Tài liệu Investigation the heavy metal contents in surface water and sediment collected in ThadLuang Marsh (Lao PDR)

Phetdalaphone BOUTTAVONG 2009-2011 VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE PHETDALAPHONE BOUTTAVONG INVESTIGATION THE HEAVY METAL CONTENTS IN SURFACE WATER AND SEDIMENT COLLECTED IN THADLUANG MARSH (LAO PDR) MASTER THESIS HANOI, 2011 1 Phetdalaphone BOUTTAVONG 2009-2011 VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE PHETDALAPHONE BOUTTAVONG INVESTIGATION THE HEAVY METAL CONTENTS IN SURFACE WATER AND SEDIMENT COLLECTED IN THADLUANG MARSH (LAO PDR) MASTER THESIS Supervisor: Assoc. Prof. PhD. Ta Thi Thao HANOI, 2011 2 Phetdalaphone BOUTTAVONG 2009-2011 Abstract In Vientiane, water and sanitation management in the urban area is experiencing stagnant pollution. Unsanitary conditions and threat of seasonal pollution in selected spots is likely to occur and increase with the growing urban population. The sanitation system entails an on-site disposal of human waste without introduction of full water-borne sewerage with treatment facility and safe disposal arrangement. The majorities of households relies on water flush latrines and are connected to a pit or chamber for containment of excreta. However, due to the low permeability of the soil and the high groundwater table around Vientiane, many soak-a-ways fail to operate effectively resulting in discharge of sewage from tanks into drainage channels or low lying areas. This pollution leads to effluent overflows, environmental degradation and health hazards. For the sake of assessment in what extent is water polluted, an analytical method with high sensitivity and the capability and providing a good accuracy and precision should be used. Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the qualitative and quantitative determination of chemical elements employing the absorption of optical radiation (light) by free atoms in the gaseous state. In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyzed. The technique makes use of absorption spectrometry to assess the concentration of an analyte in a sample. My study focuses on heavy metals content in surface water and sediment collected in ThadLuang Marsh in Vientiane Capital City. Providing an overview about alarmingly polluted situation, this research based on determination of Copper, Lead, Cadmium and Zinc by Flame – Atomic absorption spectroscopy. 3 Phetdalaphone BOUTTAVONG 2009-2011 Acknowledgements I would like to thank, DAAD, Deutscher Akademischer Austauschdienst (German Academic Exchange Service) and Technich University Dresden for providing the scholarship of the Master’s program. My sincere thanks also due to the Dean of faculty Environmental of sciences in National University of Lao P.D.R for the kind permission offered me to study. Thank Assoc. Prof. Dr. Ta Thi Thao - my supervisors for encouragement, constructive guidance's I would like to express the profound gratitude and the great appreciation to my advisor Prof. Bernd Bilitewski for his excellent guidance, excellent encouragement and valuable suggestions throughout this study. Special appreciation is extended to Prof. Dr. Nguyen Thi Diem Trang and Prof. Dr. Do Quang Trung committee members for their valuable recommendation and dedicated the valuable time to evaluate my work and my study during being in Vietnam. During studying in Hanoi University of Science, I felt very lucky, it give me the opportunity to have lots of good friends, good memories, so I would like to say thanks and pleasure to meet all of you. Even though we came from different countries, we can make friend together. I hope and wish that I would work together and meet each other again in some conferment. Finally I would like to express deep appreciation to my lovely family and relatives for their love, kind support, and encouragement for the success of this study. This thesis is dedicated for you. 4 Phetdalaphone BOUTTAVONG 2009-2011 Contents List of Figures .............................................................................................................. 7 List of Tables ................................................................................................................ 8 List of Abbreviations .................................................................................................... 9 INTRODUCTION ...................................................................................................... 10 CHAPTER 1: OVERVIEW OF WATER AND SEDIMENT POLLUTION IN THADLUANG MARSH............................................................................................10 1.1. Topography of ThadLuang marsh ................................................................... 13 1.2. Present status of water and sediment pollution in ThadLuang marsh ............. 