Vibrational spectroscopy and non-parametric analysis for biodegradation evaluation: The acrylic-emulsion paint scenario

Abstract

The utility of 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. The fresh samples had 9.50–7.00 × 108 CFU/mL; 0.07–0.12 × 106 CFU/mL; 1.54–2.70; 7.41–7.74; 1.69–1.92; 0.87–1.01 and 0.48–1.86 mg/kg for total bacterial count(TBC), total coliform count(TCC), TR, pH, OD, SG and Pb concentration respectively. Microbes observed in the fresh samples belonged to the genera Aeromonas, Bacillus, Paenibacillus, Enterobacter, Corynebacterium, Micrococcus, Pseudomonas, Burkholderia, Serratia, Klebsiella and Alcaligens. Spoilt samples had 1.80 × 109-3.20 × 1011CFU/mL; 1.02 × 105-3.30 × 106 CFU/mL; 2.69 × 109- 6.95 × 109CFU/mL; 1.21–1.71; 6.71–8.21; 1.76–1.93; 0.86–1.01 and 0.61–2.88 mg/kg for TBC, TCC, total fungal count, transmission, pH, OD600, SG and Pb respectively. The spoilt samples had the genera Pseudomonas, Staphylococcus, Streptococcus, Citrobacter, Bacillus, Enterobacter, Corynebacterium, Escherichia, Burkholderia, Alcaligens, Penicillium and Aspergillus. Raman spectroscopy indicated a shift in prominent peaks corresponding to component degradation in spoilt samples. Differences revealed by Wilcoxon Signed Rank non-parametric statistical test results further corroborate extent of microbial degradation of the paint matrix.