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At least 3 x 600mL glass beakers (7 is best because then you don't have to reuse them during the lesson).
2 clear tubes per student that can hold at least 3mL of liquid (5mL culture tubes are good).These are the spit dilution tubes. 3 clear tubes per student that can hold at least 15mL of liquid (15mL falcon tubes are good).
Digestion: A person needs to break down the large building blocks that make up food (starch, proteins, fats) into smaller ones (sugar, amino acids, fatty acids).
Enzymes: Enzymes are proteins that can (a) carry out a specific reaction and (b) do so multiple times without getting used up. When we say that an enzyme catalyzes a specific reaction we mean that it is designed to do one thing very well, to the point where it can’t do other things.
Because acid changes the shapes of proteins, which in turns damages the proteins, we use vinegar to stop the action of amylase in our experiment. How the indicator works: when the iodine atoms in the indicator are diluted in a water solution they are arranged in random order in the liquid. Amylase and Evolution: The theory of evolution states that if an environmental pressure exists that favors one genetic outcome over another, over time long periods of time the favored genetic outcome will be selected for.
Print magnetic enzyme and substrate pieces (see attachment) on magnetic printing paper and cut out the individual pieces.
THINK-PAIR-SHARE: After the students perform the demo pair the students and ask one half of the pairs to think about one question and the other half about the other question.
Use Enzyme substrate magnets to make three points:-An enzyme breaks down larger molecules into smaller molecules like sugars. Intro this part of the demo by using the magnet set to show that a protein whose shape has been changed can no longer catalyse its reaction.
Ask a student volunteer to stir in 50mL of vinegar into each one of the remaining 250mL starch-iodine solutions (there shoud be two).
Second part of the lesson: Introduces the idea that our environment can affect our genetic makeup over evolutionary time and that differences in the amount of starch in different populations' diets has led to variability in how much amylase different human populations have.
The investigation should begin with a demonstration on how to use a mirco-pippette if students are not familiar using them. Students will pipette 0.5 ml of their saliva slowly and carefully into the 5 ml PBS test tubes that are labelled with their name. Then, students should pipette 0.5 ml of their diluted saliva into the 15 ml starch iodine tube marked with their name to start the amylase reaction.
After one student in each pair finishes their reaction, partners switch roles and the second member of each pair carries out their reaction while the first acts as the timer.
After the pair has carried out their 2 reactions, one person should add 0.5 ml of vinegar into the control tube.
When all students have finished the exercise we will ask them to compare the color of their amylase reactions with the control and compare their individual reactions. Ask students to talk about their comparisons in pairs and then ask students to report out what they concluded. Point out that most of these are derived either from grains or from fruits and that grains have mostly starch in them while fruits have mostly sugars in them. Ask students what people did 100,000-10,000 years ago to get their carbs, when there were no supermarkets. SLIDESHOW: Use Slides showing how a person living tens of thousands of years ago who produces more amylase in a high starch environment will more likely be healthy and produce more offspring than somebody who has less amylase. This part of the lesson introduces the concept of positive selection of beneficial genetic mutations. Do students with a high amount of amylase in the class have an evolutinary advantage over other students with a lower amount? Once the conclusions are reached, and if there is time, you can ask students what are the possible reasons why some people's saliva reacted more than other peoples saliva other than the different copy number of amylase? Note: It is highly advised that teachers test the student experiment themselves before having students carry it out. This report contains the collective views of international groups of experts and does not necessarily represent the decisions or the stated policy of the United Nations Environment Programme, the International Labour Organization, or the World Health Organization. The first and second drafts of this monograph were prepared, under the coordination of Dr J. Published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organization, and the World Health Organization, and produced within the framework of the Inter-Organization Programme for the Sound Management of Chemicals. The International Programme on Chemical Safety (IPCS), established in 1980, is a joint venture of the United Nations Environment Programme (UNEP), the International Labour Organization (ILO), and the World Health Organization (WHO).
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The Commonwealth Department of Health and Aged Care, Australia, contributed financially to the preparation of this Environmental Health Criteria monograph.
