Heavy Metals In Aquatic Organisms Research Articles

Bioaccumulation and Health Risk Assessment of Heavy Metals in Labeo rohita and Mystus seenghala from Jhelum River, Punjab, Pakistan

The bioaccumulation of trace elements and heavy metals in aquatic organisms is a critical environmental concern due to its potential impact on ecosystem health and human safety. This study investigated the level of trace elements and heavy metals bioaccumulation in Labeo rohita and Mystus seenghala from the River Jhelum in the district Khushab, Punjab, Pakistan. The concentration of calcium, magnesium, iron, nickel, copper, arsenic, cadmium, zinc, chromium, manganese, cobalt, and lead in the gills, liver, and muscle tissues of these fish was measured using inductively coupled plasma-mass spectrometry. Then, the extent of contamination and its possible health risks were assayed. Our findings indicate significant variations in the elemental and metal concentrations among different organs and between species, reflecting their diverse feeding habits and habitats. The health risk assessment based on the estimated daily intake, estimated weekly intake, maximum permissible intake, target hazard quotient, hazard index or total target hazard quotient, health risk index, and target cancer risk revealed potential risks to human consumers of these fish. This study emphasizes the need for continuous monitoring, as new data and insights are crucial for understanding and mitigating these risks. Strict regulatory measures are also necessary to safeguard public health and preserve the ecosystem of Jhelum River.

Bioaccumulation of heavy metals in gills and muscles of selected fish species from Owerrinta section of Imo River

Bioaccumulation of heavy metals in aquatic organisms had been known to occur naturally. Over the years the levels of these accumulations keep increasing due to various human activities which make it detrimental to the life of aquatic organism and humans. The study assessed bioaccumulation of some heavy metals in the gills and muscles of some fish species. Fish samples were collected for a period of 4 months, identified and stored for further analysis. The following heavy metals: Zinc (Zn), Copper (Cu), Iron (Fe), Lead (Pb) and Cadnium (Cd) were assessed on the fish gills and muscles using standard procedure. Results showed that the fish species sampled (Clarias gariepinus, Tilapia zilli, Oreochromis niloticus, Alestes baremose and Pareutropius buffei) showed some levels of metal accumulation both in the gills and muscles. Levels of Zn in muscles of A. baremose, P. buffei, C. gariepinus, T. zilli and O. niloticus were 3.63±0.12, 1.45±0.26, 4.27±0.15, 4.03±1.42 and 2.00±0.15mg/kg respectively. The highest level of Zn (3.44±0.15mg/kg) in the gills was observed in T. zilli. Other results showed that P. buffei had the highest Pb concentrations (0.48±0.22mg/kg in muscle) and (0.17±2mg/kg in gills) while T. zilli had 2.24±0.54mg/kg and 1.46±0.65mg/l as the highest concentration of Fe in muscles and gills respectively. The levels of Zn, Cu, Fe and Pb recorded in the fish muscles where below the World Health Organization (WHO) and Food and Agricultural Organization (FAO) standards while Cadmium levels in all the fish sampled were above the recommended standard of 0.5mg/kg. This high cadmium accumulation in fish samples calls for concern considering the adverse effect it may cause if transferred to humans through fish consumption. There is therefore need to intensify efforts in mitigating some of the activities that amplify the levels of bioaccumulation of these metals in the aquatic environment towards a healthier environment.

Genotoxic potentials of some selected heavy metals exposure on Clarias gariepinus (Burchell, 1822) and Oreochromis niloticus (Linnaeus, 1758) using RAPD-PCR technique

