Abiotic degradation (photodegradation and hydrolysis) of imidazolinone herbicides

The abiotic degradation of the imidazolinone herbicides imazapyr, imazethapyr and imazaquin was investigated under controlled conditions. Hydrolysis, where it occurred, and photodegradation both followed first-order kinetics for all herbicides. There was no hydrolysis of any of the herbicides in buffer solutions at pH 3 or pH 7; however, slow hydrolysis occurred at pH 9. Estimated half-lives for the three herbicides in solution in the dark were 6.5, 9.2 and 9.6 months for imazaquin, imazethapyr and imazapyr, respectively. Degradation of the herbicides in the light was considerably more rapid than in the dark with half lives for the three herbicides of 1.8, 9.8 and 9.1 days for imazaquin, imazethapyr and imazapyr, respectively. The presence of humic acids in the solution reduced the rate of photodegradation for all three herbicides, with higher concentrations of humic acids generally having greater effect. Photodegradation of imazethapyr was the least sensitive to humic acids. The enantioselectivity of photodegradation was investigated using imazaquin, with photodegradation occurring at the same rate for both enantiomers. Abiotic degradation of imidazolinone herbicides on the soil surface only occurred in the presence of light. The rate of degradation for all herbicides was slower than in solution, with half-lives of 15.3, 24.6 and 30.9 days for imazaquin, imazethapyr and imazapyr, respectively. Abiotic degradation of these herbicides is likely to be slow in the environment and is only likely to occur in clear water or on the soil surface.     

Full life-cycle toxicity assessment using rotifer resting egg production: implications for ecological risk assessment

The majority of standardized toxicity tests incorporate only a fraction of the test organism's life-cycle. However, in natural ecosystems, organisms may be exposed at various times during their life-cycle or throughout their life-cycle. Thus, ecotoxicological data from standardized toxicity tests is of limited ecological relevance. Existing standardized toxicity tests using the freshwater rotifer Brachionus calyciflorus utilize 24-h survival or 48-h asexual reproduction as endpoints, despite evidence that sexual reproduction is more sensitive. A 96-h B. calyciflorus resting egg toxicity test was developed and used to estimate the toxicity of pentachlorophenol (PCP) and copper. Results were compared to a variety of acute and sublethal endpoints for both toxicants. The B. calyciflorus 96-h resting egg production NOEC for PCP of 10 micrograms/l was 20 times lower than the 48-h asexual reproduction no observed effect concentration (NOEC) and 120 times lower than the 24-h acute lethal concentration 50%. The 96-h resting egg production NOEC for copper of 2.8 micrograms/l was 7 times lower than the 48-h asexual reproduction NOEC and nine times lower than the 24-h acute LC50. Resting egg production was a more sensitive indicator of toxicity than several other sublethal endpoints as well. These results indicate that partial life-cycle toxicity tests are not sufficiently sensitive to detect ecologically relevant adverse effects.     

Factors influencing the total mercury and methyl mercury in the hair of the fishermen of Kuwait

Total and methyl mercury (MeHg) levels in the hair of fishermen are described anticipating that they represent the critical group for dietary exposure. One-hundred human hair samples were collected from fishermen (Egyptians: age range 25-60), living in Doha Fishing Village, Kuwait. Thirty-five additional samples were taken from a control group working in a local construction company (age range 26-35). Overall mean concentrations in the hair of the population of fishermen are 4.181+/-3.220 and 4.025+/-3.130 microg g(-1) for total and MeHg, respectively. The equivalent values for the control are 2.617+/-1.404 and 2.556+/-1.391 microg g(-1) for total and MeHg, respectively. MeHg concentrations are strongly correlated to those of total Hg ( [Formula: see text], [Formula: see text] ) and MeHg concentrations in human hair are unrelated to age and duration of residence in Kuwait but show a positive correlation with the quantity of fish consumed. Levels of Hg in hair also show a tendency to increase in those who prefer to eat the entire fish, including the heads. In general, the concentrations of total and MeHg in fishermens' hair are twice the WHO 'normal' level (2.0 microg g(-1)) but are still less than the WHO threshold level (10.0 microg g(-1)). The results also show that grey hair contains undetectable amounts of Hg and therefore does not reflect individual exposure to this contaminant.     

Queen regulates biogenic amine level and nestmate recognition in workers of the fire ant, <Emphasis Type="Italic">Solenopsis invicta</Emphasis>

Nestmate recognition is a critical element in social insect organization, providing a means to maintain territoriality and close the colony to parasites and predators. Ants detect the colony chemical label via their antennae and respond to the label mismatch of an intruder with aggressive behavior. In the fire ant, Solenopsis invicta, worker ability to recognize conspecific nonnestmates decreases if the colony queen is removed, such that they do not recognize conspecific nonnestmates as different. Here, we tested the hypothesis that the presence of the colony queen influences the concentration of octopamine, a neuromodulator, in worker ants, which in turn has an effect on nestmate recognition acuity in workers. We demonstrate that queenless workers exhibit reduced brain octopamine levels and reduced discriminatory acuteness; however, feeding queenless workers octopamine restored both. Dopamine levels are influenced by honeybee queen pheromones; however, levels of this biogenic amine were unchanged in our experiments. This is the first demonstration of a link between the presence of the colony queen, a worker biogenic amine, and conspecific nestmate recognition, a powerful expression of colony cohesion and territoriality.     

