Insights into the Roles of Melatonin in Alleviating Heavy Metal Toxicity in Crop Plants

Alleviating heavy metal pollution in farmland soil,and heavy metal toxicity in plants is the focus of global agricultural environmental research.Melatonin is a kind of indoleamine compound that wide exists in organisms;it is currently known as an endogenous free radical scavenger with the strongest antioxidant effect.As a new plant growth regulator and signaling molecule,melatonin plays an important role in plant resistance to biotic or abiotic stress.Recent studies indicate that melatonin can effectively alleviate heavy metal toxicity in crop plants,which provides a new strategy to minimize heavy metal pollution in crop plants.This study summarizes the research progress on the role of melatonin in alleviating heavy metal toxicity in crop plants and the related physiological and ecological mechanisms such as reducing the concentration of heavy metals in the rhizosphere,fixing and regionally isolating of heavy metals,maintaining the mineral element balance,enhancing the antioxidant defense system and interacting with hormonal signaling.Furthermore,future prospects for the mechanism of melatonin in regulating heavy metal toxicity,the pathway regulating synthesis and catabolism,and the interaction mechanism of melatonin signaling and other phytohormones are presented in this paper,with the goal of providing a theoretical basis for controlling heavy metal ion accumulation in crop plants grown in contaminated soil.

Health risk assessment of heavy metal pollution in groundwater of a karst basin,SW China

To investigate the presence of metal elements and assess their health risk for the populace in the Nandong Underground River Basin(NURB),we conducted an analysis of eleven common heavy metals in the water body.A Health risk assessment(HRA)model was employed to analyze 84 water samples from the NURB.The detection results revealed the following order of heavy metals concentrations:Fe>Al>Mn>Zn>As>Cd>Pb>Cr>Ni>Cu>Hg.Correlation analysis indicated a certain similarity in material source and migration transformation among these eleven metal elements.Our study identified that the health risks for local residents exposed to metal elements in the water of NURB primarily stem from carcinogenic risk(10^(−6)–10^(−4)a^(−1))through the drinking water pathway.Moreover,the health risk of heavy metal exposure for children through drinking water was notably higher than for adults.The maximum health risks of Cr in both underground and surface water exceeded the recommendation standard(5.0×10^(−5)a^(−1))from ICRP,surpassing the values recommended by the Swedish Environmental Protection Agency,the Dutch Ministry of Construction and Environment and the British Royal Society(5.0×10^(−6)a^(−1)).The results of the health risk assessment indicate that Cr in the water of NURB is the primary source of carcinogenic risk for local residents,followed by Cd and As.Consequently,it is imperative to control these three carcinogenic metals when the water was used as drinking water resource.

Toxic chemistry of heavy metals on hochrysis galbana (parke)in inshore water

Effects of heavy metals on Isochrysis galbana (Parke ) were studied in our laboratory. The research focused on toxic effects of metals on algal cells, effects of water-soluble and lipid-soluble organic ligands on metal toxicity and processes of metal uptake by cells. Interactions between two metals and the mechanisms involved were also studied in detail. Finally, some relationships between toxicity and chemical property of metals were revealed.

Growth, Metabolism and Yield of Rice Cultivated in Soils Amended with Fly Ash and Cyanobacteria and Metal Loads in Plant Parts

Soil amendment with fly ash（FA） and combined supplementation with N_2-fixing cyanobacteria masses as biofertilizer were done in field experiments with rice. Amendments with FA levels, 0, 0.5, 1.0, 2.0, 4.0, 8.0 and 10.0 kg/m2, caused increase in growth and yield of rice up to 8.0 kg/m2, monitored with several parameters. Pigment contents and enzyme activities of leaves were enhanced by FA, with the maximum level of FA at 10.0 kg/m2. Protein content of rice seeds was the highest in plants grown at FA level 4.0 kg/m2. Basic soil properties, p H value, percentage of silt, percentage of clay, water-holding capacity, electrical conductivity, cation exchange capacity, and organic carbon content increased due to the FA amendment. Parallel supplementation of FA amended plots with 1.0 kg/m2 N_2-fixing cyanobacteria mass caused further significant increments of the most soil properties, and rice growth and yield parameters. 1000-grain weight of rice plants grown at FA level 4.0 kg/m2 along with cyanobacteria supplementation was the maximum. Cyanobacteria supplementation caused increase of important basic properties of soil including the total N-content. Estimations of elemental content in soils and plant parts（root and seed） were done by the atomic absorption spectrophotometry. Accumulations of K, P, Fe and several plant micronutrients（Mn, Ni, Co, Zn and Cu） and toxic elements（Pb, Cr and Cd） increased in soils and plant parts as a function of the FA gradation, but Na content remained almost unchanged in soils and seeds. Supplementation of cyanobacteria had ameliorating effect on toxic metal contents of soils and plant parts. The FA level 4.0 kg/m2, with 1.0 kg/m2 cyanobacteria mass supplementation, could be taken ideal, since there would be recharging of the soil with essential micronutrients as well as toxic chemicals in comparative lesser proportions, and cyanobacteria mass would cause lessening toxic metal loads with usual N_2-fixation.

