3 research outputs found
Electron-Donating Phenolic and Electron-Accepting Quinone Moieties in Peat Dissolved Organic Matter: Quantities and Redox Transformations in the Context of Peat Biogeochemistry
Electron-donating
phenolic and electron-accepting quinone moieties
in peat dissolved organic matter (DOM) are considered to play key
roles in processes defining carbon cycling in northern peatlands.
This work advances a flow-injection analysis system coupled to chronoamperometric
detection to allow for the simultaneous and highly sensitive determination
of these moieties in dilute DOM samples. Analysis of anoxic pore water
and oxic pool water samples collected across an ombrotrophic bog in
Sweden demonstrated the presence of both phenolic and quinone moieties
in peat DOM. The pore water DOM had higher quantities of phenolic
but not quinone moieties compared with commonly used model aquatic
and terrestrial DOM isolates. Significantly lower phenol content in
DOM from oxic pools than DOM from anoxic pore waters indicated oxidative
DOM processing in the pools. Consistently, treatment of peat DOM with
laccase, a phenol-oxidase, under oxic conditions resulted in an irreversible
removal of phenols and reversible oxidation of hydroquinones to quinones.
Electron transfer to peat DOM was fully reversible over an electrochemical
reduction and subsequent O<sub>2</sub>-reoxidation cycle, supporting
that quinones in peat DOM serve as regenerable microbial electron
acceptors in peatlands. The results advance our understanding of redox
processes involving phenolic and quinone DOM moieties and their roles
in northern peatland carbon cycling
Effects of Toxic Leachate from Commercial Plastics on Larval Survival and Settlement of the Barnacle <i>Amphibalanus amphitrite</i>
Plastic pollution represents a major
and growing global problem.
It is well-known that plastics are a source of chemical contaminants
to the aquatic environment and provide novel habitats for marine organisms.
The present study quantified the impacts of plastic leachates from
the seven categories of recyclable plastics on larval survival and
settlement of barnacle <i>Amphibalanus</i> (=<i>Balanus</i>) <i>amphitrite</i>. Leachates from plastics significantly
increased barnacle nauplii mortality at the highest tested concentrations
(0.10 and 0.50 m<sup>2</sup>/L). Hydrophobicity (measured as surface
energy) was positively correlated with mortality indicating that plastic
surface chemistry may be an important factor in the effects of plastics
on sessile organisms. Plastic leachates significantly inhibited barnacle
cyprids settlement on glass at all tested concentrations. Settlement
on plastic surfaces was significantly inhibited after 24 and 48 h,
but settlement was not significantly inhibited compared to the controls
for some plastics after 72–96 h. In 24 h exposure to seawater,
we found larval toxicity and inhibition of settlement with all seven
categories of recyclable commercial plastics. Chemical analysis revealed
a complex mixture of substances released in plastic leachates. Leaching
of toxic compounds from all plastics should be considered when assessing
the risks of plastic pollution
Indications of Transformation Products from Hydraulic Fracturing Additives in Shale-Gas Wastewater
Unconventional natural
gas development (UNGD) generates large volumes
of wastewater, the detailed composition of which must be known for
adequate risk assessment and treatment. In particular, transformation
products of geogenic compounds and disclosed additives have not been
described. This study investigated six Fayetteville Shale wastewater
samples for organic composition using a suite of one- and two-dimensional
gas chromatographic techniques to capture a broad distribution of
chemical structures. Following the application of strict compound-identification-confidence
criteria, we classified compounds according to their putative origin.
Samples displayed distinct chemical distributions composed of typical
geogenic substances (hydrocarbons and hopane biomarkers), disclosed
UNGD additives (e.g., hydrocarbons, phthalates such as diisobutyl
phthalate, and radical initiators such as azobisÂ(isobutyronitrile)),
and undisclosed compounds (e.g., halogenated hydrocarbons, such as
2-bromohexane or 4-bromoheptane). Undisclosed chloromethyl alkanoates
(chloromethyl propanoate, pentanoate, and octanoate) were identified
as potential delayed acids (i.e., those that release acidic moieties
only after hydrolytic cleavage, the rate of which could be potentially
controlled), suggesting they were deliberately introduced to react
in the subsurface. In contrast, the identification of halogenated
methanes and acetones suggested that those compounds were formed as
unintended byproducts. Our study highlights the possibility that UNGD
operations generate transformation products and underscores the value
of disclosing additives injected into the subsurface