Fish health and the aquatic ecosystem are strongly interwoven and interrelated. The aquatic ecosystem receives a range of anthropogenic chemicals which have toxicological or lethal health effects on the aquatic animals. The aim of this study was to determine the level of induced mutation and genomic stability of different sub-lethal doses (25%, 50% and 75% LC50) of heavy metal [Nickel (Ni), Mercury (Hg), Lead (Pb)and Zinc (Zn)] in Clarias gariepinus (Burchell, 1822) andOreochromis niloticus (Linnaeus, 1758) using RAPD-PCR technology over a period of 21 days. Four highly polymorphic RAPD markers were evaluated on isolated DNA from both heavy metal exposed fishes and control fishes after exposure. Observation of RAPD profiles in C. gariepinus revealed more damaging effect as sub lethal doses increased with zinc (a + b = 44 bands) mercury (a + b = 41 bands) nickel (a + b = 37 bands) lead (a + b = 35 bands) than with nickel (a + b = 37 bands) zinc (a + b = 34 bands) lead (a + b = 32 bands) mercury (a + b = 31 bands) for O. niloticus when compare to the control groups. Although, the genomic stability template decreased sub lethal heavy metal doses, higher stability was observed in O. niloticus (GTSPb = 26.32% GTSHg = 18.42% GTSZn = 10.53% GTSNi = 2.63%) than in C. gariepinus (GTSPb = 5.41% GTSNi = 0.0% GTSHg = -10.81% GTSZn = -18.92%). The results obtained showed differential variation in heavy metal induced genetic mutation and genomic stabilty in C. gariepinus and O. niloticus. These observable differences might be due to the physiological structure of the fish species evaluated. This study also confirms that RAPD–PCR technology is a useful tools in detecting the genotoxic effect of heavy metals in aquatic organisms but due to low reproducibility of RAPD results, it is recommended that this technology should be used along with other molecular techniques in fish genotoxicity studies.Keywords: Heavy metals, Induced, Genotoxicity, Fish, RAPD-PCR Technique

Assessing the Impact of a Hydropower Plant on Changes in the Properties of the Sediment of the Bystrzyca River in Poland

This study aimed to assess the impact of a hydropower plant (HP) on the Bystrzyca River (left tributary of the Odra River, Poland) on selected parameters of the bottom sediment within this hydrotechnical structure. The following parameters were examined as part of the analyses: particle size distribution, pH, electrical conductivity (EC), and concentrations of Cd, Cu, Cr, Ni, Pb and Zn. Field studies were carried out upstream and downstream of the HP and at reference points. In addition, the risk of heavy metals in aquatic organisms was assessed using an ecotoxicological method. Based on the Wilcoxon signed-rank test, it was found that the HP influenced all of the parameters tested, except pH. Comparing the points closest to and downstream of the HP, an increase in the average grain diameter of D50(on average by 750%), and a decrease in the concentrations of most heavy metals: Ni (271%), Zn (216%), Cu (163%), Cr (83.0%), and Cd (74.2%), was observed. The ecotoxicological classification of heavy metal concentrations in sediments indicates, in most cases, little or no impact on aquatic organisms; the values of Ni and Zn in some samples upstream of the HP are exceptions, where remediation using synthetic zeolites, metal accumulation plants, or by electrokinetic methods, is necessary. Fine-grained fractions dominate the clays and sandy clays upstream of the hydropower plants, while sands, sandy clay loams, or sandy clays are dominated downstream. Frequent occurrence of skeletal fractions (>2.0 mm) was observed downstream, i.e., an average of 23.30% in each sample compared to 1.82% upstream of the HP, which is mainly due to greater anthropogenic pressure, especially tourism. The dominance of fine-grained fractions upstream of the HPs favors the accumulation of metals due to the high sorption capacity of these fractions. When comparing the analyzed groups of points, the average pH values are arranged in the following sequence: upstream HP (U) > downstream HP (D) > reference points (R), while EC has opposite values (i.e., U < D < R). This study may support sustainable sediment management and may allow for the development of recommendations related to the rational management of HPs.

Human-induced sediment degradation of Burullus lagoon, Nile Delta, Egypt: Heavy metals pollution status and potential ecological risk

Heavy metals contamination level and their ecological risk of the Burullus lagoon were estimated using four cores and twelve surficial sediment samples. The distributions maps of Fe, Mn, Zn, Hg, Cu, and Pb indicate an increase toward drains areas, whereas Cd rises toward the Boughaz El-Burullus. The geoaccumulation index (Igeo) and contamination factor (CF) for heavy metal displayed the following order: Cd > Zn > Fe > Cu > Pb > Mn > Hg. The degree of contamination (Cd) indicates a considerable degree of contamination for 81.25% of the studied stations, and the pollution load index (PLI) suggested deterioration in 100% of sediments. Regarding the potential ecological risk (RI), the metals were arranged as: Cd > Hg > Cu > Pb > Zn, with considerable risk at the eastern part. According to sediment quality guidelines (SQGs), Zn concentrations suggest frequently adverse impacts on biota while Cu and Cd indicating an occasional adverse impact. Periodic monitoring of heavy metals in aquatic organisms is recommended to assess their toxic risk.

