Influence of pH and Dissolved Organic Matter on Iron Speciation and Apparent Iron Solubility in the Peruvian Shelf and Slope Region.

The chemical speciation of iron (Fe) in oceans is influenced by ambient pH, dissolved oxygen, and the concentrations and strengths of the binding sites of dissolved organic matter (DOM). Here, we derived new nonideal competitive adsorption (NICA) constants for Fe(III) binding to marine DOM via pH-Fe titrations. We used the constants to calculate Fe(III) speciation and derive the apparent Fe(III) solubility (SFe(III)app) in the ambient water column across the Peruvian shelf and slope region. We define SFe(III)app as the sum of aqueous inorganic Fe(III) species and Fe(III) bound to DOM at a free Fe (Fe3+) concentration equal to the limiting solubility of Fe hydroxide (Fe(OH)3(s)). A ca. twofold increase in SFe(III)app in the oxygen minimum zone (OMZ) compared to surface waters is predicted. The increase results from a one order of magnitude decrease in H+ concentration which impacts both Fe(III) hydroxide solubility and organic complexation. A correlation matrix suggests that changes in pH have a larger impact on SFe(III)app and Fe(III) speciation than DOM in this region. Using Fe(II) measurements, we calculated ambient DFe(III) and compared the value with the predicted SFe(III)app. The underlying distribution of ambient DFe(III) largely reflected the predicted SFe(III)app, indicating that decreased pH as a result of OMZ intensification and ocean acidification may increase SFe(III)app with potential impacts on surface DFe inventories.

Dissipation dynamics and final residues of cloransulam-methyl in soybean and soil.

This work is the first report on the dissipation and final residue of cloransulam-methyl on soybean plant at field conditions. A fast, simple, and reliable residue analytical method for determination of cloransulam-methyl in soybean matrices and soil was developed based on quick, easy, cheap, effective, rugged, and safe (QuEChERS) sample preparation and liquid chromatography-tandem mass spectrometry (LC-MS/MS) detection. The average recoveries of cloransulam-methyl in soybean matrices and soil ranged from 80 to 105%, with RSDs between 3-11%. The limit of detection (LOD) was 0.001 mg kg(-1) for soybean grain, plant, and soil and was 0.005 mg kg(-1) for soybean straw. This method was then used to characterize dissipation of cloransulam-methyl in soybeans and soil from three locations in China for the first time. Cloransulam-methyl dissipated quickly in soybean plant with half-lives (T1/2) of 0.21-0.56 days. The dissipation dynamic in soil was characterized using both first-order kinetics model and two-compartment model, and the half-lives were similar, ranging from 0.44 to 5.53 days at three experimental sites in 2012 and 2013. The final residue data showed a very low level of cloransulam-methyl in soil (≤0.026 mg kg(-1)), soybean grain (≤0.001 mg kg(-1)), and straw (≤0.005 mg kg(-1)) samples at harvest time. With the faster and simple analytical method on soybean and soil, rapid dissipation of cloransulam-methyl was observed at three geospatial locations in China, and the terminal residue levels were negligible, so mammalian ingestion exposure is minimal.

Dissipation and residues of picoxystrobin in peanut and field soil by QuEChERS and HPLC-MS/MS.

The dissipation and final residues of picoxystrobin in peanut and soil were determined by a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method and high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The dissipation and final residue of picoxystrobin at three different provinces (Hebei, Hubei, and Shandong) in China were studied. The fortification experiments at three different spiking levels of 0.01, 0.05, and 0.5 mg kg(-1) in all matrices (soil, peanut seedling, shell, stalk, and kernels) were conducted, and the recoveries were 79-114% with relative standard deviations of 3-12 (n = 5). The dissipation half-lives of picoxystrobin were 1.5-8.6 days in soil, and 2.1-2.8 days in seedlings. The final residues of picoxystrobin in supervised field trials were 0.05-6.82 mg kg(-1) in stalk, ≤0.381 mg kg(-1) in soil, ≤0.069 mg kg(-1) in shells, and ≤0.005 mg kg(-1) in peanut kernels. Considering the final residue levels and the maximum residue limits (MRLs), the pre-harvest interval of 14 days was recommended for the safe use of picoxystrobin in peanut crop.

