What is the Meaning of Heavy Metals?: A Case Study in Korean Textbooks Kyung Ah Moon Hee K. Chae* Department of Chemistry Education, Seoul National University, KOREA hkchae1@snu.ac.kr Abstract The purpose of this study is to investigate the conceptual conflict of the definition of heavy metals which were expressed in the Korean secondary science textbooks in terms of the 'hazardous' concept. We analyzed the terminology of heavy metals in the textbooks, and compared the definition of heavy metals with each other. Initial results show that most of textbooks define a heavy metal as a metal or metal element with the or > 4-5 g/cm 3 and describe it as a metal which is hazardous and accumulated in the human body. The definition by the density, however, is vague and it is not directly related to the toxicity. The definition also confines its terminology to a metal or metal element, even though in fact most of heavy metals react in ionic forms in the environment or some of them are non-metals such as arsenic. Such an ambiguous definition may lead students to cause an alternative conception of heavy metals, which means that heavy metals could be identical with toxins. Here we suggest that the word 'heavy metal' should be avoided in the textbook. INTRODUCTION The language of science is not a part of students' native languages in the school, and it rather sounds foreign and uncomfortable to most students until they have got accustomed using it for a long time (Danili & Reid, 2004). According to studies by Piaget, Vygotsky, Bruner and many others, the development of language and understanding are closely interwoven (Sinclair, 2004). When a word is learned by the student, the word at first is a generation of the most primitive type. As the student's intellect develops, it is replaced by generations of a higher type which leads to the formation of true concepts. Understanding is also a constructive process in which students interact with the textbook. Science educators, therefore, are more aware of the part that a language plays in the growth of ideas. Nevertheless investigations into the language of science education still show serious problems which were reported by some researchers: 1) there are clearly gaps between real science, as carried out in professional fields, and school science, as enacted in the classroom (Mortier and Scott, 2004), 2) science textbooks overload too many concepts at a high level without dealing with them in sufficient depth (Gilbert, 2006), and 3) students object to the technical words and ambiguous definitions used ( Keeports, 2006).
According to the Seventh National Education Curriculum of Korea, Korean eleventh-grade students learned the definition of heavy metals in the metals and their utilization chapter which was introduced by the effect of Society-Technology-Society (STS) approach, even though they have already got accustomed to the word via various sources including media. Unfortunately, its definition is not existed in any inorganic chemistry textbooks, and never defined in the nomenclature by even authoritative International Union of Pure and Applied Chemistry (IUPAC). Cognitive studies of the vocabulary heavy metals have been very limited in Korea or abroad. The purpose of this investigation, therefore, was to (1) analyze and identify the nomenclature of heavy metals explained in the Korean Secondary Science textbooks, and (2) find the negative description of the word in the textbooks. Furthermore, based on these analyses, we suggest a new word to replace vague heavy metals in terms of chemical, biological and toxic languages. THEORETICAL BACKGROUND The word of pollution is an emotive term, meaning different things to different people: a reasonable general definition might be too much of something in the wrong place (Harrison, 1990). Thus the standard of chemical pollution in the human being or living systems can be based on the essential elements to be consisted of. Analysis has been shown that only eleven elements appear to be about constant and predominant in all biological systems (Cox, 1995). In the human body these constitute 99.9% of the total number of atoms present but just four of them-c, H, O and N-correspond to 99% of the total. The very large percentages of oxygen and hydrogen arise from the high water content of all living systems. Carbon and nitrogen, next in importance, together with oxygen and hydrogen, are the basic elements of the organic structures and metabolites of living systems. The other seven elements, which together represent about 0.9% of the total number of atoms in the human body, are Na, K, Ca, Mg, P, S and Cl. Besides these 11 elements, which are absolutely essential, some of seventeen others-metals and non-metals that are V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, B, Si, Se, F, I, As, Br and Sn-are required by most biological systems, but not necessarily by all biological systems. The levels of the requirement of these 17 elements are generally different and we note particularly the relatively large amounts of iron and zinc present in most if not all species. The heavy post-transition metals such as Cd, Hg and Pb, however, are toxic because of the very strong complexing ability of soft cations such as Hg 2+ (Frausto da Silva & Williams, 1993). They have low concentrations in natural waters because they form insoluble sulfides. Compounds that are either more soluble in water or volatile pose an environmental hazard. Of these elements, lead has been widely used
