No abstract

No abstract

Soil microbes are central to many soil processes, but due to the structural complexity of soil organic matter, the accurate quantification of microbial biomass contributions continues to pose a significant analytical challenge. In this study, microbes from a range of soils were cultured such that their molecular profile could be compared to that of soil organic matter and native vegetation. With the use of modern NMR spectroscopy, the contributions from microbial species can be discerned in soil organic matter and quantified. On the basis of these studies, the contributions of microbial biomass to soil organic matter appear to be much higher than the 1-5% reported by other researchers. In some soils, microbial biomass was found to contribute >50% of the extractable soil organic matter fractions and approximately 45% of the humin fraction and accounted for >80% of the soil nitrogen. These findings are significant because organic matter is intimately linked to nutrient release and transport in soils, nitrogen turnover rates, contaminant fate, soil quality, and fertility. Therefore, if in some cases soil organic matter and soil organic nitrogen are predominately of microbial origin, it is likely that this fraction, whether in the form of preserved material or living cells, plays an underestimated role in several soil processes.

Humic substances (HS) are an operationally defined fraction of soil organic matter, and they represent the largest pool of recalcitrant organic carbon in the terrestrial environment. It has traditionally been thought that extractable HS consist of novel categories of cross-linked macromolecular structures. In this study, advanced nuclear magnetic resonance approaches were used to study the major components (proteins, carbohydrates, aliphatic biopolymers, and lignin) that are known to be present in HS, and to identify their fingerprints in humic mixtures. Theoretically, once all known components have been identified, the remaining signals should be from materials with novel structures, themselves forming a distinct chemical category of humic materials. Surprisingly, nearly all of the NMR signals in traditional HS fractions could be assigned to intact and degrading biopolymers. We therefore suggest that the vast majority of operationally defined humic material in soils is a very complex mixture of microbial and plant biopolymers and their degradation products but not a distinct chemical category. It is important to note this work in no way rules out the existence of a distinct category of humic macromolecules, either at low abundance in the soluble fraction from young soils, in diagenetically evolved samples (for example lignites, etc.), or in the nonextractable humin fraction.

A simplified microbiological assay for vitamin B12 estimation, completed on microtitre plates using a colistin sulphate resistant strain of Lactobacillus leichmannii (NCIB 12519), and cryopreserved cultures is described. The new assay correlated well with a more conventional "tube" assay and was not influenced by the presence of antibiotics in serum. Evaluation of assay performance showed excellent interassay and intra-assay precision with quantitative recovery of added cyanocobalamin over a wide range of additions (94.9%-102.1%). The advantages of short incubation time, easy reading, and minimal reagent costs make this assay an attractive option in the routine clinical laboratory and in research.

Reports concerning the quantitative analysis of pharmaceuticals in marine ecosystems are somewhat limited. It is necessary to determine pharmaceutical fate and assess any potential risk of exposure to aquatic species and ultimately, seafood consumers. In the work presented herein, analytical methods were optimised and validated for the quantification of pharmaceutical residues in wastewater effluent, receiving marine waters and marine mussels (Mytilus spp.). Selected pharmaceuticals included two non-steroidal anti-inflammatory drugs (NSAIDs) (diclofenac and mefenamic acid), an antibiotic (trimethoprim), an antiepileptic (carbamazepine) and a lipid regulator (gemfibrozil). This paper also presents the results of an in situ study in which caged Mytilus spp. were deployed at three sites on the Irish coastline over a 1-year period. In water samples, pharmaceutical residues were determined using solid phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The extraction of pharmaceuticals from mussel tissues used an additional pressurised liquid extraction (PLE) step prior to SPE and LC-MS/MS. Limits of quantification between 15 and 225 ng·L(-1) were achieved in wastewater effluent, between 3 and 38 ng·L(-1) in marine surface water and between 4 and 29 ng·g(-1) dry weight in marine mussels. Method linearity was achieved for pharmaceuticals in each matrix with correlation coefficients of R(2)≥0.976. All five selected pharmaceuticals were quantified in wastewater effluent and marine surface waters. This work has demonstrated the susceptibility of the Mytilus spp. to pharmaceutical exposure following the detection of pharmaceutical residues in the tissues of this mussel species at measurable concentrations.

Since the isolation of soil organic matter in 1786, tens of thousands of publications have searched for its structure. Nuclear magnetic resonance (NMR) spectroscopy has played a critical role in defining soil organic matter but traditional approaches remove key information such as the distribution of components at the soil-water interface and conformational information. Here a novel form of NMR with capabilities to study all physical phases termed Comprehensive Multiphase NMR, is applied to analyze soil in its natural swollen-state. The key structural components in soil organic matter are identified to be largely composed of macromolecular inputs from degrading biomass. Polar lipid heads and carbohydrates dominate the soil-water interface while lignin and microbes are arranged in a more hydrophobic interior. Lignin domains cannot be penetrated by aqueous solvents even at extreme pH indicating they are the most hydrophobic environment in soil and are ideal for sequestering hydrophobic contaminants. Here, for the first time, a complete range of physical states of a whole soil can be studied. This provides a more detailed understanding of soil organic matter at the molecular level itself key to develop the most efficient soil remediation and agricultural techniques, and better predict carbon sequestration and climate change.

A comprehensive analytical investigation of the sorption behaviour of a large selection of over-the-counter, prescribed pharmaceuticals and illicit drugs to agricultural soils and freeze-dried digested sludges is presented. Batch sorption experiments were carried out to identify which compounds could potentially concentrate in soils as a result of biosolid enrichment. Analysis of aqueous samples was carried out directly using liquid chromatography-tandem mass spectrometry (LC-MS/MS). For solids analysis, combined pressurised liquid extraction and solid phase extraction methods were used prior to LC-MS/MS. Solid-water distribution coefficients (K(d)) were calculated based on slopes of sorption isotherms over a defined concentration range. Molecular descriptors such as log P, pK(a), molar refractivity, aromatic ratio, hydrophilic factor and topological surface area were collected for all solutes and, along with generated K(d) data, were incorporated as a training set within a developed artificial neural network to predict K(d) for all solutes within both sample types. Therefore, this work represents a novel approach using combined and cross-validated analytical and computational techniques to confidently study sorption modes within the environment. The logarithm plots of predicted versus experimentally determined K(d) are presented which showed excellent correlation (R(2) > 0.88), highlighting that artificial neural networks could be used as a predictive tool for this application. To evaluate the developed model, it was used to predict K(d) for meclofenamic acid, mefenamic acid, ibuprofen and furosemide and subsequently compared to experimentally determined values in soil. Ratios of experimental/predicted K(d) values were found to be 1.00, 1.00, 1.75 and 1.65, respectively.