Cellular and molecular damage caused by high UV-C irradiation of the cave-harvested green alga Chlorella minutissima: Implications for cave management

International audienceAlgal biofilms in caves visited by tourists are a significant threat to karstic formations. They cause a dirty greenish appearance on cave formations and provoke biophysical and biochemical erosion. Seeking an alternative to the use of chemicals, we investigated the effects of high doses of UV-C irradiation on the green algae Chlorella minutissima-dominating biofilms in the Moidons Cave (Jura, France). The algae were harvested and subjected to laboratory subculturing under conditions similar to the conditions in the cave (low temperatures and a short photoperiod with weak light intensities). After one or two doses of UV-C of 150 or 300 kJ m−2, the samples were incubated for 21 days, and the physiological parameters (pigment concentrations and photosynthetic activity) were monitored every seven days. Hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations were also measured to detect oxidative stress, and analyses of DNA integrity were performed. The results showed that all UV-C treatments caused chlorophyll bleaching with completely inhibited metabolic activity. In addition, high UV-C doses caused oxidative stress and programmed cell death. Irradiation was tested on a natural biofilm that proliferated in the Moidons Cave. Colorimetric measurements of the treated biofilm indicated that UV-C treatment caused significant chlorophyll bleaching

Effects of sodium chloride salinity on ecophysiological and biochemical parameters of oak seedlings (Quercus robur L.) from use of de-icing salts for winter road maintenance

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Sewage sludge application in a plantation: effects on trace metal transfer in soil-plant-snail continuum

International audienceWe studied the potential bioaccumulation of Cu, Zn, Pb and Cd by the snail Cantareus aspersus and evaluated the risk of leaching after application of sewage sludge to forest plantation ecosystems. Sewage sludge was applied to the soil surface at two loading rates (0, and 6 tons ha− 1 in dry matter) without incorporation into the soil so as to identify the sources of trace metal contamination in soil and plants and to evaluate effects on snail growth. The results indicated a snail mortality rate of less than 1% during the experiment, while their dry weight decreased significantly (< 0.001) in all treatment modalities. Thus, snails showed no acute toxicity symptoms after soil amendment with sewage sludge over the exposure period considered. Additions of sewage sludge led to higher levels of trace metals in forest litter compared to control subplots, but similar trace metal concentrations were observed in sampling plants. Bioaccumulation study demonstrated that Zn had not accumulated in snails compared to Cu which accumulated only after 28 days of exposure to amended subplots. However, Pb and Cd contents in snails increased significantly after 14 and 28 days of exposure in both the control and amended subplots. At the last sampling date, in comparison to controls the Cd increase was higher in snails exposed to amended subplots. Thus, sludge spread therefore appears to be responsible for the observed bioaccumulation for Cu and Cd after 28 days of exposure. Concerning Pb accumulation, the results from litter–soil–plant compartments suggest that soil is this metal's best transfer source

Sewage sludge as a soil amendment in a Larix decidua plantation: Effects on tree growth and floristic diversity

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Sewage sludge fertilization in larch seedlings: effects on trace metal accumulation and growth performance

International audienceThe spreading of sewage sludge (SS) among forest plantations may provide interesting results for firewood production. While sludges are good fertilizers, they may nevertheless contain trace metals, which can reduce productivity and lead to environmental risks. We investigated the effects of SS application on nutrient uptake and growth parameters in larch seedlings (Larix decidua) and determined trace metal and mineral distribution. Without incorporation into the soil, sludge was applied to the soil surface at three rates (0, 30 and 60 t dry weight DW ha−1). The plants were harvested after 12 months. The results showed significantly increased nitrogen and phosphorus concentrations in the top soil layer in pots amended with sludge, whereas no changes appeared in the lower layers. Similar results were obtained for the Cu, Zn and Cd concentrations. However, no differences were observed for the other measured soil mineral elements. Nitrogen concentrations in needles increased with rising sewage sludge application rates, yet the sludge had no effect on the P, Mg, Zn, Pb and Cd concentrations. In addition, Cu accumulated only in the lateral roots of seedlings that received the highest sludge loading rate. Sludge application improved the net photosynthesis, which resulted in higher chlorophyll contents in the needles. Following application, the dry matter accumulation rate increased due to the excessive availability of N, whereas available mineral elements in the plant tissues were diluted. Furthermore, amending the soil with sewage sludge can promote a higher biomass yield which may result in an increased trace metal bioaccumulation capacity in plants. Though this investigation has established the benefits of municipal SS application, further studies are needed to assess the potential transfer of TM to groundwater and through the food chain

