Tracing the dynamic changes of element profiles by novel soil porewater samplers with ultralow disturbance to soil-water interface

In flooded soils, soil-water interface (SWI) is the key zone controlling biogeochemical dynamics. Chemical species and concentrations vary greatly at micro- to cm-scales. Techniques able to track these changing element profiles both in space and over time with appropriate resolution are rare. Here, we report a patent-pending technique, the Integrated Porewater Injection (IPI) sampler, which is designed for soil porewater sampling with minimum disturbance to saturated soil environment. IPI sampler employs a single hollow fiber membrane tube to passively sample porewater surrounding the tube. When working, it can be integrated into the sample introduction system, thus the sample preparation procedure is dramatically simplified. In this study, IPI samplers were coupled to ICP-MS at data-only mode. The limits of detection of IPI-ICP-MS for Ni, As, Cd, Sb, and Pb were 0.12, 0.67, 0.027, 0.029, and 0.074 μg·L , respectively. Furthermore, 25 IPI samplers were assembled into an SWI profiler using 3D printing in a one-dimensional array. The SWI profiler is able to analyze element profiles at high spatial resolution (∼2 mm) every ≥24 h. When deployed in arsenic-contaminated paddy soils, it depicted the distributions and dynamics of multiple elements at anoxic-oxic transition. The results show that the SWI profiler is a powerful and robust technique in monitoring dynamics of element profile in soil porewater at high spatial resolution. The method will greatly facilitate studies of elements behaviors in sediments of wetland, rivers, lakes, and oceans

Arsenic behavior across soil-water interfaces in paddy soils: coupling, decoupling and speciation

The sharp redox gradient at soil-water interfaces (SWI) plays a key role in controlling arsenic (As) translocation and transformation in paddy soils. When Eh drops, As is released to porewater from solid iron (Fe) and manganese (Mn) minerals and reduced to arsenite. However, the coupling or decoupling processes operating within the redox gradient at the SWI in flooded paddy soils remain poorly constrained due to the lack of direct evidence. In this paper, we reported the mm-scale mapping of Fe, As and other associated elements across the redox gradient in the SWI of five different paddy soils. The results showed a strong positive linear relationship between dissolved Fe, Mn, As, and phosphorus (P) in 4 out of the 5 paddy soils, indicating the general coupling of these elements. However, decoupling of Fe, Mn and As was observed in one of the paddy soils. In this soil, distinct releasing profiles of Mn, As and Fe were observed, and the releasing order followed the redox ladder. Further investigation of As species showed the ratio of arsenite to total As dropped from 100% to 75.5% and then kept stable along depth of the soil profile, which indicates a dynamic equilibrium between arsenite oxidization and arsenate reduction. This study provides direct evidence of multi-elements’ interaction along redox gradient of SWI in paddy soils

Potentially toxic elemental contamination in Wainivesi River, Fiji impacted by gold - mining activities using chemometric tools and SOM analysis

Potentially toxic element (PTE) contamination in Wainivesi River, Fiji triggered by gold-mining activities is a major public health concern deserving attention. However, chemometric approaches and pattern recognition of PTEs in surface water and sediment are yet hardly studied in Pacific Island countries like Fijian urban River. In this study, twenty-four sediment and eight water sampling sites from the Wainivesi River, Fiji were explored to evaluate the spatial pattern, eco-environmental pollution, and source apportionment of PTEs. This analysis was done using an integrated approach of self-organizing map (SOM), principle component analysis (PCA), hierarchical cluster analysis (HCA), and indexical approaches. The PTE average concentration is decreasing in the order of Fe > Pb > Zn > Ni > Cr > Cu > Mn > Co > Cd for water and Fe > Zn > Pb > Mn > Cr > Ni > Cu > Co > Cd for sediment, respectively. Outcomes of eco-environmental indices including contamination and enrichment factors, and geo-accumulation index differed spatially indicated that majority of the sediment sites were highly polluted by Zn, Cd, and Ni. Cd and Ni contents can cause both ecological and human health risks. According to PCA, both mixed sources (geogenic and anthropogenic such as mine wastes discharge and farming activities) of PTEs for water and sediment were identified in the study area. The SOM analysis identified three spatial patterns, e.g., Cr–Co–Zn–Mn, Fe–Cd, and Ni–Pb–Cu in water and Zn–Cd–Cu–Mn, Cr–Ni and Fe, Co–Pb in sediment. Spatial distribution of entropy water quality index (EWQI) values depicted that northern and northwestern areas possess “poor” to “extremely poor” quality water. The entropy weights indicated Zn, Cd, and Cu as the major pollutants in deteriorating the water quality. This finding provides a baseline database with eco-environmental and health risk measures for the Wainivesi river contamination

DataSheet1_Prevalence of arsenic contamination in rice and the potential health risks to the Bahamian population—A preliminary study.docx

