A historical review and bibliometric analysis of research on estuary pollution.
ABSTRACT A bibliometric method based on Science Citation Index-Expanded published by the Thomson Reuters was used to quantitatively assess the global estuary pollution research from 1991 to 2010. The main results were as follows: there had been a notable growth trend in publication outputs. Marine Pollution Bulletin was the most active journal. Environmental sciences were top popular subject categories. USA produced the most single, internationally collaborative, first authored and corresponding authored articles. The Chinese Academy of Sciences was the most productive institute for the total articles. Sediment was the most active research topic, which ranked 1st in article title, article abstract, author keyword, and KeyWords Plus analysis, respectively. Heavy metals received stable focus on a high degree in the field of estuary pollution research. Mostly refractory organic compounds (e.g. PAHs) became more active. Biomarkers and bioaccumulation both were active issues. Eutrophication of estuarine waters receives increasing concern in estuary pollution research.
- SourceAvailable from: Bernardo Duarte[Show abstract] [Hide abstract]
ABSTRACT: Early diagenetic processes and anthropogenic activities are responsible for metal enrichment in estuarine sediments. The Tagus estuary (Portugal) is no exception, and as a result of past and present pressures, surface sediment contamination is still an issue in some areas. Since such metal loads may be incorporated by benthic organisms, this study analyzed the accumulation of trace metals in the Lusitanian toadfish (Halobatrachus didactylus) in the Tagus estuary. In order to determine the role played by the seasonal reproductive cycle of the Lusitanian toadfish in the bioaccumulation process of trace metals in its tissues, the concentrations of Cd, Co, Cr, Cu, Ni, Pb and Zn were determined in the liver of male and female specimens captured during reproductive and non-reproductive periods. The results showed that metal accumulation in the liver was related simultaneously with gender and season, with females having higher levels of Cd, Cu and Zn during the reproductive period. The metabolic roles of Cu and Zn in embryonic development may explain such results, as both metals accumulated in the female liver to be transported to the gonads later on. Cd, on the other hand, does not have a metabolic role, and the higher concentrations of this metal found in spawning females could be related to the high affinity of Cd to vitellogenin, which is produced in the liver. To assess the species’ potential as an indicator of metal contamination, the concentrations of the seven elements were compared in the muscle tissue of adult, type I males (age ≥ 5), from two areas with distinct sediment metal loads. Non-essential metals in the muscle reflected the same differences between areas that were found in the sediment samples, evidencing H. didactylus as a potential indicator of those elements bioavailability from the sediment. The results showed that the muscle tissue of adult specimens of a relatively sedentary species such as H. didactylus is a useful indicator of long term accumulation of trace metals. On the contrary, liver concentrations of trace metals showed variation according to the reproductive status, which could lead to overestimate of the environmental status concerning trace metals bioavailability. Spawning season and liver tissue should thus be avoided in biomonitoring studies targeting this benthic fish.Ecological Indicators 09/2014; 48:370-379. · 3.23 Impact Factor
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ABSTRACT: s u m m a r y A bibliometric analysis was conducted to evaluate groundwater research from different perspectives in the period 1993–2012 based on the Science Citation Index-Expanded (SCIE) database. The bibliometric analysis summarizes output, categorical, geographical, and institutional patterns, as well as research hot-spots in global groundwater studies. Groundwater research experienced notable growth in the past two decades. ''Environmental sciences'', ''water resources'' and ''multidisciplinary geosciences'' were the three major subject categories. The Journal of Hydrology published the largest number of groundwater-related publications in the surveyed period. Major author clusters and research regions are located in the United States, Western Europe, Eastern and Southern Asia, and Eastern Australia. The United States was a leading contributor to global groundwater research with the largest number of independent and collaborative papers, its dominance affirmed by housing 12 of the top 20 most active institutions reporting groundwa-ter-related research. The US Geological Survey, the Chinese Academy of Sciences, and the USDA Agricul-tural Research Service were the three institutions with the largest number of groundwater-related publications. A keywords analysis revealed that groundwater quality and contamination, effective research technologies, and treatment technologies for water-quality improvement were the main research areas in the study period. Several keywords such as ''arsenic'', ''climate change'', ''fluoride'', ''groundwater management'', ''hydrogeochemistry'', ''uncertainty'', ''numerical modeling'', ''seawater intrusion'', ''adsorption'', ''remote sensing'', ''land use'', ''USA''(as study site), and ''water supply'' received dramatically increased attention during the study period, possibly signaling future research trends.Journal of Hydrology 11/2014; 519. · 2.69 Impact Factor
