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.

Natural Dietary Compounds in the Treatment of Arsenic Toxicity

Chronic exposure to arsenic (As) compounds leads to its accumulation in the body, with skin lesions and cancer being the most typical outcomes. Treating As-induced diseases continues to be challenging as there is no specific, safe, and efficacious therapeutic management. Therapeutic and preventive measures available to combat As toxicity refer to chelation therapy, antioxidant therapy, and the intake of natural dietary compounds. Although chelation therapy is the most commonly used method for detoxifying As, it has several side effects resulting in various toxicities such as hepatotoxicity, neurotoxicity, and other adverse consequences. Drugs of plant origin and natural dietary compounds show efficient and progressive relief from As-mediated toxicity without any particular side effects. These natural compounds have also been found to aid the elimination of As from the body and, therefore, can be more effective than conventional therapeutic agents in ameliorating As toxicity. This review provides an overview of the recently updated knowledge on treating As poisoning through natural dietary compounds. This updated information may serve as a basis for defining novel prophylactic and therapeutic formulations.

Usage of Si, P, Se, and Ca Decrease Arsenic Concentration/Toxicity in Rice, a Review

Rice is one of the most important routes for arsenic to enter the human food chain and threatens more than half of the world’s population. In addition, arsenic-contaminated soils and waters increase the concentration of this element in various tissues of rice plants. Thus, direct or indirect—infecting livestock and poultry—increase diseases such as respiratory diseases, gastrointestinal tract, liver, and cardiovascular diseases, cancer, and ultimately death in the long term. Therefore, finding different ways to reduce the uptake and transfer of arsenic by rice would reduce the contamination of rice plants with this dangerous element and improve animal and human nutrition and ultimately disease and mortality. In this article, we aim to take a small step in improving sustainable life on earth by referring to the various methods that researchers have taken to reduce rice contamination by arsenic in recent years. Adding micronutrients and macronutrients as fertilizer for rice is one way to improve this plant’s growth and health. In this study, by examining two types of macronutrients and two types of micronutrients, their role in reducing arsenic toxicity and absorption was investigated. Therefore, both calcium and phosphorus were selected from the macronutrients, and selenium and silicon were selected from the micronutrients, whose roles in previous studies had been investigated.

Identification of arsenic-tolerant and arsenic-sensitive rice (Oryza sativa L.) cultivars on the basis of arsenic accumulation assisted stress perception, morpho-biochemical responses, and alteration in genomic template stability

Arsenic toxicity is the most commonly experienced challenge of rice plants due to irrigation with arsenic-polluted groundwater and their cultivation in water logging environment which poses threat to human health, particularly in Bangladesh and West Bengal (India). In the present study, hydroponically grown eight rice cultivars, viz., Bhutmuri, Kumargore, Binni, Vijaya, Tulsibhog, Badshabhog, Pusa basmati, and Swarnadhan, were screened for arsenic tolerance by using physiological and molecular parameters. Treatment with 25 μM, 50 μM, and 75 μM arsenate resulted in dosage-based retardation in growth and water content in all the tested cultivars due to accumulation of total arsenic along with the enhanced activity of arsenate reductase with more severe effects exhibited in cvs. Swarnadhan, Pusa basmati, Badshabhog, and Tulsibhog. Arsenic sensitivity of rice cultivars was evaluated in terms of oxidative stress markers generation, antioxidant enzyme activities, and level of genotoxicity. Under arsenate-challenged conditions, the levels of oxidative stress markers, viz., H₂O₂, MDA, and proline, and activities of antioxidant enzymes, viz., SOD and CAT, along with the level of genotoxicity analyzed by RAPD profiling were altered in variable levels in all tested rice cultivars and showed a significant alteration in band patterns in arsenate-treated seedlings of cvs. Swarnadhan, Pusa basmati, Badshabhog, and Tulsibhog in terms of appearance of new bands and disappearance of normal bands that were presented in untreated seedlings led to reduction in genomic template stability due to their high susceptibility to arsenic toxicity. Cultivar- and dose-dependent alteration of parameters tested including the rate of As accumulation showed that cvs. Kumargore, Binni, and Vijaya, specially Bhutmuri, were characterized as arsenate tolerant and could be cultivated in arsenic-prone areas to minimize level of toxicity and potential health hazards.

