Toxic Effects Of Heavy Metals Research Articles

Alcaligenes sp.의 생장과 인 제거에 미치는 이종 중금속 혼합의 독성 효과

BACKGROUND: This study was initiated to quantitatively evaluate the effects of five heavy metals on the growth and P removal efficiencies of Alcaligenes sp., known as the Phosphorus Accumulating Organisms (PAOs). It was cultivated in the batch system with five heavy metals, such as Cd, Cu, Zn, Pb and Ni, added in single and binary mixtures, respectively. METHODS AND RESULTS: IC50 (half of inhibition concentration of bacterial growth) and EC50 (half of effective concentration of phosphorus removal Efficiencies) were used to quantitatively evaluate the effects of heavy metals on the growth and phosphorus removal Efficiencies of Alcaligenes sp. In addition, Additive Index Value (A.I.V.) method was used to evaluate the interactive effects between Alcaligenes sp. and heavy metals. As a result, as the five heavy metals were singly added to Alcaligenes sp., the greatest inhibitory effects on the growth and P removal efficiencies of each bacteria was observed in the cadmium (Cd). In the binary mixture treatments of heavy metals, the treatments of lowest IC50 and EC50 were the Cd + Cu treatment. Based on the IC50 and EC50 of the binary mixtures of heavy metals treatments, most interactive effects between the heavy metals were found to be antagonistic. CONCLUSION: Based on the results obtained from this study, it appears that they could provide the basic information about the toxic effects of the respective treatments of single and binary mixtures of heavy metals on the growth and P removal efficiencies of Alcaligenes sp. through further study about the characterization of functional proteins involved in toxic effects of heavy metals.

Cytoprotective and Antioxidant Effects of an Edible Herb, Enhydra fluctuans Lour. (Asteraceae), against Experimentally Induced Lead Acetate Intoxication.

BackgroundEnhydra fluctuans Lour. (Asteraceae), an edible aquatic herb, is traditionally employed against toxic effects of heavy metals in India. The present study was planned to discover the protective effect of edible extract of E. fluctuans (AEEF) against Pb toxicity.MethodsThe cytoprotective role of AEEF was determined on murine hepatocytes employing MTT assay and Hoechst staining. The effects on lipid peroxidation, protein carbonylation, endogenous redox systems and the transcription levels of apoptotic proteins were studied after incubating the hepatocytes with AEEF (400 μg/ml) + Pb-acetate (6.8 μM). The defensive role of AEEF (100 mg/kg) against Pb-acetate (5 mg/kg) intoxication was measured in mice by in vivo assays. Biochemical, haematological and histological parameters, intracellular Pb burden and redox status were measured.ResultsAEEF exhibited a concentration dependent cytoprotective effect against Pb-induced cytotoxicity in vitro. Pb-acetate incubation significantly (p < 0.01) altered the extents of ROS production ↑, protein carbonylation ↑, lipid peroxidation ↑, endogenous antioxidant enzymes ↓ and GSH ↓ in vitro. Besides, Pb-acetate significantly (p < 0.01) induced apoptosis in the hepatocytes apparent from the altered expressions of apoptotic proteins viz. Apaf-1 ↑, Bad ↑, Bcl-2 ↓, Cyt C ↑, cleaved caspases↑, Bid ↑ and Fas ↑. However, AEEF (400 μg/ml) could significantly (p < 0.05–0.01) attenuate the Pb-acetate mediated toxic manifestation in vitro. In in vivo assay, Pb-acetate (5 mg/kg) treated mice exhibited significantly (p < 0.01) high intracellular Pb content. A high Pb-burden within the tissues caused significant (p < 0.05–0.01) patho-physiological alterations viz. ROS production ↑, protein carbonylation↑, lipid peroxidation ↑, DNA fragmentation ↑, ATP formation ↑, mitochondrial co-enzymes Q ↓, endogenous antioxidant enzymes ↓ and GSH ↓ within the selected tissues. The haematological and serum biochemical parameters were significantly (p < 0.05–0.01) different in the Pb-acetate treated mice. Finally, histological assessment imposed significant toxic occurrence within the organs of Pb-intoxicated animals. However, concurrent administration of AEEF (100 mg/kg) could significantly (p < 0.05–0.01) reinstate the Pb-acetate mediated toxicity.ConclusionPresence of metal chelators and phyto-antioxidants within AEEF would offer overall protection through promoting Pb clearance coupled with restoring redox balance.

