A statewide investigation of urban creek sediment toxicity was conducted in California in recognition of increased incidences of toxicity linked to pyrethroid pesticides. The goals were to examine ...the spatial occurrence and magnitude of sediment toxicity in California urban creeks, and to examine the role of pyrethroids in toxic urban creek sediment samples. After a preliminary screening of 90 sites, 30 creeks were sampled in eight geographical regions. Sediment toxicity was assessed using 10 day bioassays with the resident amphipod Hyalella azteca. Bioassays were conducted at two test temperatures of 23 °C and at 15 °C to provide evidence of the cause of toxicity, and to more accurately reflect ambient environmental temperatures. Twenty-five of 30 samples were toxic when tested at 23 °C, and all 30 samples were toxic when tested at 15 °C. The magnitude of toxicity increased in samples tested at 15 °C suggesting the influence of pyrethroids, which are more toxic at colder temperatures. Pyrethroids were present in all sediment samples and were the only compounds detected at concentrations toxic to H. azteca. Bifenthrin was the pyrethroid of greatest toxicological concern, occurring in all 30 samples at concentrations up to 219 ng/g. Pyrethroid contamination of urban creeks was most severe in the Los Angeles, Central Valley, and San Diego regions, respectively. However, pyrethroids were also linked to urban creek aquatic toxicity in all regions sampled, including the less urbanized areas of the North Coast and Lake Tahoe.
The antibiotic oxytetracycline (OTC) is a fluorochrome marker, and fluorescence microscopy is used to view OTC marks in fishes' calcified structures. However, OTC marks have been observed in ...calcified structures using standard light microscopy for multiple species. Therefore, we conducted an experiment to investigate potential factors (i.e., season, total length of fish, growth rate, and sex) influencing the observation of OTC in calcified structures (otoliths and fin rays or spines) from channel catfish Ictalurus punctatus, gray redhorse Moxostoma congestum, Guadalupe bass Mircopterus treculii, and redbreast sunfish Lepomis auritus viewed using standard light and fluorescence microscopy. OTC stains were not observed in any otoliths under standard light; however, OTC marks were commonly observed in I. punctatus spines using standard light microscopy (56.2%). Ninety‐nine percent of otoliths and 88.9% of spines and fin rays had a visible fluorescent OTC mark when viewed using fluorescence microscopy. There was a negative relationship between the observed OTC mark and total length of fish for each season, but fish injected in the summer had the most structures with an observed OTC mark under either light condition. Understanding how OTC marking is affected by biological processes and environmental conditions will assist in future studies that rely on chemical marking of calcified structures by increasing efficacy of OTC marking and interpretation of marks.
We present an initial demonstration of a velocity-map imaging (VMI) experiment using a back-irradiation laser-based desorption source directly integrated into the electrode assembly. This has the ...potential to greatly expand the utility of the popular VMI approach by permitting its use with high density plumes of non-volatile molecular samples. Photoelectron circular dichroism measurements on the phenylalanine molecule using 400 nm multiphoton ionization are used to illustrate this novel method, revealing forward-backward emission asymmetries on the order of 7%.
We present an initial demonstration of a velocity-map imaging (VMI) experiment using a back-irradiation laser-based desorption source directly integrated into the electrode assembly.
We have investigated the electronic relaxation dynamics of gas-phase piperidine (a secondary aliphatic amine) using time-resolved photoelectron imaging. Following 200 nm excitation, spectrally sharp ...and highly anisotropic photoelectron data reveal ultrafast (60 fs) internal conversion between the initially excited 3p
x
Rydberg state and the lower-lying 3s Rydberg state, mediated by the evolution of nσ* valence character along the 3p
x
N-C bond. This behaviour is in good agreement with previously reported findings for several tertiary aliphatic amines. In contrast to the these systems, however, much broader photoelectron signals exhibiting only very small angular anisotropy and two distinct decay timescales (180 fs and 1.7 ps) were also observed. As confirmed by our supporting calculations, this is attributable to nσ* valence character now evolving along the N-H stretching coordinate within the 3s Rydberg state as the molecule starts dissociating to yield H atom photoproducts in conjunction with ground state piperidinyl radicals. By analogy with systems such as ammonia and morpholine, we conclude this event may occur either promptly or, alternatively,
via
a "frustrated" process where the system repeatedly traverses the upper cone of a conical intersection with the ground state until the required region of phase space is sampled to facilitate non-adiabatic population transfer. Our findings reveal the role of several different nuclear coordinate motions in driving stepwise internal conversion across multiple potential energy surfaces and the distinct photoionization signatures that are associated with these processes.
Time-resolved photoelectron spectroscopy reveals distinct ionization signatures of Rydberg-to-valence state evolution in the secondary aliphatic amine piperidine.
Objective
Age estimation methods have not been validated for many species. Thus, we focused this age estimation study on four species from central Texas: the Guadalupe Bass Micropterus treculii, ...Channel Catfish Ictalurus punctatus, Gray Redhorse Moxostoma congestum, and Redbreast Sunfish Lepomis auritus. Our objectives for each species were to (1) investigate whether increments form annually in otoliths, fin rays, or spines; (2) determine the seasonal timing of zone deposition in each calcified structure; and (3) compare age estimates between otoliths and fin rays or spines.
