Mercury concentrations in fish from Lake Mead, USA, related to fish size, condition, trophic level, location, and consumption risk.

Total mercury (Hg) concentrations were determined in the skeletal muscle of 339 fish collected during the fall of 1998 and spring of 1999 from Lake Mead, USA, the nation's largest human-made reservoir. Five species of fish representing a range of trophic levels and the lake's principal game fishes were studied. Hg generally increased with trophic level and fish size. Median Hg concentrations (ng/g wet mass) were 277 in striped bass, 168 in channel catfish, 160 in largemouth bass, 75 in bluegill, and 8 in blue tilapia. Overall, fish from Las Vegas Bay and Boulder Basin had the lowest Hg concentrations, possibly a result of biodilution in this biologically productive area. In general, fish-mercury advisories might include a warning about consuming fillet from emaciated fish, based on the finding that Hg concentrations in 59 striped bass (captured during a scarce-food season) correlated inversely ( r = -0.89, p < 0.001) with a fish nutritional-status factor. This is consistent with starvation-concentration, whereby Hg in fish muscle is lost at a slower rate than the muscle mass. The median concentration found for 139 striped bass corresponds to a recommended risk-based consumption limit of three 8-oz. (227-g) meals per month for a 70-kg adult. Finally, this paper serves as a useful archive for future research and long-term studies of Hg in Lake Mead fish.

Ultrasensitive detection of atmospheric constituents by supersonic molecular beam, multiphoton ionization, mass spectroscopy.

An ultrasensitive detection method for atmospheric monitoring has been developed based on the technique of supersonic molecular beam, resonance enhanced multiphoton ionization, and time-of-flight mass spectroscopy (MB/REMPI/TOFMS). Several organophosphonate and organosulfide compounds, representing simulants to a class of toxic compounds, were studied. Detection levels as low as 300 ppt (dimethyl sulfide) were obtained. Single-vibronic-level REMPI of the cooled molecules in conjunction with TOFMS provided selectivity of ~10(4) against chemically similar compounds in humid air expansions. The fragment ions formed by REMPI excitation are shown for diisopropyl methylphosphonate to depend strongly on the resonant intermediate state of the neutral molecule.

Interaction of ethylene and a cytokinin in promoting hypocotyl elongation in a dwarf strain of watermelon.

Experiments were conducted to study the interaction of ethylene and the cytokinin N(6)-benzyladenine (BA) in promoting hypocotyl elongation in a dwarf strain of watermelon (Citrullus lanatus [Thunb] Matsu. and Nakai). Optimum promotion of hypocotyl elongation is elicited by an apical treatment with 0.2 microgram BA. At dosages above 0.3 microgram per apex, BA-enhancement of elongation is reduced concomitant with stimulation of ethylene production and lateral expansion of hypocotyls. Application of the ethylene biogenesis inhibitor, aminoethoxyvinylglycine, at dosages from 0.3 to 10 micrograms per apex inhibited BA-induced ethylene production. In seedlings treated with 0.2 microgram BA, 10 micrograms aminoethoxyvinylglycine per apex reduced ethylene production to about one-third of control levels and reduced BA stimulation of hypocotyl elongation by 74%. Exposure of watermelon seedlings to 60 +/- 10 nanoliters per liter of ethylene in a flowing system nearly eliminated aminoethoxyvinylglycine inhibition of BA-promoted growth. The results suggest that physiological levels of internal ethylene are required for cytokinin promotion of hypocotyl elongation in watermelon.