Polycyclic aromatic hydrocarbon record in an urban secondary carbonate deposit over the last three centuries (Paris, France).

Preserving water resources and limiting pollution are central environmental issues in the current context of intense anthropization. Among organic pollutants, polycyclic aromatic hydrocarbons (PAHs) are commonly analysed as part of water quality assessments. After being emitted into the atmosphere, these persistent organic pollutants are deposited on the continental surface, where they are transported to the aquatic environment by run-off and infiltration waters. Mainly due to anthropogenic emissions, PAHs can therefore be considered as a proxy for human activities. Urban secondary carbonate deposits (USCDs), similar to cave speleothems, have recently been studied for their potential as natural archives of water quality. However, USCDs have never been used to trace water organic pollution and only a few studies on PAHs in speleothems are available. This study focuses on a well-dated USCD covering the last 300 years from the Great Aqueduct of Belleville (north-east of Paris, France). The aim is to determine the nature and variation of trapped organic compounds over time and to discuss their origin, transport, and link with changes in soil occupation due to human activities. To do so, high-resolution solid-phase UV fluorescence imaging analyses were combined with chemical analyses of PAHs and organic carbon carried out on low-weight samples. The results show that PAHs have been present in urban surface water for 300 years. Over the last few decades, a 7-fold increase is observed, accompanied by a change in the pollution source, enriched in high-molecular-weight PAHs, probably linked to urban dust. This study also reveals modes of transport directly influenced by changes in the soil occupation that are very different from those usually encountered in natural environments. This work thus paves the way for a better long-term understanding of the impact of human activity on the transfer of pollutants to sub-surface waters.

The biological invasion of an apex predator (Silurus glanis) amplifies PCB transfer in a large lake food web.

Invasive species can affect food web structure possibly modifying the transfer of pollutants in ecosystems but this facet of biological invasion remains largely unexplored. We examined how trophic and ontogenetic characteristics of the invasive European catfish could differ from its native counterpart, the Northern pike, possibly resulting in the amplification of PCB transfer to the higher trophic levels in a large lake food web. The PCB contents of catfish and pike were on average low (Æ©7 PCBi 42.4 ± 38.6 ng g-1 ww and 37.9 ± 49.4 ng g-1 ww respectively) and dominated by PCB153 (~35 % of the PCB contamination). Only the largest pike (126 cm) slightly exceeded the European sanitary threshold of 125 ng g-1 ww Æ©6 PCBi-NDL. Both species increased in trophic position with body size while catfish had clearly higher littoral reliance than pike indicating they exploited complementary trophic niches. PCB biomagnification was identified only for catfish (PCB153, Æ©7 PCBi) leading to trophic magnification factor of ~5. PCB ontogenetic bioaccumulation was pervasive for catfish (PCB101, PCB118, PCB153, PCB138 and Æ©7 PCBi) and identified for pike only regarding PCB101. The derived size accumulation factors (~1.02) indicated a size-doubling PCB contamination of ~40 cm for catfish. This finding suggested that catfish would exceed the European sanitary threshold at body size larger than 168 cm possibly constraining their commercial exploitation. Our results highlighted that the invasive catfish was a littoral-oriented apex predator occupying an alternative trophic niche as compared to pike thereby modifying the lake food web structure that resulted in an enhancement of PCB transfer to higher trophic levels. The biomagnification and ontogenetic bioaccumulation of catfish underlined the impact of this biological invasion on the fate of PCB in the ecosystem. Finally, the remarkable inter-individual PCB contamination suggested variable inter-individual PCB exposure likely associated to localized hotspots of PCB contamination in the lake.

Polycyclic aromatic hydrocarbon dynamics in soils along proglacial chronosequences in the Alps.

