Environmental Science: Processes & Impacts blog

Research into how microbial organisms are adapting to the ever increasing levels of nanoparticles is important in assessing the impact of nanomaterials on various environmental systems and processes. However, the surprising ability of microorganisms to turn metals in the environment into nanoparticles is often overlooked and could be making a significant contribution to this rise of nanoparticles in the environment.

In this HOT article, Monika Mortimer et al. study the ability of Tetrahymena thermophile, a fresh-water inhabiting protozoa, to reduce silver ions to silver nanoparticles. It is the soluble extracellular fraction (SEF) of the protozoa in which this occurs. The team demonstrate that the protein fraction of this SEF is associated with the formation of silver nanoparticles.

The ability of some microorganisms to carry out this conversion is surprising due to the toxicity of many silver compounds and the well-known antibacterial properties of silver nanoparticles.

In this study, the protozoa do show a negative response to the silver compound (AgNO₃) within 2 hours of exposure, but then they convert AgNO₃ to less toxic nanoparticles, resulting in a recovery period over 24 hours. This supports the theory that it is not silver nanoparticles themselves that cause the toxicity but remaining dissolved silver ions.

This HOT article increases our knowledge of this surprising defence mechanism against toxic silver compounds and adds evidence to the ongoing debate surrounding the mechanism of toxicity of silver nanoparticles.

This article is free to access for 4 weeks*, read it by clicking the link below:

Extracellular conversion of silver ions into silver nanoparticles by protozoan Tetrahymena thermophila
Katre Juganson, Monika Mortimer, Angela Ivask, Kaja Kasemets and Anne Kahru
DOI: 10.1039/C2EM30731F

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Detecting carbon nanotubes by trying to detect the carbon content is tricky in complex environments, as environmental concentrations require sensitive techniques. A team including researchers at the Colorado School of Mines, Johns Hopkins University and the University of Michigan, USA, use the traces of catalytic metals present in carbon nanotubes as an alternative in this Environmental Science: Processes & Impacts HOT article.

The team use single particle-inductively coupled plasma-mass spectrometry. Carbon is not detectable with normal ICP-MS techniques, but metal particles are and they are usually present in trace amounts after carbon nanotubes’ manufacture. The challenge the group faced was to separate the metal signal from the background.

The developed technique can detect carbon nanotubes at the nanogram per litre level and can also detect changes in nanotube concentrations when they have been released into the environment from a nanomaterial. Further work will focus on improving the quantification ability of the technique.

Read the detail of how they managed to overcome the difficulty of background and how they intend to improve the quantification in the full article, which is free to access for the next 4 weeks*, by clicking on the link:

Detection of single walled carbon nanotubes by monitoring embedded metals
Robert B. Reed, David G. Goodwin, Kristofer L. Marsh, Sonja S. Capracotta, Christopher P. Higgins, D. Howard Fairbrother and James F. Ranville
DOI: 10.1039/C2EM30717K

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Understanding the transport of microorganisms in soil is key to evaluating the impact of releasing them into the environment through such processes as contaminated wastewater effluents. This article by Jean Martins et al. at Domaine Universitaire, Grenoble, France, looks at the mobility of E. coli, as a substitute for pathogenic cells, in undisturbed natural soil in conditions that simulate land effluent application.

Most interesting is the study of E. coli cell transport using repeated injections of bacterial suspension. The majority of cells injected were recovered in the resulting effluent and the leaching of the cells from the soil occurred very quickly post-injection. The cells did not reach the whole volume of the soil. The study revealed a dual mode of fast and slow transport, the slow transport being dominant, indicating that the soil structure was gradually affected during the flow giving preferred flow pathways of bacteria. The pore network was hydrodynamically active, changing over time. The fast component of the transport appears to cancel out the effect that high salinity usually has on bacterial of aggregation as the cells didn’t aggregate, no matter what the ionic strength, and most were isolated in the soil.

It is the dominance of the hydrodynamic properties of the soil that is the important conclusion from this work. Undisturbed natural soil is recommended in experiments studying bacteria mobility if natural media is to be used due to the unstable nature of the pore structure compared to model porous media. The effects that usually dominate in model media may be overshadowed in natural media by the influence of hydrodynamics.

All of our HOT articles are free to access for 4 weeks*, so why not have a read now?