A review on the ecotoxicological effects of heavy metals on aquatic organisms-siftdesk

In recent years, with the rapid development of the global economy, heavy metals have been widely used in industrial production and daily life because of their unique properties. This, however, has simultaneously led to heavy metal pollution due to various reasons. After entering the aquatic environment, heavy metals are not easily decomposed by microorganisms and become toxic when they reach a certain concentration. Heavy metals can easily enter the liver and other vital organs of aquatic organisms, where they accumulate and severely affect the growth and reproduction of these organisms. They can also threaten human health through the food chain. Therefore, heavy metal pollution has potential ecological and health risks. This paper summarizes the sources and hazards of heavy metals in water, the pattern of enrichment of heavy metals in aquatic organisms, the toxic effects of heavy metals on aquatic organisms, the tolerance mechanism of aquatic animals to heavy metals, and the factors affecting the toxicity of heavy metals. The authors put forward three feasible suggestions for the study of ecotoxicological effects of heavy metals on aquatic organisms in the future. The results of this study have considerable significance for aquaculture and environmental management and even for humans.

Heavy Metals in Marsh Clam (Polymesoda expansa) as Bioindicators for Pollution in Industrial and Sand Mining Area of Kelantan River Basin, Malaysia

Industrial and sand mining activities have severely degraded the water quality of the Kelantan River, as well as the river ecosystem. However, there have been inadequate studies on the effect of industrial and sand mining on organisms in the Kelantan River. Therefore, this study assessed the concentrations of Pb, Cd, Zn and Cu in the bivalves of genus (Polymesoda expansa) marsh clams from the Kelantan River tributaries, namely the Geting River and the Semarak River, which are located near to an industrial and a sand mining area, respectively. More than 50 marsh clams were collected at these sites. Heavy metals in marsh clams were extracted using aqua regia methods and analyzed using a Flame Atomic Absorption Spectrometer (FAAS). The mean concentrations of Pb, Cd, Zn and Cu at the Semarak River were 4.61, 2.16, 194 and 6.20 mg/kg, respectively. Accordingly, the concentrations at the Geting River were 4.43, 2.50, 196 and 7.90 mg/kg, respectively. The pattern of metal concentrations within the whole tissue of marsh clams from the Geting River and the Semarak River were in the following order: Zn > Cu > Pb > Cd (concentration in mg/kg). The mean concentration of selected metals (Zn, Cd, Pb) in the studied samples exceeded the permissible limit set by the Malaysia Food Safety and Food Regulation 1985, the Food and Agricultural Organization, the World Health Organization, the Ministry of Health Thailand, and the Food and Drug Administration of United States (USFDA). Therefore, continuous monitoring of these bioindicators is essential to minimize the increasing health risk for aquatic life, as well as in food sources for human consumption, in the Kelantan River Basin. HIGHLIGHTS Heavy metals in Marsh Clam (Polymesoda expansa) tissues shows higher concentration in the small and medium sizes compare to big size The concentration of heavy metals (Zn, Cd and Pb) in Marsh Clam (Polymesoda expansa) tissues have exceeded the permissible limit set by Food and Drug Administration of United States (USFDA) and Malaysia Food Safety and Food Regulation Monitoring of heavy metals in aquatic organisms especially near to industrial and sand mining areas should be conducted regularly to reduce the risk to human health GRAPHICAL ABSTRACT

Occurrence, potential health risk of heavy metals in aquatic organisms from Laizhou Bay, China

Heavy metal pollution is a serious environmental problem. Up to date, research regarding distribution, accumulation and potential risk assessment of metals in aquatic organisms in Laizhou Bay, China is scarce. This study aims to investigate metals in aquatic organisms in this region. The results demonstrated that great variability of metals content occurred among species and sampling locations. Fe was the most abundant metal, followed by Zn, Mn, Cu, Ni, Cr, Cd and Pb. Overall, shellfish and crab displayed high enrichment ability compared with fish and shrimp. There was no significant correlation between metals and samples weight, δ13C and δ15N values. Principal component analysis (PCA) indicated that metals in samples were mainly derived from anthropogenic activities. Health risk of metals was evaluated on the basis of estimated daily intake (EDI) and target hazard quotient (THQ) values. The results indicated that metals in studied seafood had no significant risks for ordinary consumers.

