Occurrence of heavy metals and radionuclides in sediments and seawater in mangrove ecosystems in Pattani Bay, Thailand

Phytotoxicity of radionuclides: A review of sources, impacts and remediation strategies

Various anthropogenic activities and natural sources contribute to the presence of radioactive materials in the environment, posing a serious threat to phytotoxicity. Contamination of soil and water by radioactive isotopes degrades the environmental quality and biodiversity. They persist in soils for a considerable amount of time and disturb the fauna and flora of any affected area. Hence, their removal from the contaminated medium is inevitable to prevent their entry into the food chain and the organisms at higher levels of the food chain. Physicochemical methods for radioactive element remediation are effective; however, they are not eco-friendly, can be expensive and impractical for large-scale remediation. Contrastingly, different bioremediation approaches, such as phytoremediation using appropriate plant species for removing the radionuclides from the polluted sites, and microbe-based remediation, represent promising alternatives for cleanup. In this review, sources of radionuclides in soil as well as their hazardous impacts on plants are discussed. Moreover, various conventional physicochemical approaches used for remediation discussed in detail. Similarly, the effectiveness and superiority of various bioremediation approaches, such as phytoremediation and microbe-based remediation, over traditional approaches have been explained in detail. In the end, future perspectives related to enhancing the efficiency of the phytoremediation process have been elaborated.

A comprehensive review on chromium (Cr) contamination and Cr(VI)-resistant extremophiles in diverse extreme environments

Chromium (Cr) compounds are usually toxins and exist abundantly in two different forms, Cr(VI) and Cr(III), in nature. Their contamination in any environment is a major problem. Many extreme environments including cold climate, warm climate, acidic environment, basic/alkaline environment, hypersaline environment, radiation, drought, high pressure, and anaerobic conditions have accumulated elevated Cr contamination. These harsh physicochemical conditions associated with Cr(VI) contamination damage biological systems in various ways. However, several unique microorganisms belonging to phylogenetically distant taxa (bacteria, fungi, and microalgae) owing to different and very distinct physiological characteristics can withstand extremities of Cr(VI) in different physicochemical environments. These challenging situations offer great potential and extended proficiencies in extremophiles for environmental and biotechnological applications. On these issues, the present review draws attention to Cr(VI) contamination from diverse extreme environmental regions. The study gives a detailed account on the ecology and biogeography of Cr(VI)-resistant microorganisms in inhospitable environments, and their use for detoxifying Cr(VI) and other applications. The study also focuses on physiological, multi-omics, and genetic engineering approaches of Cr(VI)-resistant extremophiles.

Phytoremediation of 137Cs: factors and consequences in the environment

Radionuclide contamination is a concerning threat due to unexpected nuclear disasters and authorized discharge of radioactive elements, both in the past and in present times. Use of atomic power for energy generation is associated with unresolved issues concerning storage of residues and contaminants. For example, the nuclear accidents in Chernobyl 1986 and Fukushima 2011 resulted in considerable deposition of cesium (Cs) in soil, along with other radionuclides. Among Cs radioactive variants, the anthropogenic radioisotope ¹³⁷Cs (t_½ = 30.16 years) is of serious environmental concern, owing to its rapid incorporation into biological systems and emission of β and γ radiation during the decaying process. To remediate contaminated areas, mostly conventional techniques are applied that are not eco-friendly. Hence, an alternative green technology, i.e., phytoremediation, should in future be considered and implemented. This sustainable technology generates limited secondary waste and its objectives are to utilize hyper-accumulating plants to extract, stabilize, degrade, and filter the radionuclides. The review highlights plant mechanisms for up-taking radionuclides and influences of different environmental factors involved in the process, while considering its long-term effects.

Ecological-Health Risk Assessments of Heavy Metals (Cu, Pb, and Zn) in Aquatic Sediments from the ASEAN-5 Emerging Developing Countries: A Review and Synthesis