in pipes for drinking water, in paints and in gasoline additives, while mercury has been known in hat-making and in industrial applications including electrolysis. Natural mercury concentrations in the environment are very low. A significant amount of cycling may occur through the release of the volatile element from volcanoes, but acute Hg poisoning have been resulted from eating fish in water polluted by industrial Hg compounds. Some organisms convert inorganic complexes into ones containing [CH 3 Hg] +, which are extremely toxic and easily absorbed by the body. The first appearance of heavy metals in the literature, however, has been gone back to European journals in 1890s, until Bierrum defined it as those metals with elemental densities above 7 g/cm 3 in 1936 (Braun, 1892; Duffus,2002). The term heavy metal has been getting into common use for indicating hazardous inorganic materials in the textbook, scientific journal and media without any scientific basis, even though the value of its density changed to 4 or 5 g/cm 3 (Duffus,2002). METHODOLOGY To assess the definition and meaning of heavy metals in the textbook, we studied terms of heavy metals in the metals and their utilization chapter in eight textbooks of Chemistry I for the 11th grade, which texts are revised by the 7 th National Education Curriculum of Korea in 2006 as following; Suh, Jung Sang et al (Kum Sung Publishing, A), Woo, Kyu Hwan et al (Institute for Better Education, B), Yeo, Sang In et al (Jihaksa, C), Yeo, Soo Dong et al (Cheong Moon Gak, D), Kim, Hie-Joon et al (Chunjae Education, E), Lee Doek Hwan et al (Daehan Printing & Publishing, F), Song, Bong Ho et al (Hyungseul Publishing, G), and Yun, Yong et al (Kyohaksa, H). The chapter including the metals and their utilization in each text was analyzed and classified by terminologies, definitions, chemical meanings and types of heavy metal. In addition, the effect of the terminology on negative cognitions including hazardousness or toxicity was studied. Specifically, the following research directions were addressed. (1) Classify textbooks by definitions and their explanations of heavy metals in the Chemistry I. (2) Analyze the contents in the text by meaning of heavy metals in the Chemistry I. (3) Count the number of heavy metals in the Chemistry I and compare the text with each other. (4) Break up chapter frames and explanations of heavy metals into the parts to figure out negative feelings and thoughts about heavy metals.
RESULTS & DISCUSSION Texts Analysis of Heavy Metal Definition Most of the Chemistry I textbooks defined heavy metals as metal or metallic materials and described them as metals which are toxic and accumulated in the human body as shown in the Table 1. Texts E and G did not define them but introduced some examples such as cadmium and arsenic. The definition was based on the density but unfortunately there was no explanation between the density (specific gravity) and accumulation or toxicity in the texts. The reason why the text could not described the biological properties of the heavy metal is that there is not any relationship between the density and the toxicity. Therefore the definition by the density is meaningless. This obscuring description of the heavy metal may lead students to have misconception which the accumulation of the heavy metal in the human body comes from physical heaviness of the metal. Furthermore, the definition confined the material to metal or metal element, which may also cause misconception that a metal itself can be accumulated in the body. There have been many deep-seated misconceptions in the science textbooks. For instance, photosynthesis has been rated as one of the most difficult topics and the most common misconceptions in the biology text (Marmaroti & Galanopoulou, 2006), and impulsive tensions in strings has been a century of misconception in the physics textbooks (O Sullivan, 1988). In order to avoid such a serious misconception, it would be better using the other word instead of heavy metal in the chemistry textbook. Example All of texts gave students three or more examples of heavy metals from 11 elements (D) to three toxic heavy metals (G). Among the texts D and E include arsenic (As) as an example but As is one of non-metals and 17 important elements in the biological systems (Cox, 1995). Most of texts except E and G also contain chrome which is required in the bio materials. In addition, vanadium, manganese, copper and zinc are important in some living systems (D and F), even though in fact the amount of the requirement of these 17 elements are generally different. Thus these ambiguous explanations between important trace elements and heavy metals can result in leading students to form alternative conceptions for these elements.
