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 Poisoning

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

• Alpha lipoic acid (ALA)
• Aminiphenoxyethane-tetraacetic acid (BAPTA)
• Deferasirox
• Deferiprone
• Deferoxamine
• Diethylene triamine pentaacetice acid (DTPA)
• Dimercapto-propane sulphonate (DMPS)
• Dimercaptosuccinic acid (DMSA)
• Ethylenediamine tetraacetic acid (calcium disodium versante) (CaNa²-EDTA)
• Ethylene glycol tetraacetic acid (EGTA)
• D-penicillamine

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.

Conclusion

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.

References

1. Wikipedia, 26/01/2010, Lead; Characteristics; Isotopes; Chemistry; Chloride complexes; Phase diagrams of solubilities; History; Occurrence; Ore processing; Production and recycling; Applications; Applications; Health effects, Viewed 08 February 2010, http://en.wikipedia.org/wiki/Lead
2. Dane T. Lamba,b, Hui Minga,b, Mallavarapu Megharaj a,b, Ravi Naidua,b,∗ 2009, Heavy metal (Cu, Zn, Cd and Pb) partitioning and bioaccessibility in uncontaminated and long-term contaminated soils, Journal of Hazardous Materials, Volume 171, pp 1150–1158
3. Maxim Khotimchenko, Valeri Kovalev, and Yuri Khotimchenko 2007, Equilibrium studies of sorption of lead (II) ions by different pectin compounds, Journal of Hazardous Materials, Volume 149, pp693-699.
4. Y.N. Mata, M.L. Blázquez∗, A. Ballester, F. González, J.A. Mu˜noz 2009, Sugar-beet pulp pectin gels as biosorbent for heavy metals: Preparation and determination of biosorption and desorption characteristics, Chemical Engineering Journal 150 (2009) 289–301
5. Yan Crettaci and Patrick J.Parsons, 2010, Localized accumulation of lead within and among bones from lead-dosed goats, Environmental Research, Volume 110, pp 26-32.
6. Wikipedia, 11/1/10, Lead poisoning; Classification; Signs and symptoms; Acute poisoning; Chronic poisoning; Exposure routes; Occupational exposure; Paint; Soil; Water; Lead-containing products; Pathophysiology; Enzymes; Neurons; Complications, Viewed 12 January 2010, http://en.wikipedia.org/wiki/Lead_poisoning
7. Wikipedia, 17/01/2010, Pectin, Biology, Chemistry, Sources and Production, Uses, Legal Status, History, Viewed 18 January 2010, http://en.wikipedia.org/wiki/Pectin
8. Silke Schiewer, Ankit Balaria,(2009),Biosorption of Pb2+ by original and protonated citrus peels: Equilibrium,kinetics, and mechanism, Chemical Engineering Journal, Volume 146, pp 211–219.
9. Khotimchenko et al (2007) ibid
10. Maha Tahiri, Patrice Pellerin, Jean Claude Tressol, Thierry Doco, Denise Pe´ pin,Yves Rayssiguier and Charles Coudray, 2000, The Rhamnogalacturonan-II Dimer Decreases Intestinal Absorption and Tissue Accumulation of Lead in Rats, The Journal of Nutrition, Volume 130, pp 249–253.
11. Zhao.Z.Y et al, 2008, The role of modified citrus pectin as an effective chelator of lead in children hospitalised with toxic lead levels, Alternative Therapies in Health and Medicine, Volume 14(4), pp34-38.
12.  M. Yu. Khotimchenko and E. A. Kolenchenko, Efficiency of Low-Esterified Pectin in Toxic Damage to the Liver Inflicted by Lead Treatment, Bulletin of Experimental Biology and Medicine, Vol. 144, No. 1, 2007 PHARMACOLOGY AND TOXICOLOGY, http://link.springer.com/article/10.1007%2Fs10517-007-0254-0
13. Y.N. Mata et al (2009) ibid
14. National Institute of Environmental Health Sciences –National Institutes of Health , Lead, http://www.niehs.nih.gov/health/topics/agents/lead/index.cfm Viewed on 25th March 2010
15. Wikipedia, 15/03/2010 Chelation therapy, Viewed on 25 March 2010, http://en.wikipedia.org/wiki/Chelation_therapy
16. Swaran J.S. Flora, (2009) Lead toxicity and chelation treatment, www.scitopics.com/Lead_toxicity_and_chelation_treatment.html 
    Chelation in Metal Intoxication Swaran J.S. Flora * and Vidhu Pachauri. 
    Int. J. Environ. Res. Public Health 2010, 7(7), 2745-2788 http://www.mdpi.com/1660-4601/7/7/2745/htm 
17. Brent L. Ridley, Malcolm A. O’Neill and Debra Mohnen (2001), Pectins: structure, biosynthesis, and oligogalactutonide-related signalling, Phytochemistry, 57 (6): 929-967
18. Trakhtenberg IM, Lukovenko VP, KOrolenko TK, Ostroukhova VA, Demchenko PI, Rabotiaga TE, Krotenko VV (1995), The prophylactic use of pectin in chronic lead exposure in industry, Jan-Feb;(1-2):132-6