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ABSTRACT: A bibliometric analysis based on the Science Citation Index Expanded was conducted to provide insights into the publication performance and research trend of quantitative structure-activity relationship (QSAR) and quantitative structure-property relationship (QSPR) from 1993 to 2012. The results show that the number of articles per year quadrupled from 1993 to 2006 and plateaued since 2007. Journal of Chemical Information and Modeling was the most prolific journal. The internal methodological innovations in acquiring molecular descriptors and modeling stimulated the articles’ increase in the research fields of drug design and synthesis, and chemoinformatics; while the external regulatory demands on model validation and reliability fueled the increase in environmental sciences. “Prediction endpoints”, “statistical algorithms”, and “molecular descriptors” were identified as three research hotspots. The articles from developed countries were larger in number and more influential in citation, whereas those from developing countries were higher in output growth rates.Molecular Informatics. 09/2014;
A historical review and bibliometric analysis of research on estuary pollution
Jinshui Suna, Ming-Huang Wangb, Yuh-Shan Hob,c,⇑
aGuangxi Water Resources Department, Nanning 530023, PR China
bDepartment of Environmental Sciences, Peking University, Beijing 100871, PR China
cTrend Research Centre, Asia University, Taichung 41354, Taiwan
a r t i c l ei n f o
Web of Science
a b s t r a c t
A bibliometric method based on Science Citation Index-Expanded published by the Thomson Reuters was
used to quantitatively assess the global estuary pollution research from 1991 to 2010. The main results
were as follows: there had been a notable growth trend in publication outputs. Marine Pollution Bulletin
was the most active journal. Environmental sciences were top popular subject categories. USA produced
the most single, internationally collaborative, first authored and corresponding authored articles. The
Chinese Academy of Sciences was the most productive institute for the total articles. Sediment was the
most active research topic, which ranked 1st in article title, article abstract, author keyword, and Key-
Words Plus analysis, respectively. Heavy metals received stable focus on a high degree in the field of estu-
ary pollution research. Mostly refractory organic compounds (e.g. PAHs) became more active. Biomarkers
and bioaccumulation both were active issues. Eutrophication of estuarine waters receives increasing con-
cern in estuary pollution research.
? 2011 Elsevier Ltd. All rights reserved.
Estuaries are semi-enclosed bodies of water where freshwater
from rivers and a coastal stream merges with the ocean. Further-
more, this mixing of waters with such different salt concentrations
and variable physical conditions characteristics forms multiple un-
ique habitats that support highly diverse communities and provide
crucial links to nearby ecosystems (McLusky and Elliott, 2004). Be-
cause of rapid population growth and uncontrolled development in
many coastal areas worldwide estuaries exhibit severe pollution
impacts by introduction of a wide variety of chemical contami-
nants. Many of the chemicals substances are known to concentrate
in the water, or accumulate in estuarine sediments (McCain et al.,
1988) or bioaccumulate by sediment-dwelling organisms (Meador
et al., 1995). Pollutants enter estuaries through storm drains;
industrial discharges; runoff from lawns, streets, and farmlands;
discharges from sewage treatment plants; and atmospheric
A main emphasis of estuary research is to study the effects of
pollution. Estuaries can be affected by contamination in the follow-
ing major ways: oxygen depletion (e.g. hypoxia, anoxia) (SaizSali-
nas, 1997), toxic substances accumulation or bioaccumulation
(e.g. toxic organic compounds, petroleum products, and heavy
metals) (Bryan and Langston, 1992), spills (e.g. oil spills) (Colombo
et al., 2005), pathogens (e.g. from sewage) (Lipp et al., 2001), and
thermal pollution (e.g. heated effluent from power plants) (Keser
et al., 2005). In addition, Sediment quality also has received
increasing concern because sediment is known to act as both a
repository for contaminants and as a pollutants source with poten-
tial impacts on the quality of estuary ecosystem (Budzinski et al.,
1997; Santos et al., 2009). Researchers all over the world have
studied the trends of estuary pollution research and published
many papers related to those topics (Van Geen et al., 1997; Davis
et al., 2000). However, a comprehensive statistical review of the
global estuary pollution research has never been done.
Bibliometrics, were firstlyintroduced by Pritchard, which means
the application of mathematical and statistical methods to books
and other media of communication (Pritchard et al., 1969). Citation
analysis and content analysis are commonly used bibliometric
methods. Bibliometrics have wide applications in various areas to
elevate research performance or assess the research trends by
investigating the publication characteristics, such as authorship,
sources, subjects, geographical origins, and citations (Small,
2003). Bibliometric analysis was performed for ‘‘estuaries and
coasts’’ published since 1960 by the Coastal and Estuarine Research
Federation, the bibliographic analysis of data was compiled by the
onlineversion ofthe Science
(SCI-Expanded) during the period of 1992–2005 (Fourqurean
et al., 2008). In their study, variations of the journal’s name, the
page size, the number of papers and pages published per year, the
number of papers downloaded per month since 1999, the impact
factor, authorship, countries, and institutions of the published
0025-326X/$ - see front matter ? 2011 Elsevier Ltd. All rights reserved.
⇑Corresponding author at: Trend Research Centre, Asia University, Taichung
41354, Taiwan. Tel.: +866 4 2332 3456x1797; fax: +866 4 2330 5834.
E-mail address: email@example.com (Y.-S. Ho).
Marine Pollution Bulletin 64 (2012) 13–21
Contents lists available at SciVerse ScienceDirect
Marine Pollution Bulletin
journal homepage: www.elsevier.com/locate/marpolbul
articles were analyzed, additionally, the number of citations of the
authors and publications were also identified, the results showed
Estuaries and Coasts was acted as a journal on the rise that stood
up in comparisons of quality and citation rate with other journals
in its field after the scope of Estuaries and Coasts was broadened.
