Neonicotinoids (NEOs) and fipronil are widely used in pest control, but their spatiotemporal distribution and risk levels in the "river-estuary-bay" system remain unclear. Between 2018 and 2021, 148 water samples from rivers to inshore and offshore seawater in Laizhou Bay, China were collected to investigate the presence of eight NEOs and fipronil and its metabolites (FIPs). Significant seasonal variations in NEOs were observed under the influence of different cultivation practices and climatic conditions, with higher levels in the summer than in the spring. The average concentrations of total neonicotinoids (ΣNEOs) and ∑FIPs decreased from rivers (63.64 ng/L, 2.41 ng/L) to inshore (22.62 ng/L, 0.14 ng/L) and offshore (4.48 ng/L, 0.10 ng/L) seawater of Laizhou Bay. The average concentrations of ΣNEOs decreased by 85.3 % from 2018 to 2021. The predominant insecticides in the study area were acetamiprid, thiamethoxam, imidacloprid, and fipronil sulfone, with a gradual shift toward low-toxicity and environmentally friendly species over time. Influenced by agricultural intensity, ∑NEOs were mostly distributed in the Yellow River, Xiaoqing River, and their estuaries, where they pose chronic ecological risks. However, FIP exhibited high risk in certain rivers and sewage treatment plants owing to the use of animal repellents or landscape gardening insecticides. This study provides evidence of the transfer of NEOs and FIPs from rivers to the ocean and also clarifies their transition dynamics and changes in risk levels from rivers to oceans. Additionally, the study offers data support for identifying critical pesticide control areas.

The TetraEther indeX of 86 carbon atoms (TEX86) is widely used as a proxy to reconstruct past sea surface temperatures. Most current applications of TEX86 are primarily based on analyzing the composition of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) that comprise TEX86 in sediments, with the assumption that the sedimentary isoGDGTs are mainly derived from the surface mixed layer. Here we report on the variations in the isoGDGT distribution, archaeal abundance and community through the water column of the Western Pacific Ocean, directly testing the export depth of isoGDGTs and constraining the temperature records of TEX86. Our data show that maximum isoGDGT concentrations occurred in subsurface waters (150-200 m) with maximum archaeal abundances. The ratio between isoGDGTs bearing 2 vs. 3 cyclopentane moieties, i.e. [2/3] ratio, increased with depth, which is likely related to the shift of the archaeal community from Ca. Nitrosopelagicusdominance to norank_f__Nitrosopumilaceae-dominance. Models based on the [2/3] ratios in the water column predicted an average export depth of isoGDGTs to sediments of around 150-200 m, consistent with the robust relationship between the compiled sedimentary TEX86 and the annual mean subsurface temperature. Taken together, our findings support that TEX86 records subsurface rather than surface temperatures in the open ocean.

AbstractThere is evidence that sedimentary organic matter is prone to lateral transport under hydrodynamic processes before its final deposition on the seafloor, restricting the applicability of molecular proxies. In this study, we examine the abundances of marine and terrestrial biomarkers in bulk and the grain‐size fractionated samples (<20, 20–63, and >63 μm fractions) from surface sediments in the South Yellow Sea to decipher the spatial influences of hydrodynamic processes on the biomarker distributions and molecule‐proxies' applications. Our results show that spatial deviations between proxies‐derived sea surface temperature (SST; the ′ and TEX86 indexes) and satellite‐derived annual mean SST may result from the lateral transportation of the alkenones and isoprenoid Glycerol Dialkyl Glycerol Tetraethers driven by dominated nearshore coastal currents. We propose a spatial‐SST correction approach to obtain more accurate SST information by removing the hydrodynamically introduced SST bias. Our investigations imply that hydrodynamic processes could be an important factor for controlling the spatial distribution of biomarkers in the ocean, further influencing the applications of biomarker‐based proxies for paleo‐environmental reconstruction. We suggest that this investigation would shed new light on the biogeochemical dynamics of sedimentary organic carbon pump in the shallow ocean, particularly in the passive continental marginal seas with strong hydrodynamic conditions.

