ABSTRACT
The freshwater benthic pearl clam, Hyriopsis schlegeli, was experimentally exposed to Cryptosporidium parvum oocysts, and it was verified that the oocysts were eliminated predominantly via the fecal route, retaining their ability to infect cultured cells (HCT-8). The total fecal oocyst elimination rate was more than 90% within 5 days after exposure to the oocysts. H. schlegeli was able to survive in the final settling pond of a sewage plant for long periods, as confirmed by its pearl production. In the light of these findings, the clam was placed in the final settling pond in a trial to test its long-term efficacy in depleting oocysts contaminating the pond water. The number of clams placed was set to ensure a theoretical oocyst removal rate of around 50%, and the turbidity and the density of feed microbes in the overflow trough water of the pond were about 35% and 40 to 60% lower, respectively, than in the control water throughout the year. It was found that the clam feces containing oocysts were sufficiently heavy for them to settle to the bottom of the pond, despite the upward water flow. From these results, we concluded that efficient depletion of oocysts in the sewage water of small or midscale sewage treatment plants can be achieved by appropriate placement of H. schlegeli clams.
Subject(s)
Cryptosporidium parvum/isolation & purification , Sewage/parasitology , Unionidae/growth & development , Unionidae/parasitology , Animals , Feces/parasitology , Geologic Sediments/parasitology , Oocysts , Survival Analysis , Water Purification/methodsABSTRACT
The effects of nitrogenous synergists on the potentiometric responses to divalent transition metal ions were investigated concerning polymeric liquid membranes containing thenoyltrifluoroacetone (Htta) as an ionophore. The tested synergists were pyridine (py) and 4,4'-dioctyl-2,2'-bipyridyl (C8bpy). The potentiometric responses to metal ions, such as Cd2+, Co2+, Ni2+ and Zn2+, were induced by adding the synergists into the liquid membrane systems. The coexistence of Htta and a synergist was necessary for generating the membrane potential. The tta- anion adsorbed at the liquid membrane/solution interface and the complex formation between the synergist and a given metal ion appeared to participate in preferential uptake of metal ions.
Subject(s)
Electrochemistry/methods , Ionophores/chemistry , Nitrogen/chemistry , Polymers/chemistry , Thenoyltrifluoroacetone/chemistry , Cadmium/chemistry , Cobalt/chemistry , Hydrogen-Ion Concentration , Ions , Membrane Potentials , Membranes/chemistry , Models, Chemical , Potentiometry , Solvents/chemistry , Zinc/chemistryABSTRACT
The level of radioactive cesium (the sum of (134)cesium (Cs) and (137)Cs) was investigated in total diet samples collected from adults living in the Sapporo area, Hokkaido. They were ashed, and examined with a germanium semiconductor detector. The maximum and average radioactivities of cesium in an indivividual's daily food intake were as follows: 1.0 Bq and 0.24 Bq in July 2011, 1.3 Bq and 0.30 Bq in November 2011, 3.9 Bq and 1.0 Bq in February 2012, and 0.34 Bq and 0.12 Bq in July 2012, respectively. The committed effective dose would be 0.022 mSv/year in the case of continued intake of meals containing the maximum cesium concentration.