Archive for the ‘Hot Articles’ Category

Naphthalene-eating bacteria

Most petroleum hydrocarbons are dangerous for the environment and are known to be toxic. These chemicals can cause severe respiratory problems, mutations and cancer. A very particular type of hydrocarbons, known as polycyclic aromatic hydrocarbons (PAHs), represents a serious environmental threat. PAHs can obviously be dangerous when directly inhaled, but they are especially harmful since they can accumulate in water, sediments and soil, taking decades to decompose and thus polluting ecosystems for generations.

A few years ago, some scientists observed that certain species of bacteria had developed, by the means of natural selection, the ability to degrade molecules like hydrocarbons or polymers. Some of these species have evolved to degrade PAHs such as naphthalene, phenanthrene or pyrene, which means that they can be used to treat the waste of certain chemical plants, lowering the amount of these dangerous products released in to the environment.

Using tools like artificial selection or genetic engineering could enhance the efficacy of these bacteria. Moreover, the influence of some external factors may be optimized to improve the conversion of pollutants to non-toxic substances. In this article, recently published in Environmental Science: Processes & Impacts, Professor Mutai Bao and his team studied the effects of supporting bacteria on biodegradable, porous, low-cost materials like semi-coke, walnut shells and activated carbon. Immobilization methods are widely used and accepted by the scientific community because they are versatile and straightforward. Moreover, these systems can be easily cleaned and reused.

Before performing the experiment, scientists had to choose the right species of bacteria. They also had to let them adapt until they were able to properly digest PAHs. To facilitate this, bacteria were fed small amounts of classic carbon sources: glucose, lactose, starch or urea. The ones that received the combination of lactose and PAHs gave the best biodegradation results and were used for the optimization.

After a series of experiments, the authors concluded that immobilized bacteria degrade up to 47% more PAHs than free microbes. Semi-coke was the best support for these microorganisms, followed by walnut shell and activated carbon. In addition to this, they found bacteria to be adaptable to a broad range of pH and salinity. These biodegradation systems could be used in real-life situations such as oil spills in the ocean, where usually other techniques are less productive.

Interested in this research? Click on the link below to read the full article for free*

Biodegradation of different petroleum hydrocarbons by free and immobilized microbial consortia
Tiantian Shen, Yongrui Pi, Mutai Bao, Nana Xu, Yiming Li and Jinren Lu
Environ. Sci.: Processes Impacts, 2015, 17, 2022-2033
DOI: 10.1039/C5EM00318K

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About the webwriter

Fernando Gomollón-Bel is a PhD Student at the ISQCH (CSIC-University of Zaragoza). His research focuses on asymmetric organic synthesis using sugars as chiral-pool starting materials towards the production of fungical transglycosidase inhibitors.

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* Access is free until 18/02/2016 through a registered RSC account.

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Charcoal from summer barbecuing to soil remediation?

Well, not quite. But in recent years researchers have been exploring the potential of using “biochar” to remediate soil contaminated with organic chemicals. Similar to but definitely not the charcoal commonly used during barbecue season, biochar is made by heating biomass such as fruit peels in oxygen-limited conditions. Its physical and chemical characteristics impart an exceptional ability to sorb chemicals, especially organic chemicals, and reduce their bioavailability in soil.

A new study by Xu and co-workers at Peking University and the Chinese Academy of Agricultural Sciences focuses on two widespread organic chemicals: bisphenol A (BPA) and 17α-ethylyneestradiol (EE2). BPA is used for manufacturing polycarbonate plastics and epoxy resins. Thus, it is found in a multitude of commonly used products such as cars, food storage containers, and electronic equipment. EE2 is a synthetic estrogen most commonly used as an ingredient in birth control pills.

Both of these chemicals have been found to be endocrine disrupters, and can be transported to soils via wastewater irrigation, sludge fertilizers and landfill leachates. As both chemicals are quite hydrophobic, Xu et al. hypothesized that biochar added to soil would significantly sorb BPA and EE2, and as a result would also affect leaching and dissipation of the chemicals.

The researchers tested this hypothesis by adding biochar derived from corn stalks to soil in a series of lab experiments. First, sorption studies involved adding biochar at a level of 4 wt% to soils spiked with 0.01 or 0.1 mg/L of both BPA and EE2, and measuring the amount of the chemicals in both the soil solids and the soil water after equilibrium was established in about 7 days.