Methods
Fish were sampled from central Texas waters and injected with oxytetracycline (OTC) quarterly in 2021. In July 2022, otoliths and fin rays or spines were collected to determine whether the increments formed annually and to estimate age.
Result
On average, two readers identified the correct number of annuli after the OTC mark in at least 95% of Gray Redhorse, Guadalupe Bass, and Redbreast Sunfish otoliths but in only 69% of Channel Catfish otoliths. However, the more experienced reader identified the correct number of annuli in at least 95% of otoliths from age‐2–4 Channel Catfish. Compared to otoliths, the correct number of annuli after the OTC mark was identified in a smaller percentage of fin rays or spines (47–62%). The probability of identifying the correct number of annuli after the OTC mark differed between the two readers for all spines and fin rays. Age difference plots revealed that age estimates based on fin rays or spines were either overestimated or underestimated compared to otolith‐based ages for all species.
Conclusion
We consider annual increment formation in otoliths to be validated for all age‐classes of Gray Redhorse, Guadalupe Bass, and Redbreast Sunfish examined and for ages 2–4 of Channel Catfish. Differences in correctness between readers were most likely due to differences in age estimation experience. Given the level of error observed in our study, caution is advised if using age estimates from unvalidated structures and species.
Impact statement
We validated annual increment formation in otoliths from Guadalupe Bass, Gray Redhorse, and Redbreast Sunfish but not in otoliths from Channel Catfish. Annual increment formation was not validated for fin rays or spines from any species examined.
We report the first excited state dynamics study of gas-phase 5,6-dihydroxyindole (5,6-DHI), a key building block of eumelanin pigments that are found throughout nature and serve as important ...photo-protective compounds. Time-resolved ion-yield measurements over the 241-296 nm ultraviolet photoexcitation region revealed non-adiabatic processes occurring on up to three distinct timescales. These reflect ultrafast (i.e. sub-picosecond) internal conversion within the excited state singlet manifold, and much longer-lived processes ranging from 10 ps to in excess of 1 ns. Our investigation paves the way for precisely targeted future studies of 5,6-DHI that exploit more differential measurement techniques. The work was facilitated by the use of soft laser-based thermal desorption to introduce 5,6-DHI samples into the gas phase. This approach, based on low-cost, readily available diode lasers, is straightforward, easily controllable and potentially applicable to a wide range of non-volatile molecular species.
Fly ash represents a promising alternative source of rare earth elements (REE). However, information on REE containing mineral phases and their association with other fly ash components, vital for ...REE recovery from fly ash, is currently lacking. Herein, the mass fraction, distribution, crystallography and solid-state chemistry of REE, U and Th in Nigerian simulated fly ash samples were characterised using a range of laboratory and synchrotron x-ray based analytical techniques to underpin future extraction methodologies. Inductively coupled plasma mass spectrometry following full-acid digest of forty-five samples revealed recoverable average total REE content which ranged between 442 mgkg−1and 625 mgkg−1, comprising over 30 wt% of the critical REE Nd, Eu, Tb, Dy, Y and Er. These REE within the fly ash samples were found to be most frequently associated with discrete monazite, xenotime and Y-bearing zircon mineral particles, with the former the most detected, which could be beneficiated through gravity separation. Analysis of monazite particles isolated from the composite samples through a complimentary suite of analytical synchrotron radiation techniques revealed a core-shell pattern, with the shell rich in colocalised Ce, Nd and La, and the core enrich in both U and Th. Ce in monazite was found to exist in a mixed trivalent and tetravalent oxidation state, with the monazite structure amorphized due to the high temperature combustion process. Such results demonstrate the strong co-association and physical distribution of REE, U and Th within monazite in fly ash; knowledge of which can subsequently be used to optimise or develop a more selective, cost-effective and environmentally friendly solvent extraction methodology, by targeting the strongly colocalised and surface bound REE in fly ash monazite particles.
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•The total rare earth content of the studied samples is promising for recovery.•Critical rare earths comprised over 30wt% of rare earth content of samples studied.•Micromanipulation method employed to isolate individual monazite particles.•Radial zonation observed in monazite particles, with rim rich in rare earths.•Ce oxidised and monazite structure amorphized, increasing chemical reactivity.
We report the first excited state dynamics study of gas-phase 5,6-dihydroxyindole (5,6-DHI), a key building block of eumelanin pigments that are found throughout nature and serve as important ...photo-protective compounds. Time-resolved ion-yield measurements over the 241-296 nm ultraviolet photoexcitation region revealed non-adiabatic processes occurring on up to three distinct timescales. These reflect ultrafast (
i.e.
sub-picosecond) internal conversion within the excited state singlet manifold, and much longer-lived processes ranging from 10 ps to in excess of 1 ns. Our investigation paves the way for precisely targeted future studies of 5,6-DHI that exploit more differential measurement techniques. The work was facilitated by the use of soft laser-based thermal desorption to introduce 5,6-DHI samples into the gas phase. This approach, based on low-cost, readily available diode lasers, is straightforward, easily controllable and potentially applicable to a wide range of non-volatile molecular species.
Laser-based thermal desorption facilitates the first gas-phase study of ultrafast non-adiabatic dynamics operating in 5,6-dihydroxyinole following ultraviolet excitation.
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