Health Impact Assesment: Hints and Cautions from Critical Epidemiology

Under the format of this conference, to convey the possibilities for health impact assessment of Latin American Critical Epidemiology, sometimes referred to under the tautological designation of “social epidemiology”, I will try to sum up in the next few minutes some reflections based on them.

A Field Evaluation of the Time-of-Detection Method to Estimate Population Size and Density for Aural Avian Point Counts

The time-of-detection method for aural avian point counts is a new method of estimating abundance, allowing for uncertain probability of detection. The method has been specifically designed to allow for variation in singing rates of birds. It involves dividing the time interval of the point count into several subintervals and recording the detection history of the subintervals when each bird sings. The method can be viewed as generating data equivalent to closed capture–recapture information. The method is different from the distance and multiple-observer methods in that it is not required that all the birds sing during the point count. As this method is new and there is some concern as to how well individual birds can be followed, we carried out a field test of the method using simulated known populations of singing birds, using a laptop computer to send signals to audio stations distributed around a point. The system mimics actual aural avian point counts, but also allows us to know the size and spatial distribution of the populations we are sampling. Fifty 8-min point counts (broken into four 2-min intervals) using eight species of birds were simulated. Singing rate of an individual bird of a species was simulated following a Markovian process (singing bouts followed by periods of silence), which we felt was more realistic than a truly random process. The main emphasis of our paper is to compare results from species singing at (high and low) homogenous rates per interval with those singing at (high and low) heterogeneous rates. Population size was estimated accurately for the species simulated, with a high homogeneous probability of singing. Populations of simulated species with lower but homogeneous singing probabilities were somewhat underestimated. Populations of species simulated with heterogeneous singing probabilities were substantially underestimated. Underestimation was caused by both the very low detection probabilities of all distant individuals and by individuals with low singing rates also having very low detection probabilities.

Vertical current flow through extensive layer clouds

The global atmospheric electrical circuit sustains a vertical current density between the ionosphere and the Earth's surface, the existence of which is well-established from measurements made in fair-weather conditions. In overcast, but non-thunderstorm, non-precipitating conditions, the current travels through the cloud present, despite cloud layers having low electrical conductivity. For extensive layer clouds, this leads to space charge at the upper and lower cloud boundaries. Using a combination of atmospheric electricity and solar radiation measurements at three UK sites, vertical current measurements have been categorised into clear, broken, and overcast cloud conditions. This approach shows that the vertical “fair weather” current is maintained despite the presence of cloud. In fully overcast conditions with thick cloud, the vertical current is reduced compared to thin cloud overcast conditions, associated with the cloud's resistance contributions. Contribution of cloud to the columnar resistance depends both on cloud thickness, and the cloud's height.

Influence of aluminum hydroxide on potassium release from two Colombian soils

The effect of sesquioxides on the mechanisms of chemical reactions that govern the transformation between exchangeable potassium (Kex) and non-exchangeable K (Knex) was studied on acid tropical soils from Colombia: Caribia with predominantly 2 : 1 clay minerals and High Terrace with predominantly 1 : 1 clay minerals and sesquioxides. Illite and vermiculite are the main clay minerals in Caribia followed by kaolinite, gibbsite, and plagioclase, and kaolinite is the major clay mineral in High Terrace followed by hydroxyl-Al interlayered vermiculite, quartz, and pyrophyllite. The soils have 1.8 and 0.5% of K2O, respectively. They were used either untreated or prepared by adding AlCl3 and NaOH, which produced aluminum hydroxide. The soils were percolated continuously with 10mM NH4OAc at pH 7.0 and 10 mM CaCl2 at pH 5.8 for 120 h at 6 mL h(-1) to examine the release of Kex and Knex. In the untreated soils, NH4+ and Ca-2(+) released the same amounts of Kex from Caribia, whereas NH4+ released about twice as much Kex as Ca2+ from High Terrace. This study proposes that the small ionic size of NH4+ (0.54nm) enables it to enter more easily into the K sites at the broken edges of the kaolinite where Ca2+ (0.96 nm) cannot have access. As expected for a soil dominated by 2 : 1 clay minerals, Ca2+ caused Knex to be released from Caribia with no release by NH4+. No Knex was released by either ion from High Terrace. After treatment with aluminum hydroxide, K release from the exchangeable fraction was reduced in Caribia due to the blocking of the exchange sites but release of Knex was not affected. The treatment increased the amount of Kex released from the High Terrace soil and the release of Knex remained negligible although with Ca2+ the distinction between Kex and Knex was unclear. The increase in Kex was attributed to the initially acidic conditions produced by adding AlCl3 which may have dissolved interlayered aluminum hydroxide from the vermiculite present, thus exposing trapped K as exchangeable K. The subsequent precipitation of aluminum hydroxide when NaOH was added did not interfere with the release of this K, and so was probably formed mostly on the surface of the dominant kaolinite. Measurement of availability of K by standard methods using NH4 salts could result in overestimates in High Terrace and this may be a more general shortcoming of the methods in kaolinitic soils.