Assessing micrometer-scale contamination from organic materials in serpentinite analysis.

Serpentinization of peridotite provides a significant source of energy for the subseafloor biosphere and abiotic organic synthesis. The presence of diverse micrometer-scale organic matter in serpentinites offers insights into deep carbon cycling and the origin of life on Earth. It is critical to maintain stringent lab protocols in analyzing serpentinite samples, limiting the contact with organic materials that could contaminate serpentinites and cause misinterpretations. However, the extent to which these organic materials (e.g. latex gloves or nylon polishing disc) can introduce contamination remains unclear. Here we subject serpentinite samples from the Yap Trench in the western Pacific Ocean to multi-stage cutting and polishing procedures prior to analysis. Our findings from electron microscopy reveal that micrometer-scale organic matter in serpentinites is randomly distributed either on the sample surface or within Cr-spinel fractures. Further analysis using Raman spectroscopy indicates that the organic matter contains several hydrogen bonding moieties, similar to those found in the latex gloves or nylon polishing disc used during the treatment of serpentinite samples. Our results suggest that the detected organic matter is likely due to contamination from the organic materials involved during sample processing. Thus, future studies need to carefully assess micrometer-scale organic contamination and limit the use of organic materials when analyzing organic compounds hosted in serpentinites, not only on Earth but also on other rocky planets.

Trace metal stoichiometry of dissolved organic matter in the Amazon plume.

Dissolved organic matter (DOM) is a distinct component of Earth's hydrosphere and provides a link between the biogeochemical cycles of carbon, nutrients, and trace metals (TMs). Binding of TMs to DOM is thought to result in a TM pool with DOM-like biogeochemistry. Here, we determined elemental stoichiometries of aluminum, iron, copper, nickel, zinc, cobalt, and manganese associated with a fraction of the DOM pool isolated by solid-phase extraction at ambient pH (DOMSPE-amb) from the Amazon plume. We found that the rank order of TM stoichiometry within the DOMSPE-amb fraction was underpinned by the chemical periodicity of the TM. Furthermore, the removal of the TMSPE-amb pool at low salinity was related to the chemical hardness of the TM ion. Thus, the biogeochemistry of TMs bound to the DOMSPE-amb component in the Amazon plume was determined by the chemical nature of the TM and not by that of the DOMSPE-amb.

Phycosphere pH of unicellular nano- and micro- phytoplankton cells and consequences for iron speciation.

Surface ocean pH is declining due to anthropogenic atmospheric CO2 uptake with a global decline of ~0.3 possible by 2100. Extracellular pH influences a range of biological processes, including nutrient uptake, calcification and silicification. However, there are poor constraints on how pH levels in the extracellular microenvironment surrounding phytoplankton cells (the phycosphere) differ from bulk seawater. This adds uncertainty to biological impacts of environmental change. Furthermore, previous modelling work suggests that phycosphere pH of small cells is close to bulk seawater, and this has not been experimentally verified. Here we observe under 140 µmol photons·m-2·s-1 the phycosphere pH of Chlamydomonas concordia (5 µm diameter), Emiliania huxleyi (5 µm), Coscinodiscus radiatus (50 µm) and C. wailesii (100 µm) are 0.11 ± 0.07, 0.20 ± 0.09, 0.41 ± 0.04 and 0.15 ± 0.20 (mean ± SD) higher than bulk seawater (pH 8.00), respectively. Thickness of the pH boundary layer of C. wailesii increases from 18 ± 4 to 122 ± 17 µm when bulk seawater pH decreases from 8.00 to 7.78. Phycosphere pH is regulated by photosynthesis and extracellular enzymatic transformation of bicarbonate, as well as being influenced by light intensity and seawater pH and buffering capacity. The pH change alters Fe speciation in the phycosphere, and hence Fe availability to phytoplankton is likely better predicted by the phycosphere, rather than bulk seawater. Overall, the precise quantification of chemical conditions in the phycosphere is crucial for assessing the sensitivity of marine phytoplankton to ongoing ocean acidification and Fe limitation in surface oceans.