Bibliometric analysis was also performed by Clarke et al. (2007)
in the field of public health research literature for Europe, the re-
search articles were based on the Science Citation Index Expanded
(SCI-Expanded) and the Social Science Citation Index (SSCI) dat-
abases for published between 1995 and 2004; output for country
by population, Gross Domestic Product (GDP), burden of disease
usingDALYs,andlanguage wereanalyzed,the resultsindicatedthat
there was obvious variation in public health publication by country
in Europe, Eastern, and southern European countries showed un-
der-invest in public health research compared with northern Euro-
pean countries and compared to relative health need. Zhang et al.
(2010a) used the paper title, abstract, author keyword, and Key-
Words Plus analysis method to quantitatively assessing current re-
search trends on volatile organic compounds, by using the related
literature in the Science Citation Index Expanded (SCI-Expanded)
database from 1992 to 2007. The research trends could be evalu-
ated by analysis on the frequency of words in title, words in ab-
stract, author keywords, and KeyWords Plus in different periods
(Zhang et al., 2010b). Moreover, a method named ‘‘word cluster
analysis’’ was presented to find research hotspots of risk assess-
ment research field (Maoet al., 2010). In this study, bibliometricap-
proaches were used to quantitatively and qualitatively investigate
the global research trends of estuary pollution during the period
of 1991–2010. Research performances of country and institute with
five indicators such as total, collaborative, independent, first
authored, corresponding authored articles, were also presented
(Hu et al., 2010).
2. Data sources and methods
The data used in this study were based on the online version of
the Science Citation Index Expanded (SCI-Expanded) which was ac-
cessed from the Thomson Reuters Web of Science. According to
Journal Citation Reports (JCR), it indexes 8005 major journals with
citation references across 174 scientific disciplines in 2010. The on-
line version of SCI-Expanded was searched with keywords (‘‘pollu-
‘‘pollutants’’, ‘‘pollute’’, ‘‘pollutes’’, ‘‘contamination’’, ‘‘contamina-
tions’’, ‘‘contaminate’’, ‘‘contaminant’’, ‘‘contaminants’’, ‘‘contami-
‘‘estuarius’’, ‘‘estuaria’’, ‘‘estuaries’’, ‘‘estuarial’’, ‘‘estuarian’’, and
‘‘estuarine’’) to compile a bibliography of all articles related to the
research on estuary pollution. Articles originating from England,
Scotland, Northern Ireland, and Wales were grouped under the
UK heading. Articles from Hong Kong were included in China. The
impact factor (IF) of a journal was determined for each document
as reported in the JCR 2010. Contributions of different institutes
and countries were estimated by the affiliation of at least one
author to the articles. Collaboration typewas determined by the ad-
dresses of the authors, where the term ‘‘single country articles’’ was
assigned if the researchers’ addresses were from the same country.
The term ‘‘internationally collaborative articles’’ was designated to
those articles that were coauthored by researchers from multiple
countries. The term ‘‘single institute article’’ was assigned if the
researchers’ addresses were from the same institute. The term ‘‘in-
ter-institutionally collaborative articles’’ was assigned if authors
were from different institutes (Li and Ho, 2008).
All the articles referring to estuary pollution from 1991 to 2010
were analyzed as follows. The aspects covered document type and
language of publications, characteristics of publication outputs,
distribution of output in subject categories and journals, publica-
tion outputs of country and institute; and word in article title, ab-
stract, author keyword, and KeyWords Plus.
3. Results and discussion
3.1. Document type and language of publication
The total papers met the selection criteria mentioned in the Web
of Science database from 1991 to 2010 are 5976. From the distribu-
tionanalysis,12 documenttypes werefound.Article(5026)wasthe
most-frequently used document type comprising 84% of the total
publications, followed by proceedings paper articles (674; 11%), re-
views (204; 3.4%), editorial materials (24; 0.40%), and meeting ab-
stracts (22; 0.37%). The others showing less significance were
notes (10), letters (9), corrections (2), discussions (2), and one for
news item, book chapter review, book chapter article about an indi-
vidual, and biographical-item, respectively. Only 5026 original arti-
cles were considered for further analysis. Languages of all articles
were grouped. Ninety-eight percent of all these journal articles
were published in English (4947). Several other languages also ap-
peared, containing Spanish (21), Portuguese (19), French (19), Ma-
lay (2), Japanese (2), Polish (2), German (1), and Russian (1). English
was by far the dominant language in estuary pollution research be-
cause it was the main language in many fields (Hsieh et al., 2004).
Moreover, more journals listed in Web of Science were English-lan-
guage publications (Chiu and Ho, 2007). However it should be
pointed out that the SCI-Expanded database has been criticized
for its heavy bias in favor of English-language publications (Kurmis,
3.2. Characteristics of publication outputs
The estuary pollution research was growing during the last
100 years, from 1 article in 1902 to 33 articles in 2010 by using
the searching keywords in title words only (Fig. 1). The earliest
articles were published in 1902 and 1904. In 1902, Paton et al. re-
ported the influence of pollution upon fish in Tyne estuary, using
dissolved oxygen (DO) as the measure of the degree of pollution
(Paton, 1902). In 1904, ‘‘The pollution of tidal estuaries’’ was pub-
Fig. 1. Number of SCI-Expanded publications referring to searching keywords in the
title only during the last 100 years.
