Chlorophyll Fluorescence and Colorimetric Analysis for Monitoring the Algal Development on Biocide-Treated Stone

International audienc

Chl.a fluorescence as a tool to monitor algal development on stone during a biocide test

International audienc

A new preventive coating for building stones mixing a water repellent and an eco-friendly biocide

International audienceThe durability of stone monuments is a constant problem as their decay through weathering is irremediable andendless. Fortunately, coatings are becoming more and more efficient and tailored to specific alterations of thestone material. This study aimed at developing an eco-friendly coating with both hydrophobic and biocideproperties based on a silane/siloxane emulsion as a water repellent combined with chitosan and silver nitrate asbiocides. Chitosan was first added at different concentrations to the water repellent and its efficacy was tested inlaboratory conditions by the inoculation of axenic suspension of the green algae Chlorella vulgaris on a buildingporous limestone. Chlorophyll a fluorescence analysis displayed the chitosan acted on the photosystem of algaeand limited their development but its effect was not optimal and higher dose modified the aspect of the stone.Low concentration of silver nitrate achieved a good performance thanks to the combination with the chitosanand the water repellent. The properties of coated stones and the efficacy of the formulation were assessed at twodifferent doses of coating. The results showed that the lowest dose gathered all requirements to both preserve thestone monument with a weak colour change over time and to reach optimal biocide effect and a good hydro-phobicity

A flow-cytometry-based method for detecting simultaneously five allergens in a complex food matrix

peer reviewe

Assessment of new protective treatments for porous limestone combining water-repellency and anti-colonization properties

International audienceWater is known to be the main deteriorating agent of building geomaterials. Owing to the presence of water, the alteration phenomena observed particularly on limestones are transportation of soluble salts, dissolution of calcite and development of micro-organisms. In restoration works, several chemical treatments can be used, such as biocides to remove existing biofouling and water-repellents to prevent the ingress of water and its deteriorating effects. The aim here was to combine these two properties in one treatment that could be applied at the end of the restoration work and to develop treat-ments based on natural products and that are safer for the users and the environment. Products with water-repellent and/or anti-colonization properties were developed and tested on a bioclastic limestone both in laboratory and outdoor conditions. They were compared with commercial water-repellents and a preventive anti-colonization treatment. Samples were exposed for 2years in a forest environment, where the hydrophobicity and the colonization were evaluated every 6months. In the laboratory, anti-colonization effects were determined through algae growth measurements. The product that confirmed an efficient hydrophobicity and anti-colonization effect will be applied on a restored site to test it under real conditions

Efficacy of different chemical mixtures against green algal growth on limestone: A case study with Chlorella vulgaris

International audienceThis study aimed to develop nine biocide mixtures that prevent the weathering and biofouling of stone monuments. Tetraethoxysilane (TEOS) was combined with one, two or three active components: chitosan (a biopolymer used for its antimicrobial potential), silver nitrate and hydrophobic silica.A laboratory test was set up, consisting of the inoculation of untreated (control) and treated limestone (“Dom stone”) slabs with an axenic suspension of the green alga Chlorella vulgaris. The biocide efficacy was evaluated by non-destructive methods such as colourimetry and chlorophyll a fluorescence analysis. The latter method supplements the information provided by the measurement of the colourimetric changes of stone surface and characterizes how the biocide acts on the alga PSII photosynthetic activity. Results revealed different patterns of algal development according to treatment efficacy. The combination of silver nitrate and hydrophobic silica, both at high dosages, provided the best biocide effect. When chitosan was added, a similar biocide effect was obtained using a lower concentration of chemicals. This synergy was not observed when hydrophobic silica was either absent or present at a higher dose