The chronic toxicity of molybdate to marine organisms. I. Generating reliable effects data.

A scientific research program was initiated by the International Molybdenum Association (IMOA) which addressed identified gaps in the environmental toxicity data for the molybdate ion (MoO(4)(2-)). These gaps were previously identified during the preparation of EU-REACH-dossiers for different molybdenum compounds (European Union regulation on Registration, Evaluation, Authorization and Restriction of Chemical substances; EC, 2006). Evaluation of the open literature identified few reliable marine ecotoxicological data that could be used for deriving a Predicted No-Effect Concentration (PNEC) for the marine environment. Rather than calculating a PNEC(marine) using the assessment factor methodology on a combined freshwater/marine dataset, IMOA decided to generate sufficient reliable marine chronic data to permit derivation of a PNEC by means of the more scientifically robust species sensitivity distribution (SSD) approach (also called the statistical extrapolation approach). Nine test species were chronically exposed to molybdate (added as sodium molybdate dihydrate, Na(2)MoO(4)·2H(2)O) according to published standard testing guidelines that are acceptable for a broad range of regulatory purposes. The selected test organisms were representative for typical marine trophic levels: micro-algae/diatom (Phaeodactylum tricornutum, Dunaliella tertiolecta), macro-alga (Ceramium tenuicorne), mysids (Americamysis bahia), copepod (Acartia tonsa), fish (Cyprinodon variegatus), echinoderms (Dendraster exentricus, Strongylocentrotus purpuratus) and molluscs (Mytilus edulis, Crassostrea gigas). Available NOEC/EC(10) levels ranged between 4.4 mg Mo/L (blue mussel M. edulis) and 1174 mg Mo/L (oyster C. gigas). Using all available reliable marine chronic effects data that are currently available, a HC(5,50%) (median hazardous concentration affecting 5% of the species) of 5.74(mg Mo)/L was derived with the statistical extrapolation approach, a value that can be used for national and international regulatory purposes.

The chronic toxicity of molybdate to freshwater organisms. I. Generating reliable effects data.

The European Union regulation on Registration, Evaluation, Authorization and Restriction of Chemical substances (REACH) (EC, 2006) requires the characterization of the chronic toxicity of many chemicals in the aquatic environment, including molybdate (MoO(4)(2-)). Our literature review on the ecotoxicity of molybdate revealed that a limited amount of reliable chronic no observed effect concentrations (NOECs) for the derivation of a predicted no-effect concentration (PNEC) existed. This paper presents the results of additional ecotoxicity experiments that were conducted in order to fulfill the requirements for the derivation of a PNEC by means of the scientifically most robust species sensitivity distribution (SSD) approach (also called the statistical extrapolation approach). Ten test species were chronically exposed to molybdate (added as sodium molybdate dihydrate, Na(2)MoO(4)·2H(2)O) according to internationally accepted standard testing guidelines or equivalent. The 10% effective concentrations (EC10, expressed as measured dissolved molybdenum) for the most sensitive endpoint per species were 62.8-105.6 (mg Mo)/L for Daphnia magna (21day-reproduction), 78.2 (mg Mo)/L for Ceriodaphnia dubia (7day-reproduction), 61.2-366.2 (mg Mo)/L for the green alga Pseudokirchneriella subcapitata (72h-growth rate), 193.6 (mg Mo)/L for the rotifer Brachionus calyciflorus (48h-population growth rate), 121.4 (mg Mo)/L for the midge Chironomus riparius (14day-growth), 211.3 (mg Mo)/L for the snail Lymnaea stagnalis (28day-growth rate), 115.9 (mg Mo)/L for the frog Xenopus laevis (4day-larval development), 241.5 (mg Mo)/L for the higher plant Lemna minor (7day-growth rate), 39.3 (mg Mo)/L for the fathead minnow Pimephales promelas (34day-dry weight/biomass), and 43.2 (mg Mo)/L for the rainbow trout Oncorhynchus mykiss (78day-biomass). These effect concentrations are in line with the few reliable data currently available in the open literature. The data presented in this study can serve as a basis for the derivation of a PNEC(aquatic) that can be used for national and international regulatory purposes and for setting water quality criteria. Using all reliable data that are currently available, a HC(5,50%) (median hazardous concentration affecting 5% of the species) of 38.2 (mg Mo)/L was derived with the statistical extrapolation approach.

Standardization of 99mTc and 99Mo by the use of a 4pibeta-4pigamma counter.

Technetium-99m is widely used for many diagnostic investigations in nuclear medicine, thus the standardization of this nuclide is important. In classical 4pibeta-gamma coincidence counting of (99m)Tc, the steep slope of the efficiency function and the large extrapolation range may cause a large measurement uncertainty. In order to overcome these difficulties, we apply the 4pibeta+4pigamma sum counting technique for the standardization. Furthermore, we adopt both the 4pibeta-4pigamma coincidence counting method and the 4pibeta+4pigamma sum counting technique for the standardization of its parent nuclide (99)Mo. High efficiencies for both nuclides were easily achieved by the use of our 4pibeta-4pigamma counter. All the results were consistent with the reference value obtained by the conventional method obtained by NMIJ.

[Determination of molybdenum in supported catalysts by ICP-AES].

The supported Mo catalysts were pretreated using hydrofluoric acid. Then Mo was determined by inductively coupled plasma atomic emission spectrometry(ICP-AES). In the present method, the detection limit of Mo was 8.220 ng x mL(-1), the recovery of standard addition was 102.6%-104.3%, the relative standard deviation (n = 11) was less than 0.860%. The method is efficient, accurate, and easy to operate. Molybdenum in supported catalysts, which were prepared under different conditions, was determined by this method. The results showed that the content of Mo in supported catalysts decreased after preparation. The decreases in the content of Mo were different when the active component concentrations in impregnation solution, and the calcination temperature, changed.