The first Environmental Health Criteria (EHC) monograph, on mercury, was published in 1976 and since that time an ever-increasing number of assessments of chemicals and of physical effects have been produced. Since its inauguration the EHC Programme has widened its scope, and the importance of environmental effects, in addition to health effects, has been increasingly emphasized in the total evaluation of chemicals. The original impetus for the Programme came from World Health Assembly resolutions and the recommendations of the 1972 UN Conference on the Human Environment. The recommendations of the 1992 UN Conference on Environment and Development and the subsequent establishment of the Intergovernmental Forum on Chemical Safety with the priorities for action in the six programme areas of Chapter 19, Agenda 21, all lend further weight to the need for EHC assessments of the risks of chemicals.
The criteria monographs are intended to provide critical reviews on the effect on human health and the environment of chemicals and of combinations of chemicals and physical and biological agents. In the evaluation of human health risks, sound human data, whenever available, are preferred to animal data. The EHC monographs are intended to assist national and international authorities in making risk assessments and subsequent risk management decisions. Since the inception of the EHC Programme, the IPCS has organized meetings of scientists to establish lists of priority chemicals for subsequent evaluation. If an EHC monograph is proposed for a chemical not on the priority list, the IPCS Secretariat consults with the Cooperating Organizations and all the Participating Institutions before embarking on the preparation of the monograph. The order of procedures that result in the publication of an EHC monograph is shown in the flow chart on p.
The draft document, when received by the RO, may require an initial review by a small panel of experts to determine its scientific quality and objectivity. The Task Group members serve as individual scientists, not as representatives of any organization, government or industry. The three cooperating organizations of the IPCS recognize the important role played by nongovernmental organizations. All individuals who as authors, consultants or advisers participate in the preparation of the EHC monograph must, in addition to serving in their personal capacity as scientists, inform the RO if at any time a conflict of interest, whether actual or potential, could be perceived in their work. When the Task Group has completed its review and the RO is satisfied as to the scientific correctness and completeness of the document, it then goes for language editing, reference checking and preparation of camera-ready copy. All Participating Institutions are informed, through the EHC progress report, of the authors and institutions proposed for the drafting of the documents. A WHO Task Group on Environmental Health Criteria for Arsenic and Arsenic Compounds met at the National Research Centre for Environmental Toxicology, Brisbane, Australia, on 15–19 November 1999. After the meeting, and based on the peer reviewer comments and Task Group advice, Drs Gibb, Hopenhayn-Rich, Järup, Sim, and Aitio revised and updated the section on Effects on Human Health. The document was revised on the basis of the peer review comments received, these revisions were verified, and the document was finalized by a Review Board, consisting of Drs D.
The cut-off date for the literature searches for the document was the Task Group meeting, i.e.
The efforts of all, especially Queensland Health and the Natinal Research Centre for Environmental Toxicology, Australia, who helped in the preparation and finalization of the monograph are gratefully acknowledged.
Geographic area in south-western Taiwan, where arsenic-contaminated artesian well water has been used as drinking water, and where BFD is endemic; the area has been also called the "arseniasis" area, or "hyperendemic" area. Arsenic is present in more than 200 mineral species, the most common of which is arsenopyrite. It has been estimated that about one-third of the atmospheric flux of arsenic is of natural origin. Inorganic arsenic of geological origin is found in groundwater used as drinking-water in several parts of the world, for example Bangladesh.
Organic arsenic compounds such as arsenobetaine, arsenocholine, tetramethylarsonium salts, arsenosugars and arsenic-containing lipids are mainly found in marine organisms although some of these compounds have also been found in terrestrial species. Mining, smelting of non-ferrous metals and burning of fossil fuels are the major industrial processes that contribute to anthropogenic arsenic contamination of air, water and soil.
Arsenic is emitted into the atmosphere by high-temperature processes such as coal-fired power generation plants, burning vegetation and volcanism.
Three major modes of arsenic biotransformation have been found to occur in the environment: redox transformation between arsenite and arsenate, the reduction and methylation of arsenic, and the biosynthesis of organoarsenic compounds. Non-occupational human exposure to arsenic in the environment is primarily through the ingestion of food and water. Absorption of arsenic in inhaled airborne particles is highly dependent on the solubility and the size of particles. Levels of arsenic or its metabolites in blood, hair, nails and urine are used as biomarkers of arsenic exposure. Both inorganic and organic forms of arsenic may cause adverse effects in laboratory animals.