The ASEAN-5 countries (Malaysia, Indonesia, Thailand, Philippines, and Vietnam) of the Association of Southeast Asian Nations as a group is an ever-increasing major economy developmental hub in Asia besides having wealthy natural resources. However, heavy metal (HM) pollution in the region is of increasing environmental and public concern. This study aimed to review and compile the concentrations of Cu, Pb, and Zn in the aquatic sediments of the ASEAN-5 countries published in the literature from 1981 to February 2021. The mean values of Cu, Pb, and Zn in aquatic sediments were elevated and localized in high human activity sites and compared to the earth's upper continental crust and reference values. Based on 176 reports from 113 publications, the ranges of concentrations (mg/kg dry weight) were 0.09-3080 for Cu, 0.37-4950 for Zn, and 0.07-2666 for Pb. The ecological risk (ER) values ranged from 0.02-1077 for Cu, 0.01-95.2 for Zn, and 0.02-784 for Pb. All reports (100%) showed the Zn ER values were categorized as being between 'low potential ecological risk' and 'considerable potential ecological risk'. Almost all Cu ER values (97.7%) also showed similar ranges of the above two risk categories except for a few reports. The highest Cu level (3080 mg/kg dry weight) was reported from a mine-tailing spill in Marinduque Island of the Philippines with 'very high ecological risk'. In addition, drainage sediments in the western part of Peninsular Malaysia were categorized as Cu 'high potential ecological risk'. Almost all reports (96%) showed Pb ER values categorized as between 'low potential ecological risk' and 'moderate potential ecological risk' except for a few reports. Six reports showed Pb ER values of 'considerable potential ecological risk', while one report from Semarang (Indonesia) showed Pb ER of 'very high ecological risk' (Pb level of 2666 mg/kg dry weight). For the ingestion and dermal contact pathways for sediments from the ASEAN-5 countries, all non-carcinogenic risk (NCR) values (HI values 1.0) for Cu, Pb, and Zn reflected no NCR. The ER and human health risk assessment of Cu, Pb, and Zn were compared in an integrative and accurate manner after we reassessed the HM data mentioned in the literature. The synthesis carried out in this review provided the basis for us to consider Cu, Pb, and Zn as being of localized elevated levels. This provided evidence for the ASEAN-5 group of countries to be considered as being a new socio-economic corridor. Beyond any reasonable doubt, an ever-increasing anthropogenic input of HMs is to be expected to a certain degree. We believe that this paper provides the most fundamental useful baseline data for the future management and sustainable development of the aquatic ecosystems in the region. Lastly, we claim that this review is currently the most up-to-date review on this topic in the literature.

Environmental Assessment and Toxic Metal-Contamination Level in Surface Sediment of a Water Reservoir in the Brazilian Cerrado

Polluted sediments limit the useful and biotic life of a water reservoir. Therefore, the classification and verification of the contamination and pollution levels of water reservoirs are essentials for the preservation of the biota and to organize the actions of environmental management. Thus, the aim of this study is to determine the concentrations of potentially toxic metals [lead (Pb), zinc (Zn), nickel (Ni), copper (Cu), and cadmium (Cd)] in sediment samples collected in the water reservoir of the Foz do Rio Claro Hydroelectric Power Plant (FRCHEPP) and estimate the contamination level by using the geoaccumulation index (Igeo). All results were compared with the values established by the CONAMA Resolution 454/2012. The Cu and Cd concentrations in the sediment samples were above Level II for most of the analyzed points in comparison with the data of the CONAMA resolution, being classified as poor quality sediments. Moreover, the Igeo values indicated potential pollution of the water reservoir sediment by Cu and Cd. Hence, the water reservoir was classified between moderately and extremely polluted. From this work it is possible to conclude that the frequent monitoring of the sediment quality in the FRCHEPP water reservoir is an indispensable action for periodic evaluation of the hydrographic basin quality in the study region, considering its importance as water supply and power generation for the state of Goiás, Brazil. Overall, the results of this work can be important to study other water reservoirs around the world.

Assessment of current natural and anthropogenic radionuclide activity concentrations in the bottom sediments from the Barents Sea

The article is devoted to the study of the activity values of natural radionuclides ⁴⁰K, ²³²Th and ²²⁶Ra and technogenic radionuclide ¹³⁷Cs in the bottom sediments of the Barents Sea, which is distinguished from the rest of the Arctic seas by the fact that the largest number of radiation objects are concentrated here. The activity levels of natural radionuclides were within the range of activity values corresponding to marine sediments around the world. The highest radionuclide activities were found within the deepwater shelf of the Barents Sea. The current level of activity of the technogenic radionuclide ¹³⁷Cs is low and does not exceed 6.5 Bq·kg^-1. However, due to global climatic changes, the secondary source of radiation pollution of the sea may be the Novaya Zemlya ice sheet, in which huge quantities of technogenic radionuclides were deposited during atmospheric tests of the 1950s and 1960s.

