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It has been shown (Birch 1) that the longer a soil remains in an air-dry state the greater are the amounts of carbon and nitrogen mineralised on moistening it. These amounts were found to be a significant linear function of the log. of the time the soll was in a dry state prior to moistening. Even short periods in the dry state were sufficient to produce considerably greater amounts of mineral nitrogen, on moistening, than solls that had not been given a preliminary dryäng. Harpstead and Brage s have also reported recently that drying and storage of soils leads to a pronounced increase in their nitrifying ability, a result which they ascribe to changes in the relative numbers of various micro-organisms in the soll.The experiment from which the foregoing results were quoted is now complete and is described below. It shows the effect of different periods in the dry state on subsequent nitriIication in soils with carbon contents ranging from 1 to 7 per cent. The range of soils and drying periods covered are, it is hoped, sufficiently wide for the results to serve as a general guide in soil-nitrogen studies, particularly in countries with pronounced wet and dry seasons. The application of the results is discussed in some detail, particularly with respect to soll nitrogen. Brief reference is also made to carbon rundown in soils.

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A new analytical approach to determine the speciation of hydrophobic organic analytes is presented. The freely dissolved concentration in a sample is controlled by passive dosing from silicone (poly(dimethylsiloxane)), and the total sample concentration at equilibrium is measured. The free fraction is determined as the ratio between measured concentrations in pure water and sample. (14)C-labeled fluoranthene served as model analyte, and total sample concentrations were easily measured by liquid scintillation counting. The method was applied to surface water, stormwater runoff, and wastewater. In the untreated wastewater, 61% of the fluoranthene was bound to suspended solids, 28% was associated to dissolved organic matter, and 11% was freely dissolved, while in treated wastewater, the speciation was 16% bound to suspended solids, 4% bound to dissolved organic matter, and 80% freely dissolved. The free fraction in roof runoff (85%) and surface water (91%) was markedly higher than in runoff from paved areas, which ranged from 27 to 36%. A log K(DOC) value of 5.26 was determined for Aldrich humic acid, which agrees well with reported values obtained by fluorescence quenching and solid phase microextraction (SPME). This analytical approach combines simplicity with high precision, and it does not require any phase separation steps.

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Document VersionPeer reviewed version Link back to DTU Orbit Citation (APA): Birch, H., Andersen, H. R., Comber, M., & Mayer, P. (2017). Biodegradation testing of chemicals with high Henry's constants -separating mass and effective concentration reveals higher rate constants. Abstract from SETAC Europe: 27th Annual Meeting -Environmental Quality Through Transdisciplinary Collaboration, Brussels, Belgium.

A partitioning-based experimental platform was developed and applied to determine primary biodegradation kinetics of 53 hydrocarbons at ng/L to μg/L concentrations covering C8-C20, 11 structural classes, and several orders of magnitude in hydrophobicity and volatility: (1) Passive dosing from a loaded silicone donor was used to set the concentration of each hydrocarbon in mixture stock solutions; (2) these solutions were combined with environmental water samples in gastight auto sampler vials for 1-100 days incubation, and (3) automated solid phase microextraction (SPME) coupled to GC-MS was applied directly on these test systems for measuring primary biodegradation relative to abiotic controls. First order biodegradation kinetics were obtained for 40 hydrocarbons in activated sludge filtrate, 18 in seawater, and 21 in lake water. Water phase half-lives in seawater and lake water were poorly related to hydrophobicity and volatility but were, with a few exceptions, within a factor of 10 or shorter than BioHCwin predictions. The most persistent hydrocarbons, 1,1,4,4,6-pentamethyldecalin, perhydropyrene, 1,2,3,6,7,8-hexahydropyrene, and 2,2,4,4,6,8,8-heptamethylnonane, showed limited or inconsistent degradation in all three environmental media. This biodegradation approach can cover a large chemical space at low substrate concentrations, which makes it highly suited for optimizing predictive models for environmental biodegradation.

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