J. Sun et al./Marine Pollution Bulletin 64 (2012) 13–21
lished in Lancet (Anonymous, 1904). From 1904 to 1950, the world
academic article related estuary pollution in SCI-Expanded data-
base never appeared again. After the 1950s, some developed coun-
tries, for example, UK and Germany suffered from serious water
pollution because of rapid industrialization and population growth
(Johnstone and Horan, 1996; Seeger, 1999). Furthermore, the rapid
economic development and increasing urbanization in developing
countries, such as China and India, resulted in even more severe
water pollution problems from the 1980s (Bowonder, 1986; Wu
et al., 1999). Therefore, estuary pollution had received increasing
concern since then, and the world academic publication in SCI-Ex-
panded database had a notable growth after the 1990s. In addition,
several rules and regulations were adopted to prevent water pollu-
tion and reduction efforts had decreased contaminant levels in the
estuary environment from the 1990s (Bryan and Langston, 1992;
Harino et al., 2003; Reay, 2009). As a result, estuary pollution re-
search has became one of the most important and dynamic field
of environmental research (Carpenter et al., 1998; Santos et al.,
2009). Several publication output characteristics of current estuary
pollution research during the study period of 1991–2010 were
summarized in Table 1. The annual number of articles, the average
number of authors, and the annual number of cited references in-
creased significantly. Only 95 articles were published in 1991,
while the number of articles increased to 451 in 2010. The annual
number of journal articles published and the number of articles ci-
ted to estuary pollution research increased more than fourfold and
sevenfold, respectively. There was an average of 3.1 authors per
estuary pollution related to article in the year 1991, while the
number steadily increased to 4.7 in 2010. The gradual increases
in the number of journal articles outputs and the references re-
vealed stable growth and communication in estuary pollution re-
search during the study period.
3.3. Output in subject categories and journals
The JCR Science 2010 Edition contained 8005 major journals
with 174 subject categories in SCI. The top five popular subject cat-
egories were environmental sciences (3138; 63%), marine and
freshwater biology (1386; 28%), toxicology (734; 15%), oceanogra-
phy (520; 10%), and water resources (453; 9.0%). From 48 articles
in 1991 to 289 articles in 2010, environmental sciences were hold-
ing primacy all through the study period, and were not exceeded
by other study fields (Fig. 2). Marine and freshwater biology and
toxicology was as follows. Publication of these subject categories
increases moderately. The growth of articles in categories of ocean-
ography and water resources was relatively slower. As the use of
statistics in any scientific discipline can be considered a key ele-
ment in evaluating its degree of maturity (Palmer et al., 2005),
the statistical analysis result could provide a current view of the
international estuary pollution research emphases of this topic. Ta-
ble 2 listed the top 20 most active journals producing articles on
estuarine pollution including
SCI-Expanded category of the journal, the position of the journal
in its category, the number of articles, and the percentage of total
articles. The IF of a journal was determined for each document as
reported in the year 2010 JCR. Marine Pollution Bulletin, a quarterly
journal published by Elsevier Science, ranked first with 424 (8.4%)
published articles; Science of the Total Environment ranked second
with 218 (4.3%) articles; Environmental Toxicology and Chemistry,
Environmental Monitoring and Assessment, and Environmental Pollu-
tion ranked 3rd, 4th, and 5th, respectively.
theimpact factor (IF),the
3.4. Country/territory publications
There were eight articles (0.16%) without author address infor-
mation. Thus 5018 articles with author address information,
published from 1991 to 2010 were analysis. This covered 112
countries/territories, of which 4008 (80%) were single country arti-
cles covering 72 countries/territories and 1010 (20%) were inter-
nationally collaborative articles
territories. Table 3 lists the countries/territories published over
100 articles on estuarine pollution during the study period. Num-
ber of total, single country, internationally collaborative, first
authored, and corresponding authored articles, together with their
percentage are exhibited in Table 3. The number of countries in-
volved in estuary pollution research increased rapidly. Seventeen
European countries, seven Asian countries/territories, four Ameri-
can countries, two African countries, and one Oceania country
were ranked in the top 30 productive countries of articles. The
Characteristics by year of publication outputs including total publications, number of
authors, page counts, and number of cited references.
PY TPAUAU/TPNRNR/TP PG PG/TP
TP, number of articles; AU, number of authors; PG, page count; NR, cited reference
count; AU/TP, PG/TP, and NR/TP, average of authors, pages, and references in a
Fig. 2. Comparison of the growth trends of the top six subject categories during
J. Sun et al./Marine Pollution Bulletin 64 (2012) 13–21
USA published the most articles (1354) and completed the most
single and collaborative articles. Moreover, the first authored
and corresponding authored articles of the USA were also ranked
top one. UK followed distantly behind the United States, and
ranked the 2nd position in terms of all indicators. The seven major
industrial countries (G7: Canada, France, Germany, Italy, Japan, the
UK, and the USA), were all ranked in the top 15 of total articles.
