Arsenic adsorption and plant availability in an agricultural soil irrigated with As-rich water: Effects of Fe-rich amendments and organic and inorganic fertilisers

A review on arsenic pollution, toxicity, health risks, and management strategies using nanoremediation approaches

OBJECTIVES

Over 50 countries are affected by arsenic contamination. The problem is becoming worse as the number of affected people increases and new sites are reported globally.

CONTENT

Various human activities have increased arsenic pollution, notably in both terrestrial and aquatic environments. Contamination of our water and soil by arsenic poses a threat to our environment and natural resources. Arsenic poisoning harms several physiological systems and may cause cancer and death. Excessive exposure may cause toxic build-up in human and animal tissues. Arsenic-exposed people had different skin lesion shapes and were vulnerable to extra arsenic-induced illness risks. So far, research shows that varying susceptibility plays a role in arsenic-induced diseases. Several studies have revealed that arsenic is a toxin that reduces metabolic activities. Diverse remediation approaches are being developed to control arsenic in surrounding environments.

SUMMARY AND OUTLOOK

A sustainable clean-up technique (nanoremediation) is required to restore natural equilibrium. More research is therefore required to better understand the biogeochemical processes involved in removing arsenic from soils and waters.

Arsenic species in soil profiles from chemical weapons (CWs) burial sites of China: Contamination characteristics, degradation process and migration mechanism

In this study, soil profiles and pore water from Japanese abandoned arsenic-containing chemical weapons (CWs) burial sites in Dunhua, China were analyzed to understand the distribution of arsenic (As) contamination, degradation, and migration processes. Results of As species analysis showed that the As-containing agents underwent degradation with an average rate of 87.55 ± 0.13%, producing inorganic pentavalent arsenic (As5+) and organic arsenic such as 2-chlorovinylarsonic acid (CVAOA), triphenylarsenic (TPA), and phenylarsine oxide (PAO). Organic arsenic pollutants accounted for 1.27-18.20% of soil As. In the vertical profiles, total As concentrations peaked at about 40-60 cm burial depth, and the surface agricultural soil exhibited moderate to heavy contamination level, whereas the contamination level was insignificant below 1 m, reflecting As migration was relatively limited throughout the soil profile. Sequential extraction showed Fe/Al-bound As was the predominant fraction, and poorly-crystalline Fe minerals adsorbed 33.23-73.13% of soil As. Oxygen-susceptible surface soil formed poorly-crystalline Fe3+ minerals, greatly reducing downward migration of arsenic. However, the reduction of oxidizing conditions below 2 m soil depth may promote As activity and require attention.

Geospatial assessment of groundwater quality using entropy-based irrigation water quality index and heavy metal pollution indices

Groundwater contamination has become a serious environmental threat throughout the world in the era of Anthropocene. Thus, the present study examined the groundwater quality for irrigation purposes based on the entropy method and heavy metal pollution indices. To compute the entropy-based groundwater irrigation quality index (EIWQI), physicochemical parameters such as pH, chloride (Cl-) and nitrate (NO3-), irrigation indices including electrical conductivity (EC), sodium absorption ratio (SAR), sodium percentage (%Na), soluble sodium percentage (SSP), residual sodium carbonate (RSC), magnesium hazard (MH), Kelley's ration (KR), permeability index (PI) and heavy metals such as manganese (Mn), iron (Fe), zinc (Zn) and arsenic (As) have been employed for the 37 sample wells of the Damodar fan delta (DFD), India, which is a semi-critical agriculture-dominated region. Shannon's entropy method has been used to assign the weights of the different parameters for constructing the EIWQI. The results portray a spatial variation of the irrigation water quality in the DFD. The EIWQI revealed that 27.03%, 59.46%, 8.11%, 2.7% and 2.7% of the sample wells, respectively, contain excellent, good, moderate, poor and very poor quality of irrigation water. On the other hand, heavy metal pollution indices (modified degree of contamination, pollution load index, Nemerow index and modified heavy metal pollution index) show that 15-20% of sample wells of the DFD are contaminated by heavy metal pollution. The pockets of pollution are concentrated in the southwestern, northeastern and central parts of the DFD. The study found that the spatial variation in groundwater quality is controlled by the higher sodium concentration, carbonate weathering and expansion of agricultural and urban-industrial areas.