Distributed mining of molecular fragments

In real world applications sequential algorithms of data mining and data exploration are often unsuitable for datasets with enormous size, high-dimensionality and complex data structure. Grid computing promises unprecedented opportunities for unlimited computing and storage resources. In this context there is the necessity to develop high performance distributed data mining algorithms. However, the computational complexity of the problem and the large amount of data to be explored often make the design of large scale applications particularly challenging. In this paper we present the first distributed formulation of a frequent subgraph mining algorithm for discriminative fragments of molecular compounds. Two distributed approaches have been developed and compared on the well known National Cancer Institute’s HIV-screening dataset. We present experimental results on a small-scale computing environment.

Role of polyhydroxybutyrate and glycogen as carbon storage compounds in pea and bean bacteroids

Rhizobium leguminosarum synthesizes polyhydroxybutyrate and glycogen as its main carbon storage compounds. To examine the role of these compounds in bacteroid development and in symbiotic efficiency, single and double mutants of R. legumosarum bv. viciae were made which lack polyhydroxybutyrate synthase (phaC), glycogen synthase (glgA), or both. For comparison, a single phaC mutant also was isolated in a bean-nodulating strain of R. leguminosarum bv. phaseoli. In one large glasshouse trial, the growth of pea plants inoculated with the R. leguminosarum bv. viciae phaC mutant were significantly reduced compared with wild-type-inoculated plants. However, in subsequent glasshouse and growth-room studies, the growth of pea plants inoculated with the mutant were similar to wildtype-inoculated plants. Bean plants were unaffected by the loss of polyhydroxybutyrate biosynthesis in bacteroids. Pea plants nodulated by a glycogen synthase mutants or the glgA/phaC double mutant, grew as well as the wild type in growth-room experiments. Light and electron micrographs revealed that pea nodules infected with the glgA mutant accumulated large amounts of starch in the II/III interzone. This suggests that glycogen may be the dominant carbon storage compound in pea bacteroids. Polyhydroxybutyrate was present in bacteria in the infection thread of pea plants but was broken down during bacteroid formation. In nodules infected with a phaC mutant of R. leguminosarum bv. viciae, there was a drop in the amount of starch in the II/III interzone, where bacteroids form. Therefore, we propose a carbon burst hypothesis for bacteroid formation, where polyhydroxybutyrate accumulated by bacteria is degraded to fuel bacteroid differentiation.

A temporal limit to the association between flag leaf life extension by fungicides and wheat yields

Three field experiments, each repeated over two or three seasons, on winter wheat investigated a possible limit to the association between grain yield and flag leaf life, as extended by fungicide application. The experiments involved up to six cultivars and different application rates, timings and frequencies of the strobilurin azoxystrobin and the triazole epoxiconazole. In the 2000/01 and 2001/02 seasons, the relationships between the thermal time to 37 % green flag leaf area (m) and yield deviated from linearity. 'Broken stick' models were fitted to cultivar x experiment combinations within each season and the limit to the benefit to yield associated with extending flag leaf life was 700 degrees C days (S.E. = 20.7) and 725 degrees C days (S.E. = 9.33) after anthesis in 2000/01 and 2001/02, respectively. In 2002/03, the relationship between yield and in did not deviate significantly (P > 0.05) from linearity, but in this latter year the fungicide application failed to increase In past 700 degrees C days. (c) 2004 Elsevier B.V. All rights reserved.

