Anthropogenic influences on the sources and distribution of organic carbon, black carbon, and heavy metals in Daya Bay's surface sediments

Pyrogenic PAHs Have Different Biogeochemical Fates in the Eastern Indian Ocean

Understanding the fate of polycyclic aromatic hydrocarbons (PAHs) in the deep ocean is crucial for elucidating the biogeochemical cycle of organic carbon under anthropogenic influences. In this study, surface sediments were collected from the deep sea of the Eastern Indian Ocean (water depth: 2161-4545 m) and analyzed for 29 semivolatile organic compounds (SVOCs), including parent PAHs and their alkylated derivatives, as well as source biomarkers. The target SVOCs (∑29SVOCs: 23.0-183 ng/g, ∑16PAHs: 11.3-93.3 ng/g) were mainly from pyrogenic sources, namely coal combustion, traffic emissions, and wood burning. The contributions from wood burning and coal combustion exhibited distinct trends with increasing total organic carbon contents, suggesting different dominant biogeochemical behaviors. Major fractions of PAHs from wood burning can be biodegraded or photodegraded, leading to a depletion-dominated fate in the water column. Conversely, PAHs from coal combustion showed an accumulation-dominated fate via their sedimentation due to their persistence and hydrophobicity. This study highlights the distinct biogeochemical fates of PAHs from biomass or fossil fuel combustion in deep oceans and has implications for the marine cycle of refractory organic carbon under anthropogenic impacts.

Field evidence and modeling validation of biogeochemical controls on the deposition of persistent organic pollutants in the deep ocean

Deposition in the deep ocean plays a crucial role in the global sink of persistent organic pollutants (POPs), yet observation-based assessments of their biogeochemical cycling are scarce. In this study, surface sediments were collected from deep sea of the Eastern Indian Ocean (2161-4545 m) and analyzed for organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). Long-range atmospheric transport was identified as the dominant pathway for OCPs (36.7-762.0 pg/g) and PCBs (25.5-110.0 pg/g) to reach the basin area from surrounding agricultural, manufacturing, and combustion emissions. Besides the TOC-dependent deposition, unique hydrodynamic conditions in the mid-ocean ridge might influence the transport and accumulation of POPs by altering their resuspension and repartitioning processes. Results of the machine learning analysis suggested that logKOW, TOC content, and pollutant residence time in the ocean are important parameters in determining PCB concentrations in the Indian Ocean. Additionally, concentrations of POPs generally exhibited logarithmic relationships with microplastic abundances, indicating that microplastics act as potential carriers for transporting these pollutants to deep-sea sediments. This study revealed the biogeochemical controls on the deposition of OCPs and PCBs in the Indian Ocean by combining field observation and model simulation. Given the rapid rate of surface warming and various biogeochemical responses in the Indian Ocean, it is recommended to conduct long-term, high-resolution field observations to understand the dynamic fate of POPs in these changing ocean environments.

Molecular features of uranium-binding natural organic matter in a riparian wetland determined by ultrahigh resolution mass spectrometry

Tims Branch riparian wetland located in South Carolina, USA has immobilized 94 % of the U released >50 years ago from a nuclear fuel fabrication facility. Sediment organic matter (OM) has been shown to play an important role in immobilizing U. Yet, uranium-OM-mineral interactions at the molecular scale have never been investigated at ambient concentrations. The objectives of this study were to extract, purify, and concentrate U-bound sediment OM along the stream water pathway and perform molecular characterization using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). Out of 9614 identified formulas, 715 contained U. These U-containing formulas were enriched with Fe, N, and/or S compared to the total OM. Lignin-like and protein-like molecules accounted for 40 % and 19 % of the U-containing formulas, respectively. Phosphorus-containing formulas were found to exert an insignificant influence on complexing U. U-containing formulas in the 'mobile' (groundwater extractable) OM fraction had lower (reduced) nominal oxidation states of carbon (NOSC); and less aromatic moieties than OM recovered from the 'immobile' (sodium pyrophosphate extractable) OM fraction. U-containing formulas in the redox interfacial zones (stream banks) compared to those in nearby up-slope zones tended to have smaller molecular weights; lower NOSC; higher contents of COO and/or CONO functional groups; and higher abundance of Fe-containing formulas. Fe was present in 38 % of the U-containing formulas but only 20 % of the total OM formulas. It is postulated that Fe played an important role in stabilizing the structure of sedimentary OM, especially U-containing compounds. The identification for the first time of hundreds of Fe-U-OM formulas demonstrates the complexity of such system is much greater than commonly believed and numerically predicting U binding behavior in OM-rich systems may require greater use of statistical or artificial intelligence approaches rather than deterministic approaches limited to measuring metal complexation with well-defined individual analogue organic ligands.