An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Study of arsenic adsorption in calcareous soils: Competitive effect of phosphate, citrate, oxalate, humic acid and fulvic acid

Arsenic (As) bio-availability in the soil is influenced by different organic and inorganic anions. In the present study, the effects of various competitive agents, including phosphate, citrate, oxalate, humic acid (HA), and fulvic acid (FA), on the adsorption of As in calcareous soils were investigated. The results revealed the presence of phosphate, citrate, and oxalate in soil has a significant impact on the arsenic retention (adsorption) in soil which increases the As bio-availability. The negative impact of the competing anions was increased at higher concentrations. The Double Site Langmuir (DSL) isotherm was best fitted to the adsorption data, which indicates that most of the As adsorbed on the low-energy surfaces (non-specific adsorption by oxides, clays, and clay-size calcite). Accordingly, in soil 1, the DSL predicted that, due to phosphate, citrate, and oxalate competition (at a concentration of 10 mM), the adsorption capacity of the high- and low-energy surfaces decreased from 86.2 to 33.5, 82.1 and 61.3 mg/kg and from 663 to 659, 335.8, and 303.5 mg/kg, respectively, Moreover, after addition of phosphate, citrate, and oxalate to the soil-As system, the Langmuir constant of high-energy surfaces decreased from 0.686 to 0.074, 0.261, and 0.301 L/mg, respectively. No regular trend was observed for the Langmuir constant of low-energy surfaces. Similarly, in soils 2, 3, and 4, the adsorption capacities of both high- and low-energy surfaces as well as the Langmuir constant of high-energy surfaces decreased by the addition of phosphate, citrate, and oxalate to the soil-As system. HA and FA did not have a significant effect on the As adsorption behavior. Phosphate, citrate, and oxalate, as interfering oxyanions, increased the As bio-availability in the calcareous soils by decreasing the As adsorption.

Water and soil contaminated by arsenic: the use of microorganisms and plants in bioremediation

Owing to their roles in the arsenic (As) biogeochemical cycle, microorganisms and plants offer significant potential for developing innovative biotechnological applications able to remediate As pollutions. This possible use in bioremediation processes and phytomanagement is based on their ability to catalyse various biotransformation reactions leading to, e.g. the precipitation, dissolution, and sequestration of As, stabilisation in the root zone and shoot As removal. On the one hand, genomic studies of microorganisms and their communities are useful in understanding their metabolic activities and their interaction with As. On the other hand, our knowledge of molecular mechanisms and fate of As in plants has been improved by laboratory and field experiments. Such studies pave new avenues for developing environmentally friendly bioprocessing options targeting As, which worldwide represents a major risk to many ecosystems and human health.

Applications of red mud as an environmental remediation material: A review

Red mud is an alkaline by-product produced by alumina plants. The accumulation of red mud is becoming an increasingly serious problem with the growth of the aluminum industry. Various waste treatment methods utilizing red mud as an environmental remediation material have been developed. Red mud environmental remediation materials (RM-ERMs) are environmental remediation materials prepared by activating red mud, synergistically using red mud and other ingredients, or by extracting effective components from red mud. There are three general categories of use for RM-ERMs: for waste water purification, waste gas purification and soil remediation. As well as providing an opportunity to improve the environment through purification technologies, the highly alkaline red mud is consumed in the production of RM-ERMs. The use of RM-ERMs has been shown to be a promising strategy for the simultaneous treatment of various wastes. In this paper, the developregeneration characteristics of various red mud granularent status of RM-ERMs is described, the physical and chemical properties of red mud are introduced, and the active mechanism of RM-ERMs on target pollutants in waste water, waste gas and soil is summarized. Moreover, a discussion on the current existing problems of RM-ERMs provides important tips and suggestions for future research on RM-ERMs.

Major As species, lipid peroxidation and protein carbonylation in rice plants exposed to increasing As(V) concentrations

Arsenic (As) uptake by plants is mainly carried out as arsenate (As(V)), whose chemical analogy with phosphate is largely responsible for its elevated toxicity. Arsenate is known to stimulate reactive oxygen species (ROS) formation in plants that provoke oxidative stress. This manuscript reports the results of a hydroponics study using rice (Oryza sativa L.) seedlings as a test plant, where the effects of increasing arsenate concentrations (0–10 mg L⁻¹) on both lipid and protein oxidation, as well as As accumulation and speciation in plant roots and shoots were examined. Plant yield was negatively affected by increasing As concentration. Accumulation in plant roots was higher than in shoots at low arsenate doses (0.5–2.5 mg L⁻¹), while root to shoot transport was drastically enhanced at the highest doses (5 and 10 mg L⁻¹). Moreover, As(V) was the dominating species in the shoots and As(III) in the roots. Rice leaves in the 10 mg As L⁻¹ treatment showed the highest lipid peroxidation damage (malondialdehyde concentration), whilst protein oxidation was not remarkably influenced by As dose. Lipid peroxidation seems to be therefore conditioned by As accumulation in rice plants, particularly by the presence of high As(V) concentrations in the aerial part of the plants as a consequence of unregulated translocation from roots to shoots above a threshold concentration (1.25–2.5 mg L⁻¹) in the growing media. These results provide relevant information regarding As(V) toxic concentrations for rice plants, highlight the importance of major As species analysis in plant tissues regarding As toxicity and contribute to better understand plants response to elevated As concentrations in the growing media.

