Accurate characterization of dissolved organic matter (DOM) in soil is vital for understanding its functional significance. In this study, we used ultrafiltration to determine the molecular weight (MW) distribution of dissolved organic C (DOC), N (DON), and phenolics in two contrasting agricultural grassland soils. This MW fractionation (>100, 10–100, 1–10, and <1 kDa) was undertaken with soil solutions, distilled water extracts, and 2 mol L −1 KCl extracts. We showed that water or KCl extracts removed different amounts and forms of DOM than those in soil solution extracted by the centrifugation technique. Therefore, the ecological significance of such batch extraction methods and associated data requires careful consideration. Overall, soil solutions from the two grassland soils possessed different MW signatures, although the majority of DON and DOC was recovered in the higher MW fractions (>1 kDa) in both soils. This high‐MW fraction contained a significant amount of organic N, however, and was no more enriched in phenolic‐containing substances than the low‐MW fraction. Our results are consistent with the view that soil solutions contain a diverse size range of organic compounds but that the high‐MW fraction does not contain a disproportionate amount of phenolics or N.
Cross-sectional survey results from a COVID19 plane infection risk survey conducted between the 22<sup>nd</sup> to 23<sup>rd</sup> October, 2020. Participants (<em>n</em> = 2103) were aged 18 years or older, were living in the UK and had undertaken foreign air travel. The survey consisted of 18 closed-ended questions, with seventeen of the questions addressing issues associated with travelling by air and 11 questions addressing specific demographic topics. The questionnaire was designed by the research team, consisting of environmental microbiologists, public health specialists and social scientists, based on the study objectives and incorporating information from previous studies on same topic. The draft questionnaire was then tested on an expert panel, a panel of non-experts, a local ethics committee. First, perceived risks, concerns, and subjective knowledge of COVID-19 symptoms were measured using 16 options that included 14 actual symptoms and 2 which were not. Other questions about perception and risk were measured by statements with a 5-point Likert scale (e.g. strongly disagree to strongly agree).
The detection sensitivity and potential interference factors of a commonly used assay based on real-time polymerase chain reaction (PCR) for Escherichia coli O157:H7 using eae gene-specific primers were assessed. Animal wastes and soil samples were spiked with known replicate quantities of a nontoxigenic strain of E. coli O157:H7 in a viable or dead state and as unprotected DNA. The detection sensitivity and accuracy of real-time PCR for E. coli O157:H7 in animal wastes and soil is low compared to enrichment culturing. Nonviable cells and unprotected DNA were shown to produce positive results in several of the environmental samples tested, leading to potential overestimates of cell numbers due to prolonged detection of nonviable cells. This demonstrates the necessity for the specific calibration of real-time PCR assays in environmental samples. The accuracy of the eae gene–based detection method was further evaluated over time in a soil system against an activity measurement, using the bioluminescent properties of an E. coli O157:H7 Tn5luxCDABE construct. The detection of significant numbers of viable but nonculturable (VBNC) as well as nonviable and possibly physically protected cells as shown over a period of 90 days further complicates the use of real-time PCR assays for quick diagnostics in environmental samples and infers that enrichment culturing is still required for the final verification of samples found positive by real-time PCR methods.Key words: Escherichia coli O157:H7, real-time PCR, animal waste, soil, VBNC.
No abstract is provided for this article.
Soil is known to play an important role in the cycling of the human pathogen Escherichia coli O157 in the environment. Here we investigated whether residence time in soil influenced its ability to not only survive but subsequently reactivate after release into water during a simulated rainfall event. We inoculated an agricultural soil with chromosomally lux-marked E. coli O157 and then incubated it at 4 or 15 °C for up to 120 d, at which point the pathogen was recovered by extracting the soil with rainwater and its reactivation measured by monitoring bioluminescence over a 9 h period. We found that with increasing residence time in soil, E. coli O157 exhibited a reduction in both numbers and reactivation capacity as measured by cells' energy status (bioluminescence). As the degree of cell activity is linked to infectivity, this indicates that transmissibility may be reduced after a period within soil. This should be considered when assessing the degree of risk from environmental exposure to bacterial pathogens.
Toxicity studies tend to use pure pesticides with single organisms. However, natural systems are complex and biological communities diverse. The organophosphate pesticide propetamphos (PPT) has been found exceeding regulatory limits (100ngL−1) in rivers. We address whether solution properties affect the fate of Analar (Analar-PPT) or industrial PPT (PPT-Ind) propetamphos formulations and whether propetamphos and metal toxicant effects are additive, antagonistic or synergistic? The sorption, desorption, biodegradation and microbial toxicology of Analar-PPT and PPT-Ind were investigated in Conwy River and estuary sediment. Results showed elevated salinity enhanced PPT sorption, while higher salinities increased PPT-Ind retention. Higher dissolved organic matter (DOM) and low salinity slowed Analar-PPT biodegradation (1.9×10−3 h−1). Analar-PPT and PPT-Ind biodegradation was further reduced by low salinity, high DOM and dissolved Zn and Pb (6.3×10−4 h−1, 1100h t ½ for Analar-PPT; 7.5×10−4 h−1, 924h t ½ for PPT-Ind). Toxicity effects of PPT, Zn and Pb in equitoxic ratio were higher for PPT-Ind (4.7μgPPT-Indg−1; 581μgZng−1; 395μgPbg−1) than for Analar-PPT (34.6μgPPTg−1; 312μgZng−1; 212μgPbg−1) whilst a toxicant ratio 1:100:10 suggested small quantities of Analar-PPT (EC10 =0.06μgg−1) affected microbial communities. The combined toxicity effect was more than additive. Thus, industrial formulations and pollutant mixtures should be considered when assessing environmental toxicity.
Drained and cultivated fen peats represent some of the world's most productive soils, however, they are susceptible to degradation and typically exhibit high rates of greenhouse gas (GHG) emission. We hypothesised that GHG losses from these soils could be reduced by manipulating water table depth, tillage regime, crop residue application or horticultural fleece cover. Using intact soil columns from a horticultural peatland, emissions of CO2, N2O and CH4 were monitored over a six-month period, using a closed-chamber method. Concurrent measurements of soil properties allowed identification of the key controls on GHG emissions. Raising the water table to the soil surface provided the strongest reduction in global warming potential (GWP 100; 25 ± 6 kg CO2-e ha−1 d−1), compared to a free-draining control (80 ± 1 kg CO2-e ha−1 d−1), but this effect was partially negated by an emission pulse when the water table was subsequently lowered. The highest emissions occurred when the water table was maintained 15 cm below the surface (168 ± 11 kg CO2-e ha−1 d−1), as this stimulated N2O loss. Placement of horticultural fleece over the soil surface during spring had no significant effect on GWP 100, but prolonged fleece application exacerbated GHG emissions. Leaving lettuce crop residues on the surface increased soil GWP 100 (105 ± 4 kg CO2-e ha−1 d−1) in comparison to when residues were incorporated into the soil (85 ± 4 kg CO2-e ha−1 d−1), however, there was no evidence that this promoted positive priming of native soil organic matter (SOM). For maximum abatement potential, mitigation measures should be applied during the growing season, when GHG emissions are greatest. Our results also suggest that introduction of zero- or minimum-till practices may not reduce GHG emissions. Maintaining a high water table was the only option that reliably reduced GHG emissions, however, this option is impractical to implement within current horticultural systems. We conclude that alternative strategies or a major change in land use (e.g., conversion from horticulture/arable to wetland) should be explored as a means of preserving these soils for future generations.
