Environmental Science: Processes & Impacts blog

The (Mad) Hatter from Carroll's Alice in Wonderland (Illustration by John Tenniel - Public Domain)

The Hatter in Alice in Wonderland may not have been mad after all. He might have suffered from mercury poisoning! Thankfully, nowadays we know mercury is a dangerous element in almost all its forms. Organomercury compounds such as monomethylmercury (MMHg) and dimethylmercury (DMHg) are especially hazardous: not only because of their extreme toxicity but also because they can be bio-magnified in the food web. Moreover, mercury can travel the biosphere through air, water and soil, increasing the danger.

Even if we have stopped using mercury thermometers, a big number of household and industrial products still use this liquid metal. A lot of these products end up in landfills where they are treated as conventional waste, and may liberate dangerous amounts of this toxic metal to the atmosphere and soil.

In this critical review published in Environmental Science: Processes & Impacts, scientists analyze solid waste management in landfills and the chemistry of mercury, as well as the release of this metal into the environment and the possible bio and geological transformations it may suffer. As a conclusion, researchers review a series of studies that should be considered in depth in order to understand the problem of mercury release and to, eventually, find a solution.

As described in this work, landfills –mainly when they undergo the so-called anaerobic phase– present the ideal conditions (pH, redox, organic matter) for mercury to be speciated and transformed, then dissolved, mobilized and disseminated within the biosphere. It is mostly released as Hg(0) in gas form, but other species like MMHg and DMHg may also be produced and incorporated to soil and water reservoirs.

Whether you are a specialist in mercury or not, this review will surely captivate you. Landfills may seem boring, but the chemistry underneath is fascinating, like the liquid metal that fascinated alchemists for centuries. Remember, mercury was the prima materia from which all metals were formed!

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

Biogeochemical transformations of mercury in solid waste landfills and pathways for release
Sung-Woo Lee, Gregory V. Lowry and Heileen Hsu-Kim.
Environmental Science: Processes & Impacts 2016, 18, 176-189
DOI: 10.139/C5EM00561B

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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 18/03/2016 through a registered RSC account.

Passive air samplers (PAS) have found great utility in monitoring environmental concentrations of semivolatile organic contaminants (SVOCs) all over the world. They provide a picture of longer-term average air concentrations of SVOCs while being relatively portable, low-cost and extremely low-maintenance. Knowing the deployment time, the amount of chemical accumulated in the passive sampling medium (PSM), and the sampling rate derived when a PAS is first calibrated before widespread use, a time-averaged volumetric air concentration can be calculated.

Graphical Abstract

A key assumption underlying the calculation of PAS-derived air concentrations is that the passive sampling medium takes up chemicals uniformly. But this assumption has not been thoroughly tested so far and studies to date have indicated that the sampling rates of some commonly used PSM can differ with position inside a sampler housing. For example, sampling rates decreased with increasing distance from the opening at the bottom of a cylindrical sampler housing for the commonly used styrene-divinylbenzene copolymer or “XAD” resin.

In a study recently published in Environmental Science: Processes & Impacts, Zhang and co-workers at the University of Toronto Scarborough have put their XAD PAS to the test once more to determine if exposure to sunlight, wind, and the presence of multiple units of XAD-filled mesh cylinders in one PAS housing caused differential chemical uptake across the length of a single cylinder.

The chemicals of interest in this series of experiments, polychlorinated biphenyls (PCBs), were chosen because their environmental partitioning properties are inclusive of a range of SVOCs commonly measured in the environment. One indoor experiment included axially segmented PAS at four indoor locations, one of which also used fans to simulate the effect of wind. At one of the indoor locations, a similar experiment was conducted outdoors, where the effect of heat conduction resulting from sunshine was also tested. This involved using PAS with regular housings, housings painted black to enhance heat absorption, and housings shaded by a steel cover.

Two additional experiments varied the number of mesh cylinders inside each housing. One experiment deployed a pair of PAS containing one and four mesh cylinders at one outdoor and one indoor location. A final outdoor experiment attempted to incorporate a variety of temperatures and wind speeds by deploying PAS at nine locations on the Big Island of Hawaii. Each site had one PAS containing one XAD-filled mesh cylinder and another containing two.

Environmental Science: Processes & Impacts front cover image highlighting the article

In the first indoor experiment, the total amount of PCBs accumulated in all segments was not significantly different from the amount accumulated in a mesh cylinder that had not been segmented. In those cylinders that were axially segmented, the amount of PCBs accumulated in the bottom segments was significantly higher than in the upper two segments in office and storage areas, and assumed to have little activity and therefore air turbulence. But this difference was not significant in the mesh cylinder placed in a cargo-loading area, presumably because of the relatively higher level of activity and therefore air turbulence. Similarly, gradients within PAS deployed outdoors were also not as strong, and the samplers exposed to fans indoors showed no significant gradients – strong indications that increased air turbulence allows for more uniform uptake across the length of the sampler.

The effect of heat convection on total accumulation and axial distribution of PCBs was determined to be minor, as was the presence of multiple mesh cylinders within one housing, but only outdoors. Indoors, the amount of PCB accumulated per sampler was significantly lower in those PAS with four mesh cylinders, and the gradient was also steeper.

The final outdoor deployment across varying temperature and wind conditions in Hawaii, which measured accumulation of PCBs, pesticides, polycyclic aromatic hydrocarbons, and polybrominated diphenyl ethers, showed no significant difference in chemical accumulation in PAS with one versus two XAD-filled mesh cylinders. The finding that uptake of SVOCs by XAD PAS is affected very little by the presence of multiple mesh cylinders in one housing in a variety of outdoor conditions means that fewer housings can be used during a given sampling campaign that uses XAD PAS. This augments the low-maintenance nature of this monitoring method, and thus the value of this particular PAS as a tool for monitoring SVOCs in the environment.

To read the full Open Access article, click the link below:

Exploring the role of the sampler housing in limiting uptake of semivolatile organic compounds in passive air sampler
Xianming Zhang, Michelle Hoang, Ying D. Lei, and Frank Wania
Environ. Sci.: Processes Impacts, 2015, 17, 2006-2012
DOI: 10.1039/C5EM00447K

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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.

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.

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.

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?

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.

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.

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.

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.