Several animal carcinogenicity studies on arsenic have been carried out, but limitations such as high dose levels, limited time of exposure and limited number of animals make these inconclusive. Soluble inorganic arsenic is acutely toxic, and ingestion of large doses leads to gastrointestinal symptoms, disturbances of cardiovascular and nervous system functions, and eventually death.
Long-term exposure to arsenic in drinking-water is causally related to increased risks of cancer in the skin, lungs, bladder and kidney, as well as other skin changes such as hyperkeratosis and pigmentation changes. Occupational exposure to arsenic, primarily by inhalation, is causally associated with lung cancer. Even with some negative findings, the overall weight of evidence indicates that arsenic can cause clastogenic damage in different cell types with different end-points in exposed individuals and in cancer patients.
Chronic arsenic exposure in Taiwan has been shown to cause blackfoot disease (BFD), a severe form of peripheral vascular disease (PVD) which leads to gangrenous changes. Conclusions on the causality of the relationship between arsenic exposure and other health effects are less clear-cut.
Aquatic and terrestrial biota show a wide range of sensitivities to different arsenic species. Arsenic compounds cause acute and chronic effects in individuals, populations and communities at concentrations ranging from a few micrograms to milligrams per litre, depending on species, time of exposure and end-points measured.
Elemental arsenic (As) is a member of Group 15 of the periodic table, with nitrogen, phosphorus, antimony and bismuth.
This monograph deals with arsenic and inorganic and organic arsenic compounds, except arsine (AsH3), for which a Concise International Chemical Assessment Document (CICAD) is being prepared. Arsenical salts exhibit a range of aqueous solubilities depending on the pH and the ionic environment.
Under oxidizing and aerated conditions, the predominant form of arsenic in water and soil is arsenate. Historically, colorimetric and gravimetric methods have been used for the determination of arsenic. Hydride generation followed by cryogenic trapping and AAS detection is a relatively inexpensive technique for the speciation of inorganic arsenic and its methylated metabolites (Ng et al., 1998a), although more expensive hyphenated techniques may also be used. Care must be taken to avoid contamination and prevent speciation changes during sample collection and storage.
There are very few publications on the use of supercritical fluid extraction (SFE) for the determination of arsenic. Most procedures for the separation and determination of arsenic are based on distillation and hydrogen sulfide precipitation methods.
Human populations have variable copy numbers of the amylase gene due to differences in the amount of starch in their diet. This will be referred to as "vinegar" however, vinegar is normally only 8% glacial acetic acid, so this solution is more acidic. The first set demonstrates that amylase is a digestive enzyme that degrades starch into sugar, can do so repeatedly and, like many enzymes, is sensitive to acid.


This is done so that we can use these small building blocks to make our own proteins and fats, as well as so that we can use sugar for energy. For example, although amylase can break down the sort of bond that joins glucose in starch chains it cannot break apart the bond that joins glucose in cellulose chains, despite the fact that both chains are made up of glucose joined together. Examples of what we mean by environment are things such as the temperature an enzyme is in or the acidity of the liquid they are in. Because acid changes the shape of proteins you also see that the solution of amylase with vinegar is cloudier than the solution of amylase without vinegar in it.
In humans this has been very hard to show, and the paper included in this lesson is one of the only known examples in which evolution seems to have acted on a human trait. In some cases the number of genes a person has in their DNA can be very different from person to person. This means that a person who has only 2 copies of the amylase gene in their DNA is likely to have less amylase protein in their saliva than a person that has 4 copies of the amylase gene in their DNA.
In this case the environmental pressure that selects a genetic outcome would be how much starch a human population normally eats.
The high starch populations were two agricultural populations (one European, one Japanese) as well as Hadza hunter-gatherers from Tanzania who rely extensively on starch-rich roots and tubers. They suggest that this is evidence of a selective pressure (diet) leading to a genetic outcome (number of amylase genes in DNA).