Residue Analysis of 60 Pesticides in Red Swamp Crayfish Using QuEChERS with High-Performance Liquid Chromatography-Tandem Mass Spectrometry.

In this study, a multi-residue analytical method using quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction and dispersive solid-phase extraction (d-SPE) cleanup, followed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), was investigated for rapid determination of 60 pesticide residues in whole crayfish and crayfish meat. The final method used 10 mL of acetonitrile for extraction, 3 g of NaCl for partitioning, and 50 mg of primary secondary amine for d-SPE cleanup. The method was validated at three spiking levels (10, 50, and 100 ng/g) using triphenyl phosphate as an internal standard and both gradient and isocratic HPLC elution. Under gradient conditions, satisfactory recoveries (70-120%) and relative standard deviations of ≤20% were achieved for 83 and 88% of pesticides in whole crayfish and crayfish meat, respectively. Matrix effects were estimated using both gradient and isocratic HPLC elution. To our knowledge, this is the first study involving multi-residue analysis of HPLC-amenable pesticides in crayfish and mantis shrimp. The final method was successfully applied for analysis of 11 crayfish and mantis shrimp samples from markets in China, and propamocarb (

The complete mitochondrial genome of the hybrid of Siniperca chuatsi (♀) × Siniperca kneri (♂).

In this study, we reported the complete mitochondrial DNA sequence of the hybrid of Siniperca chuatsi (♀)×Siniperca kneri (♂). The total length of the mitochondrial genome is 16,493 bp, with the base composition of 28.61% A, 29.21% C, 16.21% G, and 25.97% T. It contains 2 rRNA genes, 13 protein-coding genes, 22 tRNA genes, and a major non-coding control region (D-loop region). The composition and order of these genes are identical to most of other vertebrates. All the protein initiation codons are ATG, except for COX1 that begins with GTG. The complete mitogenome of the hybrid of Siniperca chuatsi (♀) × Siniperca kneri (♂) provides an important data set for the study in genetic mechanism.

The complete mitochondrial genome of the hybrid of Siniperca kneri (♀) × Siniperca chuatsi (♂).

The complete mitochondrial genome sequence of the hybrid of Siniperca kneri (♀) × Siniperca chuatsi (♂) is described in this study. The 16,488 bp long circular molecule consisted of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a control region, showed a typical vertebrate pattern. The overall base composition of the heavy strand is 28.59% A, 29.20% C, 16.25% G, and 25.96% T, with a slight AT bias of 54.55%. Except for eight tRNA and ND6 genes, all other mitochondrial genes are encoded on the heavy strand. There are 5 regions of gene overlap totaling 14 bp and 20 intergenic spacer regions totaling 91 bp. The complete mitogenome of the hybrid of S. kneri (♀) × S. chuatsi (♂) could provide an important data set for the study in mitochondrial inheritance mechanism.

Multiresidue Analysis of Pesticides in Straw Roughage by Liquid Chromatography-Tandem Mass Spectrometry.

A multiresidue analytical method using a modification of the "quick, easy, cheap, effective, rugged, and safe" (QuEChERS) sample preparation approach combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was established and validated for the rapid determination of 69 pesticides at different levels (1-100 ng/g) in wheat and rice straws. In the quantitative analysis, the recoveries ranged from 70 to 120%, and consistent RSDs ≤ 20% were achieved for most of the target analytes (53 pesticides in wheat straw and 58 in rice straw). Almost all of the analytes achieved good linearity with R(2) > 0.98, and the limit of validation levels (LVLs) for diverse pesticides ranged from 1 to 10 ng/g. Different extraction and cleanup conditions were evaluated in both types of straw, leading to different options. The use of 0.1% formic acid or not in extraction with acetonitrile yielded similar final outcomes, but led to the use of a different sorbent in dispersive solid-phase extraction. Both options are efficient and useful for the multiresidue analysis of targeted pesticides in wheat and rice straw samples.