- Medical Definition of Toxicity
- 6 Side Effects of Too Much Vitamin D
- Chemical and materials selection
In this biotransformation process, these inorganic arsenic species iAs are converted enzymetically to methylated arsenicals which are the end metabolites and the biomarker of chronic arsenic exposure. Biomethylation is a detoxification process and end products are methylated inorganic arsenic such as MMA V and DMA V , which excreted through urine are bioindication of chronic arsenic exposure. Monomethylarsonic acid MMA III , an intermediate product, is found to be highly toxic compared to other arsenicals, potentially accountable for arsenic-induced carcinogenesis Singh et al.
Lead is a highly toxic metal whose widespread use has caused extensive environmental contamination and health problems in many parts of the world. Lead is a bright silvery metal, slightly bluish in a dry atmosphere. It begins to tarnish on contact with air, thereby forming a complex mixture of compounds, depending on the given conditions. The sources of lead exposure include mainly industrial processes, food and smoking, drinking water and domestic sources. In the US, more than to , tons of lead per year is being released from vehicle exhausts.
Some is taken up by plants, fixation to soil and flow into water bodies, hence human exposure of lead in the general population is either due to food or drinking water Goyer, Lead is an extremely toxic heavy metal that disturbs various plant physiological processes and unlike other metals, such as zinc, copper and manganese, it does not play any biological functions. A plant with high lead concentration fastens the production of reactive oxygen species ROS , causing lipid membrane damage that ultimately leads to damage of chlorophyll and photosynthetic processes and suppresses the overall growth of the plant Najeeb et al.
Some research revealed that lead is capable of inhibiting the growth of tea plant by reducing biomass and debases the tea quality by changing the quality of its components Yongsheng et al. Even at low concentrations, lead treatment was found to cause huge instability in ion uptake by plants, which in turn leads to significant metabolic changes in photosynthetic capacity and ultimately in a strong inhibition of plant growth Mostafa et al. Lead metal causes toxicity in living cells by following ionic mechanism and that of oxidative stress.
Many researchers have shown that oxidative stress in living cells is caused by the imbalance between the production of free radicals and the generation of antioxidants to detoxify the reactive intermediates or to repair the resulting damage.
Figure 3 shows the attack of heavy metals on a cell and the balance between ROS production and the subsequent defense presented by antioxidants. Antioxidants, as e. Under the influence of lead, however, the level of the ROS increases and the level of antioxidants decreases.
Medical Definition of Toxicity
In the presence of the enzyme glutathione peroxidase, reduced glutathione readily binds with another molecule of glutathione after donating the electron and forms glutathione disulfide GSSG. Another biomarker for oxidative stress is lipid peroxidation, since the free radical collects electron from lipid molecules present inside the cell membrane, which eventually causes lipid peroxidation Wadhwa et al. At very high concentrations, ROS may cause structural damage to cells, proteins, nucleic acid, membranes and lipids, resulting in a stressed situation at cellular level Mathew et al.
The attack of heavy metals on a cell and the balance between ROS production and the subsequent defense presented by antioxidants. The ionic mechanism of lead toxicity causes significant changes in various biological processes such as cell adhesion, intra- and inter-cellular signaling, protein folding, maturation, apoptosis, ionic transportation, enzyme regulation, and release of neurotransmitters. Lead can substitute calcium even in picomolar concentration affecting protein kinase C, which regulates neural excitation and memory storage Flora et al. The metallic mercury is a naturally occurring metal which is a shiny silver-white, odorless liquid and becomes colorless and odorless gas when heated.
Mercury is very toxic and exceedingly bioaccumulative. Its presence adversely affects the marine environment and hence many studies are directed towards the distribution of mercury in water environment. Major sources of mercury pollution include anthropogenic activities such as agriculture, municipal wastewater discharges, mining, incineration, and discharges of industrial wastewater Chen et al. Mercury exists mainly in three forms: metallic elements, inorganic salts and organic compounds, each of which possesses different toxicity and bioavailability. These forms of mercury are present widely in water resources such as lakes, rivers and oceans where they are taken up by the microorganisms and get transformed into methyl mercury within the microorganism, eventually undergoing biomagnification causing significant disturbance to aquatic lives.