Polycyclic aromatic hydrocarbons (PAHs) were studied in the soils of three proglacial areas in France (Noir and Chardon Glaciers) and Italy (Miage Glacier). PAH contents, PAH stocks and PAH contents normalized to the total organic carbon contents (PAHs/TOC ratio) were investigated along proglacial soil chronosequences to infer their evolutions with soil age (from 3 to 4200 years), where the PAH contamination was only related to long-range atmospheric transport. Evolutions of PAH and TOC contents, PAHs/TOC ratio and PAH stock were fitted with exponential and logarithmic relations. For the three proglacial areas, PAH contents increased rapidly during the first 150 years of soil development, ranged from 4 to 152 ng·g-1, and showed a strong relationship with total organic carbon (TOC) contents (r = 0.83, p < 0.05). The joint increase of PAH and TOC contents suggested that PAH accumulation in soils were not only driven by PAH inputs but also by the capacity of soils to store these contaminants. PAH contents in the oldest soils (from 1200 BCE and 2200 BCE) were similar than for soils from 1850 CE. The period 1850-2019 CE corresponded to a decrease in the PAHs/TOC ratio suggesting both a faster accumulation of TOC than PAHs and a dilution effect of PAHs already present in soils. For the oldest soils, the PAHs/TOC ratio appeared similar to those for soils from 1850 CE, with values ranging from 0.48 to 2.06 ng·mg-1, suggesting an equilibrium between both parameters for soils older than 170 years. Finally, PAH stocks ranged from 0.41 mg·m-2 to 6.80 mg·m-2 in the youngest and oldest soils, respectively. These results do not allow us to identify the same period of greatest emission as other studies (estimated ~1960), but they revealed changes in the capacity of soils to store these pollutants.

Evolution of pace-of-life syndrome under conditions of maternal PCB contamination and global warming in early life stages of cold stenothermic fish (Arctic char).

The end of the 20th century was characterised by rapid modifications of ecosystem functioning under different pressures (such as eutrophication and toxic pollution). Increasing temperatures in the context of global warming could have indirect consequences, such as increased bioavailability of hydrophobic organic pollutants amongst aquatic species. According to the "pace-of-life syndrome" (POLS) theory, these stressors could lead to covariations in many life traits. Lake Bourget is the largest natural lake in France and has been highly polluted from the fifties to the eighties both with a high load of nutrients (wastewater discharge) and polychlorinated biphenyls (PCBs) (industrial effluent discharge). Despite improvements in water quality since the 21st century, PCB levels are still higher than the United States Environmental Protection Agency cut-off for wildlife protection. The population of Arctic char, a cold stenothermic salmonid, has remained low in Lake Bourget for the last ten years despite restocking efforts and complete re-oligotrophication. We hypothesised that PCB pollution can affect the Arctic char population and that the increase in water temperature could magnify the effects of PCB. Thus, this study aimed to investigate the effects of maternal PCB contamination on offspring using a multiparametric and multiscale approach. Female Arctic char were contaminated with PCB before spawning, and each fertilised spawn was incubated at two temperatures (4 and 8.5 °C). The results showed that co-exposure to increased temperature and maternal PCB contamination influenced biodemographic, physiological, and behavioural parameters. The effects were highly dependant on the developmental stage. Based on the POLS theory, a continuum of life traits that may reflect potential physiological and behavioural modifications in response to these concurrent stressors is highlighted.

Diversity, Functions and Antibiotic Resistance of Sediment Microbial Communities From Lake Geneva Are Driven by the Spatial Distribution of Anthropogenic Contamination.

