-
1.
Removal of toxic metals from wastewater in constructed wetlands as a green technology; catalyst role of substrates and chelators.
Batool, A, Saleh, TA
Ecotoxicology and environmental safety. 2020;:109924
Abstract
In recent years knowledge in regard to phytoremediation for removal of metals from wastewater has been extensively developed. Despite advance treatment methods; different plants were widely used for wastewater treatment that may affect the efficiency of plants by stressing their natural ability. Therefore, this paper reviews the catalytic role of constructed wetlands, spiking of chelators and substrates to enhance phytoremediation for removal of metals. Catalytic combination of substrates, chelators with plants helped to remove different metals from wastewater simultaneously without compromising the plant's health. Moreover, this paper summarizes the interaction mechanism of plants with the chelators and substrates within constructed wetlands. In addition, this paper also discusses the potential research needs for this field.
-
2.
Emerging Roles of microRNAs in Plant Heavy Metal Tolerance and Homeostasis.
Ding, Y, Ding, L, Xia, Y, Wang, F, Zhu, C
Journal of agricultural and food chemistry. 2020;(7):1958-1965
Abstract
Heavy metal stress is a major growth- and yield-limiting factor for plants. Heavy metals include essential metals (copper, iron, zinc, and manganese) and non-essential metals (cadmium, mercury, aluminum, arsenic, and lead). Plants use complex mechanisms of gene regulation under heavy metal stress. MicroRNAs are 21-nucleotide non-coding small RNAs as important modulators of gene expression post-transcriptionally. Recently, high-throughput sequencing has led to the identification of an increasing number of heavy-metal-responsive microRNAs in plants. Metal-regulated microRNAs and their target genes are part of a complex regulatory network that controls various biological processes, including heavy metal uptake and transport, protein folding and assembly, metal chelation, scavenging of reactive oxygen species, hormone signaling, and microRNA biogenesis. In this review, we summarize the recent molecular studies that identify heavy-metal-regulated microRNAs and their roles in the regulation of target genes as part of the microRNA-associated regulatory network in response to heavy metal stress in plants.
-
3.
Mechanisms of Co, Ni, and Mn toxicity: From exposure and homeostasis to their interactions with and impact on lipids and biomembranes.
Sule, K, Umbsaar, J, Prenner, EJ
Biochimica et biophysica acta. Biomembranes. 2020;(8):183250
Abstract
Anthropogenic activity has increased human exposure to metals and resulted in metal induced toxicity. Essential trace elements like cobalt (Co), nickel (Ni), and manganese (Mn) are best known for their roles as important cofactors in many enzymes involved in signalling, metabolism, and response to oxidative stress. However, deficiencies as well as long-term overexposure to these metals can result in negative health effects. Co has been associated with cardiomyopathy, lung disease, and hearing damage, while Ni is a known carcinogen, as well as a common sensitizing metal. Mn is best classified as a neurotoxicant that causes a disorder alike to idiopathic Parkinson's disease known as Manganism. Although the mechanisms of Co, Ni, and Mn toxicity are complex and have yet to be fully elucidated, research over the years has provided useful insights into understanding metal-induced detrimental effects at the cellular and molecular level. One area of research that has been explored in less detail are metal interactions with lipids and biological membranes, which are a potentially critical target as membranes are the first point of contact for cells. This review covers the current understandings of Co, Ni and Mn toxicity, in terms of human exposure, homeostasis and mechanisms of transport, potential cellular targets, and, of primary focus, metal interactions with lipid and biomembranes. A variety of effects like membrane rigidification, leakage affecting membrane potentials, lipid phase changes, alterations in lipid metabolism and changes of cellular morphology illustrate the vast potential for metal-based membrane effects contributing to their toxicity.
-
4.
Nitric oxide-mediated regulation of oxidative stress in plants under metal stress: a review on molecular and biochemical aspects.
Sharma, A, Soares, C, Sousa, B, Martins, M, Kumar, V, Shahzad, B, Sidhu, GPS, Bali, AS, Asgher, M, Bhardwaj, R, et al
Physiologia plantarum. 2020;(2):318-344
Abstract
Given their sessile nature, plants continuously face unfavorable conditions throughout their life cycle, including water scarcity, extreme temperatures and soil pollution. Among all, metal(loid)s are one of the main classes of contaminants worldwide, posing a serious threat to plant growth and development. When in excess, metals which include both essential and non-essential elements, quickly become phytotoxic, inducing the occurrence of oxidative stress. In this way, in order to ensure food production and safety, attempts to enhance plant tolerance to metal(loid)s are urgently needed. Nitric oxide (NO) is recognized as a signaling molecule, highly involved in multiple physiological events, like the response of plants to abiotic stress. Thus, substantial efforts have been made to assess NO potential in alleviating metal-induced oxidative stress in plants. In this review, an updated overview of NO-mediated protection against metal toxicity is provided. After carefully reviewing NO biosynthetic pathways, focus was given to the interaction between NO and the redox homeostasis followed by photosynthetic performance of plants under metal excess.
