Search

Organic contaminants in agricultural soils are widely reported; however, their accumulation patterns are quite different among regions. This study reports the distribution, accumulation and risk assessment of polycyclic aromatic hydrocarbons (PAHs), dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) in soils from the Corn Belt of northeast China at a regional scale. Concentrations of PAHs, DDT and HCH were 306‐5300, 6.00–82.0 and 4.07–15.6 ng g−1, respectively. Source analysis suggests PAHs were derived from regional combustion of biomass and coal, except where sites are strongly affected by local sources. The DDT and HCH residues in soils are likely to be derived from previous agricultural applications that have persisted due to slow microbiological degradation under low mean temperatures. Precipitation was only significantly correlated with PAH concentrations, suggesting that precipitation affected PAH but not DDT and HCH distributions at a regional scale. Positive correlations between DDT concentrations and total organic carbon (TOC) contents of soils suggest hydrophobic organic contaminants were associated with organic matter. In contrast, TOC contents were correlated with PAHs in alfisols but not in pedocals. Pedocals contained mainly high molecular weight PAHs, indicating that eluviation affected the accumulation of less hydrophobic organic contaminants. Different correlations between low‐molecular‐weight PAH and HCH concentrations with TOC contents were found in alfisols, suggesting that contaminant structure may also affect the accumulation of less hydrophobic organic contaminants in these soils. Risk analysis suggested that potential ecological risks related to soils in the Corn Belt may lead to reduced maize production and the potential for human health risks in the future. Highlights: Few studies focus on regional‐scale factors that affect organic contaminant accumulation in soils.Environmental process affects less hydrophobic organic contaminant distribution at regional scale.Precipitation and eluviation affected accumulation of less hydrophobic contaminants in soils.PAH and OCP residues in the soil of maize fields may pose ecological risks affecting future crop production and human health. [ABSTRACT FROM AUTHOR]

Quantifying the fate of organic nitrogen in aquatic systems is important to improve understanding of its recycling efficiency and long‐term preservation. The fate of organic nitrogen can be investigated with 15N labeling techniques, but relative amounts of 15N in different chemical forms are difficult to quantify. We present a "streamlined" method by combining Ammonium Retention Time Shift‐High Performance Liquid Chromatography with zinc reduction, and UV oxidation. This method does not require a pre‐isolation step of different forms of nitrogen from the sample. At a sample volume of 50 mL, and a total N concentration in the range of 0.5–40 μmol N L−1, and an 15N atom% of 20–80%, 15N concentrations for all N forms can be measured with this streamlined method, with a precision of within ±7%, and an accuracy of over 97%. We applied the method to investigating the short‐term fates of 15N during the degradation of 15N‐labeled amino acid and peptide. Recovery rates ranged from 93% to 110%, with an average of 102 ± 1.94%. As spiked 15N labeled alanine and/or peptide (Ala‐Val‐Phe‐Val) disappeared during sample incubations, a large fraction (ca. 13–66%) of the 15N was progressively transformed to non‐amino acid or non‐peptide dissolved organic nitrogen. This streamlined method offers quantitative estimates of potential fates of labile organic N compounds added to water samples containing in situ microbial consortia, and helps fulfill knowledge gaps in building the budget of N transformations of labile amino acids and peptides in aquatic systems. [ABSTRACT FROM AUTHOR]

It is critical to understand the chemical structures and lability of dissolved organic matter (DOM) in aquatic environments, as DOM represents one of the largest reduced carbon pools on earth. To achieve a comprehensive view of its composition and reactivity, DOM from both riverine and coastal waters were concurrently extracted via both ultrafiltration and modified styrene divinyl benzene polymer (PPL) based solid-phase-extraction (SPE), and further compared through multi-dimensional angles, including elemental analysis, total hydrolyzable amino acid composition, high-resolution liquid chromatography mass spectrometry (under both electrospray ionization modes), and thermochemical analysis. With a very low percentage (< 5%) of shared molecules, ultrafiltered-DOM (UDOM) and SPE-extracted DOM (SPEDOM) showed distinct differences in their bio- and thermal labilities. SPEDOM not only contained more "degraded" biomarkers, such as glycine, β-alanine, and γ-aminobutyric acid, but was also dominated by a higher abundance of more bio-recalcitrant lignin-like structures. Furthermore, thermogravimetric analysis revealed a higher activation energy of SPEDOM (138.8 ± 0.5 kJ·mol−1) than that of UDOM (125.4 ± 2.8 kJ·mol−1), suggesting that SPEDOM is more thermally recalcitrant than UDOM. Consistently, thermal slicing ramped pyrolysis showed a lower percentage of recalcitrant pyrolyzates (e.g., aromatic and phenol structures), but a higher contribution of labile compound classes (e.g., aliphatic structures) in UDOM, as well as a higher diversity of pyrolyzates from UDOM than SPEDOM. Taken together, our results demonstrated a highly heterogeneous nature in DOM composition and distinctly different bio- and thermal labilities between UDOM and SPEDOM, indicating that characterization of different fractions of DOM is needed for a comprehensive evaluation of natural DOM. • Multi-dimensional approaches were applied to investigate DOM isolated through ultrafiltration and solid phase extraction. • Thermogravimetric analysis and thermal slicing ramped pyrolysis were applied on UDOM and SPEDOM for the first time. • The diverse nature of DOM is shown by the differences in structures, bio-, and thermal labilities between UDOM and SPEDOM. • Caution is needed when extrapolating results from specific isolation techniques to the total DOM pool. [ABSTRACT FROM AUTHOR]