14 1.3. Toxicity of Cadmium Cd, Copper Cu, Lead Pb, Zinc Zn ................................ 16 1.3.1. Cadmium Cd .............................................................................................. 16 1.3.2. Copper Cu .................................................................................................. 17 1.3.3. Lead Pb ...................................................................................................... 18 1.3.4. Zinc Zn ...................................................................................................... 20 1.4. Analytical methods for determination of heavy metals in water and sediment samples .................................................................................................................... 22 1.4.1. Electrochemical methods ........................................................................... 22 1.4.2. Spectrophotometric methods ..................................................................... 24 CHAPTER 2: EXPERIMENTS ................................................................................. 28 2.1. Research Objects and research contents .......................................................... 28 2.1.1. Research objects ........................................................................................ 28 2.1.2. Research contents ...................................................................................... 28 2.2. Chemicals and Apparatus ................................................................................ 29 2.2.1. Chemicals .................................................................................................. 29 5 Phetdalaphone BOUTTAVONG 2009-2011 2.2.2. Apparatus ................................................................................................... 29 2.2.3. Equipments ................................................................................................ 30 2.3 Sampling and Sample Preparation .................................................................... 30 2.3.1. Study Area ................................................................................................. 30 2.3.2. Sampling and sample preparation ............................................................. 35 2.3.3. Sediment samples ...................................................................................... 35 2.4. Analytical methods for determination of Cu, Pb, Cd, Zn ................................ 36 2.4.1. Flame atomic absorption spectroscopy method (F-AAS): determination of heavy metal content in sediment samples ........................................................... 36 2.4.2. Inductive couple plasma – mass spectrophotometry (ICP-Ms) for the determination of heavy metal contents in surface water samples ....................... 40 2.4.3. Quality control of analytical methods ....................................................... 43 CHAPTER 3: RESULTS AND DISCUSSION ......................................................... 45 3.1. Optimizations of some chemical factors influencing to absorbance in F- AAS method ..................................................................................................................... 45 3.1.1. Study the effects of sample matrix and matrix modifier to F-AAS .......... 45 3.1.2. Calibration curves of Pb, Cd, Zn and Cu measurements. .......................... 49 3.1.3. Limit of detection (LOD) and Limit of quantitation (LOQ) ..................... 53 3.1.4. Effect of interferences to the determination of Pb, Cd and Cu, Zn by FAAS. .................................................................................................................. 54 3.2. Determination of Pb, Cu, Zn, Cd in surface water samples using ICP-MS .... 57 3.2.1. Calibration curves for the determination of Cu, Zn, Pb and Cd in water samples. ............................................................................................................... 57 3.2.2. Method validation ...................................................................................... 59 3.3. Total concentrations of Cu, Pb, Cd, Zn in surface water and sediment of ThadLuang marsh ................................................................................................... 60 3.3.1. Water sample: ............................................................................................ 60 3.3.2. Sediment sample ........................................................................................ 60 3.4. Application of GIS to find out spartial distribution of heavy metals .............. 