Sediment samples were collected to a depth of 60 cm along a 350-m sampling belt in a short-term-flooding riparian wetland in the Yellow River Delta of China in three sampling seasons. Contents of heavy metals were determined to investigate their spatial and temporal distributions, sources and ecotoxities. Our results showed that As contents in the top 20 cm sediments increased before decreasing along the sampling belt in summer, whereas they kept stable before increasing in fall and spring. Cd contents increased along the sampling belt in three sampling seasons, whereas Ni and Cr generally exhibited a decreasing tendency. Comparatively, Cu, Pb and Zn consistently increased at the first 50 m distance and then decreased before increasing from the distance of 150 m in summer and fall and increased to the maximum at the distance of 250 m and then showed a decrease in spring. Two “hotspots” of heavy metal accumulation in sediment cores along the belt were observed at the distance from 50 to 100 m in summer and at the distance from 200 to 300 m in spring. Most of sediment samples contained higher heavy metals in excess of threshold effect levels except for Zn and Pb in three sampling seasons and the values of toxic units in more than 30% of sediment samples exceeded 4 in summer. As, Ni and Cr had relatively higher contribution to the values of toxic units compared with other heavy metals in three sampling seasons. Multivariance analysis showed that As and Cd might originate from the same source and Cu, Zn, Cr, Pb and Ni might derive from another similar source. Cd was significantly correlated with salinity (p < 0.01) and pH (p < 0.05). Meanwhile, these heavy metals were also significantly correlated with other properties such as S, Al, TP, SOM and Silt + Clay.

Application of empirical models to adsorption of contaminants on natural heterogeneous sorbents is often challenging due to the uncertainty associated with fitting experimental data and determining adjustable parameters. Sediment samples from contaminated and uncontaminated portions of a study site in Maine, USA were collected and investigated for adsorption of arsenate [As(V)]. Two kinetic models were used to describe the results of single solute batch adsorption experiments. Piecewise linear regression of data linearized to fit pseudo-first order kinetic model resulted in two distinct rates and a cutoff time point of 14–19 h delineating the biphasic behavior of solute adsorption. During the initial rapid adsorption stage, an average of 60–80% of the total adsorption took place. Pseudo-second order kinetic models provided the best fit to the experimental data (R2 > 0.99) and were capable of describing the adsorption over the entire range of experiments. Both Langmuir and Freundlich isotherms provided reasonable fits to the adsorption data at equilibrium. Langmuir-derived maximum adsorption capacity (St) of the studied sediments ranged between 29 and 97 mg/kg increasing from contaminated to uncontaminated sites. Solid phase As content of the sediments ranged from 3.8 to 10 mg/kg and the As/Fe ratios were highest in the amorphous phase. High-pH desorption experiments resulted in a greater percentage of solid phase As released into solution from experimentally-loaded sediments than from the unaltered samples suggesting that As(V) adsorption takes place on different reversible and irreversible surface sites.

Arsenic (As) can cause serious hazards to human health, especially in mining areas. Soil bacterial communities, which are critical parts of the soil ecosystem, were analyzed directly for soil environmental factors. As a consequence, it is of great significance to understand the ecological risk of arsenic contamination on bacteria, especially at the local scale. In this study, 33 pairs of soil and grain samples were collected from the corn and paddy fields around an arsenic mining area in Shimen County in Hunan Province, China. Significant differences were found between the soil nitrogen, As concentrations, and bacteria activities among these two types of land use. According to the structural equation model (SEM) analysis, compared with other environmental factors, soil As was not the key factor affecting the bacterial community, even when grain As was beyond the threshold of the national food hygiene standards of China. In the corn field, soil pH was the main factor dominating the bacterial richness, composition and grain As. Meanwhile, in the paddy field the soil total nitrogen (TN) and total carbon (TC) were the main factors impacting the bacterial richness, and the bacterial community composition was mainly affected by pH. The interactions between grain As and soil As were weak in the corn field. The bacterial communities played important roles in the food chain risk of As. The local policy of transforming paddy soil to dry land could greatly reduce the health risk of As through the food chain.

