Hg reactions in the presence of chlorine species: homogeneous gas phase and heterogeneous gas-solid phase

The kinetics of Hg chlorination (with HCl) was studied using a flow reactor system with an online Hg analyzer, and speciation sampling using a set of impingers. Kinetic parameters, such as reaction order (alpha), overall rate constant (k'), and activation energy (Ea), were estimated based on the simple overall reaction pathway. The reaction order with respect to C(Hg), k', and Ea were found to be 1.55, 5.07 x 10(-2) exp(-1939.68/T) [(microg/m3)(-055)(s)(-1)]. and 16.13 [kJ/ mol], respectively. The effect of chlorine species (HCl, CH2Cl2) on the in situ Hg capture method previously developed (28) was also investigated. The efficiency of capture of Hg by this in situ method was higher than 98% in the presence of chlorine species. Furthermore, under certain conditions, the presence of chlorine enhanced the removal of elemental Hg by additional gas-phase oxidation.     

Trophic ecology of Rimicaris exoculata : a combined lipid abundance/stable isotope approach

The alvinocaridid shrimp Rimicaris exoculata is an abundant component of the biota of Mid-Atlantic Ridge hydrothermal vents. To determine the nutritional strategy of this organism, we analysed the molecular abundance and carbon isotopic composition of its phospholipid fatty acids. High abundances of n-7 fatty acids (>40% total fatty acids) were observed in R. exoculata muscle tissues, in bacterial epibionts scraped from its gill bailers, and from the bacterially infested metal sulphides that the shrimp ingest. The phospholipid fatty acid abundance data indicates that the bacteria in the sulphides are closely related to the bacterial epibiota inhabiting the shrimp gill bailers, carapace and other body parts. Compound specific δ¹³C analyses of the phospholipid fatty acids gave average values of −12‰ for the epibiont bacteria and −21‰ for the sulphide bacteria. This difference may be largely due to the expression of different forms of RuBisCO (Forms I and II) which fractionate against ¹³C to different extents. Carbon limitation within the shrimp epibiont population may be an additional factor. The δ¹³C values (mean = −13‰) of the saturated and monounsaturated fatty acids isolated from the muscle tissues of R. exoculata were very close to those of the epibionts, indicating that the predominant source of dietary carbon for the shrimp is their epibionts, with a lesser contribution from free-living bacteria. The δ¹³C values (−26‰) of shrimp cholesterol were much more negative than those of the fatty acids, and this cholesterol is likely to have derived from the oceanic photic zone. Received: 26 June 1997 / Accepted: 6 November 1998     

Directions in Conservation Biology: Comments on Caughley

The recent review by Caughley (1994) on approaches used in conservation biology suggested that there are two: the small population paradigm and the declining population paradigm. We believe that this division is overly simplistic and that it should not be perpetuated. Both the deterministic factors that reduce population size and the stochastic factors that lead to the final extinction of a small population are critical to consider in preventing extinction. Only through an overall and comprehensive effort, which we call inclusive population viability analysis, can extinction processes be understood and mitigated. In this context we discuss Caughley's comments about genetics, demography, and general population viability, with particular attention to cheetahs (Acinonyx jubatus) and Pacific salmon (Oncorhynchus sp. ) .     

Characterization of activated carbon fiber filters for pressure drop, submicrometer particulate collection, and mercury capture

The use of activated carbon fiber (ACF) filters for the capture of particulate matter and elemental Hg is demonstrated. The pressure drop and particle collection efficiency characteristics of the ACF filters were established at two different face velocities and for two different aerosols: spherical NaCl and combustion-generated silica particles. The clean ACF filter specific resistance was 153 kg m-2 sec-1. The experimental specific resistance for cake filtration was 1.6 x 10(6) sec-1 and 2.4 x 10(5) sec-1 for 0.5- and 1.5-micron mass median diameter particles, respectively. The resistance factor R was approximately 2, similar to that for the high-efficiency particulate air filters. There was a discrepancy in the measured particle collection efficiencies and those predicted by theory. The use of the ACF filter for elemental Hg capture was illustrated, and the breakthrough characteristic was established. The capacity of the ACF filter for Hg capture was similar to other powdered activated carbons.     