64 6 Phetdalaphone BOUTTAVONG 2009-2011 CHAPTER 4: CONCLUSION .............................................................................. ….66 REFERENCE..............................................................................................................65 List of figures Figure 1.1: Target Villages around ThadLuang Marsh Figure 2.1: Spectrometer atomic absorption novAA 6800, Shimazhu Figure 2.2: The map of Thatluang marsh showing water sampling sites. Figure 2.3: The map of Thadluang marsh showing sediment sampling sites. Figure 2.4: Operation principle of an atomic absorption spectrometer Figure 2.5: Block diagram of atomic absorption spectrometer Figure 2.6: Instrumentation for low-resolution ICP-MS. Figure 3.1: The investigation of linear ranges for the determination of Pb, Cd, Zn and Cu using F-AAS Figure 3.2: The calibration curves for the determinations of Pb, Cd, Zn and Cu in standard solutions Figure 3.3: Calibration curves for the determination of Cu, Cd, Pb and Zn using ICPMS. Figure 3.4: The Map of water quality of Thadluang Marsh. Figure 3.5: The Map of sediment quality of Thadluang Marsh. 7 Phetdalaphone BOUTTAVONG 2009-2011 List of tables Table 1.1: Some data published on pollution in ThadLuang marsh Table 2.1: Characteristics of the sampling points in Thadluang marsh Table 2.2: Characteristics of the sediment points in Thadluang marsh Table 2.3: The optimal conditions of F-AAS for measuring Pb, Cd, Zn, Cu Table 2.4: The experimental conditions for determination of Cu, Pb, Cd and Zn using ICP- MS techniques Table 3.1: Investigation of HNO3 and NH4CH3COO effects on analysis of Pb, Cd, Cu and Zn Table 3.2: Two - way ANOVA table for evaluating effects of HNO3 and NH4CH3COO Table 3.3: Influence of types of acid media HCl, HNO3 and H2SO4 effects on Cu2+ and Pb2+ analysis Table 3.4: The absorbance of each metal atom (after subtracting the absorbance of the blank solution) vs. their concentrations Table 3.5: The absorbance of each heavy metal standard solutions in the linear range of concentrations Table 3.6: LOD and LOQ of the determination of Pb, Cd, Zn and Cu using F-AAS method Table 3.7: Result of errors and repeatability of the measurements Table 3.8: Accuracy and recovery of CRM using FAAS and ICP-MS Table 3.9: The concentration of Pb, Cd, Zn, Cu in surface water samples of ThadLuang Marsh (g/L) Table 3.10: Heavy metal content (mg/kg) in sediment collected in Thadluang marsh. Table 3.11: Proposed Surface Water Quality standard 8 Phetdalaphone BOUTTAVONG 2009-2011 List of abbreviations Lao PDR The Lao People’s Democratic Republic EDTA Ethylene-diamine-tetracetic acid DME Dropping mercury electrode SMDE Static mercury drop electrode AES Atomic emission spectroscopy F-AAS Flame Atomic absorption spectroscopy ICP-Ms Inductive couple plasma – mass spectrophotometry ANOVA The analysis of variance LOL The limit of linearity LOD Limit of detection LOQ Limit of quantitation 9 Phetdalaphone BOUTTAVONG 2009-2011 INTRODUCTION The Lao People’s Democratic Republic (Lao PDR) is a small landlocked and sparsely populated country in the South East Asia. Laos is characterized by two main geographical zones: the central plains along the Mekong River and the mountainous regions to the north, east and south. Lao PDR has a land area of 236,800 square kilometers (sq. km.). It is long and slender, the length from north to south is nearly 1,000 kilometers and the width has only 150 kilometers to 400 kilometers. [STEA, 2004] The total population is approximately 5,621,982 people, in which women accounted for 51%, according to the 2005 population and housing census. The population density of the country is around 24 people per hectare which is the lowest population densities in Asia. 39% of Lao population is classified as poor and 36% are under poverty line. [MRC, 2006] Their living condition depends on nature, hunting wildlife, foraging for forest products and practicing slash and burn cultivation for their crops with a low profit in order to survive. Lao PDR has rich water resources, mainly good quality fresh water. The amount of average water flow in the Mekong and its tributaries amount to about 8,500 m3/s. Currently most of the water occurs in the agricultural sector, for instance, irrigation, fisheries, plantations and livestock watering. 60 percent of urban population and 51 percent of rural population has access to clean water. [Draft Agreement, March 2009] The total of annual water flow in Lao PDR is estimated at 270 billion cubic meters, equivalent to 35% of the average annual flow of the whole Mekong Basin. The monthly distribution of the flow of the rivers in Lao PDR closely follows the pattern of rainfall: about 80% during the rainy season (May-October) and 20% in the dry season, from November to April. For some rivers in the central and southern parts of the country (particularly Se Bang Fai, Se Bang Hieng and Se Done) the flow in the dry season is less: around 10 to 15% of the annual flow. [Agricultural Statistics 10 Phetdalaphone BOUTTAVONG 2009-2011 [April 2005]. The rivers outside the Mekong Basin flow through Viet Nam into the South China Sea. These rivers are Nam Ma, Nam Sam, and