Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardant that is distally transported to the Arctic. Little is known about the fate of PBDEs in Arctic surface waters, especially in the presence of dissolved organic matter (DOM). DOM has been shown to interact with hydrophobic organic contaminants and can alter their mobility, bioavailability, and degradation in the environment. In this study, the partitioning of six PBDE congeners between Arctic DOM (isolated via solid phase extraction) and water was measured using the aqueous solubility enhancement method. Measured dissolved organic carbon (DOC)-water partition coefficient (KDOC) values were nearly an order of magnitude lower than previously reported values for the same PBDE congeners in soil or commercial organic matter, ranging from 10(3.97) to 10(5.16) L kg(-1) of organic carbon. Measured results compared favorably with values calculated using polyparameter linear free energy models for Suwannee River fulvic acid. Log KDOC values increased with increasing PBDE hydrophobicity. Slightly lower than expected values were observed for the highest brominated congeners, which we attribute to steric hindrance. This study is the first to comprehensively measure KDOC values for a range of PBDE congeners with DOM isolated from Arctic surface waters.
Chemical actinometers are traditionally used to account for photochemical experiments conducted under different light regimes (simulated vs natural; also seasonal, daytime, cloud cover, and latitude changes). Their many limitations and the lack of a universally applicable actinometer demand development of a new approach for studying environmentally relevant photochemical processes in sunlight. We suggest the use of fluence-based rate constants (converted to time-based rate constants and half-lives with irradiance normalization), using a datalogging radiometer to track the accumulated dose of UVA and UVB radiation. Our results suggest that this method can effectively account for minor changes in cloud cover and sun angle in the photolysis of p-nitroanisole/pyridine and p-nitroacetophenone/pyridine. The greatest error is caused by factors (e.g., dense cloud cover, extreme sun angles, and changes in ozone) that affect relative UVA and UVB fluence. We believe that this simple and elegant method serves as an important bridge between laboratory and fieldbased environmental photochemistry experiments.
Tubular fossils, up to 2 mm in diameter and 60 mm in length, occur rarely in the upper Martinsburg Formation (Upper Ordovician), northeastern Tennessee Appalachians, U.S.A. The fossils are unbranched, straight or slightly bent, occasionally twisted and wrinkled, and not significantly tapered. Orientation of the fossils within shallow-marine tempestites suggests that they represent remains of organisms that were broken, transported, and deposited by storm waves and currents. The fossils are morphologically similar to many of the previously identified species belonging to the genus Sphenothallus, a relatively rare tube-dwelling Paleozoic marine invertebrate. Owing to the limited evidence for distal widening of the tubes, lack of holdfasts, and carbonaceous rather than phosphatic composition, the affinity of these fossils remains uncertain, and we refer to them as Sphenothallus-like.
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