There is evidence that sedimentary organic matter is prone to lateral transport under hydrodynamic processes before its final deposition on the seafloor, restricting the applicability of molecular proxies. In this study, we examine the abundances of marine and terrestrial biomarkers in bulk and the grain-size fractionated samples (<20, 20-63, and >63 mu m fractions) from surface sediments in the South Yellow Sea to decipher the spatial influences of hydrodynamic processes on the biomarker distributions and molecule-proxies' applications. Our results show that spatial deviations between proxies-derived sea surface temperature (SST; the UK37K' and TEX86 indexes) and satellite-derived annual mean SST may result from the lateral transportation of the alkenones and isoprenoid Glycerol Dialkyl Glycerol Tetraethers driven by dominated nearshore coastal currents. We propose a spatial-SST correction approach to obtain more accurate SST information by removing the hydrodynamically introduced SST bias. Our investigations imply that hydrodynamic processes could be an important factor for controlling the spatial distribution of biomarkers in the ocean, further influencing the applications of biomarker-based proxies for paleo-environmental reconstruction. We suggest that this investigation would shed new light on the biogeochemical dynamics of sedimentary organic carbon pump in the shallow ocean, particularly in the passive continental marginal seas with strong hydrodynamic conditions.

Paralytic shellfish toxins (PSTs) producing algae are widely distributed in the global coastal aquatic environment, posing a threat to coastal ecosystem health and mariculture safety. However, the levels and potential environ-mental risks of PSTs frequently detected in shellfish remain largely unexplored in seawater of mariculture zones. In this study, a new method for trace detection of 13 common PSTs (<1.0 ng/L) in seawater was established based on off-line solid phase extraction (SPE) and on-line SPE-liquid chromatography-tandem mass spectrometry (on-line SPE-LC-MS/MS), and a systematic investigation of PSTs in seawater of the Laizhou Bay, a typical aquaculture bay in China, was conducted to understand their pollution status, environmental impact factors and ecological risks for the first time. Eleven PSTs were detected in the seawater of Laizhou Bay with total con-centrations ranging from 0.75 to 349.47 ng/L (mean, 176.27 ng/L), which indicates the rich diversity of PSTs in the mariculture bay and demonstrates the reliability of the proposed analytical method. C1, C2, GTX2, GTX3, dcGTX2, and dcGTX3 were found to be the predominant PSTs, which refreshed the knowledge of PST contam-ination in the coastal aquatic environment. PST levels in seawater exhibited the highest levels in the southeastern mouth of Laizhou Bay and decreased toward the inner bay. Correlation analyses showed that climatic factors, nutrient status and hydrological conditions had significant effects on the distribution of PST in mariculture bay. Preliminary environmental risk assessments revealed that aquatic organisms throughout the waters of Laizhou Bay are at risk of chronic PST toxicity. These findings imply that the risk of PST in seawater of mariculture bay has previously been grossly underestimated, and that the coastal aquatic environment in North China and even the world may be at more serious risk of PST pollution, which should be taken seriously.

Hydrophilic cyanotoxins (HCTs), such as paralytic shellfish toxins (PSTs), anatoxin-a (ATX-a), and cylindrospermopsin (CYN) are highly toxic and toxin-producing algae are widely distributed worldwide. However, HCTs, especially PSTs, are rarely reported in freshwater due to analytical limitations. This may result in an underestimation of the ecological risks and health risks. This study developed a new method to detect ATX-a, CYN, and thirteen common PSTs in freshwater simultaneously by using off-line solid phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The limits of detection (LODs) of all targets were lower than 0.05 μg/L, which could meet the regulatory requirements for monitoring of HCTs in drinking water in different countries and regions. To improve the detection sensitivities for trace PSTs, a method based on off-line SPE and on-line SPE-LC-MS/MS was established with LOD around 0.001 μg/L. GTX1&4, GTX2&3, and GTX5 were detected in freshwater in China for the first time, highlighting that overall communities are facing potential risks of exposure to various PSTs in China. High concentrations of ATX-a and CYN were also detected in freshwater from Northern China. The proposed method helps to understand the pollution status of HCT in water bodies, especially during the non-algal bloom period.