They found that the soils containing biochar increased the solid-water distribution coefficients by at least 200% for BPA and EE2 respectively, relative to the soils with no biochar. Next, leaching experiments meant to simulate repeated rainfall events compared biochar-free soils to those with 1, 2 and 4 wt% of biochar, all of which were spiked with BPA and EE2 at levels reflective of environmentally contaminated soils. Biochar-amended soils decreased the amount of leached BPA by 19 to 53% and EE2 by 42 to 77%.

Biochar created by pyrolysis. Image: Wikipedia.org

A final set of incubation experiments used soils spiked in a similar manner to those used in the leaching experiments. All soils, including a biochar-free control, were left outdoors at ambient temperatures for three months. Portions of the soils were sampled at 1, 30 and 90 days, and analyzed for their total and bioavailable BPA and EE2 content. The results showed no significant effect on the dissipation of the two chemicals in soil, but large reductions in the bioavailable fractions of BPA and EE2 in soil.

In addition to holding much promise for removing various organic residues from soil, other benefits of biochar in soil include carbon sequestration, reducing greenhouse gas emissions, and improving crop production. The long-term stability of biochar in soil further highlights the multi-faceted potential of biochar as a soil amendment.



To read more about Xu and co-workers’ investigation into biochar’s ability to reduce the mobility of two widespread organic contaminants, download a copy of the full article for free*:

Influence of biochar on sorption, leaching and dissipation of bisphenol A and 17α-ethynylestradiol in soil
N Xu, B Zhang, G Tan, J Li and H Wang
Environ. Sci.: Processes Impacts, 2015, 17, 1722-1730
DOI: 10.1039/C5EM00190K

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About the webwriter

Abha Parajulee is a Ph.D. student at the University of Toronto Scarborough. She is interested in water resources and the behavior of organic contaminants in urban environments.

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* Access is free until 01/12/2016 through a registered RSC account.

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Tracking down europium

We have used nuclear energy for a while now. It is a clean form of energy, except for one little thing: what happens with radioactive waste? Scientists think the best solution is burying it deep in the ground and labelling it clearly enough so that future generations (or aliens!) will not dare to look inside. However, is this really the best solution? What happens with radioactive nuclei once they are inside the nuclear graveyard?

DOI C5EM00412H

Scientists need to study the interactions of radioactive elements with the environment that surrounds them in the ground. But using radioactive elements is tricky: they can be dangerous and unstable, and most of them tend to decay in a few seconds (minutes, if you are lucky). Hence, researchers have determined to use models that mimic the behaviour of elements such as americium, curium or plutonium. Right in the row above actinides we find lanthanides, which have very similar oxidation states and comportment.

Image from Wikipedia

Source: Wikipedia.org

Scientists dig into europium. Not only because of its stability, but also because of its high fluorescence. This makes europium easy to track down in the lab. Outside the lab, europium is also very useful: the European Central Bank (ECB) uses europium as a fluorescent marker to fight counterfeit banknotes. Rumour has it the ECB intended the euro pun when choosing this particular element.

A group of researchers in China have studied the interactions of europium with alumina and humic acid (HA). These two substances represented the average inorganic and organic components of soil. In previous studies, they investigated the effect of reaction time, pH or ionic strength. In this paper, recently published in Environmental Science: Processes & Impacts, researchers examined the influence of temperature in the interactions of europium. And temperature is important when it comes to radioactive wastes: nuclear debris can keep temperatures of up to 100ºC during at least 1000 years, due to exothermic radioactive effects such as decomposition.

Luckily, the results were quite positive. Apparently, at high temperatures the formation of very stable structures is favoured, and the sorption of europium in alumina and alumina/HA systems is slightly increased with temperature. Nonetheless, trivalent cations are not the only substances present in nuclear waste. The interactions between soil-like substances (like alumina or HA) and other type of nuclei remain to be studied in depth.


Click on the link below to read the full article for free*

Sequestration and speciation of Eu(III) on gamma alumina: role of temperature and contact order
Yawen Cai, Xuemei Ren, Yue Lang, Zhiyong Liu, Pengfei Zong, Xiangke Wanga and Shitong Yang
Environ. Sci.: Processes Impacts, 2015, 17, 1904-1914
DOI: 10.1039/C5EM00412H

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About the webwriter

Fernando Gomollón-Bel is a PhD Student at the ISQCH (CSIC-University of Zaragoza). His research focuses on asymmetric organic synthesis using sugars as chiral-pool starting materials towards the production of fungical transglycosidase inhibitors.

