Multivariate linear regression model for source apportionment and health risk assessment of heavy metals from different environmental media.

The study evaluated source apportionment of heavy metals in vegetable samples from the potential sources of fertilizer, water and soil samples collected along the Changjiang River delta in China. The results showed that 25.72% of vegetable samples (Brassica chinensis L.) containing Pb, and Cd, Cu, Hg and Zn at relatively serious levels were from soil. Combined with principle component analysis (PCA) and cluster analysis (CA), the results of the spatial distribution of heavy metals in different environmental media indicated that fertilizer, water and soil were the main sources of heavy metals in vegetables. The results of multivariate linear regression (MLR) using partition indexes (P) showed that fertilizer contributed to 38.5%, 40.56%, 46.01%, 53.34% and 65.25% of As, Cd, Cu, Pb and Zn contents in vegetables, respectively. In contrast, 44.58% of As, 32.57% of Hg and 32.83% of Pb in vegetables came from soil and 42.78% of Cd and 66.97% of Hg contents in vegetables came from the irrigation water. The results of PCA and CA verified that MLR using P was suitable for determining source apportionment in a vegetable. A health risk assessment was performed; As, Cd and Pb contributed to more than 75% of the total hazard quotient (THQ) values and total carcinogenic risk values (Risktotal) for adults and children through oral ingestion. More than 70% of the estimated THQ and Risktotal is contributed by water and fertilizer. Therefore, it is necessary to increase efforts in screening limits/levels of heavy metals in fertilizer and irrigation water and prioritize appropriate pollution management strategies.

Silt-size sediment provenance of the Jianggang radial sand ridges in the southwestern Yellow Sea identified by geochemistry of quartz and K-feldspar.

In this paper, the geochemistry of K-feldspar and quartz, combined with MixSIAR and MDS models, was applied to illustrate the provenance of silt-size sediments in the Jianggang RSRs of the Yellow Sea, which profoundly affect the circulation of organic matter. The geochemical distributions revealed an apparent shoreward migration for sediments in the western offshore compared to eastern offshore. The models showed that the onshore RSRs silt-size sediments were mainly from the Yangtze River Mouth and Old Yellow River Delta, with contributions of 43.5 ± 15.3 % and 48.4 ± 13.9 %, respectively. While the offshore RSRs sediments were primarily from the Yangtze River Mouth (61.9 ± 18.0 %). Meanwhile, the transport patterns of silt-size sediments were proposed for the first time. The load calculation further showed that the expansion rate of local coast in 2023-2043 will be lower than in 1997-2017. Therefore, it was recommended to take actions for coastal development.

Pb and O isotopic characteristics of single minerals in the Jianggang radial sand ridges of the southwestern Yellow Sea: Implications for provenance and pathways of silt-size sediments.

Understanding the sediment provenance of the Jianggang radial sand ridges (RSRs) along the Jiangsu coast in the southwestern Yellow Sea is crucial for sustainable coastal development and land resource management. In this study, the provenance and transport patterns of silt-size sediments in the Jianggang RSRs were explored using Quartz oxygen (O) and K-feldspar lead (Pb) isotopic compositions and their large ion lithophile elements (LILEs) concentrations. The Pb-O isotopic compositions and concentrations of most LILEs in RSRs sediments were between those of the Yangtze River Mouth (YTZ), Old Yellow River Delta (OYR), and Modern Yellow River Mouth (MYR). The Pb-O isotopic compositions and typical elemental ratios were similar between the onshore and northwest offshore RSRs sediments, implying shoreward transport of offshore silt-size sediments. Through multidimensional scaling and graphic methods, it was found that the sediments of onshore and offshore RSRs originate mainly from the YTZ and OYR. Furthermore, the MixSIAR model showed that the contributions of the YTZ to onshore and offshore RSRs reached 33 ± 4 % and 36 ± 3 %, respectively. Followed by the OYR with contributions of 36 ± 3 % and 25 ± 8 %, respectively, and the contributions of the MYR and Korean Peninsula were <21 % and 8 %, respectively. Meanwhile, contributions from the Northern Chinese Deserts (approximately 10 %) deserved attention. Through the distribution of indicators, the transport patterns of silt-size sediments were proposed and compared with those of other fractions for the first time. According to the correlation analysis, the change in the area of central Jiangsu coast was mostly affected by terrestrial river supply and coastal mariculture. Therefore, it was necessary to control the scale of river reservoir construction and strengthen mariculture for sustainable land development and management. In future, comprehensive interdisciplinary and large temporal-spatial scales are suggested to further understand the coastal development.

Seasonal variation and provenance of organic matter in the surface sediments of the three gorges reservoir: Stable isotope analysis and implications for agricultural management.