-
5.
Operational impacts of heavy metals on activated sludge systems: the need for improved monitoring.
Maal-Bared, R
Environmental monitoring and assessment. 2020;(9):560
Abstract
Biological nutrient removal is highly reliant on maintaining a heterogeneous, balanced, and metabolically active microbial community that can adapt to the fluctuating composition of influent wastewater and encompassing environmental conditions. Maintaining this balance can be challenging in municipal wastewater systems that sporadically receive wastewater from industrial facilities due to the impact of heavy metals and other contaminants on the microbial ecology of the activated sludge. A thorough understanding of the impacts of heavy metals on activated sludge and of practical monitoring options is needed to support decision-making at the wastewater utility level. This paper is divided into two parts. In the first part, the review explains what happens when heavy metals interact with activated sludge systems by highlighting biosorption and bioaccumulation processes, and when an activated sludge system switches from bioaccumulation to toxic shock. Here, it also summarizes the impacts of heavy metal exposure on plant performance. In the second part, the review summarizes practical approaches that can be used at the plant outside the realm of traditional toxicological bioassays testing to determine the possible impacts of influent heavy metal concentrations on the BNR process. These approaches include the following: monitoring operational parameters for major shifts; respirometry; microscopy; ATP; chemical analyses of heavy metals with a focus on synergistic impacts and inhibitory limits; and other novel approaches, such as EPS chemical analyses, molecular techniques, and quorum sensing.
-
6.
Environmental influence on neurodevelopmental disorders: Potential association of heavy metal exposure and autism.
Ijomone, OM, Olung, NF, Akingbade, GT, Okoh, COA, Aschner, M
Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS). 2020;:126638
-
-
Free full text
-
Abstract
Environmental factors have been severally established to play major roles in the pathogenesis of neurodevelopmental disorders including autism spectrum disorder (ASD). ASD is a neurodevelopmental disorder that is associated with symptoms that reduce the quality of life of affected individuals such as social interaction deficit, cognitive impairment, intellectual disabilities, restricted and repetitive behavioural patterns. ASD pathogenesis has been associated with environmental and genetic factors that alter physiologic processes during development. Here, we review literatures highlighting the environmental impact on neurodevelopmental disorders, and mechanisms by which environmental toxins may influence neurodevelopment. Furthermore, this review discusses reports highlighting neurotoxic metals (specifically, lead, mercury, cadmium, nickel and manganese) as environmental risk factors in the aetiology of ASD. This work, thus suggests that improving the environment could be vital in the management of ASD.
-
7.
Biochar-bacteria-plant partnerships: Eco-solutions for tackling heavy metal pollution.
Harindintwali, JD, Zhou, J, Yang, W, Gu, Q, Yu, X
Ecotoxicology and environmental safety. 2020;:111020
Abstract
Over the past 30 years, the ever-rising demands of the modern and growing population have led to the rapid development of agricultural and industrial sectors worldwide. However, this expansion has exposed the environment to various pollutants including heavy metal (HM)s. Almost all HMs are serious toxicants and can pose serious health risks to living organisms in addition to their bioaccumulative and non-biodegradable nature. Different techniques have been developed to restore the ecological functions of the HM-contaminated soil (HMCS). However, the major downfalls of the commonly used remediation technologies are the generation of secondary wastes, high operating costs, and high energy consumption. Phytoremediation is a prominent approach that is more innocuous than the existing remediation approaches. Some microbes-plant interactions enhance the bioremediation process, with heavy metal resistant-plant growth promoting bacteria (HMRPGPB) being widely used to assist phytoremediation of HMs. However, the most common of all major microbial assisted-phytoremediation disturbances is that the HM-contaminated soil is generally deficient in nutrients and cannot sustain the rapid growth of the applied HMRPGPB. In this case, biochar has recently been approved as a potential carrier of microbial agents. The biochar-HMRPGPB-plant association could provide a promising green approach to remediate HM-polluted sites. Therefore, this review addresses the mechanisms through which biochar and HMRPGPB can enhance phytoremediation. This knowledge of biochar-HMRPGPB-plant interactions is significant with respect to sustainable management of the HM-polluted environment in terms of both ecology and economy, and it offers the possibility of further development of new green technologies.
