doctor of sciences,bioaccumulation,of heavy metals,in nha trang bay- khanh hoa province,viet nam,tran thi mai phuong

Doctor of Sciences 
 

BIOACCUMULATION OF HEAVY METALS IN NHA TRANG BAY- KHANH HOA PROVINCE VIET NAM. 


 Author: TRAN THI MAI PHUONG - Supervisors: Nguyen Ky PHUNG and Nicolas MARMIER - Discipline: Science of Environment 

CHAPTER 1: LITERATURE REVIEW

1.1 PROBLEM STATUS

Pollution has considerably degraded the coastal and marine environment, including estuaries over the past 30 years. Increasing urbanization, industrialization and tourism, coupled with a growing coastal population, have degraded coastal areas, reduced water quality and increased pressures on marine resources. There have, however, been significant changes in perspective, and new concerns have emerged (MOSTE, 1999). Elevated concentrations of trace metals in aquatic bodies as a result of human activities have been recorded since ancient times. However, excessive releases of toxic trace metals into the urban environment and the associated health implications only became apparent in the 1960s when anthropogenic metal contamination of the environment was denoted. From an environmental and health perspective, this profound geographical development will have a critical influence on our immediate environment and its quality for human health. On a daily basis, numerous human activities including municipal, industrial, commercial and agricultural operations release a variety of toxic and potentially toxic pollutants into the environment (Cheung et al, 2003).

All these elements reach the ocean floor through coastal region, which connects pollutions to the marine ecosystem. Though coastal region are highly productive, dynamic and much diversified regions, the entry of these elements in the biotic system is much easier. From the marine biotic communities the bottom dwelling mollusks have a tremendous capacity of bioaccumulation. Since the coasts are more prone to the accumulation of all toxic elements and chemicals there is a higher chance of accumulation in the body of mollusks. In the dynamic lotic riverine ecosystem deposition and accumulation of such elements are rare because of its fluvial dynamics. But due to the continuous and alternate tidal actions, the retention times for such elements are high in the coastal region, which results in the better chance for their entry in to the biotic communities. The fast growing and highly edible green mussel in the coastal region are 2 more susceptible to heavy metal accumulation and act as a route of toxicity to human population.

It is widely accepted that anthropogenic activity makes a significant contribution to the total aquatic burden of toxic metals by both point source and non point source contamination can occur. Non point source contamination usually arises from agricultural, industrial, and urban effluents that reach the coast by way of waterways, surface runoff, and precipitation. Both benthic and pelagic species may thus become contaminated by direct uptake and or through biomagnifications. Nevertheless, a permanent control of water quality is indispensable. To reveal the presence of pollutants and to measure their toxic effect biological indicators can be used, which are suitable for prediction of the expectable toxic influence of known or unknown substances. (Sanjay et al, 2011)

The pollution of heavy metals in Nha Trang coastal comes from many human activity sources. About 90 percents of wastewater from Nha trang city discharged directly into the rivers without treatment then make their way to estuaries and Nha trang bay. Other major sources from industrial, agriculture activities, oil drilling, tourism and port activities may also cause the direct contamination of heavy metals in this zone. Aquaculture fish in the sea with nearly 7,000 carges caused more serious affecting to the bay nowadays. In fact, approximately 10 tons per day of solid waster were discharged into the sea by 5.000 people living in islands. In the other hand, Nha Trang bay is a tourism city, however, they are more than 40 tourist boats transports every day. (Phung et al, 2009).

In the recent year, contamination of heavy metals has been great problems to the natural environment, especially to marine ecosystems in coastal Viet Nam. Since 1996, in Viet Nam, the increase of metal concentration in the sediment had been observed in Quang Ninh, Hai Phong, Da Nang and Khanh Hoa (Phuong et al, 2012), but there have never been any published reports on the background of heavy metals in such a mollusk species, especially in Khanh Hoa coastal zone. In Nha Trang bay, the concentrations of heavy metal in surface sediments in period 1996-2011 were ranged between 4.58-43.2; 5.51-13.6; 0.32-34.1; 10.23-2,7; 0,15-0,33,0,09-0,43 (àg/g DW) For Zn, Cu, Pb, As, Cd and Hg respectively. The fine fraction of sediment in Nha Trang bay goes from moderately to strongly contamination with respect to the analysis of 4 heavy metals (Zn, As, Cu and Pb) (Phuong et al, 2012) And receives attention from local managers.