Successful long-term ultra dry storage of seed of 15 species of Brassicaceae in a genebank: variation in ability to germinate over 40 years and dormancy

Seed of 15 species of Brassicaceae were stored hermetically in a genebank (at -5 degrees C to -10 degrees C with c. 3% moisture content) for 40 years. Samples were withdrawn at intervals for germination tests. Many accessions showed an increase in ability to germinate over this period. due to loss in dormancy. Nevertheless, some dormancy remained after 40 years' storage and was broken by pre-applied gibberellic acid. The poorest seed survival occurred in Hormatophylla spinosa. Even in this accession the ability to germinate declined by only 7% between 1966 and 2006. Comparison of seeds from 1966 stored for 40 years with those collected anew in 2006 from the original sampling sites, where possible, showed few differences, other than a tendency (7 of 9 accessions) for the latter to show greater dormancy. These results for hermetic storage at sub-zero temperatures and low moisture contents confirm that long-term seed storage can provide a successful technology for ex situ plant biodiversity conservation.

Effect of harvest date on the dormancy period of yam (Dioscorea rotundata)

Tuber dormancy enables yams to survive in the ground during the dry season and post-harvest storage. Three clones of Dioscorea rotundata were harvested after five intervals and then stored in a cooler (20.6°C) or at ambient temperature (27.8°C). The time from harvest to sprouting was shorter as harvest was delayed. The period from sowing to sprouting for each clone was similar for tubers harvested from 140 days after planting, but tubers harvested earlier took longer to sprout. The cooler temperature delayed sprouting. Tubers of two clones sprouted after only 70 days of crop growth. If the dormancy period of these young tubers can be broken, the generation time of yam crop improvement programmes could be considerably reduced.

Modification of hemicellulose content by antisense down-regulation of UDP-glucuronate decarboxylase in tobacco and its consequences for cellulose extractability

Extractability and recovery of cellulose from cell walls influences many industrial processes and also the utilisation of biomass for energy purposes. The utility of genetic manipulation of lignin has proven potential for optimising such processes and is also advantageous for the environment. Hemicelluloses, particularly secondary wall xylans, also influence the extractability of cellulose. UDP-glucuronate decarboxylase produces UDP-xylose, the precursor for xylans and the effect of its down-regulation on cell wall structure and cellulose extractability in transgenic tobacco has been investigated. Since there are a number of potential UDP-glucuronate decarboxylase genes, a 490 bp sequence of high similarity between members of the family, was chosen for general alteration of the expression of the gene family. Sense and antisense transgenic lines were analysed for enzyme activity using a modified and optimised electrophoretic assay, for enzyme levels by western blotting and for secondary cell wall composition. Some of the down-regulated antisense plants showed high glucose to xylose ratios in xylem walls due to less xylose-containing polymers, while arabinose and uronic acid contents, which could also have been affected by any change in UDP-xylose provision, were unchanged. The overall morphology and stem lignin content of the modified lines remained little changed compared with wild-type. However, there were some changes in vascular organisation and reduction of xylans in the secondary walls was confirmed by immunocytochemistry. Pulping analysis showed a decreased pulp yield and a higher Kappa number in some lines compared with controls, indicating that they were less delignified, although the level of residual alkali was reduced. Such traits probably indicate that lignin was less available for removal in a reduced background of xylans. However, the viscosity was higher in most antisense lines, meaning that the cellulose was less broken-down during the pulping process. This is one of the first studies of a directed manipulation of hemicellulose content on cellulose extractability and shows both positive and negative outcomes.