Consumption of this contaminated aquatic animal is the major route of human exposure to methyl mercury Trasande et al. Mercury is extensively used in thermometers, barometers, pyrometers, hydrometers, mercury arc lamps, fluorescent lamps and as a catalyst. It is also being used in pulp and paper industries, as a component of batteries and in dental preparations such as amalgams.
6 Side Effects of Too Much Vitamin D
The global usage of mercury for various applications total in 3, metric tons. Mercury is well known as a hazardous metal and its toxicity is a common cause of acute heavy metal poisoning with cases of 3, in by the American Association of Poison Control Centers. Methylmercury is a neurotoxic compound which is responsible for microtubule destruction, mitochondrial damage, lipid peroxidation and accumulation of neurotoxic molecules such as serotonin, aspartate, and glutamate Patrick, The total amount of mercury emission into the environment has been assessed at 2, metric tons annually Ferrara et al.
Animals which are exposed to toxic mercury have shown adverse neurological and behavioral changes. Rabbits when exposed to The brain remains the target organ for mercury, yet it can impair any organ and lead to malfunctioning of nerves, kidneys and muscles. It can cause disruption to the membrane potential and interrupt with intracellular calcium homeostasis. Mercury binds to freely available thiols as the stability constants are high Patrick, Mercury vapors can cause bronchitis, asthma and temporary respiratory problems.
Mercury plays a key role in damaging the tertiary and quaternary protein structure and alters the cellular function by attaching to the selenohydryl and sulfhydryl groups which undergo reaction with methyl mercury and hamper the cellular structure. It also intervenes with the process of transcription and translation resulting in the disappearance of ribosomes and eradication of endoplasmic reticulum and the activity of natural killer cells.
The cellular integrity is also affected causing free radical formation.
The basis for heavy metal chelation is that even though the mercury sulfhydryl bond is stable and divided to surrounding sulfhydryl consisting ligands, it also contributes free sulfhydryl groups to promote metal mobility within the ligands Bernhoft, It is a by-product of zinc production which humans or animals may get exposed to at work or in the environment. Once this metal gets absorbed by humans, it will accumulate inside the body throughout life. This metal was first used in World War I as a substitute for tin and in paint industries as a pigment.
In today's scenario, it is also being used in rechargeable batteries, for special alloys production and also present in tobacco smoke. About three-fourths of cadmium is used in alkaline batteries as an electrode component, the remaining part is used in coatings, pigments and platings and as a plastic stabilizer. Humans may get exposed to this metal primarily by inhalation and ingestion and can suffer from acute and chronic intoxications.
Cadmium distributed in the environment will remain in soils and sediments for several decades. Plants gradually take up these metals which get accumulated in them and concentrate along the food chain, reaching ultimately the human body. Researches have shown that in China the total area polluted by cadmium is more than 11, hectares and its annual amount of industrial waste of cadmium discharged into the environment is assessed to be more than tons.
In Japan and China, environmental cadmium exposure is comparatively higher than in any other country Han et al.
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Cadmium is predominantly found in fruits and vegetables due to its high rate of soil-to-plant transfer Satarug et al. Cadmium is a highly toxic nonessential heavy metal that is well recognized for its adverse influence on the enzymatic systems of cells, oxidative stress and for inducing nutritional deficiency in plants Irfan et al.
The mechanism of cadmium toxicity is not understood clearly but its effects on cells are known Patrick, Cadmium concentration increases 3, fold when it binds to cystein-rich protein such as metallothionein. In the liver, the cystein-metallothionein complex causes hepatotoxicity and then it circulates to the kidney and gets accumulated in the renal tissue causing nephrotoxicity. Cadmium has the capability to bind with cystein, glutamate, histidine and aspartate ligands and can lead to the deficiency of iron Castagnetto et al.
Cadmium and zinc have the same oxidation states and hence cadmium can replace zinc present in metallothionein, thereby inhibiting it from acting as a free radical scavenger within the cell. Chromium occurs naturally by the burning of oil and coal, petroleum from ferro cromate refractory material, pigment oxidants, catalyst, chromium steel, fertilizers, oil well drilling and metal plating tanneries.