The heavy metals can be either adsorbed into sediments or accumulated in benthic organism, sometimes to toxic levels. Studies on heavy metal pollution especially in coastal zones increased over the last few decades at global scale. Therefore, the mobility, bioavailability and subsequent toxicity of metals have been a major research area (Ghabbour et al, 2006). Generally, the presence of contamination by metals have been considered only in important harbours such as New York (Feng et al, 1998), Boston (Manheim F. T and others, 1998), the Atlantic French harbours (Fichet et al, 1999) And, more recently, in Baltimore (Mason et al, 2004), Montevideo (Muniz et al, 2004) And Naples (Adamo et al, 2005). However, very few studies deal with the effect of levels of toxic elements on the health of mollusks in tropical and subtropical regions such as Vietnam and other Southeast Asian countries, particularly in Khanh Hoa province, where, in addition to human activities such as harbor activities within the estuary, industrial, agricultural and residential activities around the coastal can release heavy metals to the environment.

1.2 HEAVY METAL POLLUTIONS

1.2.1 Metals in environment

Metals are considered as important toxic pollutants and there is extensive literature concerning their accumulation in ecosystems. Some metals enter the sea from the atmosphere, by volcanoes, natural weathering of rocks, e. G. Natural inputs of metals, such as Aluminum in wind-blowing dust of rocks and shales, but also by numerous anthropogenic activities, such as mining, combustion of fuels, industrial and urban sewage and agricultural practices. On a global scale there is now abundant evidence that anthropogenic activities have polluted the environment with heavy metals from the poles to the tropics and from the mountains to the depths of the oceans.

Some metals are deposited by gas exchange at the sea surface, by fallout of particles (dry deposition) Or are scavenged from the air column by precipitation (rain) Which is called wet deposition. For example, Lead inputs in the atmosphere from industrial and vehicular exhaust are much greater than natural inputs. The natural levels of heavy metals in the environment had never been a threat to health but in the recent years increased industrial activities leading to air born emissions, auto exhausts, effluents from industries as well as solid waste dumping have 4 become the sources of large quantities of heavy metals into the environment (Mhatre G. N,1991).

Metals enter the environment by means of natural processes or are derived from human activities. For some metals, natural and anthropogenic inputs may be of the same order (Zn), whereas for others (Pb) Inputs due to human activities dwarf natural inputs (Clark R. B, 2001). Much of those human activities are located in the fluvial watersheds and in the margins of estuaries (Salomons and others, 1984), being important areas for the concentration of contaminants, due to coastal industrial activity and human settlement.

There, trade is growing rapidly and much of it depends on shipping, most of import and export travel by sea, and the marine harbour environment is degraded. The increase of metal concentrations in the sediment is a symptom of this process as has been observed in the Pacific harbours (Wolanski E, 2006). Rivers make a major contribution of metals in the marine environment. The nature of metals depends on bearing deposits in the catchments area and the discharge of human waste and discharges when the river passes through urban areas. Dredging of shipping channels produces large quantities of metal pollution. Much smaller quantities of metals are added to the sea by direct discharges of industrial and other waste and the dumping of sewage sludge. (Clark et al, 1997; Depledge et al, 1998).

Atmospheric and river inputs, dredging soil, direct discharges, industrial dumping and sewage sludge are some of the important contributors to metal pollution, which lead to the release of metals to the marine environment (Valavanidis A et al, 1999).