Modification of hemicellulose content by antisense down-regulation of UDP-glucuronate decarboxylase in tobacco and its conscequence for cellulose extractability

Extractability and recovery of cellulose from cell walls influences many industrial processes and also the utilisation of biomass for energy purposes. The utility of genetic manipulation of lignin has proven potential for optimising such processes and is also advantageous for the environment. Hemicelluloses, particularly secondary wall xylans, also influence the extractability of cellulose. UDP-glucuronate decarboxylase produces UDP-xylose, the precursor for xylans and the effect of its down-regulation on cell wall structure and cellulose extractability in transgenic tobacco has been investigated. Since there are a number of potential UDP-glucuronate decarboxylase genes, a 490 bp sequence of high similarity between members of the family, was chosen for general alteration of the expression of the gene family. Sense and antisense transgenic lines were analysed for enzyme activity using a modified and optimised electrophoretic assay, for enzyme levels by western blotting and for secondary cell wall composition. Some of the down-regulated antisense plants showed high glucose to xylose ratios in xylem walls due to less xylose-containing polymers, while arabinose and uronic acid contents, which could also have been affected by any change in UDP-xylose provision, were unchanged. The overall morphology and stem lignin content of the modified lines remained little changed compared with wild-type. However, there were some changes in vascular organisation and reduction of xylans in the secondary walls was confirmed by immunocytochemistry. Pulping analysis showed a decreased pulp yield and a higher Kappa number in some lines compared with controls, indicating that they were less delignified, although the level of residual alkali was reduced. Such traits probably indicate that lignin was less available for removal in a reduced background of xylans. However, the viscosity was higher in most antisense lines, meaning that the cellulose was less broken-down during the pulping process. This is one of the first studies of a directed manipulation of hemicellulose content on cellulose extractability and shows both positive and negative outcomes.

Degradation pathway of bisphenol A: Does ipso substitution apply to phenols containing a quaternary alpha-carbon structure in the para position?

The degradation of bisphenol A and nonylphenol involves the unusual rearrangement of stable carboncarbon bonds. Some nonylphenol isomers and bisphenol A possess a quaternary alpha-carbon atom as a common structural feature. The degradation of nonylphenol in Sphingomonas sp. strain TTNP3 occurs via a type II ipso substitution with the presence of a quaternary alpha-carbon as a prerequisite. We report here a new degradation pathway of bisphenol A. Consequent to the hydroxylation at position C-4, according to a type 11 ipso substitution mechanism, the C-C bond between the phenolic moiety and the isopropyl group of bisphenol A is broken. Besides the formation of hydroquinone and 4-(2-hydroxypropan-2-yl) phenol as the main metabolites, further compounds resulting from molecular rearrangements consistent with a carbocationic intermediate were identified. Assays with resting cells or cell extracts of Sphingomonas sp. strain TTNP3 under an 18 02 atmosphere were performed. One atom of 180, was present in hydroquinone, resulting from the monooxygenation of bisphenol A and nonylphenol. The monooxygenase activity was dependent on both NADPH and flavin adenine dinucleotide. Various cytochrome P450 inhibitors had identical inhibition effects on the conversion of both xenobiotics. Using a mutant of Sphingomonas sp. strain TTNP3, which is defective for growth on nonylphenol, we demonstrated that the reaction is catalyzed by the same enzymatic system. In conclusion, the degradation of bisphenol A and nonylphenol is initiated by the same monooxygenase, which may also lead to ipso substitution in other xenobiotics containing phenol with a quaternary a-carbon.

Role of polyhydroxybutyrate and glycogen as carbon storage compounds in pea and bean bacteroids