-
8.
Bioremediation of toxic heavy metals (THMs) contaminated sites: concepts, applications and challenges.
Rahman, Z, Singh, VP
Environmental science and pollution research international. 2020;(22):27563-27581
Abstract
Heavy metal contamination is a global issue, where the prevalent contaminants are arsenic (As), cadmium (Cd), chromium (Cr)(VI), mercury (Hg), and lead (Pb). More often, they are collectively known as "most problematic heavy metals" and "toxic heavy metals" (THMs). Their treatment through a variety of biological processes is one of the prime interests in remediation studies, where heavy metal-microbe interaction approaches receive high interest for their cost effective and ecofriendly solutions. In this review, we provide an up to date information on different microbial processes (bioremediation) for the removal of THMs. For the same, emphasis is put on oxidation-reduction, biomineralization, bioprecipitation, bioleaching, biosurfactant technology, biovolatilization, biosorption, bioaccumulation, and microbe-assisted phytoremediation with their selective advantages and disadvantages. Further, the literature briefly discusses about the various setups of cleaning processes of THMs in environment under ex situ and in situ applications. Lately, the study sheds light on the manipulation of microorganisms through genetic engineering and nanotechnology for their advanced treatment approaches.
-
9.
Increased Thyroid Cancer Incidence in Volcanic Areas: A Role of Increased Heavy Metals in the Environment?
Malandrino, P, Russo, M, Gianì, F, Pellegriti, G, Vigneri, P, Belfiore, A, Rizzarelli, E, Vigneri, R
International journal of molecular sciences. 2020;(10)
Abstract
Thyroid cancer incidence is significantly increased in volcanic areas, where relevant non-anthropogenic pollution with heavy metals is present in the environment. This review will discuss whether chronic lifelong exposure to slightly increased levels of metals can contribute to the increase in thyroid cancer in the residents of a volcanic area. The influence of metals on living cells depends on the physicochemical properties of the metals and their interaction with the target cell metallostasis network, which includes transporters, intracellular binding proteins, and metal-responsive elements. Very little is known about the carcinogenic potential of slightly increased metal levels on the thyroid, which might be more sensitive to mutagenic damage because of its unique biology related to iodine, which is a very reactive and strongly oxidizing agent. Different mechanisms could explain the specific carcinogenic effect of borderline/high environmental levels of metals on the thyroid, including (a) hormesis, the nonlinear response to chemicals causing important biological effects at low concentrations; (b) metal accumulation in the thyroid relative to other tissues; and (c) the specific effects of a mixture of different metals. Recent evidence related to all of these mechanisms is now available, and the data are compatible with a cause-effect relationship between increased metal levels in the environment and an increase in thyroid cancer incidence.
-
10.
Adsorption of heavy metal ions by sodium alginate based adsorbent-a review and new perspectives.
Gao, X, Guo, C, Hao, J, Zhao, Z, Long, H, Li, M
International journal of biological macromolecules. 2020;:4423-4434
Abstract
With the development of modern industry, heavy metal pollution is one of the most important environmental issues. Due to its simplicity and low-cost, adsorption is considered as a green and environmental friendly method to remove heavy metals from industrial effluents. Sodium alginate is a natural polysaccharide, which consists of abundant hydroxyl and carboxyl groups, has been widely reported as the raw material for the adsorption of heavy metals from aqueous solutions. By surface grafting and cross-linking, adsorbents synthesized from sodium alginate have exhibited large uptake capacities as well as high removal rates for heavy metal ions. However, the poor physical strength and plain thermostability have significantly limited the utilization of sodium alginate based materials in industrial applications. Moreover, reductions of specific metal ions were observed in some studies, of which the reduction mechanism is not clearly clarified. In this work, the development of sodium alginate based adsorbents was summarized, including the physicochemical properties of the polymer, the modification of sodium alginate, sodium alginate based composite materials, and the adsorption behaviors as well as the mechanism. Chelation, electrostatic interaction, ion exchange, reduction and photocatalytic reduction were involved in the adsorption process, which can be determined by chemical characterization with further elucidation by density functional theory calculation. Finally, the limitations of sodium alginate based adsorbents were revealed with suggestions for future research.