A kinetic analysis of oxidation of the antioxidant N-acetyl-l-cysteine (NAC) by Pt(IV) complexes

N-acetyl-l-cysteine (NAC) is an antioxidant and a supplement and has been demonstrated to have protective effects for a variety of toxic effects of heavy metals. Although previous works have shown that NAC can ameliorate the severe toxic effects of cisplatin, there is a lack of understanding of the interactions between NAC and Pt(IV)-based prodrugs. In this work, the oxidation of NAC by a cisplatin prodrug (cis-[Pt(NH3)2Cl4]), by a prototype of Pt(IV) anticancer drug ormaplatin ([Pt(dach)Cl4]) and by a model compound (trans-[PtCl2(CN)4]2–) was characterized in detail. NAC was oxidized to NAC-disulfide as identified by mass spectrometric analysis. Time-resolved spectral and stopped-flow kinetic measurements were carried out over a wide pH range, demonstrating that the oxidation followed overall second-order kinetics. The observed second-order rate constants k′ versus pH profiles were established. A reaction mechanism was deduced, involving three parallel rate-determining steps; conceivable transition states were also proposed for these steps. Rate constants of the rate-determining steps, obtained from the simulations of rate equation to the k′–pH profiles, were largely correlated with the electron density on the sulfur atom in NAC. The Pt(IV) prodrugs can execute oxidative stress in the biological systems of the human body by direct oxidation of relevant molecules, similar to HOCl/OCl− and chloroamines. Instead, the oxidative stress involved in the severe toxic effects of cisplatin is produced via a different mode. NAC could be a chemoprotecting agent also for the Pt(IV) anticancer drugs if recent drug delivery technologies are used.

Effect of Chitosan Powder Prepared from Snail Shells to Remove Lead (II) Ion and Nickel (II) Ion from Aqueous Solution and Its Adsorption Isotherm Model

The toxic effects of heavy metals have remained a major source of concern globally because of their non-biodegradable nature which makes heavy metal pollution a serious environmental problem. The extents of removal for two heavy metals were investigated on adsorbent dose, temperature, pH, contact time and initial metals ion concentration. Maximum adsorption was obtained at pH 5 for Pb²⁺ ion and pH 7 for Ni²⁺ ion with 82.1% and 68.28%, at maximum adsorption temperature 335K and 355K for both metal ions with 87% and 80% metal removal respectively. The study shows that initial metal ion concentration and adsorbent dose on metals adsorption increases for both metal ions having a maximum adsorption dose at 99.93% and 70.58% removal at 180mins contact time for both metal ions with 99.83% and 70.37%. FTIR spectrum of raw chitosan showed the following peaks; 3263cm^-1, 3109.25cm^-1, 1627cm^-1 and 2854cm^-1 denoting –NH₂/-NH asymmetric stretching,-OH stretching,-C=O stretching and –CH group showing that binding process for both metal ions onto chitosan bands at 3109.25cm^-1 and 2854cm^-1 in the spectrum. The spectra indicated –NH group was involved in the binding process due to substantial changes in absorption intensity of –NH stretching after adsorption and peak 1627cm^-1 assigned to C=O occurred before the binding process. The two peaks in the 2800-2900 cm^-1 region was observed in Pb²⁺ ion which disappear in the Ni²⁺ ion laden spectrum, the spectrum for Ni²⁺ ion has only one peak observed in this region while the Pb²⁺ ion has two and in the finger print region, 600-1000 cm^-1, the spectra of Ni²⁺ ion and Pb²⁺ exhibited two and one peaks respectively. This supported the higher sorption capacity of Pb²⁺ ion over Ni²⁺ ion. The data were evaluated using Langmuir, Frieundlich and Temkin isotherms, the data complied with Frieundlich isotherm with high R² values 0.984 and 0.971 for both metal ions while Temkin isotherm shows high R² values 0.991 and 0.981 for both Pb²⁺ and Ni²⁺ ions respectively.