The result indicated that the developed countries hold a dominant
position in estuary pollution research as this pattern has occurred
in most scientific fields (Mela et al., 1999). Moreover, some devel-
oping countries, such as BRIC (China, India, Brazil, and Russia)
were also listed as productive countries.
The top 20 most active journals producing articles on estuarine pollution with the number, impact factor, Web of Science subject category of journals, and the position of the
journal in its category during the period of 1991–2010.
Journal title TP (%)IF 2010Subject categoryPosition
Marine Pollution Bulletin424 (8.4)2.359 Environmental sciences
Marine and freshwater biology
Marine and freshwater biology
Marine and freshwater biology
Meteorology and atmospheric sciences
Marine and freshwater biology
Marine and freshwater biology
Marine and freshwater biology
Science of the Total Environment
Environmental Toxicology and Chemistry
Environmental Monitoring and Assessment
Estuarine Coastal and Shelf Science
Environmental Science & Technology167 (3.3) 4.825
Marine Environmental Research
Archives of Environmental Contamination and Toxicology112 (2.2)1.930
Water Air and Soil Pollution 88 (1.8) 1.765
Water Research84 (1.7)4.546
2.133 (2007 JCR)
Marine Ecology-Progress Series 77 (1.5) 2.483
Marine Chemistry67 (1.3) 2.751
Journal of Coastal Research 60 (1.2) 0.679
IF, impact factor; TP, total publications; N/A, not applicable.
Top 15 most productive countries/territories of articles on estuarine pollution during 1991–2010.
Country/territoryTP TP R (%) SP R (%)CP R (%)FP R (%) RP R (%)C%
TP, total articles; SP, single country articles; CP, internationally collaborative articles; FP, articles with first author; RP, articles with corresponding author; %, share in articles;
R, Rank; %C, the percentage of internationally collaborative articles in total articles for each country.
J. Sun et al./Marine Pollution Bulletin 64 (2012) 13–21
The time-trend analysis among the top five productive countries
of peer-reviewed scientific publications on estuarine pollution is
displayed in Fig. 3. The USA has exhibited its dominant position
in estuary pollution research since 1991. An apparent turning point
was appeared at 1999 in UK, which may be due to a series of posi-
aries pollution gained some improvement (Richards et al., 2000;
Galante-Oliveira et al., 2009). China had a high growth pace in re-
cent 10 years, and finally ranked 2nd in 2010. Estuary pollution-re-
lated studies grow more attention due to serious environmental
pollution problems, which mainly resulted from the rapid eco-
nomic and industrial development (Wong et al., 2002).
3.5. Institute publications
A total of 5018 articles with author address information pub-
lished from 1991 to 2010 were analyzed. There were 3160
institutes devoted to the estuary pollution related research. The
top 20 most productive institutions with their respective outputs
are displayed in Table 4. There were seven USA, two UK, two Por-
tugal, two Spain, two France, two Canada, one China, one Brazil,
and one Australia research institutions ranked in the top 20 re-
search institutions. The Chinese Academy of Sciences was the most
productive institute for the total articles (145), as well as single
institute articles (45), first authored articles (106), and correspond-
ing authored articles (104), while the inter-institutionally collabo-
rative articles (100) ranked 1st. There is a bias for the Chinese
Academy of Sciences, as it has many branches in many cities. In
this study, the articles of these institutes were pooled under one
heading, dividing the articles among the branches would have gi-
ven different rankings (Li et al., 2009b).
3.6. Distribution of words in article title, abstract, author keywords,
and KeyWords Plus analysis
Article title, which always contained the information of the
whole paper, is important to help readers find the information they
arelookingfor. An abstractis a briefsummaryof a research paper or
any in-depth analysis of a particular subject or discipline, and is of-
ten used to help the reader quickly ascertain the paper’s purpose.
Article title and abstract analysis both were effective word statisti-
cal analysis, which could be used to make inferences of the scien-
tific literature or to identify the subjective focus and emphasis
specified by authors. Author keywords are the words that are used
to reveal the internal structure of an author’s reasoning. Author
keywords analysis could offer the information of research trend
that is concerned by researchers (Li et al., 2009a). KeyWords Plus
is a kind of automatic indexing used in the citation databases pro-
duced by Web of Science, which provided additional search terms
extracted from the titles of articles cited by authors in their bibliog-
raphies and footnotes (Garfield, 1990). The KeyWords Plus analysis
as an independent supplement, reveals the articles contents with
more details. Using the keywords to analyze the trend of research
by bibliometric method could be found recently (Zhang et al.,
2009). In this paper, the research tendency of this field was
analyzed by using word statistical analysis technique. The title
and abstract were firstly divided into single words then statistical
method was used to analyze them. Some prepositions apparently
were used frequently during our study period but were useless
Fig. 3. Comparison of the growth trends of the top 5 productive countries in
publications on estuarine pollution during 1991–2010.
Twenty most productive institutions publishing articles on estuarine pollution from 1991 to 2010.