Legacies and health risks of heavy metals,polybrominated diphenyl ethers,and polychlorinated dibenzo-dioxins/furans at e-waste recycling sites in South China

Informal electronic-waste(e-waste)recycling sites pose substantial health risks to surrounding environments and populations,yet they are not properly regulated.In this study,the soil levels of copper,lead,cadmium,eight polybrominated diphenyl ethers(PBDEs),and 18 polychlorinated dibenzo-dioxins/furans(PCDD/Fs)were measured at two e-waste recycling sites in South China between 2014 and 2019.Both sites have been abandoned for natural restoration.Our results indicate that the mean Cd and PCDD/F levels at Site A in 2019 were higher than those recommended by current safety guidelines.Meanwhile,the highest exposure among children was 1.36×10^(−2)mg/(kg·d)for Cu,followed by 5.05×10^(−3)mg/(kg·d)for Pb,9.71 ng/(kg·d)for PBDEs,and 6.82 ng TEQ/(kg·d)for PCDD/Fs.Children were at elevated risk for health problem posed by Pb and Cu exposure at both sites(hazard quotient>1)and by PCDD/Fs at Site A.Further risk assessment was conducted on the target organs and endpoints of heavy metals and PCDD/Fs.The hazard index(HI)for the target organ mixed-risk of heavy metals was high(HI=1.27),as was that of PCDD/Fs(HI=1.66),which can disrupt endocrine function and pose a risk of reproductive toxicity in children.Owing to incomplete cleaning,contaminants persist in soils over long periods and may harm nearby environments and communities.Our study demonstrates that heavy metal,PBDE,and PCDD/F contamination have not yet been remediated,and intervention is needed to reduce pollution and associated risks in areas affected by e-waste.

Effects on the population dynamics of Brachionus rubens(Rotifera)caused by mercury and cadmium administered through medium and algal food Chlorella vulgaris

Due to industrial activities,heavy metal concentrations in aquatic systems of Mexico,are on the rise.Zooplankton,particularly rotifers,being sensitive and common components of freshwater,are widely used in ecotoxicological tests for establishing water quality criteria.Depending on the route of exposure(i.e.via medium or algal food),the toxicity of heavy metals varies.In the present study we evaluated the effect of cadmium and mercury exposed through medium and via algal food for the rotifer B.rubens.For both the heavy metals,we exposed rotifers via medium containing Chlorella at 0.5×10^(6)cells/ml or fed daily on previously exposed(1,2 and 4 h)alga to the toxicants(using 5 times the value of LC_(50)for B.rubens).For cadmium toxicity through medium,we used 3 toxicant levels(0.1,0.2 and 0.4 mg/L)and for mercury,we used 0.005,0.010 and 0.015 mg/L.Based on the LC_(50),B.rubens was 24 times more sensitive to mercury(0.035±0.002 mg/L)than cadmium.At a concentration of 0.4 mg/L,cadmium through the medium caused increased lag phase of B.rubens.When grown on Chlorella exposed for different durations to cadmium,the rotifer density decreased with the increasing duration of algal exposure to the heavy metal.When mercury was used in the medium or via algal food,the trends in the population growth of B.rubens were similar to those for cadmium.An increase in heavy metal concentration in the medium resulted in a decrease of the rate of population increase per day(r).The r varied from 0.33(in control)to 0.02 d^(-1)(in heavy metal treatment)depending on the mode of exposure though medium or via algal food.