Rhizobium leguminosarum synthesizes polyhydroxybutyrate and glycogen as its main carbon storage compounds. To examine the role of these compounds in bacteroid development and in symbiotic efficiency, single and double mutants of R. legumosarum bv. viciae were made which lack polyhydroxybutyrate synthase (phaC), glycogen synthase (glgA), or both. For comparison, a single phaC mutant also was isolated in a bean-nodulating strain of R. leguminosarum bv. phaseoli. In one large glasshouse trial, the growth of pea plants inoculated with the R. leguminosarum bv. viciae phaC mutant were significantly reduced compared with wild-type-inoculated plants. However, in subsequent glasshouse and growth-room studies, the growth of pea plants inoculated with the mutant were similar to wildtype-inoculated plants. Bean plants were unaffected by the loss of polyhydroxybutyrate biosynthesis in bacteroids. Pea plants nodulated by a glycogen synthase mutants or the glgA/phaC double mutant, grew as well as the wild type in growth-room experiments. Light and electron micrographs revealed that pea nodules infected with the glgA mutant accumulated large amounts of starch in the II/III interzone. This suggests that glycogen may be the dominant carbon storage compound in pea bacteroids. Polyhydroxybutyrate was present in bacteria in the infection thread of pea plants but was broken down during bacteroid formation. In nodules infected with a phaC mutant of R. leguminosarum bv. viciae, there was a drop in the amount of starch in the II/III interzone, where bacteroids form. Therefore, we propose a carbon burst hypothesis for bacteroid formation, where polyhydroxybutyrate accumulated by bacteria is degraded to fuel bacteroid differentiation.

Bending, twisting, and breaking CuCN chains to produce framework materials: the reactions of CuCN with alkali-metal halides

The reactions of the low-temperature polymorph of copper(I) cyanide (LT-CuCN) with concentrated aqueous alkali-metal halide solutions have been investigated. At room temperature, KX (X = Br and I) and CsX (X = Cl, Br, and I) produce the addition products K[Cu-2(CN)(2)Br](H2O)-H-. (I), K-3[Cu-6(CN)(6)I-3](.)2H(2)O (II), Cs[Cu-3(CN)(3)Cl] (III), Cs[Cu-3(CN)(3)Br] (IV), and Cs-2[Cu-4(CN)(4)I-2](H2O)-H-. (V), with 3-D frameworks in which the -(CuCN)- chains present in CuCN persist. No reaction occurs, however, with NaX (X = Cl, Br, I) or KCl. The addition compounds, I-V, reconvert to CuCN when washed. Both low- and high-temperature polymorphs of CuCN (LT- and HT-CuCN) are produced, except in the case of Cs[Cu-3(CN)(3)Cl] (III), which converts only to LT-CuCN. Heating similar AX-CuCN reaction mixtures under hydrothermal conditions at 453 K for 1 day produces single crystals of I-V suitable for structure determination. Under these more forcing conditions, reactions also occur with NaX (X = Cl, Br, I) and KCl. NaBr and KCl cause some conversion of LT-CuCN into HT-CuCN, while NaCl and NaI, respectively, react to form the mixed-valence Cu(I)/Cu(II) compounds [Cu-II(OH2)(4)][Cu-4(I)(CN)(6)], a known phase, and [Cu-II(OH2)(4)][Cu-4(I)(CN)(4)I-2] (VI), a 3-D framework, which contains infinite -(CuCN)- chains. After 3 days of heating under hydrothermal conditions, the reaction between KI and CuCN produces [Cu-II(OH2)(4)][Cu-2(I)(CN)I-2](2) (VII), in which the CuCN chains are broken into single Cu-CN-Cu units, which in turn are linked into chains via iodine atoms and then into layers via long Cu-C and Cu-Cu interactions.

A DFT study of free radicals formed from artemisinin and related compounds

Ab initio calculations using density functional theory have shown that the reactions that occur between artemisinin, 1, a cyclic trioxane active against malaria, and some metal ions and complexes lead to a series of radicals which are probably responsible for its therapeutic activity. In particular it has been shown that the interaction of Fe(H) with artemisinin causes the O-O bond to be broken as indeed does Fe(III) and Cu(I), while Zn(II) does not. Calculations were carried out with Fe(II) in several different forms including the bare ion, [Fe(H2O)(5)](2+) and [FeP(Im)] (P, porphyrin; Im, imadazole) and similar results were obtained. The resulting oxygen-based radicals are readily converted to more stable carbon-based radicals and/or. stable products. Similar radicals and products are also formed from two simple model trioxanes 2 and 3 that show little or no therapeutic action against malaria although some subtle differences were obtained. This suggests that the scaffold surrounding the pharmacophore may be involved in molecular recognition events allowing efficient uptake of this trioxane warhead into the parasite. (C) 2004 Elsevier B.V. All rights reserved.