The construction of the Three Gorges Dam has altered the hydrology and increased the trapping of sediment in the reservoir. This has also changed the composition and export of particulate organic matter in the Yangtze River. To understand the seasonal variations and sources of organic matter in sediments, total organic carbon (TOC), total nitrogen (TN), δ13Corg and δ15N in surface sediment samples from the mainstream and tributaries of the Three Gorges Reservoir were measured in the summer (July) and winter (December) of 2017, respectively. The results showed that the concentrations of TOC and TN in the surface sediments of the Three Gorges Reservoir were 0.79 %-1.46 % and 0.07 %-0.13 %, respectively. The ranges of δ13Corg and δ15N were - 26.35 ‰ to-24.70 ‰ and 2.59 ‰ to 5.67 ‰, respectively. According to δ13Corg and the TOC/TN ratio, the source range of organic matter was determined, and the contributions of different organic matter sources were quantified using a Bayesian mixed model. The results showed that soil organic matter and river plankton were the main sources of surface sediment organic matter in summer, whereas soil organic matter and aquatic vascular plants were the main sources in winter. The source of organic matter is related to biological factors in summer, whereas it is mainly caused by hydrodynamic conditions in winter. The analysis of δ15N further reveals that there are obvious external pollutants in the Three Gorges Reservoir, mainly related to artificial nitrogen fertiliser and domestic sewage. This study highlights the influence that soil nitrogen loss may be an important reason for the impact of agricultural non-point source pollution in the reservoir area, showing seasonal differences which were mainly affected by rainfall in summer and controlled by impoundment in winter. Hence, fine nitrogen management is required to reduce pollution in the Three Gorges Reservoir.

The isotopic composition of organic carbon, nitrogen and provenance of organic matter in surface sediment from the Jiangsu tidal flat, southwestern Yellow Sea.

The Jiangsu tidal flat is a significant organic matter reservoir, but quantitative studies of organic matter sources are scarce. In this study, total organic carbon (TOC) and total nitrogen (TN) concentrations and δ13Corg and δ15Ntotal values of surface sediment from Jiangsu tidal flat were investigated for their distributions, influencing factors, and sources of organic matter. TOC and TN were high in the center of study area and correlated well with grain size, indicating hydrodynamic influence on organic matter. High TOC/TN and low δ13Corg and δ15Ntotal in estuaries were characteristic of C3 plants, soil, and fertilizer sources, suggesting source effect on the distribution of organic matter. The MixSIAR model revealed that marine sources were dominant with a contribution reaching 56.9 %, followed by uniform of C3 plants, soil and fertilizer, while domestic sewage was least prominent. This study enriched theories of the biogeochemical cycle and ecological protection in the southwestern Yellow Sea.

Chemical speciation of phosphorus in surface sediments from the Jiangsu Coast, East China: Influences, provenances and bioavailabilities.

Sixty-one surface sediment samples collected from the Jiangsu Coast (JSC), East China were investigated to explore the influences, provenances and bioavailabilities of P species. Authigenic and detrital P fractions were the dominant species, accounting for 28.53% and 44.04% of the total P content, respectively. Exchangeable, Fe-bound and organic P fractions were biologically available, with an average total of 5.94 µmol/g; this value was governed by grain sizes and the organic matter and carbonate contents. Exchangeable and organic P fractions were transformed between each other, while contributing to the formation of Fe-bound and authigenic P. Phosphorus in the JSC sediments originated mainly from the Yellow River. The unique distribution pattern of P species in the JSC depends on P sources and local environments. These findings improve our understanding of the P cycle and eutrophication in the Jiangsu Coastal Zone.

Evolution of groundwater chemistry in coastal aquifers of the Jiangsu, east China: Insights from a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach.

Groundwater salinization is currently a very serious and challenging issue in many parts of the world. With an increasing demographic pressure and remarkable changes of water and land uses over the last decades, the multilayer coastal aquifer system of Jiangsu province, east China, was affected by increasing salinization. In this study, we investigate the groundwater salinization process and the salinity sources of the aquifer system in Nantong area (southern part of the Jiangsu coastal plain) using a multi-isotope (δ2H, δ18O, 87Sr/86Sr, and δ11B) approach. The results show that the TDS (total dissolved solids) values in most deep groundwater samples are generally lower than those of the shallow groundwater samples. The TDS of both shallow and deep groundwater increase from western Nantong (inland) to the eastern coastal region of the Yellow Sea. The chemical types transform from Ca-Mg-HCO3 or Mg-Ca-HCO3 to NaCl. The stable hydrogen and oxygen isotopes signatures of the groundwater samples indicate that local precipitation likely acts as the main recharge source of both the shallow and deep confined groundwater systems. The deep groundwater shows more depleted isotopes, suggesting recharging by the precipitation under a cold climate before the Holocene period. The shallow groundwater features heavier water isotopes, indicating recharging source from recent precipitation under a warm climate. The variations in δ11B and 87Sr/86Sr of groundwater samples can be explained by the changes of solute sources. In the inland region (western Nantong), shallow groundwater with higher TDS is mainly caused by evaporation-induced concentration, whereas in coastal areas, seawater intrusion exerts a major influence on the chemical composition of the shallow groundwater. Our results show that that seawater intrusion mainly occurs in eastern and southeastern Nantong area. We also find that hydraulic connection between shallow and deep groundwater is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points. The mixing between upper saline water and deep freshwater, together with water-rock interactions, likely explain the observed low salinity in deep groundwater in coastal areas. Overall, with growing observations of salty seawater intrusion in the estuary region of the Yangtze River, future efforts are needed to prevent further seawater intrusion as sea level rises and groundwater table declines. In this context, our findings provide key information for groundwater management in other coastal aquifers, east China.