The oceans provide a vital sink for many heavy metals and their compounds. There is a growing concern that the natural cycling rates of many metals are being disturbed by anthropogenic activities, especially the release from industrial, domestic and urban effluents of increasing amounts of Pb, Zn, Cd, Hg and Cu. (Schindler P. W,1991).

Atmospheric metal pollution is responsible from most of the dissolved Cd, Cu, Fe, Zn, Ni and As in the oceans. (GESAMP, 1990). The world wide emissions of metals to the atmosphere (thousands of tons per year) By natural sources is estimated as: Ni: 26, Pb: 19, Cu: 19, As: 7.8, Zn: 4, Cd: 1.0, Se: 0.4 (tons x103/yr). Whereas, from anthropogenic sources: Pb: 450, Zn: 320, Ni: 47, Cu: 56, As: 24, Cd: 7.5, Se: 1.1 (tons x103/yr). (Clark et al, 1997). It is obvious from these numbers that Pb, Zn, As, Cd and Cu are the most important metal pollutants from human activities Metals of major interest in bioavailability studies, as listed by the U. S.

Environmental Protection Agency, are Al, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Sb (EPA, 1978). Other metals that are presently of lesser interest are Ag, Ba, Co, Mn, Mo, Na, Ti, V, and Zn. (McKinney et al, 1992). These metals were selected because of their highly toxic properties, their effects on the environment and the living organisms, their potential for human exposure and increased health risk. Some highlights concerning the bioavailability of As, Cd, Cr, Cu, Mo, Ni, Pb, and Zn in sediment are discussed in this study. An additional data are available in the references listed for some major such heavy metals are:

Arsenic (As):

Arsenic mobility, bioavailability, and toxicity are dependent on speciation: Arsenite (AsO₃-3) Forms are much more toxic to biological species and are more mobile than arsenate (AsO₄-3) Forms (Kersten, 1988). Arsenic is chemically similar to phosphorous.

Arsenate interferes with phosphate metabolism that is widespread in the biosphere. Metallo-organic forms of arsenic also may be much more bioavailable than inorganic forms; However, organic-bound arsenic is excreted by most species and does not appear to be highly toxic (Luoma S. N, 1983). Adsorption and desorption on iron and aluminum oxide minerals is the main factor controlling arsenic behavior in soil and sediment.

Maximal adsorption occurs at different pH for As {III} (pH 9.2) And As {V} (pH 5.5) As a function of the adsorbing mineral; As+ 3 mobility is enhanced under oxic conditions.

Arsenic is apparently highly mobile in anoxic sediment-water systems. Development of acidic and oxidizing conditions tends to release large amounts of arsenic into solution due to decreased sorption capacity of both forms of arsenic (Léonard A, 1991). Arsenic can be found in some film chemistry, but is not very common.

Cadmium (Cd):

The redox potential of sediment-water systems exerts controlling regulation on the chemical association of particulate cadmium, whereas pH and salinity affect the stability of its various forms (Kersten M, 1988). Elevated chloride contents tend to enhance chloride complex formation, which decreases the adsorption of cadmium on sediment, thereby increasing cadmium mobility (Bourg A. C, 1988) And decreasing the concentration of dissolved Cd+ 2 and bioavailability (Luoma S. N, 1983). In anoxic environments, nearly all 6 particulate cadmium is complexed by insoluble organic matter or bound to sulfide minerals. Greenockite (CdS) Has extremely low solubility under reducing conditions thereby decreasing cadmium bioavailability.

 Oxidation of reduced sediment or exposure to an acidic environment results in transformation of insoluble sulfide-bound cadmium into more mobile and potentially bioavailable hydroxide, carbonate, and exchangeable forms (Kersten, 1988). Studies of lake and fluvial sediment indicate that most cadmium is bound to exchangeable site, carbonate fraction, and iron-manganese oxide minerals, which can be exposed to chemical changes at the sediment-water interface, and are susceptible to remobilization in water (Schintu et al, 1991). Cadmium is a common metal found in anthropogenically contaminated aquatic environments and is toxic to aquatic biota at elevated levels. Cadmium can be found in some pigments, especially orange, red, and yellow colors. In oxidized, near neutral water, CdCO₃ limits the solubility of Cd2+ (Kersten M, 1988). In a river polluted by base-metal mining, cadmium was the most mobile and potentially bioavailable metal and was primarily scavenged by non-detrital carbonate minerals, organic matter, and iron-manganese oxide minerals (Prusty et al, 1994).