Lake sediments are natural receptors for a wide range of anthropogenic contaminants including organic matter and toxicants such as trace metals, polycyclic aromatic hydrocarbons, polychlorinated biphenyls that accumulate over time. This contamination can impact benthic communities, including microorganisms which play a crucial role in biogeochemical cycling and food-webs. The present survey aimed at exploring whether anthropogenic contamination, at a large lake scale, can influence the diversity, structure and functions of microbial communities associated to surface sediment, as well as their genetic potential for resistance to metals and antibiotics. Changes in the characteristics of these communities were assessed in surface sediments collected in Lake Geneva from eight sampling sites in October 2017 and May 2018. These sampling sites were characterized by a large concentration range of metal and organic compound contamination. Variation between the two sampling periods were very limited for all sampling sites and measured microbial parameters. In contrast, spatial variations were observed, with two sites being distinct from each other, and from the other six sites. Benthic communities from the most contaminated sampling site (Vidy Bay, near the city of Lausanne) were characterized by the lowest bacterial and archaeal diversity, a distinct community composition, the highest abundance of antibiotic resistance genes and functional (respiration, denitrification, methanogenesis, phosphatase, and beta-glucosidase) activity levels. The second sampling site which is highly influenced by inputs from the Rhône River, exhibited low levels of diversity, a distinct community composition, high abundance of antibiotic resistance genes and the highest bacterial abundance. Overall, our results suggest that local anthropogenic contamination, including organic matter and toxicants, is a major driver of the diversity and functioning of sediment-microbial communities in Lake Geneva. This highlights the need to consider benthic microbial communities and a suite of complementary ecotoxicological endpoints for more effective environmental risk assessments of contaminants in lake sediments.

Microplastic pollution of worldwide lakes.

Studies on microplastic (MP) pollution in lakes are recent, although the problem of MP particles in the oceans was first discovered in the 1970s. The first study on lakes was published in 2011. Since then, to our knowledge, 98 lakes have been investigated worldwide. In recent years, studies on this topic have increased worldwide, particularly those focusing on urbanised lakes. Most of the plastic waste in the seas and oceans originates from the terrestrial environment and inland waters. Moreover, lakes are potential temporary or long-term MP accumulators, according to the residence time of water. They are also of high interest for biodiversity, ecology, and the economy. Lacustrine ecosystems may suffer the same fate as marine ecosystems, or even worse, owing to their greater exposure. With the significant focus on ocean and sea contamination, contamination of freshwater ecosystems and lakes is a new and rising topic. However, as a new field of research, several methodological issues have been raised. The team diversity worldwide has led to contrasting sampling techniques and materials, sample treatments, analyses, and presentation of results. Consequently, it is necessary to determine several consensuses between scientific teams in order to work together with accuracy, produce comparable results, speed up knowledge sharing and reduce the reproducibility crisis. This review focuses on (1) MP contamination in 98 worldwide lakes. We identify (2) the theoretical sources of MPs and provide (3) an estimate of MP pollution in different compartments of the lakes based on current state-of-the-art methods. In addition, we also report (4) the predominant MP size classes and polymer types. Finally, we suggest (5) several recommendations to build a consensus between all the working teams to facilitate decision-making by public authorities.

Water-level fluctuation enhances sediment and trace metal mobility in lake littoral.

Water-level fluctuation (WLF) is a widespread management action in lakes and reservoirs whose impacts on contaminant fate have seldom been investigated. We used near shore hourly measurements (n = 2122) of turbidity (contaminant proxy) and water velocity (sediment resuspension proxy) to track high-frequency contaminant dynamics during a 0.6 m change in water level observed in autumn 2017 in a large French lake. Simultaneously, discrete trace metal measurements highlighted that trapped sediment was more contaminated and finer than surficial sediment supporting that suspended particles (measured by turbidity) were a preferential medium for contaminant mobility. General additive models involving tensor products revealed the enhancement of wind-speed and river discharge effects on turbidity with water draw down. The decrease of the explained deviances by the models over time-lags indicated short time-scale response of turbidity to external forcing. Three of the four major turbid events occurred at the lowest water-level and were concomitant of sediment resuspension as well as precipitation events and/or river flood suggesting a complex interplay among in-lake and watershed processes at controlling sediment mobility during the WLF. These results shed in light that WLF can affect lake littoral hydrodynamic cascading up to the enhancement of contaminant mobility. Sediment resuspension may be an overlooked feature of WLF increasing contamination risk and exposure for littoral organisms with widespread ecological consequences due to the large number of water-level regulated ecosystems.

