Heavy metals in the environment

Data Sources and Methodology

The study utilized the online version of the Science Citation Index (SCI) from the Web of Science, a comprehensive database managed by ISI in Philadelphia, USA According to the Journal Citation Reports (JCR), the SCI indexed 6,166 major journals across 172 scientific disciplines as of 2006 This research focused on 195 journals categorized under environmental engineering (35 journals), environmental sciences (144 journals), and water resources (57 journals) A search using the keyword “metal or metals” was conducted to compile a bibliography of relevant papers published between 1991 and 2006, specifically including articles from England.

Scotland, Northern Ireland, and Wales were reclassifi ed as being from the United Kingdom

Besides, the reported impact factor (IF) of each journal was obtained from the 2006 JCR

The classification of collaboration types was based on the authors' affiliations, with "single country" designating articles authored by researchers from the same nation Conversely, "international collaboration" refers to works coauthored by researchers from various countries.

Results and Discussion

Language of Publication

The analysis of written languages in metal-related environmental articles revealed that English dominated the field, accounting for 99% of publications Other languages represented included French at 0.26%, German at 0.25%, and Spanish at 0.025% Notably, French articles were primarily published in Environmental Technology, with a total of 32 contributions, and in Houille Blanche-Revue Internationale de l'Eau.

The analysis of publication trends reveals that the Water Quality Research Journal of Canada has contributed significantly with 8 articles, followed by the Journal of Environmental Engineering and Science with 6 Notably, Water Research published 3 articles, and the Science of the Total Environment added 1 In Germany, the leading journal is Gefahrstoffe Reinhaltung der Luft, which has published 34 articles, alongside contributions from Acta Hydrochimica et.

Hydrobiologica (n = 27), and Isotopes in Environmental and Health Studies (n = 1) Only one journal published Spanish articles: Ingenieria Hidraulica en Mexico (n = 6) For all practical purposes,

According to the SCI database, English has emerged as the preferred international language in metal research, highlighting its significance in global scientific communication.

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Article Output and Distribution in Journals

From 1991 to 2006, the number of published articles rose significantly, growing from 550 in 1991 to 2,871 in 2006, indicating a heightened interest in this area of research.

Between 2001 and 2006, over 55% of the total 24,409 articles were published across 173 journals, with six key journals accounting for 34% of these publications Figure 1.2 illustrates the publication trend in these six journals from 1991 to 2006.

Applied Catalysis A—General rose from the sixth rank in 1991 to the fi rst rank in 2006; also

Chemosphere rose from the fi fth rank in 1991 to the second rank in 2006.

Publication Performance: Countries, Institutes, and Authorship

Among the 24,409 articles produced in 145 countries, the top 20 most active countries produced

Out of a total of 24,409 articles, 23,062 (95%) were produced by the United States, which accounted for 25% of the total output with 6,081 articles Additionally, the U.S led in independent publications, contributing 4,859 articles, or 24% of the total The remaining 125 countries collectively produced only 1,347 articles, highlighting the dominance of the U.S in this field, particularly among the G7 nations.

Between 1991 and 2006, Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States collectively accounted for 59% of global publications The trends in article production among the top 10 countries during this period indicate a consistent increase in output for most nations, with the notable exception of China, which rose from the tenth position in rankings.

1991 to second in 2006) and Spain (whose rank changed from ninth in 2001 to third in 2006).

The top 20 most productive institutes are listed in Table 1.2 There are seven institutes from the

United States, three from Canada, two from China, and one each from Spain, Italy, France, Taiwan,

FIGURE 1.1 Publication outputs per year for the period 1991–2006.

N umb er of ar ticle s

Top 20 Most Productive Countries of Articles during 1991–2006

Country TP % %TP SP R (% %) CP R (% %) FP R (% %) RP R (% %)

Notes: TP, total publications; SP, independent publication; CP, international collaborative publication; %TP, share in publication; R, ranking; FP, fi rst author publication; and RP, corresponding author publication.