엽록소형광분석을 이용한 담수산 클로렐라(Chlorella vulgaris)에 미치는 중금속의 영향 평가

Abstract The response of the freshwater microalga, Chlorella vulgaris , to heavy metal stress was examined based on chlorophyll fluorescence analysis to assess the toxic effects of heavy metals in freshwater ecosystems. When toxic effects were analyzed using regular chlorophyll fluorescence analysis, photosystem II activity(F v /F m ) decreased significantly when exposed to Cu 2+ and Hg 2+ for 12 h, and decreased in the order of Hg 2+ > Cu 2+ > Cd 2+ > Ni 2+ when exposed for 24h. The effective photochemical quantum yield(Φ′ PSII ), chlorophyll fluorescence decrease ratio(R Fd ), minimal fluorescence yield(F o ), and non-photochemical quenching(NPQ), but not photochemical quenching(qP), responded sensitively to Hg 2+ , Cu 2+ , and Cd 2+ . These results suggest that F v /F m , as well as Φ′ PSII , R Fd , F o , and NPQ could be used to assess the effects of heavy metal ions in freshwater ecosystems. However, because many types of heavy metal ions and toxic compounds co-occur under natural conditions, it is difficult to assess heavy metal toxicity in freshwater ecosystems. When

In vitro toxic effects of heavy metals on fungal growth and phosphate-solubilising abilities of isolates obtained from Phragmites australis rhizosphere

ABSTRACT In this research, we evaluated the toxic effect of metal ions on mycelial growth and phosphate-solubilising activity of soil-borne micromycetes isolated from the Phragmites australis rhizosphere using Pikovskaya-agar plates supplemented with four metal concentrations. The diameter growth rate (DGR) decreased as the metal concentration rise for all tested fungi. Trichoderma atroviride had the fastest growth rate (1.48 cm2 day−1) and was the least susceptible to Al3+, Cd2+, Cr3+, Cu2+ and Pb2+ with a median effective concentration (MEC50) of 12.19, 0.48, 4.51, 11.44 and 50.05 mM, respectively. Aspergillus japonicus was the most tolerant to Co2+, Ni2+ and Zn2+, with MEC50 values of 3.36, 1.095 and 2.34 mM, respectively. Penicillium italicum was the most tolerant to Cr6+ (MEC50 = 0.677 mM). The ability to solubilise phosphate remained, despite the decrease in the DGR, and P. italicum and Penicillium dipodomyicola had the highest Phosphate Solubilisation Indexes (PSIs) at 1.97 and 2.12, respectively. In particular, P. italicum recorded the highest PSI of all the studied isolates at 0.62 mM Cr3+ (PSI = 4.74). A. japonicus and T. atroviride were the most tolerant isolates to all tested metals, which suggests that these isolates are promising candidates for further study with regard to mycoremediation and biofertilisation of metal-polluted soils.