Add the PBS right before the demo, so that the amylase is as fresh as possible) into one of the 250mL starch-iodine solutions. Useful examples of proteins being changed are fried eggs (the heat makes the whites turn white) or ceviche, where thin slices of meat are cooked by acid. Students should mix their saliva in with the buffer by pipetting up and down a few times. The timer's job is to start the 1 minute count down at the same time as their partner starts the amylase reaction. It might be useful to have students list the things we are controlling for in our experiment.
If you are having trouble getting the experiment to work as expected, please see the Troubleshooting Student Experiment attachment for advice. Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings. Students know the central dogma of molecular biology outlines the flow of information from transcription of ribonucleic acid (RNA) in the nucleus to translation of proteins on ribosomes in the cytoplasm. Students know how mutations in the DNA sequence of a gene may or may not affect the expression of the gene or the sequence of amino acids in an encoded protein.
Students know why natural selection acts on the phenotype rather than the genotype of an organism.
Students know variation within a species increases the likelihood that at least some members of a species will survive under changed environmental conditions. Students know how natural selection determines the differential survival of groups of organisms. Select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, collect data, analyze relationships, and display data.
Identify possible reasons for inconsistent results, such as sources of error or uncontrolled conditions. Analyze situations and solve problems that require combining and applying concepts from more than one area of science.
Investigate a science-based societal issue by researching the literature, analyzing data, and communicating the findings.
The overall objectives of the IPCS are to establish the scientific basis for assessment of the risk to human health and the environment from exposure to chemicals, through international peer-review processes, as a prerequisite for the promotion of chemical safety, and to provide technical assistance in strengthening national capacities for the sound management of chemicals. The purpose of the IOMC is to promote coordination of the policies and activities pursued by the Participating Organizations, jointly or separately, to achieve the sound management of chemicals in relation to human health and the environment.
Applications and enquiries should be addressed to the Office of Publications, World Health Organization, Geneva, Switzerland, which will be glad to provide the latest information on any changes made to the text, plans for new editions, and reprints and translations already available.
Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters. In the interest of all users of the Environmental Health Criteria monographs, readers are requested to communicate any errors that may have occurred to the Director of the International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland, in order that they may be included in corrigenda. The Task Group meeting was arranged by the National Research Centre for Environmental Toxicology, Australia.
In addition, many EHC monographs have been devoted to evaluating toxicological methodology, e.g. Subsequently the work became an integral part of the International Programme on Chemical Safety (IPCS), a cooperative programme of UNEP, ILO and WHO. Animal and in vitro studies provide support and are used mainly to supply evidence missing from human studies. They represent a thorough evaluation of risks and are not, in any sense, recommendations for regulation or standard setting.
Once the RO finds the document acceptable as a first draft, it is distributed, in its unedited form, to well over 150 EHC contact points throughout the world who are asked to comment on its completeness and accuracy and, where necessary, provide additional material.
Their function is to evaluate the accuracy, significance and relevance of the information in the document and to assess the health and environmental risks from exposure to the chemical.
Representatives from relevant national and international associations may be invited to join the Task Group as observers. After approval by the Director, IPCS, the monograph is submitted to the WHO Office of Publications for printing. A comprehensive file of all comments received on drafts of each EHC monograph is maintained and is available on request. The group reviewed the draft and the peer review comments, revised the draft and made an evaluation of the risks for human health and environment from exposure to arsenic and arsenic compounds. November 1999, with the exception of the section on effects on human health, for which the last literature searches were performed in November 2000. Aitio of the IPCS central unit was responsible for the scientific aspects of the monograph, and Kathleen Lyle for the technical editing. Volcanic action is the most important natural source of arsenic, followed by low-temperature volatilization.
Historically, use of arsenic-containing pesticides has left large tracts of agricultural land contaminated. Natural low-temperature biomethylation and reduction to arsines also releases arsenic into the atmosphere. Bioaccumulation of organic arsenic compounds, after their biogenesis from inorganic forms, occurs in aquatic organisms. Of these, food is generally the principal contributor to the daily intake of total arsenic.
However, in some places workroom atmospheric arsenic concentrations as high as several milligrams per cubic metre have been reported.