Arsenic is a non-threshold carcinogenic metalloid. Thus, human exposure should be minimised, e.g. by chemically stabilizing As in soil. Since iron is a potential As immobiliser, it was investigated whether root iron plaque, formed under aerobic conditions, affects As uptake, metabolism and distribution in Lupinus albus plants. White lupin plants were cultivated in a continuously aerated hydroponic culture containing Fe/EDDHA or FeSO4 and exposed to arsenate (5 or 20 μM). Only FeSO4 induced surficial iron plaque in roots. LA-ICP-MS analysis accomplished on root sections corroborated the association of As to this surficial Fe. Additionally, As(V) was the predominant species in FeSO4-treated roots, suggesting less efficient As uptake in the presence of iron plaque. Fe/EDDHA-exposed roots neither showed such surficial FeAs co-localisation nor As(V) accumulation; in contrast As(III) was the predominant species in root tissue. Furthermore, FeSO4-treated plants showed reduced shoot-to-root As ratios, which were >10-fold lower compared to Fe/EDDHA treatment. Our results highlight the role of an iron plaque formed in roots of white lupin under aerobic conditions on As immobilisation. These findings, to our knowledge, have not been addressed before for this plant and have potential implications on soil remediation (phytostabilisation) and food security (minimising As in crops).

This study analyzed 405 surface sediment samples, obtained from across the Bohai Sea, for concentrations of five potentially harmful elements (Ag, As, Hg, Sb, and Se) and several ancillary parameters (Al, Fe, Mn, total organic carbon (TOC), and grain size). Statistically, the spatial distributions of these elements were correlated positively with Al, Fe, TOC, and grain size, indicating natural sources for these elements or common accumulation mechanisms. The assessment of potential environmental risk with empirical sediment quality guidelines showed that a significant proportion of the samples had As and Sb concentrations that exceeded the effects range low (ERL) or T20 values in the Bohai Sea, indicating the potential for adverse biological effects. However, the assessment results differed when using evaluation methods that considered background values. Based on the geoaccumulation index (Igeo), Hg and Ag were found to have the highest percentages (35% and 60%, respectively) in samples that were moderately contaminated. The estimated contamination degree (Cd) suggested higher contamination levels for the entire area, with 69% of the samples being moderately contaminated. Generally, except for some local hotspots, such as Jinzhou Bay, the contamination levels of these elements in the Bohai Sea were established as slight to moderate. Samples from the Jinzhou Bay area had concentrations that were 10–100 times higher than in the rest of the Bohai Sea, indicating severe contamination.

Rice is one of the major pathways of arsenic (As) exposure in human food chain, threatening over half of the global population. Greenhouse pot experiments were conducted to examine the effects of Si application on iron (Fe) plaque formation, As uptake and rice grain As speciation in indica and hybrid rice genotypes with different radial oxygen loss (ROL) ability. The results demonstrated that Si significantly increased root and grain biomass. Indica genotypes with higher ROL induced greater Fe plaque formation, compared to hybrid genotypes and sequestered more As in Fe plaque. Silicon applications significantly increased Fe concentrations in iron plaque of different genotypes, but it decreased As concentrations in the roots, straws and husks by 28–35%, 15–35% and 32–57% respectively. In addition, it significantly reduced DMA accumulation in rice grains but not inorganic As accumulation. Rice of indica genotypes with higher ROL accumulated lower concentrations of inorganic As in grains than hybrid genotypes with lower ROL.

Roxarsone (ROX), the primary aromatic arsenical additive (AAA) used in animal feeding operations, is of increasing concern to environmental and human health due to land application of ROX-laden animal manure. Few studies have investigated the phytotoxicity, uptake mechanisms, and speciation of AAA in crop plants. In this study, wheat seedlings were employed to address these issues under hydroponic conditions. Compared to inorganic arsenic, ROX was less toxic to wheat root elongation. Wheat roots were more sensitive to ROX stress than shoots. For the first time, metabolized inorganic arsenic was detected in plants, although ROX was the predominant detected arsenic species in wheat seedlings. ROX uptake and toxicity to roots were inhibited by humic acid at concentrations higher than 50 mg/L due to interaction with ROX. Phosphate enhanced ROX uptake, but no trends were observed for ROX uptake in the presence of glycerol at concentrations lower than 250 mM. In addition, ROX uptake was significantly decreased by silicate (Si(IV), 0.5–10 mM) and the metabolic inhibitor, 2,4-dinitrophenol (0.5–2 mM), indicating that ROX transport into wheat roots was actively mediated by Si(IV)-sensitive transporters. These findings provide important insights into the fate and speciation of AAA in soil-water-plant systems relevant to human health.