Anthropogenically, chromium is released into the environment through sewage and fertilizers Ghani, Cr III resides in the organic matter of soil and aquatic environment in the form of oxides, hydroxides and sulphates Cervantes et al. Chromium is extensively used in industries such as metallurgy, electroplating, production of paints and pigments, tanning, wood preservation, chemical production and pulp and paper production.
These industries play a major role in chromium pollution with an adverse effect on biological and ecological species Ghani, A wide range of industrial and agricultural practices increase the toxic level in the environment causing concern about the pollution caused by chromium. Tanneries discharge numerous polluting heavy metals and compounds into the water streams Nath et al.
Due to the presence of excess oxygen in the environment, Cr III is oxidized to Cr VI , which is extremely toxic and highly soluble in water Cervantes et al. The discharge of industrial wastes and ground water contamination has drastically increased the concentration of chromium in soil Bielicka et al. During manufacturing of chromate, the deposit of the Cr residues and waste water irrigation posed a serious Cr pollution to farmland.
With the implementation of modern agriculture there is continuous release of Cr into the environment by means of Cr residues, Cr dust and Cr waste water irrigation, resulting in soil pollution affecting the soil-vegetable system and also disturbing the vegetable yield and its quality to humans Duan et al.
The presence of excess of chromium beyond the permissible limit is destructive to plants since it severely affects the biological factors of the plant and enters the food chain on consumption of these plant materials. Common features due to Cr phytotoxicity are reduction in root growth, leaf chlorosis, inhibition of seed germination and depressed biomass. Chromium toxicity greatly affects the biological processes in various plants such as maize, wheat, barley, cauliflower, citrullus and in vegetables.
Chromium toxicity causes chlorosis and necrosis in plants Ghani, Enzymes like catalase, peroxidase and cytochrome oxidase with iron as their component are affected by chromium toxicity. The catalase activity stimulated with excess supply of chromium inducing toxicity has been studied with respect to photosynthesis, nitrate reductase activity, protein content in algae and photosynthetic pigments Nath et al.
Chromium III requires a simple diffusion process to enter into the cell and does not depend on any specific membrane carrier.
Chemical and materials selection
In the environment, trivalent chromium Cr III is generally harmless due to its weak membrane permeability. Hexavalent chromium Cr VI , on the other hand, is more active in penetrating the cell membrane through passages for isoelectric and isostructural anions such as SO 4 2— and HPO 4 2— channels and these chromates are taken up through phagocytosis. Cr VI is a strong oxidizing agent and can be reduced to give ephemeral species of pentavalent and tetravalent chromium that are different from that of Cr III. Stabilization of the pentavelent form is carried out by glutathione and hence intracellular reduction of Cr[VI] is considered a detoxification mechanism when reduction occurs away from the target region.
However if intracellular reduction of Cr[VI] occurs near the target site, it may serve to activate Cr. Aluminium is the third most abundant element found in the earth's crust Gupta et al. Aluminium occurs naturally in the air, water and soil.
Recent investigations on environmental toxicology revealed that aluminium may present a major threat for humans, animals and plants in causing many diseases Barabasz et al. Many factors, including pH of water and organic matter content, greatly influence the toxicity of aluminium. With decreasing pH its toxicity increases Jeffrey et al. The mobilization of toxic aluminium ions, resulting from changes in the pH of soil and water caused by acid rains and increasing acidification of the surrounding atmosphere, has an adverse effect on the environment.
This is manifested by the drying of forests, plant poisoning, crop decline or failure, death of aquatic animals, and also by various imbalances in the function of human and animal systems Barabasz et al. Aluminium is one of the most commonly found elements in the earth crust. The common manifestations are root growth inhibition, cellular modification in leaves, small and dark green leaves, yellowing and death of leaves, chlorosis, purpling and foliar necrosis Gupta et al.
Aluminium in high concentrations is very toxic for aquatic animals, especially for gill breathing organisms such as fish, causing osmoregulatory failure by destructing the plasma and hemolymph ions.