As emerging alternatives of legacy perfluoroalkyl substances, perfluorophosphinates
(PFPiAs) and perfluorophosphonates (PFPAs) are widely applied in industrial
and agricultural fields and are supposed to be large partitioned to
soil and highly persistent. It is of particular interest to understand
their transfer from roots to shoots and transformation in plants,
such as wheat. The results of hydroponic experiments indicated that
C6/C6 PFPiA, C8/C8 PFPiA, perfluorooctanophosphonic acid (PFOPA),
and perfluorohexaphosphonic acid (PFHxPA) were quickly adsorbed on
the epidermis of wheat root (Triticum aestivum L.), which was driven by their hydrophobicity. A small fraction of the
accumulated PFPiAs and PFPAs in the wheat root was subjected to absorption
via an active process dependent on H+-ATPase. PFHxPA, which
has the smallest molecular weight and medium hydrophilicity (log K
ow < 4), displayed the strongest absorption
efficiency via the water and anion channels and had the highest translocation
potential from roots to shoots in wheat. C6/C6 and C8/C8 PFPiAs experienced
phase I metabolism in wheat, although at a low rate, to form more
persistent PFHxPA and PFOPA, respectively, as well as 1H-perfluorohexane (1H-PFHx) and 1H-perfluorooctane (1H-PFO), which were regulated
by cytochrome P450 in wheat root. As a result, exposure to PFPiAs
in roots ultimately caused the accumulation of more persistent PFPAs
in the above-ground parts of plants, raising concerns on their potential
risks on human health.
The biotransformation of organophosphate
esters (OPEs) in white
lupin (Lupinus albus) and wheat (Triticum aestivum L.) was investigated in hydroponic
experiments with different phosphorus (P)-containing conditions. The
hydrolysis rates of OPEs followed the order of triphenyl phosphate
(TPHP) > tri-n-butyl phosphate (TnBP) > tris(1,3-dichloro-2-propyl)
phosphate (TDCPP). Hydrolysis of OPEs was accelerated at P-deficient
conditions, and faster hydrolysis took place in white lupin than in
wheat. Coincidingly, the production of acid phosphatase (ACP) in both
plants was promoted, and much higher intracellular and extracellular
ACPs were observed in white lupin under P-deficient conditions. In vitro experiments revealed that ACP was a key enzyme
to hydrolyze OPEs. The hydrolysis rates of OPEs were significantly
correlated with the Hirshfeld charges, calculated by density functional
theory, of the oxygen atom in the single P–O bond. Using ultra-high-performance
liquid chromatography coupled with Orbitrap Fusion mass spectrometer,
30 metabolites were successfully identified. Some of these metabolites,
such as sulfate-conjugated products, hydration of cysteine-conjugated
products of TPHP, and reductively dechlorinated metabolites of TDCPP,
were observed for the first time in plants. It is noteworthy that
OPEs may transform into many hydroxylated metabolites, and special
attention should be paid to their potential environmental effects.
Soil Moisture Active Passive (SMAP) mission L-band brightness temperature (Tb) observations are routinely assimilated into the Catchment land surface model to generate Level-4 Soil Moisture (L4_SM) estimates of global surface and root-zone soil moisture at 9-km, 3-hourly resolution with ~2.5-day latency. The Catchment model in the L4_SM algorithm is driven with ¼-degree, hourly surface meteorological forcing data from the Goddard Earth Observing System (GEOS). Outside of Africa and the high latitudes, GEOS precipitation is corrected using Climate Prediction Center Unified (CPCU) gauge-based, ½-degree, daily precipitation. L4_SM soil moisture was previously shown to improve over land model-only estimates that use CPCU precipitation but no Tb assimilation (CPCU_SIM). Here, we additionally examine the skill of model-only (CTRL) and Tb assimilation-only (SMAP_DA) estimates derived without CPCU precipitation. Soil moisture is assessed versus in situ measurements in well-instrumented regions and globally through the Instrumental Variable (IV) method using independent soil moisture retrievals from the Advanced Scatterometer. At the in situ locations, SMAP_DA and CPCU_SIM have comparable soil moisture skill improvements relative to CTRL for the unbiased root-mean-square error (surface and root-zone) and correlation metrics (root-zone only). In the global average, SMAP Tb assimilation increases the surface soil moisture anomaly correlation by 0.10-0.11 compared to an increase of 0.02-0.03 from the CPCU-based precipitation corrections. The contrast is particularly strong in central Australia, where CPCU is known to have errors and observation-minus-forecast Tb residuals are larger when CPCU precipitation is used. Validation versus streamflow measurements in the contiguous U.S. reveals that CPCU precipitation provides most of the skill gained in L4_SM runoff estimates over CTRL.
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