Table 1. Definitions and Expression of Heavy Metals in the Textbooks Text Definition Explanation presented with definition. A B C metal element with the These heavy metals are strictly controlled in foods and air by their standard content. The sources of pollution problems are mainly mercury, lead and cadmium. These metals cause serious side effects due to their accumulation in the human body, if they are absorbed and not discharged. If they are accumulated in the body, heavy metals cause fatal side effects. The representative heavy metals are mercury and lead. D The heavy metals to bring out suffering in the human body or 5 are mercury, cadmium, lead, copper, manganese, zinc, chrome, arsenic, nickel, cobalt and vanadium. E no comment none Metals are useful materials in daily life but heavy metals F are very cautious due to intoxication by the shape of salts or vapors. Specifically, continuous exposure of heavy metals brings chronic intoxication in the human body, which produces deadly effects to the next generation suffers. G no comment none H Mercury, cadmium and lead in the heavy metals have been known as very hazardous materials which cause serious intoxication in the human body, if they were taken in more than critical dose. Analysis of Texts Description of Heavy Metal Intoxication There are limited inquiries to cause intoxication of heavy metals in the textbooks. Text F provides the subject of inquiry in order to study the state of heavy metals to get poisoned and text G shows the experiment which performs the deformation of proteins by the precipitation reaction of eggs with lead nitrate and mercury nitrate. Such inquiry activities may enhance students to understand the effect of heavy metals on the biological lives. However, most of textbooks provide odds and ends of heavy metals without explanation. Here are the examples as follows; Cr 6+ has been known as carcinogen so caused lung cancer and ulcer if exposure for a long time. (B) Absorbed mercury may be oxidized to mercury ions or reacted with other matter to become hazardous compounds to kidney or nerve system. (E) Heavy metal ions are accumulated in the lipid of the brain and interacted with its protein in order to cause the disease of brain nerve systems by disturbing enzymatic reaction and metabolism. (G) The first description used ionic Cr 6+ instead of Cr, the second sentence also contain mercury ions, and the last one mentioned metal ions in order to explain their intoxication in the body. All of them, however, are not related to their definition
which expresses a metal or metal element to be accumulated in the body. In fact the heavier metal ions prefer soft bases such as SCN -, RS -, R 3 As and R 3 P which are consisted of amino acids by hard and soft acid-base (HSAB) theory (Pearson, 1963). Therefore, resulting bulky coordination complexes are not easily discharged but instead accumulated in the body. CONCULSION & IMPLICATIONS Here we classified and identified the terminology of heavy metals in the Korean High School textbooks Chemistry I, and compared the definition of heavy metals with each other. Most of the textbooks expressed that, most of textbooks define a heavy metal as a metal or metal element with the or > 4-5 g/cm 3 and describe it as a metalwhich is hazardous and accumulated in the human body. The definition by the density, however, is vague and it is not directly related to the toxicity. In addition, the texts exampled a variety of toxic ions as well as important trace metal ions in the human body without any comments. Furthermore, there are confusion between metal and metallic ion as well as between metal and non-metal. Overall, the term of heavy metal in the chapter Metals and Their Utilization should be removed because the terminology is not defined by IUPAC, and such an unclear chemical nomenclature should pedagogically be replaced with other words in the textbook. Otherwise chemistry may also have a century of misconception in the textbook as physics had. If it is necessary to educate hazardous metals and their complexes in the curriculum, we suggest that such a chapter should be related to environment and a new word, for instance, 'hazardous inorganic compounds (HICs)' should be required by more scientific definition in terms of chemical, biological and toxic languages. REFERENCES Braun, F. (1892). Electrostenolysis. Journal of Chemical Society, 62, 393-394.. Cox, P. A. (1995). The elements on earth. New York: Oxford University Press. Danili, E. & Reid, N. (2004). Some strategies to improve performance in school chemistry, based on two cognitive factors. Research in Science & Technological Education, 22(2), 203-223. Duffus, J. H. (2002). Heavy metals a meaningless term? Pure and Applied Chemistry, 74, 793-807.
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