Performance of rose scented geranium (Pelargonium graveolens) in heavy metal polluted soil vis-à-vis phytoaccumulation of metals

ABSTRACTAn investigation was carried out to evaluate the effect of heavy metal toxicity on growth, herb, oil yield and quality and metal accumulation in rose scented geranium (Pelargonium graveolens) grown in heavy metal enriched soils. Four heavy metals (Cd, Ni, Cr, and Pb) each at two levels (10 and 20 mg kg–1 soil) were tested on geranium. Results indicated that Cr concentration in soil at 20 mg kg–1 reduced leaves, stem and root yield by 70, 83, and 45%, respectively, over control. Root growth was significantly affected in Cr stressed soil. Nickel, Cr, and Cd concentration and accumulation in plant increased with higher application of these metals. Chromium, nickel and cadmium uptake was observed to be higher in leaves than in stem and roots. Essential oil constituents were generally not significantly affected by heavy metals except Pb at 10 and 20 ppm, which significantly increased the content of citronellol and Ni at 20 ppm increased the content of geraniol. Looking in to the higher accumulation of toxic metals by geranium and the minimal impact of heavy metals on quality of essential oil, geranium can be commercially cultivated in heavy metal polluted soil for production of high value essential oil.

Bioaccumulation of heavy metals in Mbaa River and the impact on aquatic ecosystem.

The bioaccumulation and toxic effects of heavy metals have caused ecological damage to aquatic ecosystem. In this study, concentration of heavy metals including zinc, lead, cadmium, iron, and copper were determined in the sediment and water as well as in the muscle, gill, and intestine of two fish species (Pelmatochromis guentheri and Pelmatochromis pulcher) of Mbaa River in Southeastern Nigeria. Samples were collected at three different spots from the river, and the level of heavy metals specified above were determined by atomic absorption spectroscopy (AAS) after a modified wet digestion process. The results indicated that sediment had the highest concentration of the heavy metals investigated while water had the lowest concentration. Fish tissues showed appreciable bioaccumulation of these metals as evidenced by a higher concentration profile when compared with that of water. Furthermore, the concentration of these heavy metals in water and their bioconcentration factor in the fish were above the recommended limit by WHO and FEPA, indicating that Mbaa River along Inyishi may not be suitable for drinking nor the fish safe for human consumption. The study also reveals the use of fish as bioindicator of aquatic environment.

Effect of bacterial inoculation of strains of pseudomonas aeruginosa, alcaligenes feacalis and bacillus subtilis on germination, growth and heavy metal (cd, cr, and ni) uptake of brassica juncea

ABSTRACTBacterial inoculation may influence Brassica juncea growth and heavy metal (Ni, Cr, and Cd) accumulation. Three metal tolerant bacterial isolates (BCr3, BCd33, and BNi11) recovered from mine tailings, identified as Pseudomonas aeruginosa KP717554, Alcaligenes feacalis KP717561, and Bacillus subtilis KP717559 were used. The isolates exhibited multiple plant growth beneficial characteristics including the production of indole-3-acetic acid, hydrogen cyanide, ammonia, insoluble phosphate solubilization together with the potential to protect plants against fungal pathogens. Bacterial inoculation improved seeds germination of B. juncea plant in the presence of 0.1 mM Cr, Cd, and Ni, as compared to the control treatment. Compared with control treatment, soil inoculation with bacterial isolates significantly increased the amount of soluble heavy metals in soil by 51% (Cr), 50% (Cd), and 44% (Ni) respectively. Pot experiment of B. juncea grown in soil spiked with 100 mg kg−1 of NiCl2, 100 mg kg−1 of CdCl2, and 150 mg kg−1 of K2Cr2O7, revealed that inoculation with metal tolerant bacteria not only protected plants against the toxic effects of heavy metals, but also increased growth and metal accumulation of plants significantly. These findings suggest that such metal tolerant, plant growth promoting bacteria are valuable tools which could be used to develop bio-inoculants for enhancing the efficiency of phytoextraction.