Glycerol dialkyl glycerol tetraethers (GDGTs) have received considerable attention because they are useful indicators for paleoenvironment, organic matter source, and microbial community. In this study, a new simple method was developed for the analysis of GDGTs by using direct large-volume injection (LVI)-liquid chromatography (LC)-atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) to reduce the usage of sediment or seawater suspended particulate matter (SPM) samples. The parameters of accelerated solvent extraction and LVI of target GDGTs were optimized. Under optimal conditions, the LVI approach (500 mu L injection) coupled with LC-APCI-MS could determine various GDGTs even with 0.02-0.10 g of sediment samples or SPM samples collected from 0.2-1.0 L of marginal sea water or 10-20 L of open ocean seawater with satisfactory method precision (relative standard deviations <= 10.2%) and linearity (R-2 >= 0.991). Compared with the classical method, the LVI-LC-APCI-MS required significantly reduced amount of sediment or SPM sample. Finally, the proposed method was applied to determine GDGTs in real sediment samples collected from hydrothermal vent sites at the Southwest Indian Ridges. Four groups of GDGTs, namely, isoprenoid GDGTs (isoGDGTs), branched GDGTs, H-GDGTs and OH-GDGTs, and archaeol, glycerol dialkanol diethers (GDDs) and glycerol monoalkanediol diethers (GMDs) were detected with only 0.02 g of sediment sample collected from Longqi and Tianzuo hydrothermal fields. The organic matter in the sediment sample from Tianzuo was significantly affected by hydrothermal activity. In addition, isoGDGTs in seawater SPM from the open area of Eastern Indian Ocean were investigated for the first time. Six common isoGDGTs were all detected in surface and subsurface SPM samples (filtering 10 L of seawater), which indicated that the LVI approach could noticeably reduce the workload of collecting seawater SPM on board and could be used to investigate conveniently the distribution of GDGTs in water column especially in open oceans and deep seas.

Domoic acid (DA) can poison or even be fatal to marine mammals, and poses a potential risk to human health via transmission through the food chain. The level of DA in seawater will affect the safety of seafood. Therefore, a powerful method for the detection of DA in seawater, especially in the coastal mariculture zone, is needed. In order to identify different concentration levels of DA in real seawater, in this study, a method was established for the determination of trace DA in seawater by SPE-LC-MS/MS. First, the LC-MS/MS instrument and sample pretreatment conditions were optimized. Subsequently, DA was separated on a 5 TC-C18 (2) analytical column (150 mm×4.6 mm, 5 μm), and multiple reaction monitoring (MRM) was conducted in the positive electrospray ionization mode. For off-line SPE, the HLB cartridge could enrich DA in seawater. The best enrichment of DA was obtained after adding 0.32 mL formic acid to an 80.0 mL seawater sample. Four on-line SPE columns from Agilent, namely, 5 TC-C18(2) (12.5 mm×4.6 mm, 5 μm), Zorbax Eclipse Plus-C18 (12.5 mm×2.1 mm, 5 μm), Zorbax Eclipse XDB-C8 (12.5 mm×2.1 mm, 5 μm), and PLRP-S (12.5 mm×2.1 mm, 15-20 μm), were tested to determine their suitability to trap DA from seawater samples. The 5 TC-C18 (2) column offered the best retention ability and good peak shape of DA, and was selected as the on-line SPE column. Validation was then performed to assess the sensitivity, linearity, matrix effects (MEs), recoveries, and precisions of the proposed method. After simple treatment of the seawater samples by filtration and acidification, 0.6 mL of the seawater sample was injected directly for on-line SPE-LC-MS/MS. The linearity was good, and ranged from 10.0 to 500.0 ng/L (correlation coefficient R2=0.9992). The limit of detection (LOD) and limit of quantification (LOQ) of DA were 4.0 and 10.0 ng/L, respectively, with good recovery (≥81.0%) and precision (RSDs≤4.2%) at three spiked levels in the blank seawater samples. After the DA in the 80.0 mL seawater sample was enriched by off-line SPE, a 0.6 mL sample was injected for on-line SPE-LC-MS/MS. The DA in the spiked blank seawater sample showed a good linear relationship in the range of 0.3-50.0 ng/L (R2=0.9990). The LOD and LOQ were 0.1 and 0.3 ng/L, respectively. The recoveries of DA at low, medium, and high spiked levels in the blank seawater samples were all ≥69.2%, and the RSDs were ≤4.4%. The MEs of DA with both methods were 18.3% and 13.7%, respectively, indicating that the ME was mild enough to be negligible. In summary, the proposed method is simple, sensitive, robust, and powerful for the detection of DA in inshore and offshore seawater.