Both pentavalent and trivalent soluble arsenic compounds are rapidly and extensively absorbed from the gastrointestinal tract. Blood arsenic is a useful biomarker only in the case of acute arsenic poisoning or stable chronic high-level exposure. The effects induced by arsenic range from acute lethality to chronic effects such as cancer.
However, a recently reported animal model may be a useful tool for future carcinogenicity studies. In survivors, bone marrow depression, haemolysis, hepatomegaly, melanosis, polyneuropathy and encephalopathy may be observed. This disease has not been documented in other parts of the world, and the findings in Taiwan may depend upon other contributing factors.
The evidence is strongest for hypertension and cardiovascular disease, suggestive for diabetes and reproductive effects and weak for cerebrovascular disease, long-term neurological effects, and cancer at sites other than lung, bladder, kidney and skin.
These effects include lethality, inhibition of growth, photosynthesis and reproduction, and behavioural effects.
Representative marine arsenic-containing compounds, of which some are found in terrestrial systems, are shown in Table 1; their molecular structures are shown Fig. Under reducing and waterlogged conditions (< 200 mV), arsenites should be the predominant arsenic compounds.
Inductively coupled plasma-mass spectrometry (ICP-MS) offers very high sensitivity for the determination of arsenic, and coupled with HPLC enables equally sensitive estimation of a wide variety of arsenic species. Plastic containers should be acid washed and traces of oxidizing and reducing agents avoided to preserve the oxidation state of arsenic compounds. Wenclawiak & Krah (1995) reported a procedure for the measurement of arsenic species using SFE followed by GC or SFC detection. Beard & Lyerly (1961) reported a gravimetric method for the measurement of arsenic following extraction of arsenic as AsCl3 by benzene in strong hydrochloric acid.
Alternatively you can buy iodine solution as "Tincture of iodine" or " Lugol's solution" at a drugstore.
If splitting the lesson in two perform the intro and demos 1-4 on the first day and the student experiment on the second day.
Amylase is found in our saliva and is responsible for starting to break down the starch that we eat.
Amylase is specialized to recognize and cut only the type of glucose-to-glucose bond found in starch, not the different kind of glucose-to-glucose bond found in cellulose. The milk curdles because the acid in the lemon juice changes the shape of the proteins in milk causing them to bunch together. Importantly vinegar does not change the color of the Iodine indicator used in our experiments. However, when starch -which is a long chain of glucoses- is added to the water solution it grabs onto iodine and organizes it in a non-random arrangement.
For example, if a population eats a lot of starch it would be beneficial for the people in that population to have a lot of copies of the amylase gene in their DNA. The low-starch populations included Biaka and Mbuti rainforest hunter-gatherers from the Central African Republic and Congo, as well as Datog pastoralists from Tanzania and the Yakut, a pastoralist, fishing society from Siberia.
Each student will be instructed to mark one of each type of the other two tubes with their name. They should also give their partner a 30 second warning, which allows their partner to prepare for stopping the amylase reaction. Ask students to draw conclusions about the relative amount of amylase in each tube, and if there is time, order the tubes from highest to lowest amount of amylase.
Examples of issues include irradiation of food, cloning of animals by somatic cell nuclear transfer, choice of energy sources, and land and water use decisions in California. In this manner, with the strong support of the new partners, the importance of occupational health and environmental effects was fully recognized. It is mandatory that research on human subjects is conducted in full accord with ethical principles, including the provisions of the Helsinki Declaration.
A designated staff member of IPCS, responsible for the scientific quality of the document, serves as Responsible Officer (RO).
The contact points, usually designated by governments, may be Participating Institutions, IPCS Focal Points, or individual scientists known for their particular expertise.
A summary and recommendations for further research and improved safety aspects are also required.
Although observers may provide a valuable contribution to the process, they can only speak at the invitation of the Chairperson. At this time a copy of the final draft is sent to the Chairperson and Rapporteur of the Task Group to check for any errors. The Chairpersons of Task Groups are briefed before each meeting on their role and responsibility in ensuring that these rules are followed. It has been estimated that 70% of the world arsenic production is used in timber treatment as copper chrome arsenate (CCA), 22% in agricultural chemicals, and the remainder in glass, pharmaceuticals and non-ferrous alloys.