Effects of cadmium on the cuttlefish Sepia pharaonis’ arginine kinase: unfolding kinetics integrated with computational simulations

Arginine kinase is closely associated with adaptation to environmental stresses such as high salinity and heavy metal ion levels in marine invertebrates. In this study, the effects of Cd2+ on the cuttlefish Sepia pharaonis’ arginine kinase (SPAK) were investigated. SPAK was isolated from the muscles of S. pharaonis and upon further purification, showed a single band on SDS-PAGE. Cd2+ effectively inactivated SPAK, and the double-reciprocal kinetics indicated that Cd2+ induced non-competitive inhibition of arginine and ATP. Spectrofluorometry results showed that Cd2+ induced tertiary structure changes in SPAK with the exposure of hydrophobic surfaces that directly induced SPAK aggregation. The addition of osmolytes, glycine, and proline successfully blocked SPAK aggregation and restored the conformation and activity of SPAK. Molecular dynamics simulations involving SPAK and Cd2+ showed that Cd2+ partly blocks the entrance of ATP to the active site, and this result is consistent with the experimental results showing Cd2+-induced inactivation of SPAK. These results demonstrate the effect of Cd2+ on SPAK enzymatic function and unfolding, including aggregation and the protective effects of osmolytes on SPAK folding. This study provides concrete evidence of the toxicity of Cd2+ in the context of the metabolic enzyme SPAK, and it illustrates the toxic effects of heavy metals and detoxification mechanisms in cuttlefish.

Wybrane choroby nerek związane z pracą

Infections, high temperature and many of the toxic substances can cause kidney damage. Acute kidney injury is a well known complication of some work-related diseases, e.g., lead intoxication. Chronic kidney disease can also be caused by some occupational factors. Three work-related nephropathies, in which causal connection with work has been proved, are discussed in this article. There are different risk factors of nephrolithiasis, lead nephropathy and silica nephropathy, but each of them can cause chronic kidney disease. Prevention of these nephropaties seems to be relatively simple. The principles of protection from the toxic effects of heavy metals and silica dust are very specific. The most important prevention of kidney stones is correct fluid intake. In addition to providing adequate quantities of drinking water, it is also important to educate exposed workers and assure enough rest breaks at work.

Arsenic and heavy metals health risk assessment through drinking water consumption in the Peshawar District, Pakistan

ABSTRACTThis study aimed to assess the drinking water quality and human potential health risk in Peshawar, which is the most populous district of Khyber Pakhtunkhwa Province, Pakistan. Water was randomly collected throughout Peshawar District (urban = 45 samples and rural = 29 samples). These samples were analyzed for heavy metal (As, Cd, Co, Cu, Cr, Hg, Ni, Pb, and Zn) concentrations using the atomic absorption spectrometer (Perkin Elmer, AAS-PEA-700). Heavy metal concentrations in drinking water revealed the highest pollution index (PI) values—17.80, 11.92, 7.50, and 5.70 for the Pb, Cr, Cd, and Ni, respectively. The contaminations of Cd and Pb were significantly higher (p < .05) than their maximum allowable limits set by the World Health Organization. Heavy metal contaminations in drinking water were evaluated for health risk assessment: the chronic risk or hazard quotient (HQ) and cancer risk. Results revealed that HQ values were >1 for the Cd and Pb, suggesting that the exposed human beings could be at chronic risk. Therefore, serious measures such as drinking water treatments and contamination controlling policies are needed to avoid the hazardous effects of toxic heavy metals.

Enterobacter asburiae KE17 association regulates physiological changes and mitigates the toxic effects of heavy metals in soybean.

This study aimed to elucidate the role played by Enterobacter asburiae KE17 in the growth and metabolism of soybeans during copper (100 μm Cu) and zinc (100 μm Zn) toxicity. When compared to controls, plants grown under Cu and Zn stress exhibited significantly lower growth rates, but inoculation with E. asburiae KE17 increased growth rates of stressed plants. The concentrations of plant hormones (abscisic acid and salicylic acid) and rates of lipid peroxidation were higher in plants under heavy metal stress, while total chlorophyll, carotenoid content and total polyphenol concentration were lower. While the bacterial treatment reduced the abscisic acid and salicylic acid content and lipid peroxidation rate of Cu-stressed plants, it also increased the concentration of photosynthetic pigments and total polyphenol. Moreover, the heavy metals induced increased accumulation of free amino acids such as aspartic acid, threonine, serine, glycine, alanine, leucine, isoleucine, tyrosine, proline and gamma-aminobutyric acid, while E. asburiae KE17 significantly reduced concentrations of free amino acids in metal-affected plants. Co-treatment with E. asburiae KE17 regulated nutrient uptake by enhancing nitrogen content and inhibiting Cu and Zn accumulation in soybean plants. The results of this study suggest that E. asburiae KE17 mitigates the effects of Cu and Zn stress by reprogramming plant metabolic processes.