Institute TP TP R (%)SP R (%) CP R (%)FP R (%) RP R (%)C%
Chinese Academy of Sciences, China
United States Environmental Protection Agency (US EPA), USA
University of Plymouth, UK
Rutgers State University, USA
University of Aveiro, Portugal
Plymouth Marine Laboratory, UK
National Oceanic and Atmospheric Administration (NOAA), USA
U.S. Geological Survey, USA
University of Huelva, Spain
University of Bordeaux 1, France
University of Sao Paulo, Brazil
University of Sydney, Australia
Texas A&M University, USA
Fisheries & Oceans Canada, Canada
University of Porto, Portugal
University of Quebec, Canada
University of North Carolina, USA
University of South Carolina, USA
TP, total articles; SP, single institute articles; CP, inter-institutionally collaborative articles; FP, articles with first author; RP, articles with corresponding author; %, share in
articles; R, Rank; %C, the percentage of inter-institutionally collaborative articles in total articles for each institute.
J. Sun et al./Marine Pollution Bulletin 64 (2012) 13–21
for the analysis of research trend. Therefore, all these empty words,
together with the searching words were discarded in our analysis.
Based on the distribution of word in article title, article abstract,
author keyword, and KeyWords Plus analysis, popular estuary pol-
lution research issues could be roughly found by the statistically
analysis. These keywords were calculated and ranked by total 20-
year study and 4 year-time periods. ‘‘Sediments’’ and ‘‘sediment’’
was the most frequently used word, which ranked 1st in article ti-
tle, article abstract, author keyword, and KeyWords Plus analysis,
respectively. Estuary sediments provide abundant benthic commu-
nity habitats. They also act as a sink and reservoir for a variety of
environmental contaminants (Grant and Middleton, 1993). In addi-
tion, contaminants binding of sediments can spread to the sur-
roundings. They can transport from the sediment to water,
resuspend when sediments are disturbed, or be absorbed by sedi-
ment-swelling organisms (bioaccumulation). As a consequence
contaminated sediments can have severed effects on living organ-
isms and ecosystems (Budzinski et al., 1997; Santos et al., 2009).
Sediments are an important medium between chemical and biolog-
ical processes (Turner and Millward, 2002). Therefore, ‘‘sediments’’
was the most important issue in estuary pollution research field
from1992 to 2009(Bryan and Langston, 1992;Chapman and Wang,
2001; Couceiro et al., 2009). Heavy metal cycling is a serious prob-
lem faced in estuary environments due to the anthropogenic activ-
ities(Milenkovicet al., 2005). Estuarypollutionbyheavymetals has
become an issue of increasing environmental concern (Du Laing
et al., 2009). The keyword ‘‘heavy metals’’ (or ‘‘heavy metal’’)
ranked2nd and5thinthe author keywordandKeyWordsPlus anal-
ysis, respectively, while ‘‘metals’’ (or ‘‘metal’’) ranked 3rd in the
article title and abstract analysis, respectively. Mercury (Hg) is
one of the most hazardous pollutants that present in aquatic envi-
ronments (Pereira et al., 2009). The existence of mercury in estuary
systems has led to much concern over their influence on plants and
animals life in these environments (Lawson and Mason, 1998; Sun-
derland et al., 2004). Many countries have finalized strict restric-
tions on anthropogenic sources of mercury (Meybeck et al., 2007).
However, historically contaminated sediments may still act as a
source of mercury to the aquatic environment when the areas
requiring maintenance dredging or where sediments may be dis-
turbed and resuspended into the water column (Alonso et al.,
2000; De Marco et al., 2006). Therefore, the research focused on
mercury pollution has still been a hotspot in estuary during
1991–2010. The author keyword ‘‘mercury’’ ranked 47th (1.0%) in
1991–1995, and top 8th (3.2%) in 2006–2010. Other main heavy
metals, such as cadmium (Cd), copper (Cu), and lead (Pb), were ad-
dressed more concern in estuary pollution. The keyword ‘‘copper’’
ranked 13rd and 19th; the keyword ‘‘cadmium’’ ranked 20th and
16th; and the keyword ‘‘lead’’ ranked 27th and 42nd in the author
keyword and KeyWords Plus analysis, respectively. Thus, heavy
metals received stable focus on a high degree in the field of estuary
pollution research during the study period, and the reason might lie
to mine exploitation and advance in industrialization; more impor-
tantly, heavy metals’ persistence and toxicity could cause hazard-
ous impacts on the environment, especially heavy metals may be
bioconcentrated, bioaccumulated and biomagnified within food
chains (Costa et al., 2009). Salinity is the controlling factor for the
distribution of contaminants in sediment and in overlying or inter-
stitial waters (Chapman and Wang, 2001); salinity variations may
be an important factor governing the bioavailability of heavy met-