The use of arsenic in the preservation of timber has also led to contamination of the environment. Arsenic is released into the atmosphere primarily as As2O3 and exists mainly adsorbed on particulate matter. Bioconcentration factors (BCFs) in freshwater invertebrates and fish for arsenic compounds are lower than for marine organisms.
In some areas arsenic in drinking-water is a significant source of exposure to inorganic arsenic.
In many species arsenic metabolism is characterized by two main types of reactions: (1) reduction reactions of pentavalent to trivalent arsenic, and (2) oxidative methylation reactions in which trivalent forms of arsenic are sequentially methylated to form mono-, di- and trimethylated products using S-adenosyl methionine (SAM) as the methyl donor and glutathione (GSH) as an essential co-factor. Arsenic is rapidly cleared from blood, and speciation of its chemical forms in blood is difficult.
Exposure–response relationships and high risks have been observed for each of these end-points.
However, there is good evidence from studies in several countries that arsenic exposure causes other forms of PVD. In general, inorganic arsenicals are more toxic than organoarsenicals and arsenite is more toxic than arsenate. Arsenic-contaminated environments are characterized by limited species abundance and diversity.


The Chemical Abstract Service (CAS), National Institute for Occupational Safety and Health Registry of Toxic Effects of Chemicals (RTECS), Hazardous Substances Data Bank (HSDB), European Commission, and UN transport class numbers are 7440-38-2, HSB 509, CG 05235 000, 033-001-00-X and UN 1558, respectively.
However, concentrations may be higher in certain areas as a result of weathering and anthropogenic activities including metal mining and smelting, fossil fuel combustion and pesticide use. The rate of conversion is dependent on the Eh and pH of the soil as well as on other physical, chemical and biological factors. In recent years, atomic absorption spectrometry (AAS) has become the method of choice, as it offers the possibility of selectivity and sensitivity in the detection of a wide range of metals and non-metals including arsenic. For analysis of biological soft tissues by ICP techniques, a simple partial digestion in a closed vessel at low temperature and pressure is often sufficient for the sample preparation and pretreatment step. Water has been used for the extraction of soluble arsenic compounds from soil with the aid of ultrasonic treatment (Hansen et al., 1992).
The authors described a rapid extraction of organic and inorganic arsenic species from spiked sand and soil samples by SFE with on-line derivatization using thioglycollic acid methylester (TGM) under supercritical conditions. So amylase is an enzyme that carries out the specific reaction of breaking down starch into a simple sugar. Another example is that amylase cannot break down proteins, which are chains of amino acids, while proteases, which break down proteins, cannot break down starch. For example some people have as little as 2 copies of the amylase gene in their DNA while others have as many as 10 copies of the gene in their DNA.
These are the solutions to which you will add amylase or PBS in demo #3, and vinegar and Amylase or PBS in Demo #4. That blue color should eventually disappear again as the amylase breaks down the newly added starch)c) What would have happened in the original reaction, if we had a most more concentrated starch solution? These tubes will be used to carry out the amylase reactions and saliva dilutions, respectively. Explain that some differences are due to modern industrial practices but that some of them reflect historical tendencies (for example, historically there was more hunting and gathering in central africa, while in eurasia, there has been more farming. Other publications have been concerned with epidemiological guidelines, evaluation of short-term tests for carcinogens, biomarkers, effects on the elderly and so forth.
The EHC monographs have become widely established, used and recognized throughout the world. Worldwide data are used and are quoted from original studies, not from abstracts or reviews. Generally some four months are allowed before the comments are considered by the RO and author(s). The composition of the Task Group is dictated by the range of expertise required for the subject of the meeting and by the need for a balanced geographical distribution. Observers do not participate in the final evaluation of the chemical; this is the sole responsibility of the Task Group members. Under reducing conditions, arsenite (As(III)) is the dominant form; arsenate (As(V)) is generally the stable form in oxygenated environments. ICP-MS) can serve as element-specific detectors when coupled to chromatographic separation techniques (e.g. These particles are dispersed by the wind and are returned to the earth by wet or dry deposition.