Toxicities and risk assessment of heavy metals in sediments of Taihu Lake, China, based on sediment quality guidelines

The occurrence, toxicities, and ecological risks of five heavy metals（Pb, Cu, Cd, Zn and Ni） in the sediment of Taihu Lake were investigated in this study. To evaluate the toxicities caused by the heavy metals, the toxicities induced by organic contaminants and ammonia in the sediments were screened out with activated carbon and zeolite. The toxicities of heavy metals in sediments were tested with benthic invertebrates（tubificid and chironomid）.The correlations between toxicity of sediment and the sediment quality guidelines（SQGs）derived previously were evaluated. There were significant correlations（p 〈 0.0001） between the observed toxicities and the total risk quotients of the heavy metals based on SQGs,indicating that threshold effect level（TEL） and probable effect level（PEL） were reliable to predict the toxicities of heavy metals in the sediments of Taihu Lake. By contrast, the method based on acid volatile sulfides（AVS） and simultaneously extracted metals（SEM）,such as ∑SEM/AVS and ∑SEM-AVS, did not show correlations with the toxicities. Moreover,the predictive ability of SQGs was confirmed by a total predicting accuracy of 77%. Ecological risk assessment based on TELs and PELs showed that the contaminations of Pb, Cu, Cd and Zn in the sediments of Taihu Lake were at relatively low or medium levels. The risks caused by heavy metals in the sediments of northern bay of the lake, which received more wastewater discharge from upper stream, were higher than other area of the lake.

SYNTHESIS AND CHARACTERIZATION OF NOVEL OPTICALLY ACTIVE POLY(AMIDE-IMIDE)S AND POLY(ESTER-IMIDE)S CONTAINING CALIX[4]ARENE AND AMINO ACID UNITS WITH BINDING ABILITY TOWARDS ALKALI METAL AND TOXIC HEAVY METAL CATIONS

A novel calix[4]arene derivative 2 with amino functional groups at the lower rim was first prepared via introduction of nitro functional groups and amination of the dinitro derivative of calix[4]arene. The optically active monomers were synthesized by dehydration of L-leucine （and L-isoleucine） and 3,3＇,4,4＇-benzophenonetetracarboxylic- 3,3＇,4,4＇-dianhydride （3） followed by reaction with thionyl chloride to form 5a and 5b. Two methods, polymerization under microwave irradiation and solution polymerization in CH2Cl2/TEA, were then employed to carry out the condensation polymerization of 2 with the optically active monomers 5a and 5b, respectively. The polymerization conditions affected the kind of resulting polymers, poly（amide-imide）s （PAIs） 6a and 6b and poly（ester-imide）s （PEIs） 6a＇ and 6b＇ were obtained selectively in good yields and moderate inherent viscosities. Sorption-extraction experiments were carried out using cram picrate extraction method and verified good binding ability of the resulting calixarene-based polymers towards silver, alkali metal and toxic heavy metal cations. Also thermogravimetric analysis indicated that the resulting PAIs and PEIs were thermally stable.

A Review on Date Palm Tree:Properties,Characterization and Its Potential Applications

Date palm(phoenix dactylifera),which is mostly found in the middle east countries such as Iran,Iraq,Saudi Arabia,and the United States(California)that play a significant role in the economical and the environmental condition in those areas.The main purpose of planting dates is its fruit,which is consumed as fresh,dried or processed forms.There are approximately 100 million date palm trees in the worldwide that 62 million of these trees located in the Middle East and North Africa.In Saudi Arabia only,15000 tons of date palm leaves is prepared as waste materials.The leaves of date palm tree are used in several applications such as making ropes,baskets,and mats in many parts of the world.Unfortunately,the huge amount of the non-food products from the date palm remains as landfill materials without any specific usage.By attention to the date palm properties,the literature clearly showed that each part of date palm has great potential to be used for a variety of applications such as:making paper,absorption of heavy and toxic metals,energy production and soil fertilizing.Some of the obstacles and solutions for using palm date in these applications were also explored.Considering these issues and their solutions,the date palm is a favorable alternative.Despite some limited and traditional uses of these palm wastes,this review considered date palm applications and the properties’of the most important part of that tree in recent researches and related issues for future research are also spotted.