Sediment record of heavy metals in Xincun Lagoon indicating anthropogenic impact over the last 200 years

Anthropogenic metal pollution is a leading environmental problem in southern China, especially in remote regions where its impact remains poorly understood. This study investigates the historical variation of heavy metal pollution over the last 200 years using a sediment core from Xincun Lagoon, Hainan Island, South China. The temporal evolution of heavy metal pollution aligns with China's socioeconomic development. Prior to the 1950s, heavy metal concentrations were at geochemical background levels, reflecting China's agrarian status. Since the 1950s, the increased heavy metal accumulation may be attributed to intensified human activities linked to rapid urbanization and industrialization. Despite the increase in heavy metal enrichments since the 1950s, Xincun Lagoon currently faces a low ecological risk.

Pollution Characteristics and Risk Assessment of Heavy Metals in the Sediments of the Inflow Rivers of Dianchi Lake, China

To explore the contamination status and identify the source of the heavy metals in the sediments in the major inflow rivers of Dianchi Lake in China, sediment samples were collected and analyzed. Specifically, the distribution, source, water quality, and health risk assessment of the heavy metals were analyzed using correlation analysis (CA), principal component analysis (PCA), the heavy metal contamination factor (Cf), the pollution load index (PLI), and the potential ecological risk index (PERI). Additionally, the chemical fractions were analyzed for mobility characteristics. The results indicate that the average concentration of the heavy metals in the sediment ranked in the descending order of Zn > Cr > Cu > Pb > As > Ni > Cd > Hg, and most of the elements existed in less-mobile forms. The Cfwas in the order of Hg > Zn > Cd > As > Pb > Cr > Ni; the accumulation of Hg, Zn, Cd, and As was obvious. Although the spatial variability of the heavy metal contents was pronounced, the synthetical evaluation index of the PLI and PERI both reached a high pollution level. The PCA and CA results indicate that industrial, transportation, and agricultural emissions were the dominant factors causing heavy metal pollution. These results provide important data for improving water resource management efficiency and heavy metal pollution prevention in Dianchi Lake.

Turbid Waters and Clearer Standards: Refining Water Quality Criteria for Coastal Environments by Encompassing Metal Bioavailability from Suspended Particles

Suspended particulate matter (SPM) carries a major fraction of metals in turbid coastal waters, markedly influencing metal bioaccumulation and posing risks to marine life. However, its effects are often overlooked in current water quality criteria for metals, primarily due to challenges in quantifying SPM's contribution. This contribution depends on the SPM concentration, metal distribution coefficients (Kd), and the bioavailability of SPM-bound metals (assimilation efficiency, AE), which can collectively be integrated as a modifying factor (MF). Accordingly, we developed a new stable isotope method to measure metal AE by individual organisms from SPM, employing the widely distributed filter-feeding clam Ruditapes philippinarum as a representative species. Assessing SPM from 23 coastal sites in China, we found average AEs of 42% for Zn, 26% for Cd, 20% for Cu, 8% for Ni, and 6% for Pb. Moreover, using stable isotope methods, we determined metal Kd of SPM from these sites, which can be well predicted by the total organic carbon and iron content (R2 = 0.977). We calculated MFs using a Monte Carlo method. The calculated MFs are in the range 9.9-43 for Pb, 8.5-37 for Zn, 2.9-9.7 for Cu, 1.4-2.7 for Ni, and 1.1-1.6 for Cd, suggesting that dissolved-metal-based criteria values should be divided by MFs to provide adequate protection to aquatic life. This study provides foundational guidelines to refine water quality criteria in turbid waters and protect coastal ecosystems.