als towards sediment-dwelling organisms (Du et al., 2002). There-
fore, salinity also has received more attention in recent years,
which can be obviously reflected from the author keywords analy-
sis, the author keyword ‘‘salinity’’ ranked 112th (0.49%) in 1991–
1995, ranked 42nd (1.1%) in 1996–2000, ranked 33rd (1.3%) in
2001–2005, and top 35th (1.1%) in 2006–2010. Polycyclic aromatic
hydrocarbons (PAHs) are one of the most important classes of
anthropogenic organic contaminants in estuary environment. PAHs
has been paid more attention because it has mutagenic and geno-
toxic potential and its potential effects on estuarine Organism by
the long-term toxicity and persistence of PAHs (Budzinski et al.,
1997; Vane et al., 2007). The research focused on PAHs developed
considerably during 1991–2010, and was raised more concern in
recent years. The author keyword ‘‘PAHs’’ and ‘‘polycyclic aromatic
hydrocarbons’’ ranked 47nd (1.0%) and 112th (0.49%) in 1991–
1995, while they ranked 15th (2.2%) and 36th (1.2%) in 1996–
2000, ranked 8th (3.9%) and 17th (2.0%) in 2001–2005, and top
6th (3.6%) and 14th (2.3%) in 2006–2010. KeyWords Plus ‘‘PAHs’’
never appeared in 1991–1995, while it ranked 473nd (0.22%) in
1996–2000, shiftily ranked 87th (1.3%) in 2001–2005, and 39th
(2.4%) in 2006–2010. KeyWords Plus ‘‘polycyclic aromatic hydro-
carbons’’ ranked 16th (4.1%) in 1991–1995, while it ranked 15th
(4.9%) in 1996–2000, it ranked 12th (5.9%) in 2001–2005, and top
8th (8.6%) in 2006–2010. Moreover, the percentage of articles with
keywords ‘‘PAHs’’ in article title and abstract analysis went up from
0% to 4.1% in 1991–1995 to 2.4% and 10% in 2006–2010. These re-
sults were highly accorded with increasing attention given to PAHs
research in recent years (Luo et al., 2004; Beg et al., 2009). Polychlo-
rinated biphenyls (PCBs), a group of persistent organic pollutants
(POPs) derived entirely from anthropogenic sources, are wide-
spread in the estuarine environment as organic pollutants (Durell
and Lizotte, 1998). PCBs are of great environmental concern be-
cause they are potentially harmful to aquatic organisms, and pose
a health threat to the seafood-consuming public (Binelli and Pro-
vini, 2003). Although, PCBs production were banned by the United
States Congress in 1979 and by the Stockholm Convention on Per-
sistent Organic Pollutants in 2001, and reduction efforts had low-
ered their levels in the environment from the 1970s. However,
because of its persistence, PCBs concentrations almost exceeded
the threshold of concern for human health in the environment,
and continued to pollute the water column from various sources
(Santschi et al., 2001; Davis et al., 2007). The author keywords
and KeyWords Plus analysis also indicated that PCBs (or polychlori-
nated biphenyls) continue to be a problem in estuary environment.
The author keyword ‘‘PCBs’’ ranked 15th (2.0%) in 1991–1995,
while it ranked 55th (0.92%) in 1996–2000, it ranked 10th (3.3%)
in 2001–2005, and 21th (1.6%) in 2006–2010. Moreover, KeyWords
Plus‘‘PCBs’’ ranked99th(1.0%)in1991–1995,whileitranked 129th
(0.78%) in 1996–2000, it ranked 143th (0.83%) in 2001–2005, and
76th (1.4%) in 2006–2010. Tributyltin (TBT), a component of anti-
fouling paints which has been widely employed on boat hulls in
marine water, is extremely toxic and causes damages to reproduc-
tion in aquatic organisms (Langston and Pope, 1995). TBT’s high
toxicity to non-target organisms led to its regulation in several
European countries, the United States and other countries (Alzieu,
1998; Harino et al., 2003; Smith et al., 2008). Especially, when more
countries were generally in favor of this Convention and ratified the
Convention, TBT’s concentrations in estuaries had been gradually
reduced (Evans, 1999; Ruiz et al., 2008; Choi et al., 2009), which
also indicated that regulations forbidding the use of TBT-based
antifoulants on vessels <25 m in length have been an effective
way in reducing environmental levels of these compounds (Evans
et al., 2001). Its change can be obviously noticed from the author
keywords, KeyWords Plus, article title, and abstract analysis. The
author keyword ‘‘TBT’’ and ‘‘tributyltin’’ ranked 47th (1.0%) and
21st (1.5%) in 1991–1995, while they ranked 307th (0.22%) and
63rd (0.70%) in 2006–2010. KeyWords Plus ‘‘TBT’’ and ‘‘tributyltin’’
ranked 148th (0.73%) and 31st (2.9%) in 1991–1995, while they
ranked 318th (0.43%) and 188th (0.71%) in 2006–2010. The per-
centage of articles with keywords ‘‘TBT’’ in article title and abstract
analysis shiftily descended from 1.0% and 4.3% in 1991–1995 to
0.37% and 2.0% in 2006–2010. The percentage of articles with key-
words ‘‘tributyltin’’ in article title and abstract analysis dropped
J. Sun et al./Marine Pollution Bulletin 64 (2012) 13–21
from 1.0% to 3.5% in 1991–1995 to 0.55% and 1.7% in 2006–2010.