FIGURE 1.2 Comparison of the growth trends of articles in the top six active journals during the period

Applied Catalysis A-General Environmental Science & Technology Science of the Total Environment Chemosphere

Environmental Pollution Water Air and Soil Pollution

FIGURE 1.4 The growth trends of articles in the United States during the period 1991–2006.

Between 1991 and 2006, countries ranked second to ninth exhibited varying growth trends in article production, as illustrated in FIGURE 1.3 The United States maintains its position as the leading country in this domain, with its growth trend detailed in FIGURE 1.4.

UK Canada France Italy Spain Germany India China Japan

Hong Kong, the United Kingdom, Belgium, and India The highest production came from the U.S

The Environmental Protection Agency (EPA) leads with 375 contributions (1.5%), followed by the Chinese Academy of Sciences with 330 contributions (1.4%) and Spain's CSIC with 316 contributions (1.3%) The significant output from these two institutes has contributed to the recent rise in rankings for both China and Spain.

Collaboration is crucial in modern scientific research, as evidenced by bibliometric analyses of internationally coauthored papers From 1991 to 2006, out of 24,365 articles with author addresses, 54% were produced by single institutions, 30% through intranational collaboration, and 17% via international collaboration The United States led in international collaborations, contributing 1,227 articles, which represents 20% of its total output and 30% of all international collaborations worldwide.

Hong Kong leads globally with 42% of its publications resulting from international collaboration, closely followed by Germany at 41% and China at 40% Other notable contributors include France with 36%, the Netherlands at 35%, Sweden with 32%, and Finland at 30%.

It is usually assumed that the corresponding author is the seniormost among the research group

Articles lacking corresponding author address information on the ISI Web of Science were excluded from the analysis, which ultimately included 22,698 articles authored by 13,310 corresponding authors Notably, 41% of these corresponding authors, totaling 9,222, had published only a single article.

4348 (19%) published two articles as corresponding author The most active corresponding author

Top 20 Most Productive Institutes of Articles during 1991–2006

Institute TP TP R (% %) SP R (% %) CP R (% %) FP R (% %) RP R (% %)

Chinese Academy of Sciences, China 330 2 (1.4) 1 (0.99) 2 (1.8) 1 (0.99) 1 (1.0)

United States Geological Survey (USGS), USA 237 4 (0.97) 3 (0.76) 5 (1.2) 4 (0.64) 4 (0.72)

Consiglio Nazionale delle Ricerche (CNR), Italy 211 5 (0.87) 15 (0.4) 4 (1.4) 6 (0.53) 5 (0.57)

Rutgers, The State University of New Jersey, USA

Le Centre National de la Recherche

Hong Kong University of Science and

Imperial College of Science, Technology and Medicine, University of London, UK

Indian Institute of Technology, India 115 20 (0.47) 7 (0.56) 67 (0.37) 12 (0.40) 14 (0.37)

Notes: TP, total publications; SP, independent publication; CP, international collaborative publication; FP, fi rst author publication; RP, corresponding author publication; and R, ranking.

Burger J from Rutgers State University, USA, has made significant contributions to academic literature, publishing a total of 78 articles, including 68 as the corresponding author and 68 as the first author Following him is Wang W.X from National Taiwan Ocean University.

Hong Kong University of Science & Technology, who published 52 articles as corresponding author,

12 articles as fi rst author, and 63 articles as author Regarding corresponding author countries, the

United States ranked at the top (4925; 22%) followed by the United Kingdom (1285; 5.7%), Canada

The ranking of institutes based on the number of articles authored by corresponding authors differs from the overall article count The Chinese Academy of Sciences leads with 233 articles (1.0%), closely followed by the U.S EPA with 227 articles (1.0%), and Spain's CSIC with 205 articles (0.90%).

Based on the premise that the first author typically conducts the majority of the research, a study on first authorship distribution revealed that the United States leads with 5,448 first author articles, accounting for 22% of the total The United Kingdom follows with 1,432 articles, representing 5.9%, while Canada also contributes significantly to the first authorship landscape.

The Chinese Academy of Sciences leads in first author publications with 241 papers (0.99%), surpassing the CSIC, which has 221 papers (0.91%) Notably, the top-ranking institute for first author contributions is not based in the United States.