Phytosterol biomarkers in marine sediments are often used to indicate the source of the sedimentary organics in the ocean, and to reflect the evolution of marine ecosystem and environment. In this study, a novel method 14 simultaneous determination of common phytosterols in marine sediments by non-aqueous reversed-phase liquid chromatography-atmospheric pressure photoionization mass spectrometry ( LC-APPI-MS ) was established. First, the APPI-MS characteristics of phytosterols were clarified. Under the positive APPI mode, phytosterols tended to produce stable characteristic ion peaks such as [ M + H - H2O ](+) , [ M + H - H-2 ](+) and [ M + H - 2H(2) ](+) . In the process of APPI-MS2, abundant fragment ion peaks were produced mainly through i-heterolysis. Second, LC-APPI-MS conditions were optimized, and a reversed-phase C-18 column was used to separate phytosterols with pure methanol as mobile phase and toluene as APPI ionization dopant , which could realize high sensitivity of detection for phytosterols in sediments. Furthermore, the method showed strong matrix interference resistance ability , good linear relationship ( R-2 >= 0. 9990 ) , high recovery rate ( 86. 4% - 94. 9% ) and good repeatability ( RSDs >= 8. 3% ). Finally, the proposed method was applied to detect common phytosterols in the surface sediment of Laizhou Bay in China, and several sterols, such as brassicasterol , fucosterol and sitosterol, etc. , were detected in every sediment sample. The total concentration of sterols was 4. 21-12. 91 mu g/g, among which the concentration of sitosterol was the highest. To sum up , the developed LC-APPI-MS method was a powerful tool 14 determination of common phytosterols in marine sediments , with easy-operation and high sensitivity.

Lipophilic marine algal toxins (LMATs) are highly toxic secondary metabolites produced by marine microalgae that pose a great threat to marine aquaculture organisms and human health. In this study, a novel and automated method for the simultaneous determination of six groups of LMATs in seawater was developed by on-line solid phase extraction (SPE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Condition optimization and method validation were performed, and the recoveries of all 14 target LMATs featuring different properties ranged from 83.5% to 96.0%. The limits of detection of most target compounds were within ≤3.000 ng/L with good precision (relative standard deviation ≤ 12.1%) and linearity (R2≥0.9916). Compared with off-line SPE methods, the proposed on-line SPE method has better recovery, sensitivity, repeatability, and throughput; in addition, the volume of seawater sample necessary to conduct determinations is greatly reduced in the present method. Finally, the method was applied to determine LMATs in actual seawater samples collected from the Bohai and South Yellow Seas of China in summer, and okadaic acid and pectenotoxin-2 were detected in all seawater samples. The highest concentration of ∑LMATs (22.23 ng/L) occurred in the coastal mariculture area of Shandong Province. Therefore, routine monitoring of LMATs in seawater of the coastal mariculture zone is necessary to prevent shellfish contamination especially in summer, and the proposed on-line SPE-LC-MS/MS method is a powerful way for direct and automatic detection of various LMATs in coastal mariculture area.