Mollusks accumulate large concentration of calcium ranging from 1900 – 2000 ppm dry weight (Clark, 1992). Highest concentration in cadmium causes several health problems in human. Cadmium and its compounds along with mercury and some other dangerous metals are, however, included in the blacklist. It is being used routinely in different industrial processes and its potential hazard to life form is predominant. Eating food or drinking water with very high cadmium levels severely irritates the stomach, leading to vomiting and diarrhea, and sometimes death. Eating lower levels of cadmium over a long period of time can lead to a build-up of cadmium in the kidneys. If the levels reach a high enough level, the cadmium in the kidney will cause kidney damage, and also causes bones to become fragile and break easily. As a conservative approach, and based on the limited human data and the studies in rats, the United States Department of Health and Human Services (DHHS, 1999) Has determined that cadmium and cadmium compounds may reasonably be anticipated to be carcinogens.

Chromium (Cr):

The major source of chromium emission in to the environment from the chemical manufacturing industry, combustion of fossil fuel, cement producing plants, waste from 7 electroplating, leather tanning, textile industry and consumer products such as inks, paints, papers, toner powder used in copying machine… Chromium is the naturally occurring compound found in soil, rocks and plants. It is normally exists in oxidation states ranging from chromium (II) To Chromium (VI). However, two major forms trivalent (III) And hexavalent (VI) Forms have biological significance.

Physiologically chromium is considered as a trace element and it is required for the optimum function of insulin in mammalian tissues and the maintenance of normal metabolism of glucose, cholesterol and fat. The normal level of blood chromium concentration in human beings is between 20-30àg/l. It is found that the intake of chromium is about 50-200 àg/day is regarded to be safe and adequate.

Hexavalent chromium is an extremely toxic metal, which exist as an anion (CrO₄2) And most readily absorbed from the gastrointestinal tract, skin and lungs. Most reports describe the toxicity of chromium (VI) In the form of chromate of dichromate. It can cause chronic ulceration of skin surface, denaturation of tissue proteins, asthma, kidney failure, discoloration of teeth and inflammation of skin. Acute poisoning results in symptoms such as dizziness, intense thirst, abdominal pain, vomiting and shock and sometimes death may occur due to the presence of urea in blood.