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* Access is free until 20/12/2015 through a registered RSC account.

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New insights into the leaching of radioisotopes from nuclear wastes

The sites of underground repositories for radioactive waste need to be selected, designed and built adequately. This requires an in-depth understanding of the geochemical processes governing the release and transport of radionuclides from the waste to the surrounding environment. In this study published in Environmental Science: Processes & Impacts, researchers describe a technique that will improve our knowledge of potential leaching of radionuclides in these environments.

Many countries around the world now meet a substantial fraction of their energy demand through nuclear power. A key environmental issue, therefore facing these nations, is how to ensure the safe and responsible disposal of radioactive wastes. The International Atomic Energy Agency outlines a number of different potential methods for disposing of radioactive wastes and discusses the approach of different nations.

Careful burial in well-engineered ‘repositories’ at various depths below the land surface – so-called ‘geological disposal’ – is now the preferred option for the final storage of nuclear waste for most countries with advanced nuclear programmes, including the UK, Canada, Finland, France, Sweden, Switzerland, Japan and the USA. Indeed, a 2004 European Commission Report on radioactive wastes states that:

“Burial at several hundreds of metres depth in stable rock environments is the option for disposal of the most hazardous radioactive wastes because it will provide permanent safety – not just for ourselves, but for future times very much longer than the whole of past human history.”

However, in order to ensure that this statement is true, it is essential to assess to what extent radionuclides could be released to the environment. Therefore, it is of great importance to understand how long-lived radionuclides (such as 79Se, 129I, 14C or 36Cl) are chemically bound in the radioactive waste matrix. The challenge for researchers and practitioners is to provide reliable safety assessments for such nuclear waste repository sites that provide reliable long-term predictions on the release of radionuclides in waste repositories as the waste undergoes geochemical transformations in ground waters.

Radiocative wastes are typically a highly heterogeneous material made up of the fuel matrix with 3–6% fission products and minor actinides dispersed among different phases. Long-lived isotopes like 79Se, 135Cs, 129I and 36Cl are of interest because they are easily soluble in water and sorb only weakly on mineral surfaces, implying that, once dissolved, under repository conditions they will migrate through the sub-surface environment very rapidly. These compounds are therefore major contributors to the overall radiological dose calculated in risk assessments of nuclear waste repositories.

The properties and behaviour of radionuclides like 79Se in nuclear wastes are not well understood due to the technical difficulty of obtaining sound experimental data on such highly radioactive materials. This insufficient knowledge is usually compensated by conservatism in the choice of parameter values for safety assessment calculations. For example, it has previously been assumed that a significant fraction of 79Se is rapidly released from the spent fuel waste on contact with aqueous solutions and is highly mobile. This is due to the observation that selenium has an appreciable volatility under reactor operation conditions and the high solubility of oxidized Se species in water.

However, recent experiments have indicated that less than 1% of the Se in a geological disposal repository is released to aqueous solution after 1 year leaching, suggesting only a small fraction is actually leachable. This demonstrates the need to further investigate the geochemical nature and behaviour of long-lived radionuclides such as 79Se in radioactive wastes and the interaction of these isotopes with spent UO2 fuel.

This work is the result of a collaboration between Swiss, Swedish, French and American research institutes, investigating radionuclide release of 79Se from radioactive waste in a deep water-saturated repository. In the study, X-ray Absorption Near Edge Spectroscopy (XANES) measurements were made on samples from the Leibstadt Boiling Water Reactor in Switzerland.

Their results offer a mechanistic explanation why Se appears to be much less soluble in short-term aqueous leaching experiments, compared to other radionuclides like I and Ce. It was shown that these results were corroborated by a simple thermodynamic analysis, showing that selenide is the stable form of Se under reactor operation conditions.

This study provides a technique that helps improve our understanding of the geochemical transformation and transport of radioactive nuclides in wastes disposed in geological formations. Investigations like this are required to reduce conservatism and improve reliability in carrying out safety assessment calculations. This work is therefore integral to the future selection and design of potential nuclear waste repository sites.


To read more about this research, download a copy of the manuscript for free* by clicking the link below.