Effects of Different In Situ Remediation Strategies for an As-Polluted Soil on Human Health Risk, Soil Properties, and Vegetation

The demand for soils for recreational uses, gardening, or others in urban and periurban areas is increasing, and thus the presence of polluted technosols in these areas requires nature-based in situ remediation technologies. In this context, the capacity of three amendments, namely zero valent iron nanoparticles (nZVI), compost and a mixture of compost and biochar, to immobilise As in a polluted technosol simultaneously cultivated with Lolium perenne L. were tested and compared. The characteristics of the soil were comprehensively characterised by chemical and X-ray analysis to determine As contents, distribution, and mineralogy. As mobility was evaluated by the RBA methodology and then potential human health risks, both carcinogenic and non-carcinogenic, were assessed in all treatments. The nZVI treatment reduced risks due to the As immobilisation obtained (41% As decrease, RBA test), whereas the organic amendments did not imply any significant reduction of the RBA values. As to soil properties, the organic treatments applied lowered the pH values, increasing cation exchange capacity, and carbon and nutrient contents. To determine impacts over plant production, fresh biomass, As, Ca, Fe, K, Mg, Na and P were measured in Lolium under the different treatments. Notably, organic amendments improved As extraction by plants (57% increase), as well as fresh biomass (56% increase). On the contrary, nZVI diminished As extraction (65% decrease) and promoted a fresh biomass decrease of 57% due to nutrients immobilisation (61% decrease of P in plants tissues).

Influence of environmental factors on arsenic accumulation and biotransformation using the aquatic plant species Hydrilla verticillata

Hydrilla verticillata (waterthyme) has been successfully used for phytoremediation in arsenic (As) contaminated water. To evaluate the effects of environmental factors on phytoremediation, this study conducted a series of orthogonal design experiments to determine optimal conditions, including phosphorus (P), nitrogen (N), and arsenate (As(V)) concentrations and initial pH levels, for As accumulation and biotransformation using this aquatic plant species, while also analyzing As species transformation in culture media after 96-hr exposure. Analysis of variance and the signal-to-noise ratio were used to identify both the effects of these environmental factors and their optimal conditions for this purpose. Results indicated that both N and P significantly impacted accumulation, and N was essential in As species transformation. High N and intermediate P levels were critical to As accumulation and biotransformation by H. verticillata, while high N and low P levels were beneficial to As species transformation in culture media. The highest total arsenic accumulation was (197.2 ± 17.4) μg/g dry weight when As(V) was at level 3 (375 μg/L), N at level 2 (4 mg/L), P at level 1 (0.02 mg/L), and pH at level 2 (7). Although H. verticillata is highly efficient in removing As(V) from aquatic environments, its use could be potentially harmful to both humans and the natural environment due to its release of highly toxic arsenite. For cost-effective and ecofriendly phytoremediation of As-contaminated water, both N and P are helpful in regulating As accumulation and transformation in plants.

Effect of irrigation water containing arsenic on elemental composition of bean and lettuce plants cultivated in calcareous sandy soil

Background

The uptake of arsenic by vegetables from soil irrigated with arsenic enriched groundwater poses a major health hazard. The edible portion of these vegetables transfer arsenic to the human beings. The uptake of arsenic was studied in bean (Phaseolus vulgaris L.) and lettuce (Lactuca sativa L.) in a controlled greenhouse pot culture with calcareous sandy soil as substrate. The plants were irrigated with water containing sodium arsenate at concentrations 0.1, 0.25 and 0.5 mg L− 1. The total arsenic concentration of the different plants parts was determined by ICP-MS, following microwave-assisted acid digestion. The change in plant biomass production and essential macroelements (Mg, P, K) and microelements concentration (Fe, Mn, Cu, Zn) was also studied.

Results

The As concentration in the bean was in the order: root>stem>leaf>bean fruit and in lettuce: root>leaves. At the highest dose (0.5 mg L− 1) the As concentration in the bean fruit and lettuce leaves was 22.1 μg kg− 1 and 1207.5 μg kg− 1 DW, respectively. Increasing As concentration in the irrigation water resulted in decreased edible biomass production in bean, while in lettuce the edible biomass production increased. Neither plant exhibited any visible toxicity symptoms. No significant change was observed in the macro and microelements concentration. The total and the water-soluble arsenic in soil amounted to 3.5 mg kg− 1 and 0.023 mg kg− 1, respectively. The transfer factor was found to increase with increase in the As treatment applied. The transfer factor range for bean from root to fruit was 0.003–0.005, and for lettuce from root to leaves was 0.14–0.24.