Vigna radiata var. GM4 Plant Growth Enhancement and Root Colonization by a Multi-Metal-Resistant Plant Growth-Promoting Bacterium Enterobacter sp. C1D in Cr(VI)-Amended Soils

Contamination of agricultural soils by heavy metals has become a major concern due to their toxic effects on plant growth,symbiosis and consequently the yields of crops. In the present study, to enhance plant growth in Cr（VI）-amended soils, novel metalresistant plant growth-promoting bacteria（PGPB） were isolated from a soil contaminated with industrial waste effluent. One of the bacterial isolates, identified as Enterobacter sp. C1 D by 16 S r RNA gene sequencing, was found to be multi-metal resistant in nature with excellent plant growth-promoting（PGP） traits. Mung bean（Vigna radiata var. GM4） inoculation with Enterobacter sp.C1 D significantly（P ＆lt; 0.01） increased root and shoot length, shoot and root weight, and chlorophyll content in a range of Cr（VI）treatments. Plant tolerance towards Cr（VI） measured as effective concentration showed higher values with Enterobacter sp. C1 Dtreated plants compared to un-inoculated plants. Root colonization study was also carried out using green fluorescence protein-labeled Enterobacter sp. C1 D under a hydroponic system. Confocal laser scanning microscopy of the plant roots showed heavy bacterial loads on the surface of the plant root specifically at the root tip and the point of root hair/lateral root formation. The results of PGP traits showed that elevated indole acetic acid levels and 1-aminocyclopropane-1-carboxylate deaminase activity enabled Enterobacter sp. C1 D to enhance V. radiata growth in Cr（VI）-amended soils, whereby it significantly increased plant tolerance towards elevated Cr（VI） concentrations.

Growth Inhibition Occurs Independently of Cell Mortality in Tomato (Solanum lycopersicum) Exposed to High Cadmium Concentrations

In order to analyze the adaptation potential of tomato shoots to a sudden increase in Cd concentration, tomato plants （Solanum lycopersicum L. var. Ailsa Craig） were exposed under controlled environmental conditions to a high dose of this heavy metal （250 μm CdCl2） in nutrient solution for 7 and 14d. Both root and shoot growth was completely inhibited but all plants remained alive until the end of the treatment. Cell viability remained unaffected but the activity of the mitochondrial alternative pathway was stimulated by Cd stress at the expense of the cytochrome pathway. Cadmium concentration was higher in roots than in shoots and a decrease in the rate of net Cd translocation was noticed during the second week of stress. Cadmium decreased both leaf conductance （gl） and chlorophyll concentration. However, the effect on net CO2 assimilation remained limited and soluble sugars accumulated in leaves. Photochemical efficiency of PSII （FvlFm） was not affected despite a decrease in the number of reaction centers and an inhibition of electron transfer to acceptors of PSII. It is concluded that tomato shoot may sustain short term exposure to high doses of cadmium despite growth inhibition. This property implies several physiological strategies linked to both avoidance and tolerance mechanisms.

Exposures and risks of arsenic,cadmium,lead,and mercury in cocoa beans and cocoa-based foods:a systematic review

Background:The World Health Organization has expressed concern about arsenic,cadmium,lead,and mercury as potentially harmful to human health.As such,the world body has called for appropriate preventive and interventionary measures.In response,food regulatory bodies including European Food Safety Authority are monitoring the levels of these heavy metals in cocoa and cocoa products.Objective:Therefore,the objective of this paper is to synthesize the latest relevant available peer-reviewed publications on arsenic,cadmium,lead,and mercury with a view to highlighting the gaps to encourage further research and informing industry.Materials and Methods:A systematic review was conducted using the European Food Safety Authority guide in PubMed database and the result was reported according to the PRISMA checklist.Results:The results show that processing may dilute or concentrate the levels of arsenic,cadmium,lead,and mercury,depending on processing factors including the product type,processing method,and raw materials.In addition,some products exceed the European Union and Chinese Maximum Contaminant Level and may pose risk.Furthermore,the findings show that the risk of heavy metal toxicities was higher among children relative to adults at the same exposure in cocoa-based products and that correcting risk estimates for bioavailability reduces the level of estimated risk.Conclusion:Therefore,the review concludes that further research is required to clarify the effect of processing on the level of these contaminants in specific cocoa-based foods.Moreover,conducting risk studies based on age groups and correcting for bioavailability of arsenic,cadmium,lead,and mercury enhance accuracy of risk estimates.Recommendations:The review,therefore,recommends that a value chain approach be adopted to assessing the levels,exposures,and risks of arsenic,cadmium,lead,and mercury in cocoa-based foods and the effect of processing on these levels.