Characterization of selenium in UO2 spent nuclear fuel by micro X-ray absorption spectroscopy and its thermodynamic stability
E. Curti, A. Puranen, D. Grolimund, D. Jädernas,D. Sheptyakov and A. Mesbah
Environ. Sci.: Processes Impacts, 2015,17, 1760-1768
DOI: 10.1039/C5EM00275C

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About the webwriter

Ian Keyte is currently a Science Policy Intern at the Royal Society. He previously gained a PhD at the University of Birmingham investigating atmospheric pollution, and has a BSc in Environmental Chemistry from Lancaster University.

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* Access is free until 24/11/2015 through a registered RSC account.

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Teasing out the relative importance of controls on the production of a bioaccumulative neurotoxin

Environmental Science: Processes & Impacts cover highlights this research (issue 9)

Monomethylmercury (MeHg) is a chemical of great concern due to its neurotoxic nature and its efficient bioaccumulation in aquatic systems, eventually reaching humans through fish consumption.

MeHg is produced by the action of bacteria that transform the most commonly found species of mercury in aquatic environments. Remediation of mercury-contaminated sites requires insight into factors that facilitate the action of these mercury methylators. For example, anaerobic conditions and relatively large quantities of total and dissolved organic carbon both enhance production of MeHg.

The original speciation of mercury is also important, as some forms of mercure are more bioavailable to mercury methylators than others. Past work has traditionally focused on the influence of these factors individually; however, under environmental conditions these factors likely work in concert to affect mercury methylation.

Kucharzyk and co-workers at Duke University take the next step forward with their recent study published in Environmental Science: Processes & Impacts which aims to assess the relative influence of microbial productivity and mercury speciation on MeHg production. The researchers enriched cultures of mercury methylating bacteria found in two different marine sediments containing similar, elevated mercury concentrations. The cultures were determined to contain mostly one type of anaerobic bacteria known to methylate mercury.

For each of the two cultures, microbial growth was varied by adding different amounts of carbon substrate, and mercury speciation was varied with the addition of either dissolved or nanoparticulate mercury. The cultures were then incubated for 64 hours, during which two or three replicates were analyzed for various chemical and biological parameters at several time points across the incubation period.

In both cultures, mercury methylation increased with increasing concentrations of carbon substrate for a given type of mercury. When carbon substrate concentration was kept constant, the percentage of mercury that was methylated was 3 to 4 times lower in cultures amended with nanoparticulate mercury relative to those containing dissolved mercury instead. This could not have been due to differences in bacterial growth rates as the observed cell growth was the same across both types of added mercury, implying that the differences are probably a result of lower bioavailability of nanoparticulate mercury versus dissolved mercury.

The differences in microbial productivity between cultures spiked with the two different types of mercury became smaller with decreasing levels of carbon substrate. Interestingly, this data suggest there may be a threshold in the activity of mercury methylating bacteria, below which net MeHg production is controlled by the availability of carbon substrate, and above which the bioavailability of mercury becomes more important. However, further study including lower levels of carbon substrate is required to better confirm the existence of this threshold in microbial methylation activity.


Click on the link below to read the full article for free*:
Relative contributions of mercury bioavailability and microbial growth rate on net methylmercury production by anaerobic mixed cultures
Katarzyna H. Kucharzyk, Marc A. Deshusses, Kaitlyn A. Porter and Heileen Hsu-Kim
Environ. Sci.: Processes Impacts, 2015, 17, 1568-1577
DOI: 10.1039/C5EM00174A

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About the webwriter

Abha Parajulee is a Ph.D. student at the University of Toronto Scarborough. She is interested in water resources and the behavior of organic contaminants in urban environments.

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* Access is free until 18/11/2015 through a registered RSC account.

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Vehicle fire: a danger for firemen?

There are 200,000 cars fires every year in the United States. The number in the UK is even more impressive: 100,000 car fires every year (which means around 300 fires a day). Car fires are usually short, but also very intense, and release dangerous products that may not only pollute the environment, but also seriously affect the firemen tackling them. Despite the high incidence of this type of fires, very few studies have addressed the hazardous exposures firemen may be suffering.

The sampling platform used for "vacuuming" the fumes

The sampling platform used for "vacuuming" the fumes

Two researchers from Cincinnati (Ohio) have published a paper in Environmental Science: Processes & Impacts investigating the dangers of ultrafine and respirable particles released during vehicle fire suppression. They set three different cars on fire and asked a crew of firemen to suppress them with water. Meanwhile, a huge “vacuum cleaner”-like machine took samples that were later analysed by the two scientists.