Tracking sources and transfer of contamination according to pollutants variety at the sediment-biota interface using a clam as bioindicator in peri-alpine lakes.

Point pollution sources may differently impact lakes littoral, possibly leading to local ecological risks. The concomitant chemical analysis of littoral-benthic organisms and sediment can provide insights into the bioavailability and thus the ecological risk of contaminants. In this study, the autochthonous Corbicula fluminea was used to assess the sources and transfer of six trace metals (TMs) and fourteen Polycyclic Aromatic Hydrocarbons (PAHs) to the littoral-benthic biota of a large lake. The contaminant concentrations spatially varied with a value scale from 1 to 280 000 times along the lake littoral in both the sediment and clams. Multiple linear regressions were performed to explain the spatial variability of Corbicula fluminea contamination by considering both watershed and in-lake sources. The concentration of the sum of PAHs in clams was significantly correlated with sediment contamination, suggesting that PAHs contamination of the benthic biota mainly occur from the sediment. Most of the internal TM concentrations of clams were significantly correlated with stormwater drainage areas in the lake watershed, highlighting the importance of stormwater runoffs in the littoral biota contamination. The transfer of TMs and PAHs was assessed through the bioconcentration factor defined as the ratio of internal and sediment concentrations. As, Cd, Cu, Zn and light molecular weight PAHs were more bioconcentrated in C. fluminea than Pb, Sn and heavy molecular weight PAHs, suggesting differences in their bioavailability. This study underlines the relevance of using autochthonous organisms as bioindicators of lake littoral biota contamination concomitantly with sediment matrices, and illustrates the challenge of tracking pollution sources in lakes.

PCB mass budget in a perialpine lake undergoing natural decontamination in a context of global change.

Despite the fact that PCB contamination of the global environment has been extensively studied in the last decades, the fate of these compounds in freshwater ecosystems is not fully understood and an important knowledge gap remains regarding the understanding of PCB dynamics and fate in perialpine lakes. This study relied on both field sampling performed and modeling to accurately identify the main fluxes involved in the PCB dynamics into the French perialpine Lake Bourget from 2013 to 2017. Our results show that the main inputs responsible for the PCB loading of the water column are tributaries inflows (~90%) rather than atmospheric inputs which could be related to the high catchment area over lake surface area ratio (i.e., 13). The main mechanism responsible for the lake natural decontamination was sediment burial (76%) due to the effect of the biological pump coupled with a high sedimentation rate. Volatilization represented 19% of the loss of PCBs from the water column and was mainly controlled by the high PCB concentration in water. These mechanisms are susceptible to be affected by the impact of the global change (increase of temperature, modification of the primary production rate) in the near future.

Looking at biological community level to improve ecotoxicological assessment of freshwater sediments: report on a first French-Swiss workshop.

The first French-Swiss workshop on ecotoxicology of freshwater sediment communities was co-organized by the French Research Institute of Science and Technology for Environment and Agriculture (Irstea) and the Swiss Centre for Applied Ecotoxicology (Ecotox Centre EAWAG-EPFL) in Villié-Morgon (Beaujolais Region, France) on April 27-28, 2017. The workshop brought together scientists working in different fields of expertise (ecotoxicologists, ecologists, environmental chemists…), environmental stakeholder groups and managers, as well as economic players (start-ups and consultancies) to better connect research needs of potential end-users with research outputs. The objectives of this workshop were (i) to establish the state of the art of research in the characterization of sediment contamination and in the evaluation of the effects on sediment-associated biological communities and ecosystem functioning and (ii) to give an overview of the French and Swiss regulations dealing with the assessment of contaminated sediments in freshwater ecosystems. The ultimate goal was to collectively identify research needs and knowledge gaps, as well as to highlight ways to improve the ecotoxicological assessment of sediments in freshwater environments by further considering the structure and functions of associated microbial and invertebrate communities.