In these cases, arsenic in drinking-water often constitutes the principal contributor to the daily arsenic intake.
Methylation of inorganic arsenic facilitates the excretion of inorganic arsenic from the body, as the end-products MMA and DMA are readily excreted in urine. Arsenic in hair and nails can be indicators of past arsenic exposure, provided care is taken to prevent external arsenic contamination of the samples. The effects have been most thoroughly studied in Taiwan but there is considerable evidence from studies on populations in other countries as well.
If levels of arsenate are high enough, only species which exhibit resistance may be present.
Under moderately reducing conditions, arsenite (+3) may be the dominant form, but arsenate (+5) is generally the stable oxidation state in oxygenated environments. In a non-absorbing sandy loam, arsenite is 5–8 times more mobile than arsenate (Gulens et al., 1979). Popular methods for generating atoms for AAS are flame and electrothermally heated graphite furnaces.
Concentrated hydrochloric acid (1 ml to 100 ml urine) has been added to urine to prevent bacterial growth (Concha et al., 1998a). Forms of arsenic compounds can also be separated by sequential extractions based on procedures described by Tessier et al. The TGM derivatives are thermally stable, which makes them amenable to GC–SFC determination.
If we go back to the Philips head screwdriver analogy we can say that while the Philips head screwdriver works very well with Philips head screws it doesn't work at all with flat-head screws, which need another type of  “enzyme”, a flat-head screwdriver. This is because the heat from cooking changes the shape of the proteins (enzymes are proteins) in the egg white which causes them to bunch together which in turn causes them to change color. When starch gets broken down into glucose it can no longer arrange iodine non-randomly, so the solution turns yellowish clear again. Both published and unpublished reports are considered and it is incumbent on the authors to assess all the articles cited in the references.
The first draft, prepared by consultants or, more usually, staff from an IPCS Participating Institution, is based initially on data provided from the International Register of Potentially Toxic Chemicals, and reference data bases such as Medline and Toxline. A second draft incorporating comments received and approved by the Director, IPCS, is then distributed to Task Group members, who carry out the peer review, at least six weeks before their meeting. Arsines released from microbial sources in soils or sediments undergo oxidation in the air, reconverting the arsenic to non-volatile forms, which settle back to the ground.
There are major qualitative and quantitative interspecies differences in methylation, to the extent that some species exhibit minimal or no arsenic methylation (e.g. Arsenic in hair may also be used to estimate relative length of time since an acute exposure.
It is generally considered that inorganic arsenicals are more toxic than organic arsenicals, and within these two classes, the trivalent forms are more toxic than the pentavalent forms, at least at high doses. However, arsenic can produce chromosomal aberrations in vitro, affect methylation and repair of DNA, induce cell proliferation, transform cells and promote tumours. Tobacco smoking has been investigated in two of the three main smelter cohorts and was not found to be the cause of the increased lung cancer risk attributed to arsenic; however, it was found to be interactive with arsenic in increasing the lung cancer risk.
This may explain why there are interspecies differences in organism response to arsenate and arsenite.
However, a commonly used technique for the measurement of arsenic is the highly sensitive hydride generation atomic absorption spectrometric method (HGAAS). When we say that amylase can catalyze the same reaction many times over we mean that it can break the bond between two glucose molecules in starch over and over without loosing its activity. Cooking meat is another example; raw meat tastes and looks different than cooked meat because the temperature from cooking changes the proteins in the meat. Arsenic salts exhibit a wide range of solubilities depending on pH and the ionic environment. Dissolved forms of arsenic in the water column include arsenate, arsenite, methylarsonic acid (MMA) and dimethylarsinic acid (DMA). Terrestrial plants may accumulate arsenic by root uptake from the soil or by adsorption of airborne arsenic deposited on the leaves. Speciated metabolites in urine expressed either as inorganic arsenic or as the sum of metabolites (inorganic arsenic + MMA + DMA) provide the best quantitative estimate of recently absorbed dose of arsenic. Several different organ systems are affected by arsenic, including skin, respiratory, cardiovascular, immune, genitourinary, reproductive, gastrointestinal and nervous systems. One study has indicated that DMA may cause cancer of the urinary bladder in male rats at high doses. The primary mechanism of arsenite toxicity is considered to result from its binding to protein sulfhydryl groups. However, although it is suitable for total arsenic determination after appropriate digestion the technique is only routinely used to speciate a limited number of compounds – arsenite, arsenate, MMA, DMA, trimethylarsine oxide (TMAO). This means that theoretically, if you gave a single amylase protein a lot of time and ideal conditions, the single amylase could break down all the starch that it comes into contact with. We will explain to students that this sort of brainstorming is what scientists do when they are designing experiments. Unpublished data are used only when relevant published data are absent or when they are pivotal to the risk assessment. Additional sensitivity for a limited range of arsenic compounds can often be achieved by the use of hydride generation techniques.
