Action News vol 10 no 1, June 2010 ISSN 1324-6011
Incorporating Lead Aware Times ( ISSN 1440-4966) and Lead Advisory Service News (ISSN 1440-0561)
The Journal of The LEAD (Lead Education and Abatement Design) Group Inc.
Guest Editor: Monica Maharjan, Master of Science Management and Master of Applied Sciences (Biotechnology).
Editor-in-Chief: Anne Roberts
Pectin: Panacea for both lead poisoning and lead contamination
By Subothini Srikaran, Intern at The LEAD Group, Summer 2009-10
Please note that a factsheet version of this article can be found at www.lead.org.au/fs/fst57.html
Lead and Lead Contamination
Lead (Pb) is a heavy metal, which has a bluish-white colour when freshly cut, turns into a dull grayish colour upon exposure to air and has a shiny chrome silver luster when melted into a liquid. It is readily available, cheap, soft and malleable. For this reason, lead and lead compounds are being used in a wide range of products such as building constructions, paints, ceramics, pipes, solders, gasoline, batteries and cosmetics1.
Lead is a poisonous metal. Lead ions are being released into the environment due to industrial activity and technological development. This poses a significant threat to the environment and public health because of toxicity, incremental accumulation in the food chain and persistence in the ecosystem. The most common sources of lead are lead-based paint, contaminated soil, household dust, drinking water, lead-glazed pottery14 and the effluents of industrial wastewaters. Activities such as smelting, mining and agriculture have lead to contamination of soils with lead and other heavy metals in many areas of Australasia and other continents. Soils rich in heavy metals such as lead create a possible risk to human health if directly ingested or if metal(loids) are transported through food. Furthermore elevated levels of heavy metals in soil are also known to have adverse effects on micro-fauna and flora and higher order plant life at contaminated sites4 Hence, it is vital to efficiently remove before it reach to environment and food, especially from wastewater1. This not only assures lead free environment but also helps to protect natural resources3.
Lead has been removed from gasoline, household paint, solder and other consumer products which resulted in a significant decrease in environmental lead concentrations. However humans are still exposed to low levels of lead through contaminated food, water, dust, soil and occupational activities5 In adults the common cause of lead poisoning is occupational exposure whereas in children the main cause is lead paint, found in many homes particularly old ones. Other routes of lead exposure are contaminated air, water, soil, food and consumer products.
Lead interferes with various body processes and is toxic to organs such as heart, bones, intestines and kidneys; it also interferes in reproductive and nervous systems. It is predominantly toxic to children, because it interferes with the development of the nervous system thereby results in potentially permanent learning and behavior disorders.
Elevated levels of the lead in the body results in a medical condition known as lead poisoning. Lead poisoning could be either acute or chronic. Acute lead poisoning is caused by intense exposure of short duration whereas chronic lead poisoning is the result of repeated low-level exposure over an extended time. The lead toxicity is determined by both the quantity of lead in the blood and tissues and also the time course of exposure. Even at lower levels lead may impair development and have harmful health effects hence there is known safe exposure level. The amount of lead in the blood is measured in micrograms of lead per deciliter of blood (µg/dL) for the diagnosis and treatment of lead exposure. According to The US Centres for Disease Control and Prevention and The World Health Organization, a blood lead level of 10µg/dL or above is considered to be a cause for concern.
Management of lead poisoning
The management for lead poisoning includes its removal from the source and maintaining the nutritional health. It could be managed with the treatment of iron, calcium and zinc deficiencies that are associated with increased lead absorption. If materials consisting lead are found in the gastrointestinal tract whole bowel irrigation, cathartics, endoscopy or surgical removal may be utilized to remove it from the gut and avoid further exposure. Bullets consisting of lead and shrapnel may also pose a danger of further exposure and may have to be surgically removed if they are in or near fluid filled or synovial spaces. In the case of lead encephalopathy, anticonvulsants may be provided to control seizures, and treatments of corticosteroids and mannitol to control swelling of the brain. Organic lead poisoning can be treated by eliminating the lead compound from the skin, avoiding further exposure, treating seizures. And for the people with higher lead concentration, a chelation therapy could be used. This therapy is based on the use of chelating agent; a molecule with at least two negatively charged groups which enables it to generate complexes with metal ions with multiple positive charges such as lead. The chelate formed as a result of this process is non toxic and can be excreted in the urine, initially at up to 50 times the normal rate6.