Phytoremediation of engineered nanoparticles using aquatic plants: Mechanisms and practical feasibility

Certain plants have demonstrated the capability to take up and accumulate metals, thus offering the potential to remediate metal-contaminated water and sediment. Several aquatic species have further been identified which can take up metal and metal oxide engineered nanoparticles (ENPs). It is important to evaluate if aquatic plants exhibiting potential for metal phytoremediation can be applied to remediation of metallic ENPs. Understanding the interactions between ENPs and aquatic plants, and evaluating possible influences on metal uptake and phytoremediation processes is therefore essential. This review article will address the feasibility of green plants for treatment of ENP-affected aquatic ecosystems. Discussion will include common types of ENPs in current use; transformations of ENPs in aquatic systems; the importance of microorganisms in supporting plant growth; ENP entry into the plant; the influence of microorganisms in promoting plant uptake; and recent findings in phytoremediation of ENP-affected water, including applications to constructed wetlands.

Transformation of the radionuclides composition of river sediments in the area of the exploited Lomonosov diamond deposit (NW Russia)

The article is devoted to the study of the activity of the natural radionuclides ⁴⁰K, ²³²Th, ²²⁶Ra and technogenic ¹³⁷Cs radionuclide in the river sediments of watercourses around the Lomonosov diamond deposit (northwestern Russia). This is the only large diamond mining and beneficiation complex in Europe. Samples of river sediments and surface waters were taken from the Zolotitsa River and its tributaries in the area of the diamond deposit. Samples of rocks were taken from quarries. Samples of kimberlites used for enrichment and rocks entering the dumps were selected. Measurements of the activity of radionuclides in bottom sediments and rocks were conducted using the low-background semiconductor gamma spectrometry method. For measurements, a detector from high-purity germanium was used. The study of uranium isotopes in bottom sediments and waters was conducted using the alpha spectrometry method. The average activity of ¹³⁷Cs, ²²⁶Ra, ²³²Th and ⁴⁰K were 5.4, 9.0, 11.2, 318.8 Bq·kg^-1 respectively. The impact of the development of the field on the change in the radioecological state of the bottom sediments was evaluated. Several patterns of radionuclide accumulation have been found depending on the physicochemical parameters of river sediments. These patterns are due to the technogenic influence of the mining and beneficiation complex. The performed studies present the first evaluation of the impact of diamond mining on natural radionuclides' distribution and accumulation in the river sediments within the adjacent territories.

Comparative study of radioactivity levels and radionuclide fingerprints in typical marine ecosystems of coral reefs, mangroves, and hydrothermal vents

As a key environmental parameter to induce radiation dose and effect on non-human species, radioactivity level is rarely evaluated in typical ecosystems of coral reefs, mangroves, and hydrothermal vents. In this study, naturally occurring radionuclides (²³⁸U, ²²⁶Ra, ²²⁸Ra, and ⁴⁰K) in carbonate, silicate, and sulfide sediments collected from coral reefs, mangroves, and hydrothermal vents were simultaneously measured using high purity germanium (HPGe) γ spectrometry. Radioactivity levels and radionuclide fingerprints (²²⁶Ra/²³⁸U and ²²⁸Ra/²²⁶Ra) were interpreted and explored for tracking sources and formation processes of marine sediments in distinct marine ecosystems. Additionally, ionizing radiation dose rate on representative marine biotas (mollusc-bivalve, crustacean, polychaete worm, benthic fish, and pelagic fish) was evaluated using the ERICA tool with an increasing rank in coral reefs < mangroves < hydrothermal vents. Polychaete worm received the highest radiation dose relative to other marine biotas. We also emphasized the dominant contribution of ²¹⁰Po to total radiation dose rate on marine biotas.

Phytomanagement of radionuclides and heavy metals in mangrove sediments of Pattani Bay, Thailand using Avicennia marina and Pluchea indica

This study determines uptake and accumulation of radionuclides and heavy metals by Pluchea indica and Avicennia marina and evaluates phytoremediation potential via greenhouse and field experiments. P. indica and A. marina are considered excluders for ⁴⁰K and ²⁶²Ra, and Pb since roots accumulated them in higher quantities compared to other plant parts, and the bioconcentration factor (BCF) and transfer factor (TF) values for Pb, and ⁴⁰K and ²⁶²Ra were >1, respectively. Absorbed dose rate in air (D) showed significant values in sediments, which were generally over the maximum recommended value of 55nGyh^-1. Phytostabilization of radionuclides and heavy metals may serve as an appropriate strategy for mangrove-polluted areas. D values in sediments were considered sufficiently high to recommend long-term monitoring. Radionuclide activities may increase in the food chain via uptake and accumulation of edible plants, ultimately resulting in harm to human health.