Authorship analysis can be biased when multiple authors share the same name or when authors use different names throughout their careers, such as due to marriage Additionally, authors may change institutions or countries, complicating the analysis further To address these challenges, it is highly recommended that an "international identity number (IIN)" be established for each author upon their first publication in an ISI-listed journal This system would ensure accurate tracking and recording of authorship, thereby minimizing biases in the analysis.

FIGURE 1.5 Comparison of the growth trends of corresponding author articles during the period 1991–2006 in the United Kingdom, Canada, Italy, and Spain.

Number of corresponding author articles

Top 30 Most Frequency of Author Keywords Used during 1991–2006 and 4 Four-Year Periods

The Chinese Academy of Sciences and the Indian Institute of Technology have multiple branches across various cities, leading to the decision to aggregate their publications under a single category for this study Dividing the publications by branch would have resulted in varying rankings.

Research Emphasis: Author Keywords and Keywords Plus

Statistical analysis of keywords is crucial for monitoring scientific development and programs Recent bibliometric studies have highlighted the significance of author keyword analysis, although its application in trend analysis remains limited In this study, a total of 32,167 author keywords were identified, with 74% being unique to individual works, indicating a lack of continuity in research and a diverse range of research focuses The distribution of the top 30 author keywords is detailed in Table 1.3.

Between 1991 and 2006, the most frequently used author keywords included "heavy metals" (16%) and "metals" (5.9%), with specific heavy metals such as cadmium (5.9%), copper (5%), lead (4.9%), and zinc (3.4%) also being prominent Notably, the combined usage of the keywords "adsorption," "sorption," and "biosorption" reflects significant trends in research focus during this period.

Sorption-related techniques dominate metal pollution treatment, accounting for 5.2% of research keywords, with "leaching" following at 1.1% Other metal removal methods are not prominent in the top 30 keywords Over the past 16 years, the ranking of most author keywords has remained stable, indicating consistent metal research in the environmental field Notable keywords include "bioavailability," "arsenic," and "adsorption."

Recent trends in environmental research show a rising interest in "sorption" and "biosorption," highlighting them as current hotspots in the field Conversely, the frequency of keywords like "sediments," "speciation," and "nickel" has gradually decreased from 1991 to 2006, suggesting that these areas may be well-established or that research focus has shifted away from them.

Furthermore, keywords plus, which supplied additional search terms, was extracted from the titles of papers cited by authors in their bibliographies and footnotes in the ISI database [42]

Keywords plus analysis is an independent supplement that reveals article contents with more details

In source title analysis, breaking down titles into individual words allows for statistical analysis but compromises the integrity of phrases Conversely, author keywords analysis maintains the complete terms intended by the authors, enabling comparison of similar keywords and the aggregation of diverse keywords under common phrases The inclusion of "keywords plus" significantly enhances the indexing of title words and author keywords, with a total of 21,783 articles incorporating this information Table 1.4 presents the 30 most frequently used "keywords plus," along with their rankings and percentages.

Keywords plus analysis as an independent supplement reveals article contents with more details

The statistical analysis during the study period revealed both similarities and differences in trends Notably, the keywords "heavy metals," "metals," "cadmium," and "copper" ranked highest based on the frequency of author keywords and title words Interestingly, the analysis of author keywords showed that "cadmium," "copper," and "lead" received comparable levels of research attention.

The analysis reveals that "heavy metals" leads with 16%, followed by "cadmium" at 12%, while "copper" and "lead" trail behind at 8.6% and 7.2%, respectively Interestingly, "water," which ranks fifth at 7.2% in keywords plus, is absent from the top 30 author keywords, suggesting a stronger focus on metal pollution in aquatic environments Additionally, the keyword "air" also ranks significantly, reinforcing this trend in research orientation.

80th (1%) Moreover, the ranking of “water” improved from eighth during 1991–1994 to fi fth during

From 2003 to 2006, the ranking of air dropped significantly from 55th to 99th In contrast, the ranking of "mercury" in author keywords saw an improvement, rising from 15th place during the same period.