The chelation therapy had been used for the treatment of heavy metal poisoning. Numerous chelating agents had been used in the therapy. The first chelating agent dimercaprol (British Anti-Lewisite, BAL) was introduced during World War I for the treatment of arsenic-based poisonous gas (lewisite)15. Its successful application resulted in the introduction of several other chelating agents such as15
Among these EDTA and DMSA had been used in lead intoxication. But treatment with these chelators required continuous monitoring as they could bind with vital minerals (along with lead) from the body and could cause various adverse reactions. Moreover they are mostly administered intravenously and tend to be unsafe in children.10 The search for the safe chelating agent had finally resulted into study of pectin in chelation therapy.
Pectin in Chelation therapy
Pectin is a structural heteropolysaccharide found in the cell walls of terrestrial plants. It is predominantly extracted from citrus fruits and is produced commercially as a white to light brown powder and is utilized in food as a gelling agent especially in jams and jellies7. Khotimchenko et. al. have demonstrated that pectin substances are capable of binding heavy metals especially lead. Many pectin-rich by-products such as apple waste, sugar beet pulp, orange peels, orange and banana peels, citrus peels and coffee husks have been studied for their metal binding capability (biosorption) 2, which had been found to be cost effective alternative compared to traditional metal removal methods such as chemical precipitation and filtration, redox reactions, electrochemical treatments, reverse osmosis, ion exchange, adsorption and evaporation9. In addition it is also ideal for the purification of effluents with low metal concentrations. Schiewer et al suggests that orange peels could be used for lead ion biosorption but needed further studies for its practical use. Similarly, sugar-beet pectin had been used as an effective biosorbent for the treatment and recovery of Pb from wastewater. Sugar-beet pectin is derived from sugar-beet pulp, a residue of the sugar processing industry. It has an advantage over pectin derived from other sources as it is found in dry form 4.
Some biosorbents have the property of passively binding metals on chemically active sites or functional groups. The extent of metal uptake by pectin is determined by its chemical structure and found to be increased with decrease in the degree of esterification8.The cell wall of pectin is made up of three pectic polysaccharides namely homogalacturonan, rhamnogalaturonan-I (RG-I) and substituted galacturonans ( rhamnogalacturonan –II or RG-II). Among these RG-II had shown an immuno- modulating activities and binding capacity with heavy metals17 and have been studied extenively for the metal removal from environment (biosorption) as well as from our body (chelation). Tahiri et al suggested that dimer of RG-II (dRG-II) was specific and efficient in forming a complex with lead and therefore could be utilized to reduce intestinal absorption and accumulation of lead2. The pectin-vitamin preparation (PVP, 3-4g daily for one month) had been used as prophylactic measures in industrial workers with prolong lead exposures and found to be effective against chronic lead poisoning.18 In other stidies, chemically altered form of pectin, known as modified citrus pectin (MCP) had been used as chelator. MCP is a purified component of standard citrus pectin that is officially identified as generally regarded as safe (GRAS). MCP is a nutritional supplement derivative of the inner white pulp of citrus fruit peels. It had been shown that MCP is capable of binding toxic heavy metals and excreting them without perturbing the vital minerals in healthy humans. This is because MCP has the ideal structure for chelation of heavy metals; it contains approximately 10% rhamnogalacturonan II than enhances the ability of pectin to bind heavy metals rather than essential mineral cations. MCP used in the study by Zhao et al is made up of citrus pectin which has been broken down into shorter chain molecules and decreased side chain through the use of enzymes and variation in ph. The lower molecular weight of this compound enhances absorption into the bloodstream and the decreased esterification enables the molecule to bind to cations. In this study administration of MCP as the sole chelating agent to hospitalized children five to twelve years of age resulted in a huge increase in urinary excretion of lead and a significant reduction in blood lead levels9. In another study low esterified pectin has been demonstrated to promote a significant improvement of thyroid function in rats with thyroid gland pathology as a result of lead injections. In addition lead content in the livers of rats treated with pectin was significantly lower than in untreated animals10.
The studies have shown pectin could be used in chelation therapy for the treatment of lead poisoning. Various modified form of pectin had been used for lead elimination from both environment and our body. Nevertheless, further studies in rats and humans are needed prior to developing pectin as a preventive or maybe as a curative agent in Pb exposure and toxicity in humans.
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