Effects of ionization on the toxicity of silver nanoparticles to Japanese medaka (Oryzias latipes) embryos.

Increase in the use of manufactured nanomaterials (NMs) has led to concerns about the environmental impacts. Especially, hazard of metal-based NMs is more severe due to ions released from surface by water quality parameters and physicochemical properties after entering into the water environment. However, little is known about the effects of ionization on the toxicity of metal-based NMs in the water environment. To address this question, we prepared the suspensions of silver nanoparticles (AgNP) at 25 µg L(-1) containing different concentrations of Ag(+) (5, 10, 20, 45, and 75% Ag(+) to total Ag), and evaluated their toxicity to Japanese medaka (Oryzias latipes) embryos. Higher Ag(+) ratios in the AgNP suspension, suggesting the lower number of particles, led to the higher adverse effects on embryos and sac-fries. In addition, histopathology analysis revealed that AgNPs penetrated through chorion of eggs and skin membrane, and were distributed into the tissues. The results imply that the ionization could decrease the toxicity of metal-based NMs in the water environment.

Estrogenic chemicals and estrogenicity in river waters of South Korea and seven Asian countries.

The effects of treatment processes on estrogenicity were evaluated by examining estradiol equivalent (EEQ) concentrations in influents and effluents of sewage treatment plants (STPs) located along Yeongsan and Seomjin rivers in Korea. The occurrence and distribution of estrogenic chemicals were also estimated for surface water in Korea and compared with seven other Asian countries including Laos, Cambodia, Vietnam, China, Indonesia, Thailand and Malaysia. Target compounds were nonylphenol (NP), octylphenol (OP), bisphenol A (BPA), estrone (E1), 17beta-estradiol (E2), 17alpha-ethynylestradiol (EE2) and genistein (Gen). Water samples were pretreated and analyzed by liquid-liquid extraction (LLE) and gas chromatography/mass spectrometry (GC/MS). The results showed that the treatment processes of Korean STPs were sufficient to reduce the estrogenic activity of municipal wastewater. The concentrations of phenolic xenoestrogens (i.e., NP, OP and BPA) in samples of Yeongsan and Seomjin rivers were smaller than those reported by previous studies in Korea. In most samples taken from the seven Asian countries, the presence of E2 and EE2 was a major contributor toward estrogenic activity. The EEQ concentrations in surface water samples of the seven Asian countries were at a higher level in comparison to that reported in European countries, America and Japan. However, further studies with more sampling frequencies and sampling areas should be carried out for better evaluation of the occurrence and distribution of estrogenic compounds in these Asian countries.

Biomonitoring recycled water in the Santa Ana River Basin in southern California.

The Santa Ana River (SAR) is the primary source of groundwater recharge for the Orange County Groundwater Basin in coastal southern California. Approximately 85% base flow in the SAR originates from wastewater treatment plants operated by three dischargers. An on-line, flow-through bioassay using Japanese medaka (Oryzias latipes) as a means of judging potential public health impacts was employed to evaluate the water quality of the surface water and shallow groundwater originating from the SAR. Three chronic (3-4.5 mo) exposures using orange-red (outbred, OR) and see-through (color mutant, ST-II) Japanese medaka as bioindicators were conducted to evaluate endocrinologic, reproductive, and morphologic endpoints. No statistically significant differences in gross morphological endpoints, mortality, gender ratios, and vitellogenin induction were observed in fish from SAR groundwater treatment compared to the group tested in solute reconstituted reverse osmosis-treated or granular activated carbon (GAC)-treated control waters. Significant differences were observed in egg reproduction and the time to hatch in SAR groundwater; however, total hatchability was not significantly lower. To evaluate the estrogenic activity of the surfacewater source of the groundwater, SAR surface water was evaluated for vitellogenin and gonadal histopathology in juvenile medaka with no effects observed. These results demonstrate that OR Japanese medaka may be a sensitive strain as an on-line monitor to predict potential impacts of water quality, but further studies are needed to elicit causative agents within the water mixture.