Toxicity of methyl-tert-butyl ether to freshwater organisms

Increased input of the fuel oxygenate methyl-tert-butyl ether (MTBE) into aquatic systems has led to concerns about its effect(s) on aquatic life. As part of a study conducted by University of California scientists for the State of California, the Aquatic Toxicology Laboratory, UC Davis, reviewed existing literature on toxicity of MTBE to freshwater organisms, and new information was generated on chronic, developmental toxicity in fish, and potential toxicity of MTBE to California resident species. Depending on time of exposure and endpoint measured, MTBE is toxic to various aquatic organisms at concentrations of 57-> 1000 mg/l (invertebrates), and 388-2600 mg/l (vertebrates). Developmental effects in medaka (Oryzias latipes) were not observed at concentrations up to 480 mg/l, and all fish hatched and performed feeding and swimming in a normal manner. Bacterial assays proved most sensitive with toxicity to Salmonella typhimurium measured at 7.4 mg/l within 48 h. In microalgae, decreased growth was observed at 2400 and 4800 mg/l within 5 days. MTBE does not appear to bioaccumulate in fish and is rapidly excreted or metabolized. Collectively, the available data suggests that at environmental MTBE exposure levels found in surface waters (< 0.1 mg/l) this compound is likely not acutely toxic to aquatic life. However, more information is needed on chronic and sublethal effects before we can eliminate the possibility of risk to aquatic communities at currently detected concentrations.     

Genotoxic and teratogenic potential of marine sediment extracts investigated with comet assay and zebrafish test

Organic extracts of marine sediments from the North Sea and the Baltic Sea were investigated with two toxicity assays. The comet assay based on the fish cell line Epithelioma papulosum cyprini (EPC) was applied to determine the genotoxic potential; zebrafish embryos (Danio rerio) were used to quantify the teratogenic potential of the samples. EC(50) values were calculated from dose-response curves for both test systems. Highest teratogenic and genotoxic effects normalised to total organic carbon (TOC) content were detected in sediment samples of different origins. Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are not likely to be the causes of the observed effects, as demonstrated by a two-step fractionation procedure of selected extracts. The toxic potential was more pronounced in fractions having polarity higher than those possessed by PAHs and PCBs. The suitability of the two in vitro test systems for assessing genotoxic and teratogenic effects of marine sediment extracts could be demonstrated.     

Bioremediation of Chlorobenzene-Contaminated Groundwater on Granular Activated Carbon Barriers

During the past decade, various promising technologies have been developed for the decontamination of groundwater insitu which do not require long-term pumping or high energy consumption. One approach is to use funnel and gate technology. In the case described here, the combination of adsorption of contaminants on granular activated carbon (GAC) and its biodegradation is applied to considerably extend the operating time of the filling material in the barrier system. Monochlorobenzene (MCB), a recalcitrant groundwater contaminant under anaerobic conditions, undergoes high-capacity adsorption on GAC up to about 450 mg per gram. Aerobic enrichment cultures, obtained from a contaminated aquifer, were able to mineralize initially adsorbed MCB. In respirometer experiments the rate of carbon dioxide formation was dependent on the equilibrium concentration of MCB. The oxygen consumption of activated carbon by means of autoxidative reactions may delay aerobic biodegradation in GAC filters. The oxygen uptake of pristine activated carbon amounted to 5.6 mg per gram GAC in laboratory column experiments. When GAC was pre-loaded with MCB, autoxidation rates were considerably reduced. Hence, it is advisable not to stimulate the biodegradation of MCB by oxygen supply in GAC biobarriers until after an initial period of solely sorptive MCB removal from the groundwater flow.     

Die Beeinträchtigung aquatischer Ökosysteme durch die Zivilisation

The surface waters of northwestern Europe belong to the most heavily loaded waters of the world. Within the last decades, pollution by non-biogenic organic substances has often become more important than pollution by domestic sewage. Ecologic concepts aid in understanding the various modes of disturbance of aquatic ecosystems. Stream pollution control consists not only of waste treatment.

     

Simultaneous placentacentesis and amniocentesis for prenatal karyotyping: Report on 250 cases

The efficacy and risks of simultaneous transabdominal chorionic villus biopsy (placentacentesis) and amniocentesis in the second and third trimesters were evaluated in 250 singleton pregnancies. The major indications were advanced maternal age (36·0 per cent), abnormal ultrasound findings (23·2 per cent), and low maternal AFP value (17·6 per cent). Nine abnormal karyotypes were found in placental tissue (3·6 per cent). The karyotypes of placental and amniotic cells were different in three cases, including two cases of false-positive mosaicism (08 per cent) and one case of a false-negative result (0·4 per cent) obtained by placental karyotyping. The problem of discrepant karyotypes in embryonic and extra-embryonic tissue does not seem to be restricted to the first trimester. The post-procedure fetal loss rate was estimated as approximately 1·8 per cent. We conclude that the procedure presented here combines the advantages of rapid karyotyping (placentacentesis) and high diagnostic reliability (amniocentesis). It does not seem to be necessary to restrict its use to late presentations and suspicious ultrasound findings.