Riverine input of suspended particulate matter controls distribution, partitioning and transport of mercury and methylmercury in the Yellow River Estuary

Organic matter content, source, and composition varying with seasons and anthropogenic activities regulate methylmercury dynamics in the Yellow River

Organic matter (OM) in rivers, influenced by natural and anthropogenic events, plays a critical role in regulating methylmercury (MeHg) dynamics. This study investigated the spatial-temporal patterns of MeHg and OM in the Yellow River, through collecting water and sediment samples within the dry and wet seasons and human-induced water-sediment regulation scheme (WSRS) event. During the wet season, the river water was characterized by terrigenous OM, high unfiltered MeHg (UMeHg) concentration (206 ± 83.6 pg/L), and a low UMeHg percentage in unfiltered total Hg (UTHg) (UMeHg/UTHg = 0.37 ± 0.18 %). These findings may suggest that MeHg in the wet season was likely produced in the catchment and imported into the river. In contrast, autochthonous OM predominated during the dry season, probably enhancing in situ MeHg production (UMeHg/UTHg = 1.01 ± 0.50 %), although UMeHg concentration was lower (81.8 ± 25.5 pg/L) due to obviously reduced external inputs. The WSRS dramatically increased water MeHg contents (589 ± 116 pg/L) and UMeHg/UTHg ratios (0.78 ± 0.16 %) probably through direct inputs of upstream reservoirs' MeHg and resuspension of downstream sediments. Exploring the effects of OM on sediment MeHg sources suggested that MeHg in the wet season primarily originated from watershed soil inputs, while in the dry season, it mainly resulted from in situ Hg methylation. However, extremely low total Hg (THg) and MeHg/THg (0.02-0.35 %) indicated that sediment MeHg production may be of minor importance in the Yellow River.

Distribution characteristics of Hg and As in the water-SPM system in the Xiaoqing river estuary and coastal

Water and suspended particulate matter (SPM) were collected from Xiaoqing Estuary and its adjacent waters in August 2022 to study the spatial distribution and risk assessment of Hg and As. The content of Hg in SPM samples ranged from 4.7152 to 446.8678 mg kg-1, and the content of As ranged from 90.1739 to 1147.5500 mg kg-1. The content of Hg in water ranges from 0.0219 to 0.0986 μg L-1, and the content of As ranges from 1.4326 to 11.6750 μg L-1. Xiaoqing River runoff input is the main source of Hg and As. Particulate Hg and As was extremely polluted, water was much less of a risk. It indicated that SPM accumulates more dangerous pollutants (Hg and As). In both water and SPM, it turned out that Hg has a higher risk than As (i.e., CF(Hg) > CF(As), Igeo(Hg) > Igeo(As)). The analysis showed that the environmental factors of water further affected the distribution of Hg or As in water and SPM by influencing biological activity.

Towards a better understanding of ethylmercury in the environment: Addressing propylation derivatization artifact and verifying its occurrence in Chinese wetlands

Ethylmercury (EtHg), similar to methylmercury (MeHg), is highly neurotoxic and bioaccumulative. Although recent studies suggested its occurrence in natural soils and sediments, the common propylation derivatization for EtHg analysis might generate EtHg artifacts, potentially leading to its overestimation in environmental samples. Furthermore, the extensive environmental prevalence of EtHg remains unverified, keeping its importance largely uncertain. This study investigated the formation of EtHg artifacts during propylation derivatization, evaluating artifacts formation and recoveries under different extraction methods with real samples, and confirmed the widespread occurrence of EtHg in Chinese wetlands. EtHg artifacts were obviously present during the propylation derivatization and strongly dependent on the levels of Hg2+ (0.1-10 ng) in the derivatization solution (R² = 0.99), accounting for 1.38-2.14% of Hg2+. CuSO4-HNO3CH2Cl2 extraction (effectively removing Hg2+) combined with propylation derivatization offers excellent recovery (81-86%) and low artifacts (< LOD: 1.98 × 10-4 ng/g) for EtHg measurement in soils/sediments, with results aligning with those from online solid phase extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry (R2 = 0.99). Additionally, we observed the occurrence of EtHg in soil and sediment samples across 14 Chinese wetlands, with concentrations varying from 6.08 to 171 pg/g, similar to MeHg concentrations at some sites. EtHg positively correlates with MeHg, total Hg, and total organic carbon across all samples, indicating a possible biological formation. These findings help better understand and predict the prevalence of EtHg in wetlands and its key role in environmental Hg cycle.