Fucoidans of brown algae: Biosynthesis, localization, and physiological role in thallus

The issues of the structure and biosynthesis of fucose-containing sulfated polysaccharides are considered in this review; the data on the localization of fucoidans in tissues and their significance for algae are provided. Fucoidans participate in the building of cell walls and the support of their structure, as well as in extrusion of spores and gametes from reproductive organs. Due to the sulfated groups, these polysaccharides can bind cations (mainly K+, Na+, Ca2+, Mg2+) and participate in ion exchange with the environment, which facilitates adaptation of algae to water salinity fluctuations and to the toxic effects of heavy metals. Fucoidans play a substantial role in morphogenesis of zygotes of fucoid algae, as they participate in establishing the cell polarity and fixing the cell-division axis, thus determining the direction for the development of the rhizoidal and apical poles of young thalli.

Amelioration of Heavy-Metal Toxicity in Cauliflower by Application of Salicylic Acid

The important role of salicylic acid in response to different stresses is to modify and decrease the negative effects of stress. The objective of this study was to evaluate the amelioration of heavy-metal (HM) stress in cauliflower cv. Shubra by application of different concentrations of salicylic acid. In heavy-metal (cobalt, nickel, cadmium, chromium, and lead) stress, apart from appearance of visual symptoms, HM toxicity reduced dry weight and specific activity of catalase and increased the concentration of lipid peroxidation, proline, nonprotein thiol, electrolyte leakage percentage, and specific activity of peroxidase and superoxidase dismutase. Application of salicylic acid reverts back all parameters disturbed by HM stress. As opposed to other HMs, salicylic acid enhanced chromium toxicity effects in plants, showing synergism and the plants died. Application of salicylic acid (100 mM) ameliorated toxic effects of HMs to some extent, showing antagonism in cauliflower.

Toxic Effects of Heavy Metals on Bone Tissue

Toxic Effects of Heavy Metals on Bone Tissue

Combined toxic effects of heavy metals and antibiotics on a Pseudomonas fluorescens strain ZY2 isolated from swine wastewater.

A Pseudomonas fluorescens strain ZY2, isolated from swine wastewater, was used to investigate the synergistic effects of five heavy metals (Pb, Cu, Zn, Cr(VI) and Hg) on bacterial resistance to antibiotics. Results indicate that the combined effects of antibiotic type, heavy metal type and concentration were significant (p < 0.01). Cross-resistance to Hg and antibiotics was the most noticeable. Moreover, the resistance to Hg and cefradine or amoxicillin, and Cr and amoxicillin were synergistic for low heavy metal concentrations, and turned antagonistic with increasing concentrations, while the resistances to Cr or Cu and cefradine, Pb or Cu and amoxicillin, Cu and norfloxacin showed reverse effects. In addition, resistance to Zn and amoxicillin were always synergetic, while resistance to Pb and cefradine or norfloxacin, Cr or Hg and norfloxacin as well as all the heavy metals and tetracycline were antagonistic. These results indicate that bacterial resistance to antibiotics can be affected by the type and concentration of co-exposed heavy metals and may further threaten people’s health and ecological security severely via horizontal gene transfer.

Possible roles of plant sulfurtransferases in detoxification of cyanide, reactive oxygen species, selected heavy metals and arsenate.

