Widespread
application of neonicotinoids has led to their proliferation
in waters. Despite low neonicotinoid hydrophobicity, our prior studies
implicated granular activated carbon (GAC) in neonicotinoid removal.
Based on known receptor binding characteristics, we hypothesized that
the insecticidal pharmacophore influences neonicotinoid sorption.
Our objectives were to illuminate drivers of neonicotinoid sorption
for parent neonicotinoids (imidacloprid, clothianidin, thiamethoxam,
and thiacloprid) and pharmacophore-altered metabolites (desnitro-imidacloprid
and imidacloprid urea) to GAC, powdered activated carbon, and carbon
nanotubes (CNTs). Neonicotinoid sorption to GAC was extensive and
largely irreversible, with significantly greater sorption of imidacloprid
than desnitro-imidacloprid. Imidacloprid and imidacloprid urea (electronegative
pharmacophores) sorbed most extensively to nonfunctionalized CNTs,
whereas desnitro-imidacloprid (positive pharmacophore) sorbed most
to COOH-CNTs, indicating the importance of charge interactions and/or
hydrogen bonding between the pharmacophore and carbon surface. Water
chemistry parameters (temperature, alkalinity, ionic strength, and
humic acid) inhibited overall neonicotinoid sorption, suggesting that
pharmacophore-driven sorption in real waters may be diminished. Analysis
of a full-scale drinking water treatment plant GAC filter influent,
effluent, and spent GAC attributes neonicotinoid/metabolite removal
to GAC under real-world conditions for the first time. Our results
demonstrate that the neonicotinoid pharmacophore not only confers
insecticide selectivity but also impacts sorption behavior, leading
to less effective removal of metabolites by GAC filters in water treatment.
We recently reported the initial discovery of neonicotinoid pesticides in drinking water and their potential for transformation through chlorination and alkaline hydrolysis during water treatment. The objectives of this research were:(1) to determine if neonicotinoid metabolites are relevant to drinking water exposure and (2) to identify the products formed from chlorination of neonicotinoids and their metabolites. Desnitro-imidacloprid and imidacloprid-urea, two known metabolites of imidacloprid, are documented for the first time in drinking water. Desnitro-imidacloprid was present above the lower level of detection (0.03 ng/L) in 67% of samples (six of nine) from drinking water systems but detectable in all samples (up to 0.6 ng/L). Although concentrations of desnitro-imidacloprid were lower than concentrations of the parent neonicotinoids, desnitro-imidacloprid exhibits significantly greater mammalian toxicity than imidacloprid. Using LC-HR-ToF-MS/MS analysis of results from laboratory experiments, we propose structures for novel transformation products resulting from the chlorination of clothianidin, imidacloprid, desnitro-imidacloprid, imidacloprid-urea, and hydrolysis products of thiamethoxam. Formation of chlorinated neonicotinoid byproducts occurs at time scales relevant to water treatment and/or distribution for the imidacloprid metabolites (t 1/2 values from 2.4 min to 1.0 h) and thiamethoxam hydrolysis products (4.8 h). Neonicotinoid metabolites in finished drinking water and potential formation of novel disinfection byproducts during treatment and/or distribution are relevant to evaluating the exposure and potential impacts of neonicotinoids on human health.
The recalcitrance of some emerging organic contaminants through conventional water treatment systems may necessitate advanced technologies that use highly reactive, non-specific hydroxyl radical. Here, polyacrylonitrile (PAN) nanofibers with embedded titanium...
To improve the performance
of polymeric electrospun nanofiber mats
(ENMs) for equilibrium passive sampling applications in water, we
integrated two types of multiwalled carbon nanotubes (CNTs; with and
without surface carboxyl groups) into polyacrylonitrile (PAN) and
polystyrene (PS) ENMs. For 11 polar and moderately hydrophobic compounds
(−0.07 ≤ logK
OW ≤
3.13), 90% of equilibrium uptake was achieved in under 0.8 days (t
90% values) in nonmixed ENM-CNT systems. Sorption
capacity of ENM-CNTs was between 2- and 50-fold greater than pure
polymer ENMs, with equilibrium partition coefficients (K
ENM‑W values) ranging from 1.4 to 3.1 log units
(L/kg) depending on polymer type (hydrophilic PAN or hydrophobic PS),
CNT loading (i.e., values increased with weight percent (wt %) of
CNTs), and CNT type (i.e., greater uptake with carboxylated CNTs composites).
During field deployment at Muddy Creek in North Liberty, Iowa, optimal
ENM-CNTs (PAN with 20 wt % carboxylated CNTs) yielded atrazine concentrations
in surface water with a 40% difference relative to analysis of a same-day
grab sample. We also observed a mean percent difference of 30 (±20)%
when comparing ENM-CNT sampler results to grab sample data collected
within 1 week of deployment. With their rapid, high capacity uptake
and small material footprint, ENM-CNT equilibrium passive samplers
represent a promising alternative to complement traditional integrative
passive samplers while offering convenience over large volume grab
sampling.
We
recently discovered that transformation of the neonicotinoid
insecticidal pharmacophore alters sorption propensity to activated
carbon, with products adsorbing less than parent compounds. To assess
the environmental fate of novel transformation products that lack
commercially available standards, researchers must rely on predictive
approaches. In this study, we combined computationally derived quantitative
structure–activity relationship (QSAR) parameters for neonicotinoids
and neonicotinoid transformation products with experimentally determined
Freundlich partition constants (log
K
F
for sorption to carbon nanotubes [CNTs] and granular activated carbon
[GAC]) to model neonicotinoid and transformation product sorption.
QSAR models based on neonicotinoid sorption to functionalized/nonfunctionalized
CNTs (used to generalize/simplify neonicotinoid-GAC interactions)
were iteratively generated to obtain a multiple linear regression
that could accurately predict neonicotinoid sorption to CNTs using
internal and external validation (within 0.5 log units of the experimentally
determined value). The log
K
F,CNT
values
were subsequently related to log
K
F,GAC
where neonicotinoid sorption to GAC was predicted within 0.3 log-units
of experimentally determined values. We applied our neonicotinoid-specific
model to predict log
K
F,GAC
for a suite
of novel neonicotinoid transformation products (i.e., formed via hydrolysis,
biotransformation, and chlorination) that do not have commercially
available standards. We present this modeling approach as an innovative
yet relatively simple technique to predict fate of highly specialized/unique
polar emerging contaminants and/or transformation products that cannot
be accurately predicted via traditional methods (e.g., pp-LFER), and
highlights molecular properties that drive interactions of emerging
contaminants.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.