In well-oxygenated water and sediments, nearly all arsenic is present in the thermodynamically more stable pentavalent state (arsenate). Arsenic levels are higher in biota collected near anthropogenic sources or in areas with geothermal activity. Limited data indicate that approximately 25% of the arsenic present in food is inorganic, but this depends highly on the type of food ingested. However, in humans and most common laboratory animals, inorganic arsenic is extensively methylated and the metabolites are excreted primarily in the urine. However, consumption of certain seafood, mainly seaweed and some bivalves, may confound estimation of inorganic arsenic exposure because of metabolism of arsenosugars to DMA in the body or the presence of DMA in the seafood. In strongly adsorbing soils, transport rate and speciation are influenced by organic carbon content and microbial population. A detailed policy statement is available that describes the procedures used for unpublished proprietary data so that this information can be used in the evaluation without compromising its confidential nature (WHO (1990) Revised Guidelines for the Preparation of Environmental Health Criteria Monographs.
Some arsenite and arsenate species can interchange oxidation state depending on redox potential (Eh), pH and biological processes. Naturally elevated levels of arsenic in soils may be associated with geological substrata such as sulfide ores.
Factors such as dose, age, gender and smoking contribute only minimally to the large inter-individual variation in arsenic methylation observed in humans. Such food should be avoided for 2–3 days before urine sampling for monitoring of exposure to inorganic arsenic. In environments where phosphate concentrations are high, arsenate toxicity to biota is generally reduced. Both arsenite and arsenate are transported at a slower rate in strongly adsorbing soils than in sandy soils. A Philips head screwdriver can catalyze the reaction of driving a screw into wood many times over without getting used up.
Some arsenic species have an affinity for clay mineral surfaces and organic matter and this can affect their environmental behaviour.
Anthropogenically contaminated soils can have concentrations of arsenic up to several grams per 100 ml. Foodstuffs such as meat, poultry, dairy products and cereals have higher levels of inorganic arsenic. However, lower methylation efficiency in children has been observed in only one study out of three. As arsenate is a phosphate analogue, organisms living in elevated arsenate environments must acquire the nutrient phosphorous yet avoid arsenic toxicity.
Next, we will ask the students how they propose to test some of the potential variables in this experiment. There is potential for arsenic release when there is fluctuation in Eh, pH, soluble arsenic concentration and sediment organic content.
Studies in humans suggest the existence of a wide difference in the activity of methyltransferases, and the existence of polymorphism has been hypothesized. The concentration of metabolites of inorganic arsenic in urine (inorganic arsenic, MMA and DMA) reflects the absorbed dose of inorganic arsenic on an individual level. Animal and human studies suggest that arsenic methylation may be inhibited at high acute exposures.
The group of authors met at National Health and Environmental Effects Research Laboratory, US.
Many arsenic compounds tend to adsorb to soils, and leaching usually results in transportation over only short distances in soil. The metabolism and disposition of inorganic arsenic may be influenced by its valence state, particularly at high dose levels. Studies in laboratory animals indicate that administration of trivalent inorganic arsenic such as As2O3 and arsenite initially results in higher levels in most tissues than does the administration of pentavalent arsenic. However, the trivalent form is more extensively methylated, leading to similar long-term excretion. Ingested organoarsenicals such as MMA, DMA and arsenobetaine are much less extensively metabolized and more rapidly eliminated in urine than inorganic arsenic in both laboratory animals and humans.



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