Vibrational spectroscopy and non-parametric analysis for biodegradation evaluation: The acrylic-emulsion paint scenario
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In this work, we utilized Raman spectroscopy, characterized by excellent lateral resolution, in capturing the degradation of paints was investigated. Six fresh and six spoilt acrylic emulsion paint samples obtained from a paint company in Lagos, Nigeria and were used for this study. They were analyzed for microbial population and types using total viable count method and analytical profile index (API20E &20NE). Physicochemical quality markers [transmittance (TR), pH, OD600, and specific gravity (SG)] of the paints were evaluated by standard methods. Raman spectroscopy was deployed to analyze components of both fresh and spoilt paint samples. Lead (Pb) concentrations were assessed using atomic absorption spectrophotometry.
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Six fresh water-based paint samples and six different spoilt samples were collected aseptically into different capped containers from a paint manufacturing facility in Lagos, Nigeria. The samples were transported to the laboratory, stored at room temperature (27+2°C), and subjected to microbiological and analytical procedures. The media used for isolation, purification, and maintenance of microbial cell cultures included nutrient agar (NA) in Erlenmeyer flasks consisting of 5 g/L casein hydrolysate; 0.05 g/L K2HPO4; 0.01 g/L FePO4;15 g/L agar. Following autoclave sterilization for 15 minutes at 121°C, the pH of the medium was adjusted to 7.5. In addition, 40 g/L potato dextrose agar (PDA) (Oxoid) dextrose; 10 g/L Peptone;20 g/L agar (pH5.6 ± 0.2); and McConkey agar (MCA) (Oxoid) were utilized. Serial dilutions were prepared for each sample by aseptically transferring 1mL of each sample into test tubes containing 9 mL of sterile distilled water to give 10-1 dilution from which higher dilutions (10-2 to 10-8) were made. Aliquots (0.1 mL) from the low, medium, and high dilutions (10-3, 10-6, and10-8) were plated out on NA, MCA and PDA (Nwachukwu and Akpata, 2003). The NA and MCA plates were incubated aerobically at 37ºC for 18-24 h while the PDA plates were incubated at room temperature (27+2ºC) for 5 days. After incubation, growth was determined by plate counting of the resulting distinct and well defined colonies which were then purified. Pure bacterial isolates were subjected to biochemical tests to determine the presumptive identity of the organisms. Further confirmatory identification was done using the analytical profile index (API) 20NE and 20E kits (BioMerieux, Inc.). Pure fungal fungal colonies were mounted on a clean glass slide, stained with lactophenol-cotton blue to detect their individual fungal structures as described by Basu (1980). Optical density (OD600) was assessed using a SM23A Spectrophotometer (Microfield Instrument, London). The transmittance (TR) of each sample was measured using the general principles of spectrophotometry of translucent and non-transparent materials as described by Shibata (1958). Specific Gravity (SG) measurements were carried out using DUS 10 (DFI Co. Ltd, Korea) specific gravity strips. The pH was measured with the aid of a digital pH measuring device (ExStik Waterproof pH Meter, China). The meter sensor was first cleansed with distilled water and wiped carefully. Lead concentrations in both fresh and spoilt paint samples were determined using Atomic Absorption Spectroscopy (AAS). The diffuse/specular reflectance spectra of dried paint samples were measured by an Agilent Cary 5000 UV-vis-NIR spectrophotometer with an internal DRA 2500. The samples were scanned across a wavelength from 300 nm to 2500 nm. Raman analyses were carried out using a WITec alpha500 confocal Raman microscope. Non-parametric statistics was used to validate the results obtained because of its wide applicability and robustness..