Between 1991 and 2006, the ranking of certain keywords related to mercury pollution showed a notable decline, with the keyword ranking dropping from 8th to 11th and its position in keywords plus falling from 16th to 40th This decline can be attributed to global legislation aimed at reducing or eliminating mercury compounds from various products, which has shifted research focus to other pollutants Notably, terms such as “accumulation” (5.8%), “removal” (4.4%), “growth” (2.7%), and “exposure” (2.5%) appeared frequently in keywords plus but were absent from the top 30 author keywords, indicating a shift towards novel research directions Additionally, the terms “adsorption” and “sorption” saw an increase in frequency, reinforcing their significance in treatment methods, while “removal” also gained prominence, rising in both ranking and frequency.

Between 1991 and 1994, the focus on "toxicity" in metal pollution research declined, dropping to 6% by 2003–2006 This shift suggests a transition towards addressing the treatment of polluted environments rather than merely assessing pollution impacts Notably, the technique of "reduction" gained prominence, rising from 58th to 28th in ranking during the same period, indicating a growing interest in effective methods for treating metal pollution.

Conclusions

This study analyzes metal research trends in 195 journals within the environmental field from 1991 to 2006, revealing significant insights into global research patterns English emerged as the predominant language for publications, accounting for 99% of the content, highlighting its role in international communication Over the years, an increasing number of authors, institutions, and countries have participated in metal research, with the G7 countries maintaining a leading position in production Notably, China and Spain have rapidly advanced their research efforts, ranking second and third in 2006 The United States led in the number of internationally collaborative articles, while other countries like Hong Kong, Germany, China, France, and the Netherlands also demonstrated substantial international collaboration Key research keywords included “cadmium,” “copper,” and “lead.”

Top 30 Frequency of Keywords Plus Used and 4 Four-Year Periods

Notes: TP, publications in the study period; R (%), the rank and percentage of the articles.

Research conducted by National Taiwan Ocean University highlights the growing stability in the field of metal removal methods, with adsorption emerging as the most prevalent technique Additionally, other notable methods for metal removal continue to be explored and developed within this research area.

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2 Toxicity and Sources of Pb, Cd,

Hg, Cr, As, and Radionuclides in the Environment

Ghinwa M Naja and Bohumil Volesky

2.1.1 Selected Heavy Metals 14 2.1.1.1 Lead 14 2.1.1.2 Cadmium 16 2.1.1.3 Mercury 18 2.1.1.4 Chromium 21 2.1.2 Radionuclides 22 2.1.2.1 Uranium 22 2.1.2.2 Radon 24 2.1.3 Arsenic Pollution 25 2.1.3.1 Arsenic Speciation and Toxicity 25 2.1.3.2 Arsenic-Contaminated Countries 25 2.1.3.3 Clinical Effects 26 2.2 Metals in Groundwaters 27

2.2.1 Heavy Metals in Aquifers 28 2.2.2 Cases and Remediation 33 2.3 Heavy Metal Pollution Sources 35

Acid Mine Drainage (AMD) poses significant environmental challenges, with its chemistry leading to extensive damage and the potential for radioactive contamination Effective treatment methods for AMD are crucial In metal finishing and surface treatment operations, electroplating processes are common, with future trends indicating advancements in technology The leather tanning process, particularly chromium tanning, generates various wastes that require careful management and effluent treatment to minimize environmental impact Additionally, the ferrous metal industries play a vital role in metal processing, contributing to both economic development and environmental considerations.

2.3.5 Coal-Fired Power Generation 53 2.3.5.1 Coal-Fired Station Types 55 2.3.5.2 Generating Station Water Use 57 2.3.5.3 Conclusions 58 References 58

Out of 106 identified elements, approximately 80 are classified as metals, which can be divided into essential metals like iron and calcium, and toxic metals such as cadmium and lead Unlike organic substances, these toxic metals are not metabolically degradable, leading to accumulation in living tissues that poses serious health risks or even death When dissolved in wastewater and released into surface waters, these metals concentrate as they ascend the food chain, potentially reaching dangerously high toxin levels in the environment Additionally, metals that infiltrate groundwater can contaminate drinking water wells, posing significant health threats to consumers.