Nam Neune. The limited information on these rivers restricts assessment of their potential. Most of the water use occurs in the agricultural sector such as irrigation, fisheries, plantations and livestock watering. In addition the water is used for hydro-power; the country has the potential to produce 23,000 megawatts of electricity. Currently 5% of that capacity has been exploited. [Would Back, 2007] The plenteous supply of water in Lao PDR, especially in the rainy season, provides good condition for water transport, industrial development and water supply. Sixty percent of urban population and 51 % of rural population has access to clean water. Currently there are some problems related to waste and polluted water in major urban areas from varied community use (residential density, hotels, hospitals and entertainments centers). In addition there is water pollution from agricultural and industrial sectors, including mineral exploitation. This is not a major problem now, but the problem could escalate. The degradation of natural water and water catchments from sedimentation, land erosion and drying out continues. However, as continued development takes place in all of these areas, increasing scarcity and competition for water can be expected. Increasing impacts of development on water quality and on human health and the natural environment will also take place. Finally, floods and drought can have serious negative impacts and may, in fact, increase as climate change takes place. Vientiane Capital is located on an alluvial plain along the left bank of Mekong River east to west. The area of Vientiane is about 3,920 km2 and the elevation of the ground ranges from 160 m to 170 m above the sea level. The city comprises 9 districts; Chanthabuly, Hadxayfong, Meungparkngum, Naxaithong Sangthong, Sikhottabong, Sisattanak, Saysettha and Xaythany. The population is around 672,912 people. The area designated for urbanization extends along the left bank of Mekong River and occupies an area of 210 km2. [JICA, 2009] For Thadluang wetland, its water quality is a part of the water quality-monitoring project of Mekong Secretariat, in the vicinity of Vientiane Capital City. Main problems found are wastewater and sewage (from the city area) discharged into the marsh. Especially, no sooner do many factories appear and develop increasing fast than water is polluted by heavy metals is over allowable limit. Owing to not taking part in 11 Phetdalaphone BOUTTAVONG 2009-2011 biochemical process, heavy metals such as Cd, Pb, Zn, Cu … are accumulated in human body, which leads to harmfulness for organism. The fact that water is polluted by heavy metal is often seen in rivers near industrial area, big cities and minerals exploiting area. The main reason leading to heavy metals pollution is pouring into water environment a large amount of industrial and untreated wastewater. Pollution by heavy metals accumulated through foods directly into organism has negative effects on life environment. In order to reduce consequence of this problem, it is necessary to cultivate measures of water treatment. 12 Phetdalaphone BOUTTAVONG 2009-2011 CHAPTER 1: OVERVIEW OF WATER AND SEDIMENT POLLUTION IN THADLUANG MARSH 1.1. Topography of Thad Luang marsh The ThadLuang Marshland is the largest remaining wetland in Vientiane Municipality, located on the eastern edge of the capital city of Lao PDR. The marsh itself is approximately 20 km2 and is a part of the ThadLuang Basin drained from Vientiane City and surrounding areas. A large portion of the wetland has been converted to rice cultivation although changes in water regimes have resulted in annual floods and cultivation has been limited to between 700 - 1000 ha (approximately half of the wetland area) in recent years. The remaining area is covered with permanent and seasonal aquaculture ponds, shrub and grassland, and peat land. [NUOL, March, 2002] Water draining into the ThadLuang Marshland comes primarily from irrigation canal at the Donnokkoom rice field, Hong Ke and Hong Xeng stream, which collects its water from drainage canals running throughout Vientiane. Water running out of the marsh follows Houay Mak Hiao River dumping into the Mekong 64 km south east of Vientiane. Based on a recent government survey in the That Lung area, about 90 percent of households around ThadLuang Marsh are classified as poor and only 10 percent of households as relatively better off category. Because of the structure of rural employment, the livelihoods of households around ThadLuang Marsh are highly depended upon the ThadLuang marsh, and the water resources availability at the marsh. This is because agriculture and sale of agriculture produce are the primary income generating activity for over 70 % of households living around the ThadLuang marsh. About 7 percent of the total households there are without a