Plants and animals have evolved various potential mechanisms to surmount the adverse effects of heavy metal toxicity. Plants possess low molecular weight compounds containing sulfhydryl groups (-SH) that actively react with toxic metals. For instance, glutathione (γ-Glu-Cys-Gly) is a sulfur-containing tripeptide thiol and a substrate of cysteine-rich phytochelatins (γ-Glu-Cys)2–11-Gly (PCs). Phytochelatins react with heavy metal ions by glutathione S-transferase in the cytosol and afterwards they are sequestered into the vacuole for degradation. Furthermore, heavy metals induce reactive oxygen species (ROS), which directly or indirectly influence metabolic processes. Reduced glutathione (GSH) attributes as an antioxidant and participates to control ROS during stress. Maintenance of the GSH/GSSG ratio is important for cellular redox balance, which is crucial for the survival of the plants. In this context, sulfurtransferases (Str), also called rhodaneses, comprise a group of enzymes widely distributed in all phyla, paving the way for the transfer of a sulfur atom from suitable sulfur donors to nucleophilic sulfur acceptors, at least in vitro. The best characterized in vitro reaction is the transfer of a sulfane sulfur atom from thiosulfate to cyanide, leading to the formation of sulfite and thiocyanate. Plants as well as other organisms have multi-protein families (MPF) of Str. Despite the presence of Str activities in many living organisms, their physiological role has not been clarified unambiguously. In mammals, these proteins are involved in the elimination of cyanide released from cyanogenic compounds. However, their ubiquity suggests additional physiological functions. Furthermore, it is speculated that a member of the Str family acts as arsenate reductase (AR) and is involved in arsenate detoxification. In summary, the role of Str in detoxification processes is still not well understood but seems to be a major function in the organism.

Arachnids (Aranei, Opiliones) in meadows: Response to pollution with emissions from the Middle Ural Copper Smelter

Arachnids living in the herbaceous layer have been studied in 2006–2008 in secondary upland meadows along the gradient of pollution with emissions from the Middle Ural Copper Smelter (Revda, Sverdlovsk oblast). It has been shown that absolute abundance and general diversity decrease with increasing levels of technogenic pressure. Direct toxic effect of heavy metals is especially strong on taxa closely associated with soil and litter; this effect is the most likely cause of the absence of harvestmen near the smelter. The other groups of arachnids are more strongly affected by environmental changes (depletion of species diversity, simplification of architecture of the herbaceous layer, and modification of the hydrothermal regime of this layer) indirectly caused by pollution.

Auxin-mediated growth of rice in cadmium-contaminated soil

Pollution from heavy metals is a global problem that is very dangerous to the environment. Among the heavy metals, cadmium is receiving more and more attention because it is one of the most ecotoxic, making it very harmful for biological activity in soil, biodiversity, plant metabolism, and human and animal health. Phytohormones, produced by plants, control or regulate germination, growth, metabolism, or other physiological activities, and they can alleviate the toxic effects of heavy metals on plant growth. Auxin is the most abundant natural growth hormone, controlling apical dominance, tropism, elongation of shoots, and initiation of roots in plants. However, cadmium stress causes the degradation of indigenous auxin. To cope with this, auxin may be applied exogenously. To evaluate the role of auxin in cadmium -contaminated soil, different levels of the auxin precursor L-TRP were applied to plants growing in contaminated soil. Rice seedlings were dipped in a L-TRP solution for 2 h and transplanted into potted soil contaminated with 30 mg kg1 cadmium. The results showed that the exogenous application of L-TRP improved the growth and yield of treated plants both in normal and contaminated soil. The data of different parameters showed that L-TRP enhanced plant height (12.54%), the number of tillers (25.53%), the number of panicles (19.04%), the 1000 grain weight (19.28%), and the paddy yield (11.78%) in cadmium-contaminated soil, as compared to plants grown in the absence of L-TRP with the same level of contamination. L-TRP increased the uptake of cadmium in rice straw while decreasing the translocation of cadmium towards grains, as compared to plants grown in contaminated soil without L-TRP. This experiment revealed the possibility of using L-TRP to improve plant growth and soil health in contaminated soil.