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TABLE OF CONTENTS

AIM AND STEPS OF THE STUDY

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF PICTURES

LIST OF ACRONYMS

CHAPTER 1. LITERATURE REVIEW

1.1 PROBLEM STATUS

1.2 HEAVY METAL POLLUTIONS

1.2.1 Metals in environment

1.2.2 Pollution of heavy metal in marine sediments

1.3 BIOACCUMULATION OF METALS IN LIVING ORGANISMS

1.3.1 Heavy metals on benthic organisms

1.3.1.1 Metabolism and biokinetic of metal in organisms

1.3.2 Bioaccumult ion

1.3.2.1 Definition

1.3.2.2 Bioaccumulation factor (BAF)

1.3.2.3 Bioaccumulation of heavy metal in mollusks

1.3.3 Factors affecting bioaccumulation of heavy metal in mollusks

1.3.3.1 Geochemical factors

1.3.3.2 Biological factors

1.3.3.3 Mechanisms of bioaccumulation

1.4 BIOMONITORING

1.4.1 Biomonitoring

1.4.2 Bioindicator

1.4.3 Marine moluscs as biomonitors for heavy metals

CHAPTER 2. RESEARCH AREA

2.1 INTRODUCTION OF RESEARCH AREA

2.2 ENVIRONMENTAL STATE

2.2.1 Human pressure

2.2.2 Environmental quality

2.2.2.1 Water quality

2.2.2.2 Sediment quality

2.2.3 Biodiversity of bivalve molluscs in the bay of Nha Trang

2.3 SELECTION OF SAMPLING SITES

CHAPTER 3. RESEARCH METHODOLOGY

3.1. SAMPLING TIMES AND SAMPLING SITES

3.2. ANALYZING METHODS

3.2.1 Sediment samples

3.2.1.1 Method of collection sediment samples

3.2.1.2 Preparation and storage of sediment samples

3.2.1.3 Analyzing physico - chemical characteristic

3.2.1.4 Sediment digestion method

3.2.2 Mollusk samples

3.2.2.2 Preparation of tissue samples

3.2.2.3 Sample measurement

3.2.2.4 Digestion method of mollusks

3.2.3.1 Standard solutions

3.2.3.2 Lab control

3.2.3.3 Certified reference materials

3.2.3.4 Detection limit of the method

3.3 DATA ANALYSIS METHODS

3.3.1 Method assessment of heavy metal contamination in sediment

3.3.1.1 Metal assessment indices

3.3.1.2 Sediment Quality Guidelines (SQGs)

3.3.2 Evaluation of bioaccumulation

3.3.2.1 Calculation of metal indices

3.3.2.2 Assessment bioaccumulation

3.3.2.3 Bioaccumulation factor

3.3.3 Ecological risk analysis (ERA)

3.3.3.1 Potential ecological risk index (PERI)

3.3.3.2 Determination of Estimated daily intake (EDI)

3.3.3.3 The target hazard quotient (THQ)

3.3.3.4 The target cancer risk (TR)

3.3.3.5 Acceptable Tissue Levels for Humans

CHAPTER 4. RESULTS AND DISCUSSIONS

4.1 PHYSICOCHEMICAL CHARACTERISTICS OF SEDIMENT

4.1.1 Particles size of sediments

4.1.2 pH of sediment

4.1.3 Distribution of organic carbon in sediment

4.1.4 Bulk density

4.1.5 Moisture of sediment samples

4.1.6 Acid volatile sulfide (AVS)

4.2 METAL CONCENTRATIONS IN SEDIMENT SAMPLES

4.2.1 Ranges of heavy metal concentrations

4.2.3 Sediment Quality Guidelines (SQGs)

4.2.4 Interactions between metals

4.3 HEAVY METALS IN MOLLUSK TISSUES

4.3.1 Concentrations of heavy metals between shell and tissue

4.3.3 Contents of heavy metals in soft tissues

4.3.4 Metal pollution index

4.3.5 Compare with the limit MPL

4.3.6 Heavy metal concentration and biological parameters

4.3.6.1 Biometric parameters

4.3.6.2 Metals determination and condition index

4.4 EVALUATION OF BIOACCUMULATION

4.4.1 Comparison of BSAF in soft tissue and shell

4.4.2 Bioaccumulation of heavy metal in the mollusk tissues

4.5 CHOISE K. HIANTINA AS BIOINDICATEUR

4.5.1 Reasonal and locational variation

4.5.2 Metal/ shell weight indices (MSWI)

4.5.3 Bioaccumulation of heavy metal in clam K. Hiantina

4.6 RISK ASSESSMENT

4.6.1 Daily trace metal intake EDI

4.6.2 The target hazard quotient THQ

CHAPTER 5. CONCLUSION AND SUGGESTION

5.1 CONCLUSIONS

5.1.1 Heavy metal contaminations in sediment samples

5.1.2 Bioaccumulation of heavy metals in mollusks

5.1.3 Ecological risks

5.2 LIMITATIONS AND SUGGESTIONS

5.3 FURTHER RESEARCH

REFERENCES

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BIOACCUMULATION OF HEAVY METALS IN NHA TRANG BAY- KHANH HOA PROVINCE VIET NAM.