Phosphorus species in bottom sediments of the Three Gorges Reservoir during low and high water level periods.

Eutrophication and algal blooms have recently been found in the backwater areas of some tributaries in the Three Gorges Reservoir (TGR), for which phosphorus (P) is an important driving factor. However, P species in the TGR sediments at different water levels were little known. In this study, five P species of the TGR sediments during the high and low water level periods were analyzed with a sequential extraction method. The total P (TP) concentrations were 714.88 ± 37.86 µg/g and 697.57 ± 111.49 µg/g at the low and high water levels, respectively. The concentrations of P species decreased in the orders detrital P > authigenic P > organic P > iron-bound P > exchangeable P at the low water level and detrital P > organic P > authigenic P > iron-bound P > exchangeable P at the high water level. P in the TGR sediment sourced mainly from the upstream input at the low water level but from the inputs of tributaries and hillslope soils at the high water level. The bioavailable P (BAP) possessed > 29.5% of total P in the two periods. The total storages of total P and BAP were estimated to be about 1.34 × 106 t and 1.77 × 105 t, respectively during 2003-2017. It was further found that the BAP concentration significantly increased from periods I (2003-2009), II (2010-2014), to III (2015-2017), while the deposition flux and storage of BAP were the highest in period II. Our findings provide new insight into the P cycle and benefit eutrophication treatment in the TGR.

Characteristics of lead geochemistry and the mobility of Pb isotopes in the system of pedogenic rock-pedosphere-irrigated riverwater-cereal-atmosphere from the Yangtze River delta region, China.

Knowledge of the characteristics of Pb and its isotopic transfer in different compartments is scant, especially for the mobility of Pb isotopes in the geochemical cycle. The present study characterizes differential Pb transport mechanism and the mobility of Pb isotopes in the pedogenic parent rock-pedosphere-irrigated riverwater-cereal-atmosphere system in the Yangtze River delta region, by determining Pb concentration and Pb isotopic ratios of pedogenic parent rocks, fluvial suspended particle matter, tillage soils, soil profiles, irrigated riverwater, fertilizer, Pb ore, cereal roots and grains. The results show that Pb isotopes in the geochemical cycle generally follow the equation of (208)Pb/(206)Pb=-1.157×(206)Pb/(207)Pb+3.46 (r(2)=0.941). However, Pb isotopes have different mobility in different environmental matrixes. Whereas in the pedosphere, the heavier Pb ((208)Pb) usually shows stronger mobility relative to the lighter Pb, and is more likely to transfer into soil exchangeable Pb fraction and carbonates phase. The lighter Pb shows stronger transfer ability from soil to cereal grain via root compared to the heavier Pb. However, the cereal grains have lower (206)Pb/(207)Pb and higher (208)Pb/(206)Pb ratios than root and tillage soil, similar to the airborne Pb and anthropogenic Pb, implying that a considerable amount of Pb in cereal grains comes from the atmosphere. The estimate model shows that 16.7-52.6% (average: 33.5%) of Pb in rice grain is the airborne Pb.

[Characteristics of heavy metals in sediments from different sources and their ecological risks in the lower reaches of the Yangtze River].

Characteristics of heavy metals in sediments from different sources are significant varied,which impact on the degree of damage for aquatic system. Samples from municipal, mining, industrial and port sources in the lower reaches of the Yangtze River were analyzed for major elements and Cu, Zn, Pb, Cd, Cr by ICP-AES and AAS. The results showed that the concentrations were moderately and relatively uniform for heavy metals in the municipal source, Cu, Pb were dominated for the mine source. Five metals had higher concentrations in industrial source, and Cd was the highest in sediments from port source. The enrichment factors of heavy metals in sediments were high, especially Cd, up to 7.3.Through principal component analysis of major elements and heavy metals, it is concluded that heavy metals of municipal source stem from the erosion of road surface and inner pipeline in cities, heavy metals of mine source come from the mining and the leaching of tailings, heavy metals of industrial source are mostly generated by mechanical debris and metal dissolution, heavy metals of port sources are mainly from the transport ships and the intensive gas emissions from vehicles. The ecological risks of these sediments were evaluated with the Hakanson ecological risk index. It is concluded that the single factors of the ecological hazards for metals are Cd > Cu > Pb > Cr > Zn, the comprehensive index of potential ecological risks for metals from different sources decrease with port source > industrial source > mine source > municipal source.