The particle emissions were, like the fires, only present for a short period of time. However, the concentrations measured during the blaze were orders of magnitude bigger than the safe limits. They also found that cabin fire suppression is more dangerous than putting out just the engine compartment. The explanation might be simple: when the whole cabin is burning down, there is more fuel feeding the combustion, leading to more emissions and longer extinction times.

Another key aspect to consider is wind. Usually fire crews are trained to position themselves in an upwind and smoke-free spot, but you can’t control wind. When wind veered, particle emissions went off the chart, consequently increasing the risks.

Further studies will be carried out. In the meantime, the authors conclude that a self-contained breathing apparatus (a mask that works with compressed air generating a positive pressure inside it) should be worn throughout all the phases of extinguishing a vehicle fire. Otherwise, the hazardous vapours and particles released to the atmosphere may increase the risk of cancer in firemen.

Click on the link below to read the full article for free*

Ultrafine and respirable particle exposure during vehicle fire suppression
Douglas E. Evans and Kenneth W. Fent
Environ. Sci.: Processes Impacts, 2015, 17, 1749-1759
DOI: 10.1039/C5EM00233H

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About the webwriter

Fernando Gomollón-Bel is a PhD Student at the ISQCH (CSIC-University of Zaragoza). His research focuses on asymmetric organic synthesis using sugars as chiral-pool starting materials towards the production of fungical transglycosidase inhibitors.

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* Access is free through a registered RSC account.

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Re-use or miss-use? The risks and rewards of reclaimed waste water for crop irrigation

The re-use of waste waters for crop irrigation is becoming an increasingly popular practice, particularly in arid, water-stressed regions of the world. A new study by researchers from the U.S. Salinity Laboratory and the Institute of Soil and Environmental Sciences at the University of Agriculture in Faisalabad, Pakistan, investigates the potential agronomic and environmental impacts this can have on farmlands, shedding light on the challenges for long-term management of water usage and crop production.

Depletion of freshwater resources is one of the most important issues facing future global development. Finite water resources are becoming increasingly stressed by an ever-growing world population and associated demand for food production. Furthermore, the increased frequency of drought in many areas resulting from climate change and resource degradation due to pollution make the task of ensuring the global population have access to enough clean water increasingly difficult. The United Nations have warned that, under existing climate change scenarios, almost half the world’s population will be living in areas of high water stress by 2030.

An increasingly popular option to cope with increased water demand for agriculture is to re-use waste water or degraded water for crop irrigation. For example, dairy lagoon wastewater has been proposed as an alternate water resource in agriculture, as this can be a plentiful source of essential nutrients and organic matter. Indeed, the Food and Agriculture Organization (FAO) produced a report presenting “an economic framework for the assessment of the use of reclaimed water in agriculture”. This could also have the additional benefit of alleviating the need for the costly and difficult storage, treatment and disposal of large volumes of waste water.

Crop irrigation system (http://www.access-irrigation.co.uk)

However, degraded water will also contain contaminants, particularly salts and heavy metals such as zinc (Zn), copper (Cu), nickel (Ni), arsenic (As), cadmium (Cd), and lead (Pb).  This could mean the benefits of using wastewater could be offset due to increasing soil salinity and accumulation of potentially bioaccumulative toxins, which could have a negative impact on crop yield and quality, as well as wider reaching environmental problems. There is therefore a need for a greater understanding of how using dairy lagoon wastewater could impact the quality of agricultural land and the surrounding environment.

While the physical, chemical, and biological characteristics of degraded waters are generally well studied, the impact of its reuse on agricultural lands over long timescales is not well understood. In this study by Dennis Corwin and Hamaad Raza Ahmad, a field-scale impact investigation of dairy lagoon water reuse on agricultural soil characteristics was carried out. This represents the first study of this kind to be conducted at this spatial or temporal scale.

In the study, soil samples were collected at locations identified from apparent soil electrical conductivity (EC) measurements, a property of soil that reflects several soil physical and chemical properties (including soil salinity, texture, water content, bulk density, organic matter, and cation exchange capacity). Samples were taken at a number of different depth increments in an agricultural area in San Jacinto, California, first in 2007 and again in 2011, to establish the effect of using dairy lagoon water blended with recycled or well water on agricultural land over a 4 year irrigation period.