Trophic transfer of Cu, Zn, Cd, and Cr, and biomarker response for food webs in Taihu Lake, China.

Water, sediments, and aquatic organism samples were collected from Taihu Lake in China. Four types of typical heavy metal (Cu, Zn, Cd, and Cr) were analyzed to evaluate their concentrations and trophic transfer in food webs. The stable nitrogen isotope δ15N was used to investigate the trophic interactions. The concentrations of Cd and Zn in the sediments of Taihu Lake exceeded Level I of the China National Quality Standards for Soil. Zn accumulation was identified to increase with the trophic level. The bioconcentration of the four heavy metals in aquatic organisms was evident, with the invertebrates showing the highest bioconcentration factor in the food webs. Several biomarkers were investigated, including metallothionein (MT), malondialdehyde, and Na+/K+-adenosine triphosphatase activity. A positive correlation relationship was found between the MT content and heavy metal accumulation in organism tissues.

Heavy metals in aquatic organisms of different trophic levels and their potential human health risk in Bohai Bay, China.

Fourteen aquatic organism samples were collected from Bohai Bay, and concentrations of five heavy metals were measured to evaluate the pollution levels in aquatic organisms and the potential risk to human health. The concentrations of Zn and Cu were much higher than those of Cd, Cr, and Pb in all the organisms. In general, the heavy metal concentration levels were in the order phytoplankton < zooplankton < fish < shrimp < shellfish. Heavy metal concentrations in higher trophic-level aquatic organisms in Bohai Bay were compared to those in the organisms from other worldwide coastal waters. The concentration levels of most heavy metals were higher than the 75th percentile, except that Pb concentration was between the 25th and 50th percentiles. The calculated bioconcentration factors (BCF) of Cr, Cu, and Pb for phytoplankton were less than 100, indicating no accumulation in primary producers. The bioaccumulation factor (BAF) of Pb for zooplankton was the highest, indicating significant Pb accumulation in zooplankton. For higher trophic-level aquatic organisms, the order of BAF values was fish < shrimp < shellfish for most metals except for Pb. The human health risk assessment suggests that strict abatement measures of heavy metals must be taken to decrease the health risk caused by consuming aquatic products.

Distribution and bioaccumulation of heavy metals in food web of Nansi Lake, China

The concentrations of heavy metals (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were investigated in water, sediment and biota (aquatic plant, fish and shrimp) of Nansi Lake by an inductively coupled plasma-atomic emission spectrometry. The lower concentrations of heavy metals in lake water and the higher concentrations of heavy metals in sediment implied that there were low-level, persistent inputs of heavy metals in the Nansi Lake. The concentrations of Cr and Fe in aquatic plants exceeded their corresponding toxic concentrations. The correlations among the concentrations of heavy metals in water, sediment, aquatic plants and animals were lower. The factor analysis and the correlation analysis of different heavy metals in water, sediment and aquatic biota samples showed that most heavy metals had the same source except As. This finding implied that As was of different source compared to the other heavy metals in Nansi Lake. The comparison of heavy metals in different samples from upper lake and lower lake showed that the contamination of heavy metals in upper lake was more serious than that in lower lake. The intensive coal mining and more coal thermal plants were an important reason leading to contamination of heavy metals in Nansi Lake. The heavy metals in aquatic organisms were not accumulated along food web except As and Zn. There was a positive correlation between the accumulation of As and Zn and food web based on bioaccumulation factors value in Nansi Lake. Risk assessment of heavy metals in water, sediment and animals indicated that the water environment of Nansi Lake is safe at present. However, people should pay more attention to the intake of As and Zn.