Conclusion

Considering the FAO-WHO recommended maximum tolerable daily intake (MTDI) limit of 2.1 μg kg− 1 body weight, and the biomass production, both plants should not be cultivated at As treatment level higher than 0.1 mg L− 1.

Graphical abstract

Mechanisms of arsenic assimilation by plants and countermeasures to attenuate its accumulation in crops other than rice

Arsenic is a ubiquitous metalloid in the biosphere, and its origin can be either geogenic or anthropic. Four oxidation states (-3, 0, +3 and + 5) characterize organic and inorganic As- compounds. Although arsenic is reportedly a toxicant, its harmful effects are closely related to its chemical form: inorganic compounds are most toxic, followed by organic ones and finally by arsine gas. Although drinking water is the primary source of arsenic exposure to humans, the metalloid enters the food chain through its uptake by crops, the extent of which is tightly dependent on its phytoavailability. Arsenate is taken up by roots via phosphate carriers, while arsenite is taken up by a subclass of aquaporins (NIP), some of which involved in silicon (Si) transport. NIP and Si transporters are also involved in the uptake of methylated forms of As. Once taken up, its distribution is regulated by the same type of transporters albeit with mobility efficiencies depending on As forms and its accumulation generally occurs in the following decreasing order: roots > stems > leaves > fruits (seeds). Besides providing a survey on the uptake and transport mechanisms in higher plants, this review reports on measures able to reducing plant uptake and the ensuing transfer into edible parts. On the one hand, these measures include a variety of plant-based approaches including breeding, genetic engineering of transport systems, graft/rootstock combinations, and mycorrhization. On the other hand, they include agronomic practices with a particular focus on the use of inorganic and organic amendments, treatment of irrigation water, and fertilization.

Natural variation of arsenic fractions in soils of the Brazilian Amazon

Arsenic (As) in native soils of the Amazon rainforest is a concern due to its likely origin from the Andean rivers, which transport loads of sediments containing substantial amounts of trace elements coming from the cordilleras. Yet, unveiling soil As baseline concentrations in the Amazon basin is still a need because most studies in Brazil have been performed in areas with predominantly high concentrations and cannot express a real baseline value for the region. In this study, 414 soil samples (0-20, 20-40 and 40-60 cm layers) were collected from different sites throughout the Amazon basin - including native Amazon rainforest and minimally disturbed areas - and used to determine total and extractable (soluble + available) As concentrations along with relevant soil physicochemical properties. Descriptive statistics of the data was performed and Pearson correlation supported by a Principal Component Analysis (PCA) provided an improved understanding of where and how As concentrations are influenced by soil attributes. Total As concentration ranged from 0.98 to 41.71 mg kg^-1 with values usually increasing from the topsoil (0-20 cm) to the deepest layer (40-60 cm) in all sites studied. Considering the proportional contribution given by each fraction (soluble and available) on extractable As concentration, it is noticeable that KH₂PO₄-extractable As represents the most important fraction, with >70% of the As extracted on average in all the sites studied. Still, the extractable fractions (soluble + available) correspond to ~0.24% of the total As, on average. Total, available, and soluble As fractions were strongly and positively correlated with soil Al³⁺. The PCA indicated that soil pH in combination with CEC might be the key factors controlling soil As concentrations and the occurrence of each arsenic fraction in the soil layers.

Removal of Mn and As from drinking water by red mud and pyrolusite

Due to limited economic resources, which impede access to specific advanced technologies, many developing countries are still facing the challenge of reducing human exposure to heavy metals, which is primarily associated with the consumption of water contaminated through the discharge of poorly treated wastewater. In wastewater treatment technology, adsorption is sometime preferred to other approaches because of its high efficiency, easy handling, availability of different substrates and cost effectiveness. Moreover, increasing emphasis has recently been given to the use of low-cost adsorbents (generally solid wastes) for the treatment of polluted water, with a resulting double benefit for the environment. In this paper, the use of red mud and pyrolusite has been investigated for the removal of As and Mn from drinking water. Adsorption equilibrium data have been examined through the application of constant temperature models (isotherms), while batch and dynamic tests have been used to clarify the effects of pH, initial metal ion concentration and temperature on the adsorption performance, aiming at identifying the best conditions for the treatment. The combined use of the two adsorbents allows exploiting their properties synergistically, maximizing efficacy and sustainability without affecting process design and costs. In particular, 'clean' water (i.e. water with heavy metals contents below law limits) has been obtained even after the passage of a volume of solution higher than 40 bed volumes, and considering initial unrealistically high concentrations for the metals.