Avoid the PCB mistakes: A more sustainable future for ionic liquids.

Based on our original knowledge and experience on both polychlorinated biphenyls (PCBs) identification in aquatic ecosystems, and use of ionic liquids (ILs) as solvents and/or co-catalysts in green chemistry, we drawn a dared comparison between these two families. Indeed, PCBs has been used during several decades for their new properties, but are now considered as prevalent and persistent pollutants; some toxic effects on environment or human are still revealed. ILs, often designated as "green solvents" are increasingly used in numerous applications, but few studies reported about their environmental impact are still controversial. Through a parallel between properties and applications of PCBs and ILs, we wondered if history could not repeat itself, and how to provide a better future for ILs. Here, we provide some interesting comparisons and we discuss which tracks it could be important to follow for ILs applications in order to avoid the errors done with PCBs.

Particle-Dissolved Phase Partition of Polychlorinated Biphenyls in High Altitude Alpine Lakes.

We investigated whether polychlorinated biphenyls (PCBs) partitioning between the dissolved and particulate phases in two high altitude alpine lakes was determined by the quantity, size structure, or composition of suspended particles. Within- and between-lakes differences in water-particulate phase partition coefficient (Kp) were not related to total suspended matter, phytoplankton biomass, or taxonomic composition. Yet, a seasonal relationship between Kp and Kow was detected for both lakes, revealing equilibrium of PCBs partition when lakes were ice covered. On the contrary, PCBs partitioning between particles and water appeared kinetically limited during the open water season. Partition is therefore mainly governed by thermodynamic laws during the ice-covered period, while none of the tested physical or biological parameters seemed to explain the distribution of these particle-reactive contaminants in the open water period. PCBs were always mainly associated with particulate matter, but partitioning within different particulate size-fractions varied between seasons and between years during open water periods. When ice cover is absent, PCBs were mainly adsorbed on microplankton, the largest phytoplanktonic size fraction, which is the least likely to get grazed by pelagic microconsumers.

Historical profiles of PCB in dated sediment cores suggest recent lake contamination through the "halo effect".

We investigated the major sources of polychlorinated biphenyls (PCB) and interpreted the environmental fate processes of these persistent organic pollutants in the past and current PCB contamination of three large, urbanized, French peri-alpine lakes. Dated sediment cores were analyzed in order to reconstruct and compare the historical contamination in all three lakes. Stratigraphic changes of PCB contents and fluxes were considered as revealing the temporal dynamics of PCB deposition to the lakes and the distribution of the seven indicator congeners (further referred to as PCBi) as an indicator of the main contamination origin and pathway. Although located within a single PCB industrial production region, concentration profiles for the three lakes differed in timing, peak concentration magnitudes, and in the PCBi congeners compositions. PCBi fluxes to the sediment and the magnitude of the temporal changes were generally much lower in Lake Annecy (0.05-2 ng·cm(-2)·yr(-1)) as compared to Lakes Geneva (0.05-5 ng·cm(-2)·yr(-1)) and Bourget (5-290 ng·cm(-2)·yr(-1)). For all three lakes, the paramount contamination occurred in the early 1970s. In Lakes Annecy and Bourget, PCB fluxes have declined and plateaued at 0.5 and 8 ng·cm(-2)·yr(-1), respectively, since the early 1990s. In Lake Geneva, PCB fluxes have further decreased by the end of the XX(th) century and are now very low. For the most contaminated lake (Lake Bourget), the high PCBi flux (5-290 ng·cm(-2)·yr(-1)) and the predominance of heavy congeners for most of the time period are consistent with a huge local input to the lake. This still high rate of Lake Bourget is explained by transport of suspended solids from one of its affluents, polluted by an industrial point source. Intermediate historical levels and PCBi distribution over time for Lake Geneva suggest a mixed contamination (urban point sources and distant atmospheric transport), while atmospheric deposition to Lake Annecy explains its lowest contamination rate. The presently low contamination levels recorded in Lake Geneva correspond to atmospheric inputs, but the recent PCBi distribution of Lake Annecy, enriched in relatively heavy congeners, reveals a contamination by the neighboring Lake Bourget, following a halo effect of about 40 km radius.

