Bacterial Hazards of Sludge Brought Ashore by the Tsunami after the Great East Japan Earthquake of 2011

[Abstract]: [Objectives]: The aim of this study was to identify bacteria in sludge brought by the 2011 tsunami in Japan to determine the necessary precautions for workers who handle the sludge. [Methods]: Two sludge samples and one water sample were collected from each of two sites in Miyagi Prefecture in June 2011. We also obtained control samples from a paddy field and a dry beach in Fukuoka, Japan. The samples were subjected to physicochemical analyses, conventional cultivation methods, and molecular methods for bacterial flora analysis. The bacterial floras were analyzed using a clone library method employing fragments of the 16S ribosomal RNA gene (rDNA) amplified with universal primers. [Results]: We detected 51-61 genera in sludge samples and 14 and 17 genera in water samples collected in the tsunami-affected areas. In sludge samples collected in the tsunami-affected areas, more genera belonged to Proteobacteria than to Bacteroidetes, but in water samples collected in these areas, more genera belonged to Bacteroidetes than to Proteobacteria. Non-O1, non-O139 V. cholerae (non-agglutinable vibrio) was found at approximately 104 cells/m/near the coast of the tsunami affected area. Sulfate-reducing bacteria were detected in sludge collected from the paddy field, and a relatively high concentration of sulfate ions was found in the water sample (258 mg/l). [Conclusions]: Sludge brought by the tsunami contained some pathogens; therefore, frequent hand washing is recommended for workers who have direct contact with the sludge to minimize their risk of infection. Under the anaerobic conditions of paddy fields, hydrogen sulfide could be produced by sulfate-reducing bacteria metabolizing sulfate ions.