Preindustrial levels and temporal enrichment trends of mercury in sediment cores from the Gulf of Thailand.

Four sediment cores in the middle of Gulf of Thailand (GOT) and one core close to Bang Pakong River mouth were examined for total mercury (T-Hg) using direct thermal decomposition coupled with the atomic absorption spectrometry (DTD-AAS) method and acid digestion (acid-CVAAS) method, and sediment chronologies using 210Pb dating. T-Hg in the river mouth core ranged 44.49-52.76 µg/kg and higher than the cores from the middle of GOT (18.26-36.68 µg/kg). The age span obtained from the cores dated back to the 1940s with the sediment accumulation rates of 0.15-0.76 cm/year. The preindustrial levels of T-Hg showed an initial slow increase followed by a rapid elevation since the 1960s which marked the start of the industrialized period in the country. To this end, we posit that T-Hg in the GOT sediment can be attributed to not only land-based sources but also offshore activities including petroleum exploration and frequent accidental oil spills.

Bacterial community shifts in a di-(2-ethylhexyl) phthalate-degrading enriched consortium and the isolation and characterization of degraders predicted through network analyses.

Di-(2-ethylhexyl) phthalate (DEHP) is an extensively used and toxic phthalate plasticizer that is widely reported in marine environments. Degradation of DEHP by bacteria from several environments have been studied, but little is known about marine sediment bacteria that can degrade DEHP and other phthalate plasticizers. Therefore, in this study, we enriched a bacterial consortium C10 that can degrade four phthalate plasticizers of varying alkyl chain lengths (DEHP, dibutyl phthalate, diethyl phthalate, and dimethyl phthalate) from marine sediment. The major bacterial genera in C10 during degradation of the phthalate plasticizers were Glutamicibacter, Ochrobactrum, Pseudomonas, Bacillus, Stenotrophomonas, and Methylophaga. Growth of C10 on DEHP intermediates (mono-ethylhexyl phthalate, 2-ethylhexanol, phthalic acid, and protocatechuic acid) was studied and these intermediates enhanced the Brevibacterium, Ochrobactrum, Achromobacter, Bacillus, Sporosarcina, and Microbacterium populations. Using a network-based approach, we predicted that Bacillus, Stenotrophomonas, and Microbacterium interacted cooperatively and were the main degraders of phthalate plasticizers. Through selective isolation techniques, we obtained twenty isolates belonging to Bacillus, Microbacterium, Sporosarcina, Micrococcus, Ochrobactrum, Stenotrophomonas, Alcaligenes, and Cytobacillus. The best DEHP-degraders were Stenotrophomonas acidaminiphila OR13, Microbacterium esteraromaticum OR16, Sporosarcina sp. OR19, and Cytobacillus firmus OR20 (83.68%, 59.1%, 43.4%, and 40.6% degradation of 100 mg/L DEHP in 8 d), which agrees with the prediction of key degraders. This is the first report of DEHP degradation by all four bacteria and, thus, our findings reveal as yet unknown PAE-degradation capabilities of marine sediment bacteria. This study provides insights into how bacterial communities adapt to degrade or resist the toxicities of different PAEs and demonstrates a simple approach for the prediction and isolation of potential pollutant degraders from complex and dynamic bacterial communities.