primary form of income from agriculture (farming), and it is likely that they rely heavily on collecting fish and aquatic produce from the marsh area. [STO, 2009] Therefore, being one of main reasons leading to poverty, water and sediment pollution in ThadLuang marsh affect significantly on life of people here. 13 Phetdalaphone BOUTTAVONG 2009-2011 Figure 1.1.Villages around ThadLuang Marsh 1.2. Present status of water and sediment pollution in ThadLuang marsh ThadLuang Marsh receives domestic sewage discharge from a large proportion of Vientiane city by way of several canals. While Vientiane has a sewerage system, there is currently no functioning waste treatment facility near the urban area. Sewage is either hauled to a waste treatment plant 17 km outside of the city limits or, more commonly, discharged into natural water bodies, either as raw wastes or as seepage from septic tanks. Sewerage and sanitation systems rely on the infiltration of wastewater into the ground. However due to the low soil permeability and the high groundwater table in Vientiane, many soak ways fail to operate efficiently meaning that sewage is discharged from tanks and drains directly into urban wetlands. As a result of considerable quantity of household waste and sewage is discharged into Nong Chang, and then flows into ThadLuang Marsh before entering the Mekong. Textile, detergent and paper plants discharge directly into open drains without any treatment, and contribute wastewaters into ThadLuang Marsh. 14 Phetdalaphone BOUTTAVONG 2009-2011 There are two tanneries although the larger of these has sophisticated treatment facilities, in practice wastes bypass these and are discharged untreated. The brewery on the southern shore of ThadLuang passes waste through an oxidation pond. Because of the importance of ThadLuang with issues directly relating to Vientiane environment, it is irrefutable that researching water pollution in ThadLuang is necessary and must be done immediately. Some data published on pollution in ThadLuang marsh is shown in table 1.1. Table 1.1: Some data published on pollution in ThadLuang marsh. Parameters Unit 2002 2003 Standard (STEA, 2000) 7.8 8.8 6 – 9.5 C 28 32.6 * (micro/cm) 266 438 * Dissolve Oxygen (DO) mg/l 2.8 1.1 >2 Biological Oxygen Demand (BOD) mg/l 39 78.3 4 Ammonia nitrogen (NH3-N) mg/l 0.294 0.389 0.2 Nitrate-Nitrogen (NO3-N) mg/l 3.064 3.991 <5.0 PO4-P (mg/l) 5.4 6.45 30 Total-N (mg/l) 5.6 3.19 * Total-P (mg/l) * 5.951 * pH (mg/l) o Temperature Electrical Conductivity (EC) This table only mentions about some norms such as BOD, COD, EC, DO … Most scientific research has shown that there is no data on heavy metals pollution until now. This study will provide more information to this missing part. According to this table, pH, BOD, Ammonia nitrogen (NH3-N) and PO4-P parameters are much higher than standard while Dissolve Oxygen (DO) and Nitrate-Nitrogen (NO3-N) are 15 Phetdalaphone BOUTTAVONG 2009-2011 lower. There is sound that water pollution appears compared to Surface Water Quality Standard in Lao PDR. Also, by the fact that it exist wastewater and sewage (from the city area) discharged into the marsh. Especially, no sooner do many factories appear and develop increasing fast than water is polluted by heavy metals is over allowable limit. 1.3. Toxicity of Cadmium Cd, Copper Cu, Lead Pb, Zinc Zn 1.3.1. Cadmium Cd The most dangerous form of occupational exposure to cadmium is inhalation of fine dust and fumes, or ingestion of highly soluble cadmium compounds. Inhalation of cadmium-containing fumes can result initially in metal fume fever but may progress to chemical pneumonitis, pulmonary edema, and death. [Ayres, Robert U, 2003] Cadmium is also an environmental hazard. Human exposures to environmental cadmium are primarily the result of fossil fuel combustion, phosphate fertilizers, natural sources, iron and steel production, cement production and related activities, nonferrous metals production, and municipal solid waste incineration. However, there have been a few instances of general population toxicity as the result of longterm exposure to cadmium in contaminated food and water. In the decades leading up to World War II, Japanese mining operations contaminated the Jinzū River with cadmium and traces of other toxic metals.