A Critical Review of the Crucial Role of the Yellow River's Sediment in the Interfacial Migration and Fate of Pollutants and Prospects for the Application of Environmental Sediment Restoration

Considering the increasing sediment content and increasing sediment flux of the Yellow River over the years, it is of significance to investigate the potential interfacial force mechanism between pollutants and Yellow River sediment. This article has reviewed the current research on the Yellow River sediments' mineral structures while investigating the potential interaction force between sediment and pollutants in the water environment. This article has conducted a comprehensive analysis of the influence of sediment on the migration of pollutants in the water environment. What is more, the authors have provided an outlook on the future applications of sediment in ecological environmental systems. Yellow River sediment mainly included minerals and some clay phases, while its irregular surface provided sites for the interface adsorption of pollutants. The interface force between the sediment and pollutants is mainly attributed to promoting bacterial growth on the surface of sediments, physisorption, and chemisorption forces. The sediments carry and transport pollutants during the long-distance water flow migration process. The sediment should be effectively utilized and better integrated into ecological or environmental restoration systems. This article provides a reference for studying the behavior of Yellow River sediment and the direction of future efficient utilization.

Effects of hydrologic regimes on the loading and spatiotemporal variation of mercury in the microtidal river estuary

The potential effect of hydrological conditions on distribution and loadings of Hg species was investigated in the microtidal Hyeongsan River Estuary (HRE). Dissolved Hg (DHg) and dissolved methylmercury (DMeHg) from the creek receiving industrial wastes were effectively settled to sediment during the post-typhoon period, while persistent input from the Hg-contaminated creek without settling was observed during the dry periods. The event-based mean approach was applied to explore the hydrological effects on the annual flux of Hg. The largest inputs of DHg and particulate Hg (PHg) were found in the Hg-contaminated creek, and DHg input was higher in the dry than wet periods whereas PHg input was higher in the wet than dry periods. In sediment, Hg and MeHg concentrations decreased after the typhoon, attributed to erosion of surface sediments. Overall, the HRE serves as an effective sink of Hg that reduces the degree of Hg contamination in coastal water.

Confounding effects of seasonality and anthropogenic river regulation on suspended particulate matter-driven mercury transport to coastal seas

Riverine mercury (Hg) is mainly transported to coastal areas in suspended particulate matter (SPM)-bound form, posing a potential threat to human health. Water discharge and SPM characteristics in rivers vary naturally with seasonality and can also be arbitrarily disrupted by anthropogenic regulation events, but their effects on Hg transport remain unresolved. Aiming to understand the confounding effects of seasonality and anthropogenic river regulation on Hg and SPM transport, this study selected the highly sediment-laden Yellow River as a representative conduit. Significant variations in SPM concentrations (108 - 7097 mg/L) resulted in fluctuations in total mercury (THg, 3.79 - 111 ng/L) in river water corresponding to seasonality and anthropogenic water/sediment regulation. Principal component analysis and structural equation model revealed that SPM was the essential factor controlling THg and particulate Hg (PHg) in river water. While SPM exhibited equilibrium state in the dry season, a net resuspension during the anthropogenic regulation and net deposition in the wet season demonstrated the impact of SPM dynamics on Hg distribution and transport to coastal regions. Combining water discharge, SPM, and Hg concentrations, a modified model was developed to quantify Hg flux (2256 kg), over 98% of which was in particulate phase.