Land spreading of sewage sludge in forest plantations: effects on the growth of the duckweed Lemna minor and trace metal bioaccumulation in the snail Cantareus aspersus

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UV–C irradiation as a tool to eradicate algae in caves

Algal proliferation has commonly been reported to occur on monuments, such as crypts, churches, and caves, as soon as artificial lighting is used. In this work we study the effects of UV–C irradiation on algae collected in different caves in Dordogne (southwest of France). First, the effect of UV–C irradiation was tested on algal cell suspensions during increasing exposure times. After treatment, the photosynthetic capacity was assayed using a polarometric method, and algal cell viability was then estimated using a Trypan blue test after a rest period of 15 h. UV–C irradiation was then studied on algal cells cultivated on a solid support consisting of pieces of calcareous stone. Drops of concentrated algal cells were inoculated on stone and exposed to UV–C radiation for 3, 6, or 9 h. After this irradiation, half of the samples were submitted to a high white light intensity (1400 μmol m−2 s−1 of photosynthetically active radiation, PAR) for 6 h while the other half were incubated in the culture room. Subsequently, algal macroscopic parameters such as covering rate and colonized area were measured by macro photography. Both experiments led to the conclusion that UV–C irradiation has deleterious effects on photosynthetic parameters and growth of algal cells

UV IRRADIATION AS AN ALTERNATIVE TO CHEMICAL TREATMENTS: A NEW APPROACH AGAINST ALGAL BIOFILMS PROLIFERATION CONTAMINATING BUILDING FACADES, HISTORICAL MONUMENTS AND TOURISTIC SUBTERRANEAN ENVIRONMENTS

In the conservation field of buildings, historical monuments and subterranean environments, very few studies highlight the importance to find alternative methods to chemical products against algal biofilm proliferation. Indeed, biofouling by microorganisms is a well-known biodeterioration phenomenon. Algae are considered as pioneers in the biodeterioration of stone, and that's why they are subject to a special interest in this chapter. Conservators of monuments or art works used many chemical applications to prevent or to control the algal proliferation on stone. But, due to the changes in European standards on their use, the chemical products must be replaced by environmentally friendly processes. The ultraviolet irradiation appeared to be a suitable process to control algal proliferation in these environments. Firstly in this chapter, we describe the problematic of algal biofilms (proliferation and biodeterioration) on different substrata and also the effects of applied chemical treatments. Secondly, we define and characterize the UV light and its effects on living organisms. Finally, we present the experimental design and the obtained results on algae harvested in caves at the cellular and molecular scales (pigment contents, photosynthetic activity, DNA damages...) and at the biofilm scale (proliferation measurements). This study shows that the UV treatment can be used as a conservation tool to eradicate algal biofilms which proliferate in buildings and monuments

Factors driving epilithic algal colonization in show caves and new insights into combating biofilm development with UV-C treatments

International audienceThe proliferation of epilithic algae that form biofilms in subterranean environments, such as show caves, is a major problem for conservators. In an effort to reduce the use of chemical cleansers when addressing this problem, we proposed investigating the effects of UV-C on combating algal biofilm expansion in a cave located in northeastern France (Moidons Cave). First, the biofilms and cavity were studied in terms of their algal growth-influencing factors to understand the dynamics of colonization in these very harsh environments. Next, colorimetric measurements were used both to diagnose the initial colonization state and monitor the UV-C-treated biofilms for several months after irradiation. The results indicated that passive dispersal vectors of the viable spores and cells were the primary factors involved in the cave's algae repartition. The illumination time during visits appeared to be responsible for greater colonization in some parts of the cave. We also showed that colorimetric measurements could be used for the detection of both thin and thick biofilms, regardless of the type of colonized surface. Finally, our results showed that UV-C treatment led to bleaching of the treated biofilm due to chlorophyll degradation even one year after UV-C treatment. However, a re-colonization phenomenon was colorimetrically and visually detected 16 months later, suggesting that the colonization dynamics had not been fully halted