Chemical analyses of soil samples were carried out to determine key characteristics of the soil. This included the salinity, pH, SAR (sodium adsorption ratio), trace elements (As, B, Mo, Se), and heavy metals (Cd, Cu, Mn, Ni, Zn). The authors note that, from an agronomic perspective, the salinity, SAR, and B are of greatest concern, while from an environmental perspective, the salinity and Cu present the greatest potential effect upon groundwater safety.

The results suggest the reuse of dairy lagoon water presented very little detrimental environmental or agronomic impacts over the 4 years of the study duration. However, there were a number of potential long-term concerns that the study raises. For example, the pH values at all soil depths were shown to decrease. Additionally, potential long-term agronomic effect of salinity, SAR, and B levels, and the long-term environmental threat of salinity and Cu was highlighted. The accumulation of Cd, Mn, and Ni in the soil profile was also observed, raising concerns over the potential for metal contaminants such as these to leach from the soil in the future.

The authors note that, while the results demonstrated the short-term (4 year) viability of dairy lagoon water reuse as an alternative water resource for agriculture, the longer-term sustainability of dairy lagoon water reuse as a viable alternative for crop irrigation requires regular monitoring of soil properties to allow adequate site-specific management.

This study demonstrates that EC-directed soil sampling can be used to monitor spatial and temporal changes in the chemical characteristics of agricultural soils due to degraded water reuse. This could help pave the way for studies over wider spatial and longer temporal scales and can help producers optimise crop yields while at the same time mitigating detrimental environmental impacts. Based on their observations, the authors provide a number of specific recommendations for achieving this most effectively.  This method has clearly delivered an extensive spatio-temporal dataset, which highlights many of the challenges for successfully managing agricultural land irrigated by degraded wastewater.

The authors highlight the broad geographical relevance and impact of this research as it concerns the viability of degraded water reuse on irrigated, agricultural lands in arid regions throughout the world (e.g. northeast China, Middle East, North and Eastern Africa, Eastern Australia, India and Pakistan), where the reuse of degraded water is a major supplemental source of irrigation water.

To read more about this research, download a copy of the manuscript for free* by clicking the link below.

Spatio-temporal impacts of dairy lagoon water reuse on soil: heavy metals and salinity
Dennis L. Corwin and Hamaad Raza Ahmad
Environ. Sci.: Processes Impacts, 2015, Advance Article
DOI: 10.1039/c5em00196j

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About the webwriterIan Keyte

Ian Keyte is a Doctoral Researcher at the University of Birmingham. His research focuses on the sources, behavior and fate of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere.

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* Access is free until 22/10/2015 through a registered RSC account.

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Decomposition pathways of oceanic plastic debris

Bisphenol A, phtalates, PCBs and other organic pollutants often embedded in plastics have been under the spotlight for a while. However, very few people have studied the degradation pathways of oceanic plastic debris. An article recently published in Environmental Science: Processes & Impacts critically reviews this topic.

Plastics have been widely used since the 1940s. In 2013, global plastic production reached 300 mega tonnes (50 times the Great Pyramid of Giza). We discard most of the plastic right away, within 3 years of its production. Yet, it is engineered to last for hundreds or even thousands of years. Thus, tonnes of plastic debris accumulate in the environment.

Scientists are especially concerned about plastic debris accumulating in the oceans. By 2050, 99% of all seabirds will have ingested, at least, one small piece of plastic. Nowadays, plastics represent more than 60% of all the floating debris in the oceans. All these pieces of plastic may release organic pollutants to the sea, either additives or adsorbed substance. Despite their high stability, plastics might also decompose by the action of different factors, releasing potentially dangerous chemicals.

Graphical abstract - pathways of plastic degradation

Polymer degradation is, technically, a decline of its original properties. Usually it can be easily spotted by observing the colour changes or cracking of the surface. Small plastic particles decompose faster, due to their higher surface to volume ratio. Depending on the structure of their backbone, plastics can degrade in very different ways. Plastic with carbon-carbon backbones (i.e. PE, PP, PS, PVC) often suffer abiotic decomposition, usually initiated by UV radiation or thermal processes. Plastics with heteroatoms in their backbones (i.e. PU, PET) may also suffer abiotic decomposition, but in this case hydrolysis is the most common process. Furthermore, enzymes may also break amide and ester bonds, therefore these plastics are also exposed to biodegradation.