Role of macropore flow in the transport of Escherichia coli cells in undisturbed cores of a brown leached soil
Jean M. F. Martins ,  Samer Majdalani ,  Elsa Vitorge ,  Aurélien Desaunay ,  Aline Navel ,  Véronique Guiné ,  Jean François Daïan ,  Erwann Vince ,  Hervé Denis and Jean Paul Gaudet
DOI: 10.1039/C2EM30586K

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Choosing how we get to work is often based on money, time and local infrastructure; however Kam et al. have studied how this choice may also impact commuter’s exposure to pollutants and potential health risks.

This paper looks at the concentrations of a variety of particulate matter including metals and trace elements, using inductively coupled plasma mass spectrometry, and polyaromatic hydrocarbons (PAHs), via gas chromatography.  All of the compounds studied have been linked to life threatening conditions such as cancer, cardiovascular diseases and neurodegenerative disorders.

The sampling regime takes account of a variety of commuting methods in Los Angeles such as the subway, surface ‘light’ railway and a variety vehicular routes including a freeway, a surface-level street and a route used frequently by heavy duty vehicles (HDVs).

The compound profiles identified in the study fitted well with those predicted for each transport mode.  For example iron, associated with stainless steel and mechanical wear, was highest in the subway, lead and other elements associated with fuel use and vehicular traffic were higher in the road samples and elements which are greatly influenced by the environment, e.g. sodium, did not differ between the modes.  However the results also point to a more complex picture than this suggests with the season, location of the transportation and other transport users also playing significant roles in the exposure model.

Kam et al. also compared the relative potencies and unit risk factors of each individual PAH to estimate the cancer risk for commuters.  Road users were at greater risk from this pathway, particularly users of roads which have a higher HDV use.

This highly detailed study not only provides an insight into the potential long term health risks which may be associated with commuting, but is relevant to any group who lives near, works in or is routinely using these transport modes.  It also highlights the complexity involved in carrying out studies of this kind and interpreting environmental exposures.  It’s free to access* on our site for the next four weeks, so why not download the paper here:

A comparative assessment of PM2.5 exposures in lightrail, subway, freeway, and surface street environments in Los Angeles and estimated lung cancer risk
Winnie Kam, Ralph J. Delfino, James J. Schauer and C. Sioutas
DOI: 10.1039/c2em30495c

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Published on behalf of Sian Evans, Environmental Science: Processes and Impacts web science writer. Sian is a PhD student based in Bath, United Kingdom

Sewage contains a myriad of potentially life threatening chemical and biological matter.  This paper shows studying sewage is crucial to understanding its threat, but it can also unlock potential epidemiological information.

Disposing of sewage appropriately is one of the most important life-saving technologies that exist, however processing such waste poses health risks.  Some of the hazards associated with sewage are from adenoviruses, which can be infectious through direct contact, ingestion and aerosol exposure; a particular concern as solid material from sewage plants is often disposed of as agricultural fertiliser.  Previous studies have focussed on single adenovirus species or grouped them together; however the seven main species all possess unique symptoms when contracted.  Bibby and Peccia have therefore used PCR and primers able to distinguish between the species to amplify DNA from samples of sewage influent and effluent.

The results revealed that the adenovirus-C was most abundant, responsible for respiratory symptoms, followed by adenovirus-B, also associated with respiratory illnesses as well as urinary infections.  It should be noted though that increased virus abundance does not necessarily correlate with increased infectious risk.  Interestingly, wastewater treatment had no impact on the virus numbers, showing treated solid waste, spread on agricultural land, poses an equal risk as raw influent from adenoviruses.

Whilst providing information for risk assessments this data also lends support to the notion that sewage contains a great amount of information regarding its source population, negating the need for, and potential flaws in, medical data.  In this case, adenovirus C and B, the most abundant in the sewage, are also the most abundantly reported infections within the population. 

This work is of interest to a variety of people including those involved in human health risk assessments, gene amplification, sewage treatment and disposal and sewage epidemiology it’s free to access* on our site for the next four weeks, so why not download the paper here:

Prevalence of respiratory adenovirus species B and C in sewage sludge
Kyle Bibby and Jordan Peccia
DOI: 10.1039/c2em30831b

*Free access to individuals is provided through an RSC Publishing personal account. Registration is quick, free and simple

Published on behalf of Sian Evans, Environmental Science: Processes and Impacts web science writer. Sian is a PhD student based in Bath, United Kingdom