Monitoring of abiotic degradation of photocrosslinked silicone acrylate coatings: the fate of the photoinitiator.

Photocrosslinked silicone acrylates are used in a variety of applications, such as printing inks, adhesives, or adhesive release liners. Their production requires the use of a photoinitiator. Even if the photoinitiator represents a minor mass in the photocurable formulation (2-10%), it is used in excess and residual amounts may therefore remain in the polymerized products and possibly migrate into the environment during the use of the products and/or at their end-of-life stage. Little is known on the possible degradation of silicone acrylate which may increase the potential release. The present study investigated the release of Darocur 1173, the most commonly used photoinitiator, from silicone matrix and the effect of accelerated photoageing on the extent of the phenomenon. Leaching tests in water were conducted on thin-coated plastic film (release liners) made of a mixture of polypropylene and polyethylene. Results showed that 44% of the Darocur 1173 photoinitiator initially used in silicone formulation was released from silicone matrix in the leaching test. Accelerated photoageing obtained by UV irradiation of the films for up to 200 h was found to favor photoinitiator degradation but also induced a strong and fast oxidation of silicone-coated liners as compared to that of uncoated ones. Graphical abstract.

"NiCo Buster": engineering E. coli for fast and efficient capture of cobalt and nickel.

BACKGROUND: Metal contamination is widespread and results from natural geogenic and constantly increasing anthropogenic sources (mainly mining and extraction activities, electroplating, battery and steel manufacturing or metal finishing). Consequently, there is a growing need for methods to detoxify polluted ecosystems. Industrial wastewater, surface water and ground water need to be decontaminated to alleviate the contamination of soils and sediments and, ultimately, the human food chain. In nuclear power plants, radioactive metals are produced; these metals need to be removed from effluents before they are released into the environment, not only for pollution prevention but also for waste minimization. Many physicochemical methods have been developed for metal removal from aqueous solutions, including chemical coagulation, adsorption, extraction, ion exchange and membrane separation; however, these methods are generally not metal selective. Bacteria, because they contain metal transporters, provide a potentially competitive alternative to the current use of expensive and high-volume ion-exchange resins. RESULTS: The feasibility of using bacterial biofilters as efficient tools for nickel and cobalt ions specific remediation was investigated. Among the factors susceptible to genetic modification in Escherichia coli, specific efflux and sequestration systems were engineered to improve its metal sequestration abilities. Genomic suppression of the RcnA nickel (Ni) and cobalt (Co) efflux system was combined with the plasmid-controlled expression of a genetically improved version of a specific metallic transporter, NiCoT, which originates from Novosphingobium aromaticivorans. The resulting strain exhibited enhanced nickel (II) and cobalt (II) uptake, with a maximum metal ion accumulation of 6 mg/g bacterial dry weight during 10 min of treatment. A synthetic adherence operon was successfully introduced into the plasmid carrying the improved NiCoT transporter, conferring the ability to form thick biofilm structures, especially when exposed to nickel and cobalt metallic compounds. CONCLUSIONS: This study demonstrates the efficient use of genetic engineering to increase metal sequestration and biofilm formation by E. coli. This method allows Co and Ni contaminants to be sequestered while spatially confining the bacteria to an abiotic support. Biofiltration of nickel (II) and cobalt (II) by immobilized cells is therefore a promising option for treating these contaminants at an industrial scale.

Silicone-based surfactant degradation in aqueous media.

The increasing use of surfactants, such as modified polydimethylsiloxane-graft-polyethylene oxide (PDMS-g-PEO), requires studies on the fate of these compounds in the environment, and in particular in wastewater systems. A kinetic study, performed under three different pH conditions (pH2, 5.3 and 11) and using (1)H NMR (Nuclear Magnetic Resonance), proves that hydrolysis of the siloxane chain takes place in all cases, with higher rates for the two extreme conditions. Steric exclusion chromatography (SEC) clearly showed a decrease in the average molecular weight of the copolymer leading to a new molecular weight distribution, especially in acidic conditions. Degradation products, analyzed by (29)Si NMR, were found to be similar whatever the degradation pathway, namely silanediols and cyclic volatile compounds (degradation products of PDMS) and also PEO-modified silanediols and cyclic compounds. After one year, the siloxane chain completely disappeared under acidic conditions. Real wastewater medium has a strong effect on polymer stability, indicating that pH is not the only parameter which influences degradation rate.

Volatile organic silicon compounds: the most undesirable contaminants in biogases.

Recently a lot of attention has been focused on volatile organic silicon compounds (VOSiC) present in biogases. They induce costly problems due to silicate formation during biogas combustion in valorisation engine. The cost of converting landfill gas and digester gas into electricity is adversely affected by this undesirable presence. VOSiC in biogases spark off formation of silicate deposits in combustion chambers. They engender abrasion of the inner surfaces leading to serious damage, which causes frequent service interruptions, thus reducing the economic benefit of biogases. It is already known that these VOSiC originate from polydimethylsiloxanes (PDMS) hydrolysis. PDMS (silicones) are used in a wide range of consumer and industrial applications. PDMS are released into the environment through landfills and wastewater treatment plants. There is a lack of knowledge concerning PDMS biodegradation during waste storage. Consequently, understanding PDMS behaviour in landfill cells and in sludge digester is particularly important. In this article, we focused on microbial degradation of PDMS through laboratory experiments. Preliminary test concerning anaerobic biodegradation of various PDMS have been investigated. Results demonstrate that the biotic step has an obvious influence on PDMS biodegradation.

Cr(VI) reduction into Cr(III) as a mechanism to explain the low sensitivity of Vibrio fischeri bioassay to detect chromium pollution.

Vibrio fischeri bacteria, used as a biological target in either acute or chronic toxicity tests, display a low sensitivity to Cr(VI). This phenomenon could be due to the capacity of these bacteria to reduce Cr(VI) into Cr(III). This reducing capacity was found to depend on culture medium composition, pH value, incubation time and the presence of a carbon source. It also depends on the nature of the carbon source, glucose being more efficient than glycerol. This is probably related to differences in bacterial metabolism when given either glucose or glycerol. The thermostable Cr(VI)-reducing activity found in the supernatants of V. fischeri cultures grown on glucose suggests that, under these conditions, the bacteria release non-proteic reducing substances which have not been identified yet.