If you want to better understand the different degradation pathways, I strongly recommend that you go over this Environmental Science: Processes & Impacts Critical Review where all the mechanisms are carefully examined and explained.


Click on the link below to read the full article for free*:

Pathways for degradation of plastic polymers floating in the marine environment
Berit Gewert, Merle M. Plassmann and Matthew MacLeod
Environ. Sci: Processes Impacts, 2015, 17, 1513-1521
DOI: 10.1039/C5EM00207A

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About the webwriter

Fernando Gomollón-Bel is a PhD Student at the ISQCH (CSIC-University of Zaragoza). His research focuses on asymmetric organic synthesis using sugars as chiral-pool starting materials towards the production of fungical transglycosidase inhibitors.

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* Access is free through a registered RSC account.

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Going deep: investigating the physical and chemical properties of humic substances in groundwater

Humic substances play an important role in the speciation of metal ions in the aquatic environment. Understanding these processes is important to ensure the safety of drinking water. In this study, Japanese researchers reveal how physiochemical properties and ion-binding behaviour of HSs can differ between surface water and groundwater environments.

Groundwater constitutes the largest reservoir of freshwater in the world, accounting for over 97% (excluding glaciers and ice caps) of all available freshwater on the planet. It is estimated that about 75% of EU inhabitants depend on groundwater for their water supply. Groundwater also plays an integral role in the hydrological cycle, crucial to the maintenance of wetlands and river flows. Maintaining the quality of groundwater resources is therefore of major environmental, social and economic importance. This requires a good understanding of the physical and chemical processes that may influence groundwater environments.

For future use of deep underground space it is necessary to monitor and protect the quality of deep groundwater. The World Health Organisation (WHO) acknowledges the importance of groundwater resources and the potential risks that poor quality groundwater can cause to human health. Indeed, the WHO has produced a guidance document, “analysing hazards to groundwater quality, assessing the risk they may cause for a specific supply, setting priorities in addressing these, and developing management strategies for their control.”

Humic substances (HSs) are a class of natural organic molecules, ubiquitous in various environments including surface and ground water, oceans, soils, and the atmosphere. HSs are known to play an important role in freshwater systems. For example HSs can effectively capture inorganic and organic contaminants due to the tendency of protons and metal ions to readily bind to the functional groups of HS ligands e.g., carboxylic and phenolic groups and to a lesser extent amine- and sulphur-containing groups. This process can therefore alter the reactivity, bioavailability, and mobility of chemical constituents in fresh water.

The physical and chemical nature of HSs is likely to differ between deep underground and surface aquatic systems, due to slower water movement and more prolonged contact with underlying rocks and dissolved/suspended components, low oxygen, and lack of sunlight. However, while some characteristics of groundwater HSs are understood, their ion binding properties over a wide range of conditions is largely unknown. Given that in many areas, deep underground space may be used in the future for such uses as geological disposal of nuclear wastes, the potential deterioration of groundwater quality, the ion binding properties of deep groundwater HSs need to be studied carefully, and mechanistic models developed to describe these processes.

This study by Takumi Saito and co-workers investigates the physicochemical and binding properties of HSs isolated from deep groundwater in a sedimentary rock formation in the Horonobe Underground Research Laboratory of the Japan Atomic Energy Agency (JAEA). Binding isotherms of protons (H+) and copper (Cu2+) were measured over a wide range of conditions by potentiometric titration and were fitted to the NICA-Donnan model and the obtained parameters were compared with average parameters for HSs from surface environments. The oxidation state and local coordination environment of Cu2+ bound to the HA fraction of the HSs were also assessed by X-ray absorption spectroscopy (XAS).

The results clearly indicate distinctive physical and chemical characteristics for the HSs from surface and groundwater environments. It is found that the deep ground HSs were characterised by high aliphaticity and sulphur (S) content and relatively small sizes. Differences in the binding behaviours of H+ and Cu2+ with the HSs in deepwater and surface water were also observed.

The authors discuss the differences in chemical binding behaviour with reference to the unique chemical nature of the functional groups of groundwater HSs compared with those of surface waters and how the binding sites and binding mode can change with changes in conditions (e.g. pH). X-ray absorption spectroscopy also revealed that Cu2+ binds to O/N containing functional groups and to a lesser extent S containing functional groups.

