Christopher Macleod

Sequential extraction of low concentrations of pyrene and formation of non-extractable residues in sterile and non-sterile soils.

In this study, temporal changes in the extractability of C-14-pyrene, at native concentrations, were followed in two soils with differing organic matter contents, under sterile and non-sterile conditions over 24 weeks by a sequential solvent extraction scheme. No significant loss of the added C-14-pyrene was observed during the incubation. Significant decreases in methanol:water and n-butanol extractability were observed with increasing soil-pyrene contact time. Significant non-extractable residues were formed in all soils, with the largest increases found in the non-sterile soils. After 8 weeks soil-pyrene contact time, there was a significant increase in the rate and extent of sequestration of pyrene in the biologically active soils. This indicated that the aging of pyrene was initially a physical process, with active microbial communities increasing the rate and extent of residue formation after 8 weeks soil-pyrene contact time. These findings suggest that there is a need for longer term ageing experiments following the role of microbial communities on the formation of solvent non-extractable residues. The humin fraction of the soil organic matter contained the majority of the C-14-pyrene associated activity which was not extractable using the scheme of sequential solvents. Saponification of the soil humin resulted in the release of similar amounts of C-14-pyrene associated activity from sterile and non-sterile soils. Solvent extraction with methanol:water was found to significantly underestimate the bioavailable fraction, whereas n-butanol overestimated the bioavailability of the C-14-pyrene-associated activity when assessed by bacterial mineralization after 24 weeks soil-pyrene contact time

The adaptation of two similar soils to pyrene catabolism.

The development of pyrene catabolic activity was assessed in two similar soils (pasture and woodland) amended with 100 mg pyrene kg(-1) In the pasture and woodland soils, significant mineralisation of 14C-pyrene was observed after 8 and 76 weeks soil-pyrene contact times, respectively. In both soils, there were significant decreases (P<0.05) in the lag times and significant increases (P <0.05) in the maximum rates and extents of 14C-pyrene mineralised with increasing soil-pyrene contact time. A microbial inoculum was added to the woodland soil to assess if the previously added, but undegraded 14C-pyrene was bioavailable at 16 and 24 weeks. This resulted in the immediate mineralisation of the previously added 14C-pyrene, indicating that it was bioavailable but that the microbial community in the woodland soil had not developed the ability to mineralise pyrene. The relative contributions of the indigenous microflora to 14C-pyrene mineralisation were assessed by the addition of celective inhibitors, with bacteria seeming to be responsible for the mineralisation of pyrene in both soils. It is suggested that the rate of pyrene-transfer from the soil to the microorganisms was lower in the woodland soil due to its higher organic matter content.

The role of microorganisms in ecological risk assessment of hydrophobic organic contaminants in soils.

Publisher Summary This chapter discusses the importance of soil-contaminant interactions on the risks posed by Hydrophobic Organic Contaminants (HOC) in the soil environment. It is generally accepted that the longer HOCs are in contact with the soil matrix, the lower their potential for transport and availability to ecological receptors. The use of solvent non-extractable residues as an endpoint to judge remediation of contaminated soils has been suggested in the chapter. Microorganisms play a pivotal role in the functioning of the soil ecosystem and their inclusion in the assessment of HOC-contaminated soils is needed. The combination of activity based bioassays with biomarker methods seems to be a promising set of tests to be included in the Ecological Risk Assessment (ERA) process along with tests on higher soil organisms. With natural attenuation and bioremediation of hydrocarbon contaminated sites being increasingly used, ERA needs to incorporate the pivotal role of microorganisms in contaminant degradation.

Understanding spatial variability of soil properties: a key step in establishing field‐ to farm‐scale agro‐ecosystem experiments

RATIONALEnThe spatial variability of soil properties is poorly understood, despite its importance in designing appropriate experimental sampling strategies. As preparation for a farm-scale agro-ecosystem services monitoring project, the North Wyke Farm Platform, there was a need to assess the spatial variability of key soil chemical and physical properties.nnnMETHODSnThe field-scale spatial variability of soil chemical (total N, total C, soil organic matter), soil physical properties (bulk density and particle size distribution) and stable isotope ratios (δ(13) C and δ(15) N values) was studied using geostatistical approaches in an intensively managed grassland.nnnRESULTSnThe scales over which stable isotopes vary (ranges: 212-258 m) were larger than those of the total nutrients, soil organic matter and bulk density (ranges: 84-170 m). Two visually and statistically distinct areas of Great Field (north and south) were identified in terms of co-occurring high/low values of several soil properties.nnnCONCLUSIONSnThe resulting patterns of spatial variability suggest lower spatial variability of stable isotopes than that of total nutrients, soil organic matter and bulk density. Future sampling regimes should be conducted in a grid with <85 m distance between sampling locations to sufficiently capture the spatial variability of the measured soil properties on the North Wyke Farm Platform. Consultation of the management histories of the sampled field revealed that it had previously comprised two fields with contrasting management histories, suggesting an effect of management legacy (>5 years) on the patterns of spatial variability.

Mill, Intuitions, and Normativity

It is the purpose of this paper to offer an account of Mill’s metaethics, byexpanding on clues given recently by Dale Miller, and previously by JohnSkorupski, to the effect that, when it comes to the foundations of hisphilosophy, Mill might share more with the intuitionists than we areaccustomed to think. Common wisdom holds that Mill had no time forthe normativity of intuitions. I wish to dispute, or at least temper, thisdogma, by claiming that Mill’s attitude towards intuitions is far morecomplex and ambivalent than is generally thought. The investigation,then, centres on the question of whether, for Mill, intuitions carrynormative warrant: whether, in itself, the fact that a belief is intuitionalprovides reason to think that belief a warranted one. I argue that,according to Mill, our belief in the reliability of inductive moves andapparent memories, as well as the desirability of pleasure, is vindicated bysomething akin to intuition. Although his endorsement of the normativityof these intuitions might seem to be in tension with the arguments heoffers against the ‘intuitionist school’, this tension is only apparent.

The Roots of Romantic Cognitivism: (Post) Kantian Intellectual Intuition and the Unity of Creation and Discovery

During the romantic period, various authors expressed the belief that through creativity, we can directly access truth. To modern ears, this claim sounds strange. In this paper, I attempt to render the position comprehensible, and to show how it came to seem plausible to the romantics. I begin by offering examples of this position as found in the work of the British romantics. Each thinks that the deepest knowledge can only be gained by an act of creativity. I suggest the belief should be seen in the context of the post-Kantian embrace of “intellectual intuition.” Unresolved tensions in Kants philosophy had encouraged a belief that creation and discovery were not distinct categories. The post-Kantians held that in certain cases of knowledge (for Fichte, knowledge of self and world; for Schelling, knowledge of the Absolute) the distinction between discovering a truth and creating that truth dissolves. In this context, the cognitive role assigned to acts of creativity is not without its own appeal.