Pilot-scale demonstration of a two-stage methanotrophic bioreactor for biodegradation of trichloroethylene in groundwater

A two-stage methanotrophic bioreactor system was developed for remediation of water contaminated with TCE and other chlorinated, volatile, aliphatic hydrocarbons. The first stage of the reactor was a suspended-growth culture vessel using a bubbleless methane-transfer device. The second stage was a plug-flow bioreactor supplied with contaminated groundwater and cell suspension from the culture vessel. The test objectives were to determine the applicability of microbial culture conditions reported in the literature for continuous, pilot-scale TCE treatment; the technical feasibility of plug-flow bioreactor design for treatment of TCE; and the projected economic competitiveness of the technology considering the cost of methane for growth of methanotrophs. The methanotrophic organism used in the study was Methylosinus trichosporium OB3b. Information on system operation was obtained in bench tests prior to conducting the pilot tests. In bench- and pilot-scale tests, variability in the degree of TCE degradation and difficulty in maintaining the microbial culture activity led to short periods of satisfactory biotreatment. Further development of the microbial culture system will be required for long-term operation. During transient periods of high TCE degradation activity, the bioreactor concept proved feasible by exhibiting both a high degree of TCE biodegradation (typically about 90% at influent TCE concentrations of 0.5-4 ppm) and a close approximation to first-order reactor kinetics throughout the length of the reactor. Actual methane usage in the pilot-scale reactor resulted in projected methane costs of $0.33 per 1000 gallons of water treated. This cost theoretically would be reduced by system modifications. The theoretical minimum methane cost was approximately $0.05 per 1000 gallons.     

Design and performance of a field exposure system for evaluation of the ecological effects of SO2 on native grassland

We describe the design and performance of two replicate field exposure systems for evaluating the ecological effects of chronic SO₂ exposure on 0.5 ha plots of native Montana grassland. The SO₂ was supplied at a constant rate to each plot through a network of 2.5-cm inside diameter aluminum pipes set parallel to and approximately 0.7 m above the ground with 0.8-mm SO₂ release holes at 3-m intervals. The resulting SO₂ concentrations on the plots varied with micrometeorological conditions. Fumigations were essentially continuous from April through October for 5 yr on one set of four plots and for 4 yr on another set of four plots. Frequency distributions of SO₂ concentrations were approximately log-normal and qualitatively similar to those from various area and point sources. The diurnal pattern of SO₂ concentrations was strongly correlated with the reciprocal of windspeed. Nighttime concentrations averaged almost double daytime concentrations. The diurnal concentration pattern resembled an area source more closely than a point source, a direct result of using constant SO₂ source strength. Plume strikes could be simulated by turning the system on only during pre-specified meteorological conditions. Similarly, seasonal variations in area source concentrations could be simulated by varying source strength on the plots. The data from 5 years use of the system indicate that the fine-scale behavior of SO₂ concentrations would be realistic.     

Sparrow Modeling to Understand Water‐Quality Conditions in Major Regions of the United States: A Featured Collection Introduction1

Preston, Stephen D., Richard B. Alexander, and David M. Wolock, 2011. SPARROW Modeling to Understand Water‐Quality Conditions in Major Regions of the United States: A Featured Collection Introduction. Journal of the American Water Resources Association (JAWRA) 47(5):887‐890. DOI: 10.1111/j.1752‐1688.2011.00585.x     

Infrared analysis for counterfeit electronic parts detection and supply chain validation

Within the electronics industry, counterfeit electronic components entering the supply chain have steadily become an increasing threat accounting for more than 8 % of global merchandise trade and an annual $600 billion enterprise. Currently, there are not many cost-effective and nonintrusive solutions for counterfeit detection of electronic parts. In this paper, the authors present a statistical approach for detecting counterfeit components based on infrared (IR) analysis by the use of independent component analysis (ICA). As a prominent higher-order statistical analysis technique, ICA is capable of extracting relevant features from IR data. The latest applications and the extended algorithms of ICA have been elucidated for the purposes of classification and identification of counterfeit electronic parts. The theoretical framework of ICA is presented along with extensive experimental results to illustrate its feature extraction function in counterfeit electronic parts detection.     

An acoustic investigation of seagrass photosynthesis

The use of high-frequency acoustics has recently emerged as a viable method for mapping the areal coverage of seagrasses. Since the bubbles produced by seagrass plants are partly responsible for the observed acoustic signature, it is likely that sound transmission throughout a seagrass canopy varies on circadian cycles coinciding with photosynthetic bubble production. This study examined the propagation of high-frequency (100 kHz) sound energy through the seagrass canopies of Syringodium filiforme, Halodule wrightii and Thalassia testudinum in a shallow outdoor mesocosm. Relative changes in the received acoustic energy were recorded every hour during a 24-h period and compared to independently measured rates of oxygen production. The mean acoustic intensity of energy transmitted throughout the seagrass canopy varied by 3.5 dB for S. filiforme, 4.4 dB for T. testudinum and 4.7 dB for H. wrightii over a 24-h period. These transmission characteristics are encouraging for the future development of in situ acoustic assessments of seagrass photosynthesis.     

GIS-based niche modeling for mapping species' habitat

Ecological "niche modeling" using presence-only locality data and large-scale environmental variables provides a powerful tool for identifying and mapping suitable habitat for species over large spatial extents. We describe a niche modeling approach that identifies a minimum (rather than an optimum) set of basic habitat requirements for a species, based on the assumption that constant environmental relationships in a species' distribution (i.e., variables that maintain a consistent value where the species occurs) are most likely to be associated with limiting factors. Environmental variables that take on a wide range of values where a species occurs are less informative because they do not limit a species' distribution, at least over the range of variation sampled. This approach is operationalized by partitioning Mahalanobis D2 (standardized difference between values of a set of environmental variables for any point and mean values for those same variables calculated from all points at which a species was detected) into independent components. The smallest of these components represents the linear combination of variables with minimum variance; increasingly larger components represent larger variances and are increasingly less limiting. We illustrate this approach using the California Gnatcatcher (Polioptila californica Brewster) and provide SAS code to implement it.