Briefly, the main pollutants in estuaries were heavy metal and
refractory organic contaminants, and the distribution of the pollu-
tants can be showed in Fig. 4. Pollution is probably the most impor-
tant threat to water quality in estuaries. Water quality in estuaries
is often compromised bythe entrenchment of nutrientsand organic
matter, the influx of pathogens, and the accumulation of heavy
metals and chemical contaminants (Kennish, 2002). The author
keywords ‘‘water quality’’ ranked 7th (3.9%) in 1991–1995, while
it ranked 11th (2.8%) in 2006–2010. KeyWords Plus ‘‘water quality’’
ranked 148th (0.73%) in 1991–1995, while it ranked 27th (3.2%) in
2006–2010. The keywords analysis ‘‘water quality’’ indicated that
water quality was an active issue in estuary pollution research field
from 1991 to 2010 (Valiela et al., 1997; Bainbridge et al., 2009). Bio-
marker was defined as the physiological, biochemical, and histolog-
contaminants and/or of its effects at the suborganismal or organis-
mal level (Hugget et al., 1992). Compared with conventional chem-
ical residue analysis, biomarkers offered a valuable way for
monitoring environmental quality, which generally correspond
more specifically and rapidly to environmental change compared
to responses seen at the population and community level. The
author keywords ‘‘biomarkers’’ ranked 112nd (0.49%) in 1991–
1995, while it ranked 13th (2.5%) in 2006–2010. Moreover, the per-
centage of articles with keywords ‘‘biomarkers’’ in KeyWords Plus
analysis went up from 0.24% in 1991–1995 to 1.4% in 2006–2010.
Thus, it apparently indicated that increasing interest has been
raised to develop the biomarkers for monitoring environmental
quality in estuary aquatic ecosystems (Allen et al., 1999; Vieira
et al., 2009). Bioaccumulationreferredto the processby which toxic
substances (e.g. pesticides, organic chemicals, and heavy metals)
accumulate and keep on accumulating in living organisms. Several
studies have revealed that toxic substances have the ability to bio-
accumulate in the food chain, causing higher trophic organisms to
become contaminated with higher concentrations of toxic sub-
stances than their prey (Vallack et al., 1998; Lawrence and Mason,
2001). The author keywords ‘‘bioaccumulation’’ ranked 21st
(1.5%) in 1991–1995, while it ranked 7th (3.2%) in 1996–2000,
16th (2.1%) in 2001–2005, and 9th (3.1%) in 2006–2010. Moreover,
the percentageof articleswithkeywords‘‘bioaccumulation’’inKey-
Words Plus analysis increased from 0.49% in 1991–1995 to 2.3% in
2006–2010. As a result of the degree of toxic substances
contamination, researchers have made great efforts in study the
bioaccumulation of toxic substances (Wang et al., 2009). The key-
words ‘‘eutrophication’’ and ‘‘nutrients’’ have relatively high ranks.
Eutrophication is the enrichment of water as a result of nutrient
enrichment (Nixon, 1995). Potential consequences of nutrient
enrichment include ecological changes, socioeconomic impair-
ments such as fisheries, aquaculture, and tourism, and serious hu-
man health threats (Carpenter et al., 1998; Anderson et al., 2002;
Whitall et al., 2007). In the past decades, it is well known that many
of estuaries are heavily or moderately eutrophied worldwide
(Bricker et al., 1999; Cloern, 2001). Author keywords ‘‘eutrophica-
tion’’ and ‘‘nutrients’’ ranked 42nd and 112nd in 1991–1995, while
ranked 17th and 15th in 2006–2010. The results were highly in
accordance with great attention given to eutrophication research
in recent decade. The reason for increasing concern on eutrophica-
tion research was due to a wide range of human activities, which
had substantially increased the rate of delivery of plant nutrients
to many estuarine areas (Anderson et al., 2002; Kemp et al., 2009).
In this study, dealing with estuary pollution SCI-Expanded jour-
nals’ papers, some significant points on the worldwide research
trends were obtained throughout the period from 1991 to 2010. In
total, 12 document types were found in the total 5976 publications.
English was the dominant language of estuary pollution research.
Along with the development of SCI-Expanded, estuary pollution re-
to estuary pollution research would still grow rapidly in the future.
The results indicated that Marine Pollution Bulletin was the most ac-
tive journal. The results also revealed environmental sciences, mar-
ine and freshwater biology, and toxicology were top three popular
authored and corresponding authored articles. Meanwhile, China
showed a swift grow pace, and finally ranked 2nd in 2010. The Chi-
cles while US Environmental Protection Agency produced the
second inter-institutionally collaborative articles. Keywords analy-
sis obviously indicated that sediment (or sediments) was the most
active research issues in the studied period. Additionally, heavy
metals obtained stable focus on a high degree in estuary pollution
ganic compounds (e.g. PAHs, PCPs) became more active in estuary
pollution research; however, TBT was gradually under control after
In addition, biomarkers and bioaccumulation both were active is-
sues in estuary pollution research during the study period. Finally,
the rate of delivery of nutrients substantially increased in estuarine
areas due to a wide range of human activities; as a consequence,
Eutrophication of estuarine waters was becoming a global phenom-
enonwith widespread effects and would receive increasingconcern
in estuary pollution research in the future.
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