Modulation of growth, ascorbate-glutathione cycle and thiol metabolism in rice (Oryza sativa L. cv. MTU-1010) seedlings by arsenic and silicon

Arsenic is a carcinogenic metalloid, exists in two important oxidation states-arsenate (As-V) and arsenite (As-III). The influence of arsenate with or without silicate on the growth and thiol metabolism in rice (Oryza sativa L. cv. MTU-1010) seedlings were investigated. Arsenate was more toxic for root growth than shoot growth where the root lengths were short, characteristically fragile and root tips turned brown. The multiple comparison analysis using Tukey's HSD (honest significant difference) tests indicated that the rate of arsenate accumulation and its conversion to arsenite by arsenate reductase were significantly increased in all arsenate treated seedlings while in seedlings treated jointly with arsenate and silicate, arsenate accumulation and its conversion to arsenite decreased. Silicate content was detected in the seedlings treated with silicate alone and under co-application of arsenate with silicate. In the test seedlings arsenic toxicity increased ascorbate and glutathione contents along with the activities of their regulatory enzymes, viz., ascorbate peroxidase, glutathione reductase, glutathione peroxidase and glutathione-s-transferase to reduce the toxicity level induced by arsenic whereas ascorbate oxidase activity was decreased to maintain sufficient ascorbate pool under arsenate treatment. Phytochelatins production were increased in both root and shoot of the test seedlings under arsenate exposure to alter the detrimental effects of arsenic by chelation with arsenite and their subsequent sequestration into vacuole. Thus, joint application of silicate along with arsenate showed significant alterations on all the parameters tested compared to arsenate treatment alone due to less availability of arsenic in the tissue leading to better growth and metabolism in rice seedlings. Thus use of silicon in arsenic contaminated medium may help to grow rice with improved vigour.

Chronic low level arsenic exposure evokes inflammatory responses and DNA damage

The cross-sectional study investigated the impact of chronic low level arsenic (As) exposure (11-50μg/L) on CD14 expression and other inflammatory responses in rural women of West Bengal enrolled from control (As level <10μg/L; N, 131) and exposed area (As level 11-50μg/L, N, 142). Atomic absorption spectroscopy revealed that As level in groundwater was higher in endemic areas (22.93±10. 1 vs. 1.61±0.15, P<0.0001) and showed a positive correlation [Pearsons r, 0.9281; 95% confidence interval, 0.8192-0.9724] with As content in nails of the exposed women. Flow cytometric analysis showed that CD 14 expression on monocytes was significantly higher (P<0.001) in exposed women and positively correlated with groundwater As [Pearsons r, 0.9191; 95% confidence interval, 0.7584-0.9745]. Leucocytes and airway cells of As exposed women exhibited up regulation of an inflammatory mediator, tumor necrosis factor-α (TNF-α) and transcription factor, nuclear factor-κB (NF-κB) (P<0.0001). Plasma pro inflammatory cytokines like - TNF-α, interleukins (ILs) - IL-6, IL-8, IL-12 were elevated whereas anti-inflammatory cytokine IL-10 was depleted in the exposed women. Sputa of the exposed women had elevated activity of inflammatory markers - MMP-2 and MMP-9 whereas sera were observed with only increased activity of MMP-9. Airway cells of the exposed women had exacerbated DNA damage than control. Level of oxidative DNA adducts like 8-hydroxy-2'-deoxyguanosine (8OHdG) were also enhanced in plasma of exposed women. Therefore it might be indicated that low level As exposure elicited a pro-inflammatory profile which might have been contributed in part by CD14 expressing monocytes and prolong persistence of pulmonary and systemic inflammation might have promoted oxidative DNA damage in the rural women.