An attractive male trait and aggressiveness are negatively correlated in wild field crickets, but uncorrelated in lab-reared crickets

It is generally thought that attractive male traits are positively correlated with dominance (aggressiveness). However, growing evidence suggests that this is not necessarily the case. We investigated whether calling song, a male mating display used by females to evaluate potential mates in a field cricket (Gryllus integer), is correlated with aggressiveness. In this species, females prefer males with longer durations of singing time. We measured singing time by measuring song over three continuous days using a custom-designed audio-monitor and assessed aggressiveness by pairing males in agonistic interactions. Our results showed that for males caught in the field, the percentage of time spent singing was negatively correlated with aggressiveness. However, in males that were raised in the laboratory, the percentage of time spent singing was not correlated with aggressiveness. Since calling duration is an attractive male trait in these crickets, our data show that the attractiveness of males can be either negatively related to aggressiveness (field) or unrelated to aggressiveness (lab). Neither of these results fit the traditional view that preferred male mating cues should be positively correlated with dominance (aggressiveness). These results also suggest that measurements of aggressiveness made in the lab do not necessarily correspond with aggressiveness in the field.     

Environmental and Biological Assessment of Exposure to Benzene in Petroleum Workers

Occupational exposure to benzene was measured in two gasoline marketing terminals and five major refineries in Singapore. A total of 280 workers were monitored over two years. This assessment was carried out with two primary objectives: (1) To find out the extent of occupational exposure to benzene in the petroleum industry in Singapore, (2) To identify suitable biomarkers for monitoring of low levels of benzene exposure. The exposure was measured in five different categories of petroleum and petrochemical workers, i.e., truck drivers, despatch assistant, process operators, oil movements operators and laboratory technicians. The results revealed wide variations in exposure, from 0.01 to 13.6 ppm for personal time weighted average (TWA) exposure over the whole workshift. The exposure of truck drivers appeared to be the highest, with geometric mean (GM) of 1.98 ppm (ranged from 0.25 to 13.6 ppm). The average benzene exposure for process operators was relative low with a GM of 0.04 ppm. Lowest benzene exposure was found in the laboratory technicians, with a GM of 0.02 ppm. As cigarette smoking is known to affect metabolism of benzene, data analyses on the relationships with environmental exposure were conducted only on the 190 nonsmokers. The results showed that urinary trans, trans-muconic acid (ttMA), unmetabolized benzene in urine (UBZ) and benzene in blood (BBZ) were better biomarkers for low level benzene exposure as compared to urinary phenolic metabolites in urine, such as hydroquinone, phenol and catechol.     

Fitness in the Endangered Gila Topminnow

The Gila topminnow (Poeciliopsis o. occidentalis) is a small, live-bearing, endangered fish extant in a maximum of nine locales in four separate watersheds in the United States. To determine if these populations differed in their fitness, we obtained samples from the four watersheds and examined them for four fitness correlates: survival, growth rate, fecundity, and bilateral asymmetry. Earlier research found that one population, Sharp Spring, had higher allozyme heterozygosity than the other three and had higher survival, growth rate, and fecundity and lower bilateral asymmetry than a sample from one of the other populations with no polymorphic allozyme loci, Monkey Spring. We also verified that Sharp Spring fish were polymorphic for the same allozyme loci whereas the Monkey Spring population was not. We did not, however, find positive associations of allozyme heterozygosity with the four fitness correlates for the four samples. Because the earlier study had much lower survival, it is likely that the differences resulted from differential response of the two populations to a stressful laboratory environment. Whether this unknown stress occurs in natural environments or its effect is predictive of other stresses remains unresolved. As a result, we concur with suggestions in the draft recovery plan that topminnows from nearby sources be used for reintroductions and that the Sharp Spring stock not be used outside the upper Santa Cruz River drainage.