Rice is among the most important staple foods worldwide. However, the consumption of rice and rice-based food products poses a potential health risk since rice is a paddy crop that is well known to accumulate high concentrations of arsenic (As) in its grain. In The Bahamas, although rice is heavily consumed, it is not grown locally. Instead, all the consumed rice and its derived products are imported. Recent food surveys in the major rice exporting countries have shown that a significant portion of their market rice products is contaminated with As. However, to date, the prevalence of As in the rice foods available in The Bahamas remains unknown. Therefore, in this study, we surveyed the occurrence of As in a selection of rice and rice products that were on sale in the Bahamian market. A total of 21 different rice brands were collected. The concentration of As and the potential health risk were estimated by target hazard quotient (THQ), hazard index (HI), and lifetime cancer risk (LCR). Our results showed that only the blue ribbon samples had an estimated inorganic arsenic (iAs) concentration above the World Health Organization (WHO) safety limits (200 μg/kg), which is based on global average consumption. However, when we factor for average rice consumption in The Bahamas, 79% of the rice samples had iAs concentration values indicative of carcinogenic risks and 57% had iAs concentration values that suggested non-carcinogenic health risks. Based on our results, we recommend urgent follow-up studies to further test rice varieties that show the greatest LCR and HI values and to also broaden the study to include more off-brand/generic varieties, cooked rice, and drinking water.</p

Dynamics of cadmium and arsenic at the capillary fringe of paddy soils: A microcosm study based on high-resolution porewater analysis

Arsenic (As) and cadmium (Cd) are prevalent in paddy soils, posing potential threats to food safety and public health. The concentrations of soluble ​As and Cd is sensitive to moisture-driven changes in soil pH and Eh, which is barely described at the critical dry-wet interface. Here, tempo-spatial changes of soluble As and Cd were captured by In-situ Porewater Iterative samplers at the capillary fringe that extended from saturated to unsaturated moisture gradient at the millimeter scale (60 ​mm profile in depth) through two episodic dry-wet cycles (55 days in total). The As and Cd concentrations showed less significant fluctuation in second cycle compared to the initial dry-wet cycle. The study also revealed at the capillary fringe profile (20–40 ​mm), the As concentrations increased from 4.6 μg L−1 in unsaturated soils to 13.5 μg L−1 in saturated soils, while Cd decreased from 3.3 to 0.2 μg L−1. This observed correlation was aligned with the vertical changes in soil Eh (+287 to +381 ​mV) and pH (3.42–6.07). This study found a distinct zone characterized by low As and low Cd concentrations, typically situated approximately 10–30 ​mm beneath the capillary fringe. Upon further analysis, it was determined that soil with an Eh of 249 ​mV and a pH of 4.3 potentially serves as an optimal environment for decreasing As and Cd levels in porewater. These findings suggest that it is feasible to reduce As and Cd concentration in the soil by implementing appropriate depth-controlled water management techniques

Biochar for the Removal of Emerging Pollutants from Aquatic Systems: A Review

Water contaminated with emerging pollutants has become a serious environmental issue globally. Biochar is a porous and carbon-rich material produced from biomass pyrolysis and has the potential to be used as an integrated adsorptive material. Many studies have shown that biochar is capable to adsorb emerging pollutants from aquatic systems and could be used to solve the water pollution problem. Here, we provided a dual perspective on removing emerging pollutants from aquatic systems using biochar and analyzed the emerging pollutant removal efficiency from the aspects of biochar types, pollutant types and coexistence with heavy metals, as well as the associated mechanisms. The potential risks and future research directions of biochar utilization are also presented. This review aims to assist researchers interested in using biochar for emerging pollutants remediation in aquatic systems and facilitate research on emerging pollutants removal, thereby reducing their environmental risk

Nanobiochar for the remediation of contaminated soil and water: challenges and opportunities

Highlights Key synthesis technologies and properties of nanobiochars were discussed. The interactions pathways of nanobiochar with pollutants were elucidated. Role of environmental factors on pollutants remediation and life cycle was delineated. Important research outlooks on nanobiochar’s potential in pollutant remediation were elaborated

Seasonal size distribution and mixing state of black carbon aerosols in a polluted urban environment of the Yangtze River Delta region, China

The optical properties of black carbon aerosols (BC) are determined by the particles size and the associated non-BC materials, which may be source-related or modified during secondary processing. The one-year long monitoring of BC was first conducted using a Single Particle Soot Photometer (SP2) from December 2013 to November 2014 in Nanjing, a megacity in the Yangtze River Delta region of China. The seasonal variation in the BC size distribution and mixing state were investigated. There was no apparent systematic variation in the mean BC core mass median diameter between seasons, as these values were 226 +/- 12 nm, 217 +/- 13 nm, 211 +/- 15 nm and 221 +/- 12 nm for winter, spring, summer and autumn respectively. The mixing state of BC was quantified as the bulk relative coating thickness (defined as particle size D(p )over core size D-c, D-p/D-c), which ranged from 1.05 to 2.65. The BC was found to be significantly more coated in the winter (D-p/D-c = 1.50 +/- 0.30) than in other seasons (D-p/D-c = 1.27 +/- 0.09, 1.28 +/- 0.10, 1.27 +/- 0.11 in spring, summer and autumn respectively). Higher levels of coating during the winter may due to the contributions of the primary source (with the highest BC mass loadings between seasons) or secondary processes such as low temperature that facilitated the condensation. It was found that the photochemical process may enhance the coatings on BC in summer. At nighttime, the reduced and stabilized planetary boundary layer and the nighttime secondary formation may also lead to BC becoming well mixed with other components. Moreover. BC was shown to be less coated when the NOx concentration was high. However, during all seasons, the BC coating was strongly correlated with other non-BC particulate mass, which suggests that at higher pollution levels BC was more significantly coated with other existing materials through coagulation or condensation by other secondary species