title: Occurrence of tributyltin (TBT)-resistant bacteria is not related to TBT pollution in Mekong River and coastal sediment: with a hypothesis of selective pressure from suspended solid.
abstract: Tributyltin (TBT) is organotin compound that is toxic to aquatic life ranging from bacteria to mammals. This study examined the concentration of TBT in sediment from and near the Mekong River and the distribution of TBT-resistant bacteria. TBT concentrations ranged from <2.4 to 2.4 ng/g (dry wt) in river sediment and <2.4-15 ng g(-1) (dry wt) in harbor sediment. Viable count of total bacteria ranged from 2.0 x 10(4) to 1.4 x 10(7)cfu/g, and counts of TBT-resistant bacteria ranged <1.0 x 10(2) to 2.5 x 10(4)cfu/g. The estimated occurrence rate of TBT-resistant bacteria ranged from <0.01 to 34% and was highest in upstream sites in Cambodia. The occurrences of TBT in the sediment and of TBT-resistant bacteria were unrelated, and chemicals other than TBT might induce TBT resistance. TBT-resistant bacteria were more abundant in the dry season than in the rainy season. Differences in the selection process of TBT-resistant bacteria between dry and rainy seasons were examined using an advection-diffusion model of a suspended solid (SS) that conveys chemicals. The estimated dilution-diffusion time over a distance of 120 km downstream from a release site was 20 days during dry season and 5 days during rainy season, suggesting that bacteria at the sediment surface could be exposed to SS for longer periods during dry season.
authors.affiliation: Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Japan.
authors.forename: Fujiyo
authors.initials: F
authors.lastname: Suehiro
authors.forename: Hiroko
authors.initials: H
authors.lastname: Mochizuki
authors.forename: Shinji
authors.initials: S
authors.lastname: Nakamura
authors.forename: Hisato
authors.initials: H
authors.lastname: Iwata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Tanabe
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Fujimori
authors.forename: Fumitake
authors.initials: F
authors.lastname: Nishimura
authors.forename: Bui Cach
authors.initials: BC
authors.lastname: Tuyen
authors.forename: Touch Seang
authors.initials: TS
authors.lastname: Tana
authors.forename: Satoru
authors.initials: S
authors.lastname: Suzuki
mesh_terms: D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology; D007564:Japan; D008956:Models, Chemical; D045483:Rivers / Q000737:chemistry / Q000382:microbiology; D014220:Trialkyltin Compounds / Q000032:analysis*; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014220:Trialkyltin Compounds; D014874:Water Pollutants, Chemical; C011559:tributyltin