Mass budget in two high altitude lakes reveals their role as atmospheric PCB sinks.

A mass budget of polychlorinated biphenyls (PCBs) was constructed for two altitude lakes located in the French Alps to (i) quantify inward and outward PCB flux over the entire year of 2012, (ii) hierarchize the dominant pathways of PCB transfers, and (iii) evaluate to what extent these pathways vary between both lakes. The annual PCB inputs were similar, and the glacial runoff and sediment-to-water exchange were negligible sources of PCBs to the water column relative to atmospheric deposition. The annual inputs were primarily introduced by snow deposition and transferred into the lakes during the few weeks of spring thaw. While the dominant deposition pathways were similar, the main processes by which the water column lost pollutants differed between the two lakes. Despite these differences, the mass budget revealed that PCB inputs exceeded outputs for both studied lakes and that the lakes acted as atmospheric PCB sinks for the surrounding mountain environment. The differences in the PCB distribution between the key compartments (sediment and water column) are most likely due to differences in the lacustrine internal processes.

Long-term relationships among pesticide applications, mobility, and soil erosion in a vineyard watershed.

Agricultural pesticide use has increased worldwide during the last several decades, but the long-term fate, storage, and transfer dynamics of pesticides in a changing environment are poorly understood. Many pesticides have been progressively banned, but in numerous cases, these molecules are stable and may persist in soils, sediments, and ice. Many studies have addressed the question of their possible remobilization as a result of global change. In this article, we present a retro-observation approach based on lake sediment records to monitor micropollutants and to evaluate the long-term succession and diffuse transfer of herbicides, fungicides, and insecticide treatments in a vineyard catchment in France. The sediment allows for a reliable reconstruction of past pesticide use through time, validated by the historical introduction, use, and banning of these organic and inorganic pesticides in local vineyards. Our results also revealed how changes in these practices affect storage conditions and, consequently, the pesticides' transfer dynamics. For example, the use of postemergence herbicides (glyphosate), which induce an increase in soil erosion, led to a release of a banned remnant pesticide (dichlorodiphenyltrichloroethane, DDT), which had been previously stored in vineyard soil, back into the environment. Management strategies of ecotoxicological risk would be well served by recognition of the diversity of compounds stored in various environmental sinks, such as agriculture soil, and their capability to become sources when environmental conditions change.

Effect of nitrate ions on the efficiency of sonophotochemical phenol degradation.

A sonophotochemical oxidation process has been used for the treatment of an aqueous solution of phenol. The aim of this work is to evaluate the effect of nitrate ions on hydroxyl radical production and on phenol oxidation. It has been demonstrated that ultrasound can produce NOx (nitrate and nitrite), with a production rate of 2.2 µM min(-1). The photolysis of nitrate can significantly improve the hydroxyl radical production. The apparent rate constant for hydroxyl radical production increased from 0.0015 min(-1) to 0.0073 min(-1) while increasing initial nitrate concentration from 0 to 0.5mM. The concentration of hydroxyl radical was directly proportional to the initial nitrate concentration. Using US/UV process, the apparent reaction rate constant of phenol degradation in the presence of nitrate reached 0.020 min(-1), which was relatively lower than the value obtained (0.027 min(-1)) in the absence of nitrate. It appeared that, nitrate ions can inhibit the sonochemical degradation of organic compounds such as phenol.

Low frequency ultrasound-assisted leaching of sewage sludge for toxic metal removal, dewatering and fertilizing properties preservation.