Magnetic biochars (MW) prepared by chemical co-precipitation of Fe2+/Fe3+ on water hyacinth biomass followed by pyrolysis exhibited important potential in aqueous As(V) elimination. In comparison, MW2501 outperformed other MWs and exhibited the highest As(V) sorption capacity which was estimated to be 7.4 mg g−1 based on Langmuir-Freundlic model. With solution pH ranging from 3 to 10, As(V) removal efficiency by MW2501 kept stable and consistently higher than 90%. Besides, ∼100% removal of 0.5 mM As(V) can be obtained in the presence of P ≤ 0.1 mM or Cr/Sb ≤ 0.5 mM, indicating a wide applicability of MW2501 for treatment of As-containing water. The predominance of Fe3O4 on MW2501 surface was evidenced by XRD. Ligand exchange between As(V) anion and the hydroxylated surface of Fe3O4 as well as H bond was largely responsible for As(V) sorption as suggested by FTIR. XPS analysis further revealed the dominance of As(V) in the sorbed As on MW2501 surface with co-occurrence of a minor proportion of As(III) (11.45%). In parallel, oxidative transformation of Fe3O4 to Fe2O3 was also suggested by XPS. By a lab-scale column test, the potential and suitability of MW2501 in As-containing water treatment was further confirmed, which could also provide an alternative way to manage and utilize this highly problematic invasive species.

Wetland plants are considered as suitable biofilters for the removal of metal(loid)s and other contaminants from waters and wastewaters, due to their ability to accumulate and retain the contaminants in their roots. The iron plaque (IP) on the root surface influences the metal(loid)s retention processes. The stimulation of the IP development on roots of Phragmites australis by the external supply of a novel synthetic nanomaterial (nanomaghemite, nFe2O3) and FeSO4 (alone or in combination) was studied. An hydroponic experiment was carried out to evaluate the iron plaque formation after external iron addition, as well as their influence on arsenic immobilization capacity. Microscopic and spectroscopic techniques were utilized to assess the distribution of Fe and As in the roots. The addition of Fe stimulated the generation of the IP, especially when FeSO4 was involved. The nanoparticles alone were not efficient with regard to IP formation or As adsorption, even though they adhered to the root surface and did not enter into epithelial root cells. The combination of FeSO4 and nFe2O3 was the most effective treatment for improving the As removal capacity, and it seems to be an effective way to enhance the rhizofiltration potential of P. australis in As contaminated (waste)waters.

Information regarding chemical pollutant levels in farmed fish and shellfish, along with the risks associated with their consumption is still scarce. This study was designed to assess levels of exposure to 21 trace elements in fish (Dicentrarchus labrax), mussels (Mytilus galloprovincialis) and oysters (Crassostrea gigas) collected from aquaculture marine ecosystems of the northwestern Mediterranean Sea. Metal concentrations showed great variability in the three species; the highest values of the nonessential elements As and Cd were found in oysters while the highest levels of Al, Pb and V were found in mussels. The essential elements Cu, Mn and Zn were highest in oysters, but Fe, Cr, Ni, Se, Co and Mo levels were highest in mussels. Fish had the lowest concentrations for all trace elements, which were at least one order of magnitude lower than in bivalves. The rare earth elements cerium and lanthanum were found at higher levels in mussels than in oysters, but undetectable in fish. The maximum values set by European regulations for Hg, Cd and Pb were never exceeded in the examined samples. However, comparing the estimated human daily intakes (EHDIs) with the suggested tolerable copper and zinc intakes suggested a potential risk for frequent consumers of oysters. Similarly, people who consume high quantities of mussels could be exposed to concentrations of Al that exceed the proposed TWI (tolerable weekly intake).