māori fathers. The aim of this study was to explore the everyday lived reality of expectant and young Māori males as fathers and partners, within the context of a positive based approach and Kaupapa Māori research framework. A secondary objective of this study was to provide ideas to enhance parent resources for young Māori fathers, such as father centric parenting programmes and mobile applications. The research was derived from semi-structured interviews, which explored the unique experiences and narratives of eight young Māori fathers between the age of 16 and 25 years of age. Using thematic analysis, the findings were categorised into key themes that portrayed their perception and attitudes to roles, responsibility, relationships, barriers, and wellbeing strategies. The findings identified, a strong desire of young Māori fathers to be involved with their children and that the quality of whānau relationships provided resilience, support, and motivation to fulfil the responsibilities of fatherhood. The young Māori fathers had strong goals and aspirations but acknowledged barriers that delayed their ability to achieve them. In the outcome of this study, I have tried to portray a positive understanding of young Māori fathers and to challenge the negative stereotypes that persist in New Zealand society. Furthermore, this research supports the need for restorative cultural practices as the key to wellbeing for our whānau and further investigations in regards to policy reforms and resources to include full participation in society.

text: The Role of Fatherhood in the Everyday Life of Young Māori Men Little research exists that explores the positive aspects of young Māori fathers. The aim of this study was to explore the everyday lived reality of expectant and young Māori males as fathers and partners, within the context of a positive based approach and Kaupapa Māori research framework. A secondary objective of this study was to provide ideas to enhance parent resources for young Māori fathers, such as father centric parenting programmes and mobile applications. The research was derived from semi-structured interviews, which explored the unique experiences and narratives of eight young Māori fathers between the age of 16 and 25 years of age. Using thematic analysis, the findings were categorised into key themes that portrayed their perception and attitudes to roles, responsibility, relationships, barriers, and wellbeing strategies. The findings identified, a strong desire of young Māori fathers to be involved with their children and that the quality of whānau relationships provided resilience, support, and motivation to fulfil the responsibilities of fatherhood. The young Māori fathers had strong goals and aspirations but acknowledged barriers that delayed their ability to achieve them. In the outcome of this study, I have tried to portray a positive understanding of young Māori fathers and to challenge the negative stereotypes that persist in New Zealand society. Furthermore, this research supports the need for restorative cultural practices as the key to wellbeing for our whānau and further investigations in regards to policy reforms and resources to include full participation in society.

year: 2016