The aim of this research was to evaluate the efficiency of an ultrasonication process in combination with METIX-AC technology, a chemical process, for metal removal and dewatering ability, with preservation of fertilizing properties of sewage sludge. Waste activated sludge samples having a total solids concentration of 4 and 20 g L(-1), were enriched with Cu and Zn in order to exceed the limiting values recommended by Québec regulation for sludge valorization. Ultrasonication was applied at low frequency (22 kHz) at specific energies ranging from 180 to 66,000 kJ kg(-1) of dry sludge. Ultrasound-assisted leaching rates and yields were similar to chemical leaching alone for Zn, whereas solubilisation was reduced for Cu, regardless the specific energy. Fertilizing properties preservation and dewatering ability were similar in ultrasound-assisted leaching, compared to chemical leaching alone. These trends were mainly attributed to the changes of metal speciation, particle size and morphology during ultrasonication, in addition to untreated sludge properties.

Sonochemical efficiency dependence on liquid height and frequency in an improved sonochemical reactor.

The aim of this study was to evaluate the effects of liquid height and frequency on sonochemical efficiency of a cup-horn sonoreactor. The selected frequencies (22, 371, 504 kHz) and liquid height (29-348 mm) were applied while measuring acoustic yield, I(3)(-) formation rate and the resulting sonochemical efficiency. The frequency effect was shown to be coupled to liquid height effect. Indeed, acoustic zones (i.e. Fresnel and Fraunhöfer zones), which limits depends on both transducer diameter and frequency, significantly determine the production of radicalar species quantified by I(3)(-) formation rate. An increase of ultrasonic frequency results in lower acoustic yield and higher sonochemical efficiency. Theoretical physical and chemical effects attributed to collapsing bubbles were considered. Sonochemical efficiencies obtained at 500 kHz were similar or higher than those at 371 kHz, depending on liquid height. The effect of reactor configuration was further investigated as an hypothesis to explain unsignificant effect of standing waves in our study. Therefore, the dependence of sonochemical efficiency with liquid height might be firstly attributed to reactor configuration prior to frequency effects.

Swift and efficient sono-hydrolysis of nitriles to carboxylic acids under basic condition: role of the oxide anion radical in the hydrolysis mechanism.

Carboxylic acids are promising candidates for new sustainable strategies in organic synthesis. In this paper, we ascertain the potential of ultrasound for the hydrolysis of nitriles into carboxylic acids through the study of key parameters of the reaction: pH, hydrolysis medium, reaction time and activation technique. The positive influence of ultrasound under basic conditions is due to more than mechanical effects of cavitation. Indeed, the rate of hydrolysis is dramatically increased under sonication in NaOH solutions. A radical mechanism involving the oxide anion radical O(*-) is proposed.

Comparison of characterization methods in high frequency sonochemical reactors of differing configurations.

The aim of this study was to compare different characterization methods in order to evaluate the sonochemical efficiency of a cavitational reactor. The selected characterization methods were calorimetry and dosimetry based on potassium iodide oxidation or nitrite and nitrate ion formation. The effects of experimental parameters on physical and chemical effects of ultrasound were quantified with two transducers at a frequency of 366kHz. The studied factors comprised temperature (16-28 degrees C), acoustic power (6-38W), power density (4-61WL(-1)) and reactor configuration (D(reactor 1)=65mm, D(reactor 2)=102mm). Spectrophotometry was compared to ionic chromatography as a method to quantify nitrite and nitrate ions. Spectrometry was shown to be as representative as ionic chromatography. The reaction system based on the formation of both nitrite and nitrate ions was demonstrated to be as reliable as a potassium iodide dosimeter. The representativity of calorimetry was limited since part of acoustic energy was assumed to be used in the chemical reactions observed by dosimetry. Similar sonochemical efficiencies resulted from an increase of sonified surface (D(reactor 1)=65mm vs. D(reactor 2)=102mm) coupled to a 2-time decrease in power density at a constant emitting surface. The effect of emitting-to-sonified surface area ratio on the acoustic field was apparently limited by the height of the liquid.