Assessment and Implication of PAHs and Compound-Specific δ13C Compositions in a Dated Marine Sediment Core from Daya Bay, China

Current trends and challenges in the analysis of marine environmental contaminants by isotope ratio mass spectrometry

An increasing number of organic and inorganic pollutants are being detected in the marine environment, posing a severe threat to the ecosystem and human health, even in trace concentrations. Isotope ratio mass spectrometry (IRMS) is one of the critical methods for determining the origin and fate of environmental pollutants and characterising their transformation processes. It has been used for a relatively long time for ecological monitoring of some well-studied industrial hydrocarbons at contaminated sites. However, the method still faces many analytical challenges. This review provides a comprehensive overview of recent technical advances concerning IRMS analysis of various contaminants and discusses typical pitfalls encountered in marine environment analysis. Particular attention is given to the study of sampling techniques and sample preparation for examination, often the keys to successful research given the complexity of marine matrices and the diverse and numerous nature of contaminants. Prospects for developing IRMS to monitor pollution sources and pollutant transformation in the marine environment are outlined.

In situ diets of the bloom-forming dinoflagellate Noctiluca scintillans in Daya Bay

Red Noctiluca scintillans is a common heterotrophic dinoflagellate that forms blooms in temperate, subtropical, and tropical coastal ecosystems. The diet of this species plays an important role in its cell growth, development, and reproduction. Because limited gene diversity data are available regarding prey of this species, its diet in Daya Bay during a boreal winter bloom is reported using an integrated approach involving light microscopy, single cell isolation and plastid 16S rDNA cloning, and 18S rDNA V4 and V9 region amplification using isolated cells and environmental DNA as templates with high-throughput sequencing. While conventional light microscopy reveals the diet of this species to comprise Coscinodiscus sp. and Stephanopyxis turris (diatoms), copepod eggs, and detritus, plastid gene diversity identifies a diet comprising diatoms, cyanobacteria, and bacteria, and 18S rDNA high-throughput sequencing reveals a diet comprising 36 eukaryote families (primarily copepods, as well as diatoms, dinoflagellates, Ochrophyta, Haptophytes, Chordata, Cercozoans, Chlorophyta, Polychaeta, and ciliates). Dietary staples include copepods, diatoms, dinoflagellates, Ochrophyta, and Synechococcus. High copepod abundance in prey may reflect their relatively high abundance in environmental seawater. Thus, N. scintillans is generally omnivorous but prefers dominant phytoplankton taxa, including Rhizosoleniaceae, Leptocylindraceae, and Cymatosiraceae (diatoms), as well as Gonyaulacaceae (dinoflagellates). An integrated multi-disciplinary approach provides a more comprehensive picture of N. scintillans diet in Daya Bay, and an improved understanding of this species' ecological niche and trophic role in marine ecosystems.

The anthropogenic effects on organic matter in sediment core based on Bayesian mixing model: a case study of Daya Bay

Sediment is an important carrier of evidence about environmental evolution which receives huge volumes of organic material originated from both anthropogenic and natural sources. In this study, based on sedimentary chronology, the vertical trends of particle size distribution, total organic carbon (TOC), total nitrogen (TN), and their stable isotopes (δ13C, δ15N) in the sediment core of the nuclear power sea in southwest Daya Bay were analyzed, and the distribution characteristics and contribution ratios of different sources of organic matter in the sedimentary environment over the past 70 years were resolved using a Bayesian mixing model (MixSIAR). TOC, TN, δ13C, and δ15N ranged from 0.89 to 1.56%, 0.09 to 0.2%, - 22.3 to - 20.6‰, and 4.38 to 6.51‰, respectively. The organic matter in the sediment is controlled by a mixture of terrestrial input and marine autochthonous, the proportion of organic matter from terrestrial sources increases, while that from marine sources decreases in the sediment core, which persists from 1960 to 2000, yet organic matter from marine sources still dominates. The first signs of increased primary productivity occurred in 1960, and it was primarily due to agricultural activity. After the 1980s, the rapid increase in population around Daya Bay, the construction of nuclear power plants, the rise of aquaculture, and the quick expansion of industrial bases were all major factors that changed the ecological environment of Daya Bay.

Two-dimensional gas chromatography coupled to isotope ratio mass spectrometry for determining high molecular weight polycyclic aromatic hydrocarbons in sediments

The accuracy of compound-specific isotope analysis (CSIA) of trace-level pollutants in complex environmental samples has always been limited by two main challenges: poor chromatographic separation and insufficient amounts of analytes. In this study, a two-dimensional gas chromatography-isotope ratio mass spectrometry (2DGC-IRMS) system was constructed for compound-specific δ¹³C analysis of high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) in estuarine/marine sediments. This construction occurred through hyphenating an extra gas chromatography system (GC) to a conventional GC-IRMS using a commercially available multi-column switching-cryogenic trapping system (MCS-CTS). Compared with the previous 2DGC-IRMS strategy, which utilizes a Deans Switch device, the newly implemented 2DGC-IRMS scheme resulted in online purification of target analytes as well as enriched them online via duplicate injection and cryogenic trapping in CTS; this resultingly lowered the limits of detection (LOD) of CSIA. To improve the sample transfer efficiency to the IRMS, a broader-bore and longer fused-silica capillary was utilized to replace the original sample capillary running from the sample open split to the IRMS. A ẟ¹³C analysis of PAH standards showed accurate ẟ¹³C values, and high precisions (standard deviations 0.13-0.37%) were achieved, with the LOD of HMW-PAHs reduced to at least 1.0 mg/L (i.e., 0.07 to 0.09 nmol carbon per compound on-column). The successful application of this newly developed 2DGC-IRMS scheme provides a practical solution for the reliable CSIA of trace-level pollutants in complex environmental samples that cannot be measured using the conventional GC-IRMS system.