Human-induced pollution significantly increases metal concentrations in the environment, posing severe risks to both wildlife and human health The extraction of mineral resources and technological advancements have led to the release of chemicals, especially metallic elements, into ecosystems at unprecedented levels Additionally, innovations in nuclear fission technology present both opportunities and challenges, raising concerns about their environmental impact.

The discovery and handling of radioactive isotopes and new elements have reached historically unprecedented levels, raising concerns about the dangers associated with long-lived and high-radiation isotopes The risks of radioactivity have significantly impacted our lives, particularly in relation to the disposal challenges posed by radioactive waste from nuclear power plants These issues have contributed to a slowdown in the adoption of nuclear technology, which may ultimately be viewed as a temporary solution overshadowed by the dangers it presents.

Heavy metals are defined as metallic elements that form positive ions in solution and possess a density at least five times greater than that of water These elements are significant due to their toxicological impact, while also playing essential roles in the physiological functions of living organisms, fulfilling crucial nutritional requirements.

Excessive levels of essential trace elements and the presence of non-essential metals like cadmium, nickel, or silver can lead to toxicity and even death Humans obtain trace elements primarily from food and water, with plants playing a crucial role in the food chain by supporting both plant and animal life It is well-documented that metals are assimilated in both microbial and plant systems, leading to significant concentration as they move up the food chain, with enrichment coefficients reaching up to 10^7 in cells An imbalance or overload of metal species during this process can result in toxic symptoms, cellular dysfunction, long-term health issues, and ultimately death.

Lead is the most prevalent heavy element, with multiple stable isotopes, the most abundant being 208 Pb It has an average molecular weight of 207.2 and is characterized as a soft metal that exhibits resistance to corrosion.

Lead compounds have been widely used in plumbing fittings and as solder in water distribution systems, particularly in installations prior to 1945, which often utilized lead pipes This is significant from a drinking water safety perspective, as lead corrosion can pose health risks Additionally, lead has a low melting point of 327°C, making it a common choice in these applications.

Solid and liquid wastes, including sludge, contribute over 50% of lead released into the environment, primarily through landfills Additionally, lead has been widely dispersed due to atmospheric emissions, particularly from vehicle exhaust However, the shift to unleaded fuel has significantly reduced lead emissions from this source.

Approximately 3 million tons of lead are produced annually, with 40% utilized in electrical accumulators and batteries, 20% as alkyl additives in gasoline, 12% in construction, 6% for cable coatings, 5% in ammunition, and 17% for other applications Around 2 million tons are mined each year, with an estimated 10% lost during ore treatment and another 10% during pig lead production The environmental lead discharge is comparable to that weathered from igneous rocks, and the power storage battery industry has a relatively low environmental impact since about 80% of all batteries are recycled.

Lead can contaminate tap water through dissolution from natural sources or from lead-containing household plumbing systems The levels of lead dissolved from plumbing depend on factors like pH, water softness, and how long the water sits in the pipes Additionally, food may be contaminated by naturally occurring lead in the soil, atmospheric fallout, or water used during cooking.

In urban areas, children have a total lead intake of 29.5 mg/d, with 12.5 mg/d being absorbed, while adults have intakes of 63.7 mg/d and uptakes of 6.7 mg/d Water contributes approximately 9.8% to children's average lead intake and 11.3% for adults.

Since the mid-1980s, the total lead intake from the primary sources of air, food, and dust has significantly decreased due to regulatory measures and voluntary efforts aimed at controlling lead exposure from gasoline in the air and lead in canned food.

Vehicle Emission

Management, Control, and Treatment

Tiêu đề	Heavy metals in the environment
Người hướng dẫn	Lawrence K. Wang, Nazih K. Shammas, Yung-Tse Hung
Trường học	Taylor & Francis Group, LLC
Chuyên ngành	Environmental Science
Thể loại	sách
Năm xuất bản	2009
Thành phố	New York

Định dạng
Số trang	493
Dung lượng	36,65 MB