The study therefore demonstrates how HSs could influence freshwater resources differently in deep-ground and surface environments. Although the HSs in this study were derived from a single groundwater source, the authors suggest the outcomes can be applied or be a good starting point to estimate the degree of metal binding to HSs in sedimentary groundwater in general.

The authors also suggest these results should be examined in the future by performing similar investigations for HSs isolated from a range of different groundwater samples and for a wider range of metal ions. This would allow accurate and realistic parameter sets applicable for groundwater HSs to be developed for further modelling for a more extensive range of chemical species.


To read more about this research, download a copy of the manuscript for free* by clicking the link below.

Physicochemical and ion-binding properties of highly aliphatic humic substances extracted from deep sedimentary groundwater
Takumi Saito, Motoki Terashima, Noboru Aoyagi, Seiya Nagao, Nobuhide Fujitake and Toshihiko Ohnuki
Environ. Sci.: Processes Impacts, 2015,17, 1386-1395
DOI: 10.1039/C5EM00176E

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Ian Keyte

About the webwriter

Ian Keyte is a Doctoral Researcher at the University of Birmingham. His research focuses on the sources, behavior and fate of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere.

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* Access is free until 20/09/2015 through a registered RSC account.

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Assessing the impacts of human activity on plants in one of the world’s most remote regions

These days it seems human activity knows no bounds, reaching as far as the polar regions which have seen an increased flurry of anthropogenic disturbance due to research and tourism. As a result of these activities, fuel spills and their detrimental effects on the local ecosystem are not uncommon in the sub-Antarctic and Antarctic.

It has been estimated that soil in the Antarctic covering an area the size of (10 million cubic meters) is contaminated with hydrocarbons. This environment presents barriers to natural removal of hydrocarbons including low nutrient content and low temperatures that limit microbial activity, as well as low rates of volatilization and evaporation caused by the same reason. Establishing reasonable remediation targets requires a thorough understanding of the biological effects of petroleum hydrocarbons, which can be achieved using biological assays. Though international protocols for such assays have been modified for application to Arctic and cold-climate species, our knowledge of the effects of hydrocarbons on plants in these regions is still lacking.

A recent study by Macoustra and co-workers is one of the few to provide such data for the sub-Antarctic region. The researchers first collected seeds from 12 native plants on Macquarie Island, the site of one of Australia’s scientific research stations and multiple diesel fuel spills. They tested the seeds for their suitability for bioassays in the lab, and used the species that successfully germinated in a second bioassay involving exposure to a range of diesel concentrations in soils, at both high and low organic carbon contents. Only four species were able to germinate during the second bioassay, indicating that diesel-contaminated soils reduced germination success.

Using the four species that germinated during the second bioassay, a final bioassay was performed over a 28 day period, again with soils exhibiting a range of diesel contamination and either low or high organic carbon content. The endpoints assessed were germination success, and early-life root and shoot growth. The researchers found that soils with low organic carbon content were generally more toxic to plants than high organic carbon content, and attribute this to the lower bioavailability of organic contaminants associated with higher levels of organic matter, in addition to higher nutrient levels that promote plant growth and higher rates of microbial degradation of petroleum hydrocarbons. Root growth was the most sensitive endpoint, likely due to the high permeability of early-life root tissues.

Though the concentrations of petroleum hydrocarbons necessary to inhibit early growth were similar to those likely to be found very close to a spill site, the unique conditions in the sub-Antarctic that greatly inhibit hydrocarbon loss processes mean that such concentrations can persist in the environment.

Prior to this study by Macoustra and co-workers, there was no such toxicity data for early life stages of native sub-Antarctic plants exposed to petroleum hydrocarbons. This data is extremely useful for models currently being developed to assist in creating remediation targets for the sub-Antarctic, as the models require a certain number of species from a minimum number of taxonomic groups.


To read more about this research, download a copy of the manuscript for free* by clicking the link below.

Impact of hydrocarbons from a diesel fuel on the germination and early growth of subantarctic plants
GK Macoustra, CK King, J Wasley, SA Robinson and DF Jolley
Environ. Sci.: Processes Impacts, 2015, Advance Article
DOI: 10.1039/C4EM00680A

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About the webwriter

Abha Parajulee is a Ph.D. student at the University of Toronto Scarborough. She is interested in water resources and the behavior of organic contaminants in urban environments.

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* Access is free until 06/09/2015 through a registered RSC account.

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