[National Research Council (U.S.), 1969) ] As a consequence, cadmium accumulated in the rice crops growing along the riverbanks downstream of the mines. Some members of the local agricultural communities consuming the contaminated rice developed itai-itai disease and renal abnormalities, including proteinuria and glucosuria. The victims of this poisoning were almost exclusively post-menopausal women with low iron and other mineral body stores. Similar general population cadmium exposures in other parts of the world have not resulted in the same health problems because the populations maintained sufficient iron and other mineral levels. Thus, while cadmium is a major factor in the itai-itai disease in Japan, most researchers have concluded that it was one of several factors. Cadmium is one of six substances banned by the European Union's Restriction on Hazardous Substances (RoHS) directive, which bans certain hazardous substances in electrical and 16 Phetdalaphone BOUTTAVONG 2009-2011 electronic equipment but allows for certain exemptions and exclusions from the scope of the law. Although some studies linked exposure to cadmium with lung and prostate cancer, there is still a substantial controversy about the carcinogenicity of cadmium. More recent studies suggest that arsenic rather than cadmium may lead to the increased lung cancer mortality rates. Furthermore, most data regarding the carcinogenicity of cadmium rely on research confounded by the presence of other carcinogenic substances. Tobacco smoking is the most important single source of cadmium exposure in the general population. It has been estimated that about 10% of the cadmium content of a cigarette is inhaled through smoking. The absorption of cadmium from the lungs is much more effective than that from the gut, and as much as 50% of the cadmium inhaled via cigarette smoke may be absorbed. [Jarup, L. (1998)] On average, smokers have 4-5 times higher blood cadmium concentrations and 2 - 3 times higher kidney cadmium concentrations than non - smokers. Despite the high cadmium content in cigarette smoke, there seems to be little exposure to cadmium from passive smoking. No significant effect on blood cadmium concentrations has been detected in children exposed to environmental tobacco smoke. Cadmium exposure is a risk factor associated with early atherosclerosis and hypertension, which can both lead to cardiovascular disease. 1.3.2. Copper Cu Copper toxicity refers to the consequences of an excess of copper in the body. Copper toxicity can occur from eating acid food that has been cooked in un-coated copper cookware, or from exposure to excess copper in drinking water or other environmental sources. Copper in the blood exist in two forms: bound to ceruloplasmin (85–95%) and the rest "free" loosely bound to albumin and small molecules. Free copper causes toxicity as it generates reactive oxygen species such as superoxide, hydrogen peroxide, the hydroxyl radical. These damage proteins, lipids and DNA. [Federal Register, 1976] 17 Phetdalaphone BOUTTAVONG 2009-2011 Acute symptoms of copper poisoning by ingestion include vomiting, hematemesis (vomiting of blood), hypotension (low blood pressure), melena (black "tarry" feces), coma, jaundice (yellowish pigmentation of the skin), and gastrointestinal distress. Individuals with glucose-6-phosphate deficiency may be at increased risk of hematologic effects of copper. Hemolytic anemia resulting from the treatment of burns with copper compounds is infrequent. Chronic (long-term exposure) effects of copper exposure can damage the liver and kidneys. Mammals have efficient mechanisms to regulate copper stores such that they are generally protected from excess dietary copper levels. The U.S. Environmental Protection Agency's Maximum Contaminate Level (MCL) in drinking water is 1.3 milligrams per Liter. The MCL for copper is based on the expectation that a lifetime of consuming copper in water at this level is without adverse effect (gastrointestinal effect). The U.S EPA lists evidence that copper causes testicular cancer as "most adequate" according to the latest research at Sanford-Burnham Medical Research Institute. The Occupational Safety and Health Administration (OSHA) has set a limit of 0.1 mg/m3 for copper fumes (vapor generated from heating copper) and 1 mg/m3 for copper dusts (fine metallic copper particles) and mists (aerosol of soluble copper) in workroom air during an 8-hour work shift, 40-hour workweek. [Curtis D. Klassen, Ph.D., McGraw-Hill] 1.3.3. Lead Pb Lead is a poisonous metal that can damage nervous connections (especially in young children) and cause blood and brain disorders. Lead poisoning typically results from ingestion of food or water contaminated with lead; but may also occur after accidental ingestion of contaminated soil, dust, or lead based paint. Long-term exposure to lead or its salts (especially soluble salts or the strong oxidant PbO2) can cause nephropathy, and colic-like abdominal pains. The effects of lead are the same whether it enters the body through breathing or swallowing. Lead can affect almost every organ and system in the body. The main target for lead toxicity is the nervous system, both in adults and children. Long-term exposure of adults can result in decreased performance in some tests that measure functions of the nervous system. It may also cause weakness in fingers, wrists, or ankles. Lead exposure also causes small increases in blood pressure, particularly in middle-aged and older people and can cause anemia. Exposure to high lead levels can severely damage the brain and 18 Phetdalaphone BOUTTAVONG 2009-2011 kidneys in adults or children and ultimately cause death. In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure has shown to reduce fertility in males. The antidote/treatment for lead poisoning consists of dimercaprol and succimer. The concern about lead's role in cognitive deficits in children has brought about widespread reduction in its use (lead exposure has been linked to learning disabilities). Most cases of adult elevated blood lead levels are workplacerelated. High blood levels are associated with delayed puberty in girls. Lead has been shown many times to permanently reduce the cognitive capacity of children at extremely low levels of exposure. During the 20th century, the use of lead in paint pigments was sharply reduced because of the danger of lead poisoning, especially to children. By the mid-1980s, a significant shift in lead end-use patterns had taken place. Much of this shift was a result of the U.S. lead consumers' compliance with environmental regulations that significantly reduced or eliminated the use of lead in non-battery products, including gasoline, paints, solders, and water systems. Lead use is being further curtailed by the European Union's RoHS directive. Lead may still be found in harmful quantities in stoneware, vinyl (such as that used for tubing and the insulation of electrical cords), and brass manufactured in China. Between 2006 and 2007 many children's toys made in China were recalled, primarily due to lead in paint used to color the product. [Stellman, Jeanne Mager (1998).] Older houses may still contain substantial amounts of lead paint. White lead paint has been withdrawn from sale in industrialized countries, but the yellow lead chromate is still in use; for example, Holland Colours Holcolan Yellow. Old paint should not be stripped by sanding, as this produces inhalable dust. Lead salts used in pottery glazes have on occasion caused poisoning, when acidic drinks, such as fruit juices, have leached lead ions out of the glaze. It has been suggested that what was known as "Devon colic" arose from the use of lead-lined presses to extract apple juice in the manufacture of cider. Lead is considered to be particularly harmful for women's ability to reproduce. Lead (II) acetate (also known as sugar of lead) was used by the Roman Empire as a sweetener for wine, and some consider this to be the cause of the dementia that affected many of the Roman Emperors. 19 Phetdalaphone BOUTTAVONG 2009-2011 Lead as a soil contaminant is a widespread issue, since lead is present in natural deposits and may also enter soil through (leaded) gasoline leaks from underground storage tanks or through a waste stream of lead paint or lead grindings from certain industrial operations. Lead can also be found listed as a criteria pollutant in the United States Clean Air Act section 108. Lead that is emitted into the atmosphere can be inhaled, or it can be ingested after it settles out of the air. It is rapidly absorbed into the bloodstream and is believed to have adverse effects on the central nervous system, the cardiovascular system, kidneys, and the immune system. [Hong, Youlian and Bartlett, Roger, ed (2008)]. In the human body, lead inhibits porphobilinogen synthase and ferrochelatase, preventing both porphobilinogen formation and the incorporation of iron into protoporphyrin IX, the final step in hemi synthesis. This causes ineffective hemi synthesis and subsequent microcytic anemia. At lower levels, it acts as a calcium analog, interfering with ion channels during nerve conduction. This is one of the mechanisms by which it interferes with cognition. Acute lead poisoning is treated using disodium calcium edentate: the calcium chelae of the disodium salt of ethylene-diamine-tetracetic acid (EDTA). This chelating agent has a greater affinity for lead than for calcium and so the lead chelae is formed by exchange. This is then excreted in the urine leaving behind harmless calcium. 1.3.4. Zinc Zn Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption. The free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish. The Free Ion Activity Model is well-established in the literature, and shows that just micro molar amounts of the free ion kills some organisms. A recent example showed 6 micro molar killing 93% of all Daphnia in water. [Barceloux, Donald G.; (1999)]. The free zinc ion is a powerful Lewis acid up to the point of being corrosive. Stomach acid contains hydrochloric acid, in which metallic zinc dissolves readily to give corrosive zinc chloride. Swallowing a post-1982 American one cent piece (97.5% of zinc) can cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach. 20