Phragmites australis as a heavy metal bioindicator in the Anzali wetland of Iran

In this study, levels of Fe, Cu, Cd, and Ni in the sediments and organs of Phragmites australis from three different sites in the Anzali wetland were measured. Heavy metal accumulation was higher in the roots of P. australis than in the shoots and leaves. There was a significant correlation between metal concentrations in roots and sediment. This result showed that the root of P. australis can be used as bioindicator for Fe, Cu, Cd, and Ni. Metal levels in sediment were recorded higher than the interim sediment quality guideline values, and the Cd and Ni content in P. australis were higher than the unpolluted levels in plants. This indicates the necessity for continuous monitoring of the metal levels and also evaluating the hazard risk of heavy metals in aquatic organisms in the Anzali wetland.

Heavy metals induce oxidative stress and trigger oxidative stress-mediated heat shock protein (hsp) modulation in the intertidal copepod Tigriopus japonicus

Heat shock proteins (hsps) are induced by a wide range of environmental stressors including heavy metals in aquatic organisms. However, the effect of heavy metals on zooplankton at the molecular level remains still unclear. In this study, we measured the intracellular reactive oxygen species (ROS) level and the antioxidant enzyme activities for 96h after exposure to five heavy metals: arsenic (As), cadmium (Cd), copper (Cu), silver (Ag), and zinc (Zn) in the intertidal copepod Tigriopus japonicus. Activities of the antioxidant enzymes were highly elevated in metal-exposed copepods, indicating that heavy metals can induce oxidative stress by generating ROS, and stimulate the involvement of antioxidant enzymes as cellular defense mechanisms. Subsequently, transcriptional changes in hsp gene families were further investigated in the metal-exposed groups for 96h. The ROS level and glutathione (GSH) content were significantly increased in Ag-, As-, and Cu-exposed copepods, while they were only slightly elevated in Cd- and Zn-exposed groups. Based on the numbers of significantly modulated hsp genes and their expression levels for 96h, we measured the effect of heavy metals to stress genes of T. japonicus in the following order: Cu>Zn>Ag>As>Cd, implying that Cu acts as a stronger oxidative stress inducer than other heavy metals. Of them, the expression of hsp20 and hsp70 genes was substantially modulated by exposure to heavy metals, indicating that these genes would provide a sensitive molecular biomarker for aquatic monitoring of heavy metal pollution.

Heavy metals concentration in oyster Crassostrea sp. HZ, sediment and sea water, Musa estuary

Heavy metals are permanent pollutants that are able to accumulate in the tissues of marine organisms. Toxicity and bioaccumulation of heavy metals in aquatic organisms have been considered as a critical problem. New species oyster Crassostrea sp.HZ, that live near petrochemical complex in the Musa estuary, especially may be exposed to considerable amounts of heavy metals from surrounded environment. The primary goal of this study investigates the concentration of Cd, Cu, Zn and Pb in recently reported oyster Crassostrea sp.HZ and its habitat in Musa estuary. Oyster, sediment and sea water samples were obtained from six selected stations. The soft tissue of oysters was separated. All of the samples were acid digested and their heavy metals level were analyzed using atomic absorption spectrometer. The concentration of Cd, Cu, Zn and Pb in soft tissues ranged 12.21-17.5, 207.2-403.52, 90.43-104.12 and 0.07-0.95 (µg/g), respectively. The concentrations of the same metals in sediment were 0.15-0.85, 1.99-141.42, 60.42-122.1 and 2- 7.2 (µg/g) respectively. The concentrations of heavy metal in sea water was ND- 0.7, ND-3.1, 9.12- 23.03 and 0.15-2.27 (µg/g), respectively. The result showed that the level of heavy metals in soft tissue of C. sp.HZ was higher than general standard. * Corresponding Author: A. Safahieh  a.safahieh@kmsu.ac.ir

Distribution and bioaccumulation of heavy metals in aquatic organisms of different trophic levels and potential health risk assessment from Taihu lake, China

Aquatic organisms of different trophic levels were taken from Taihu lake. Heavy metals (Cu, Zn, Cr, Ni, Cd, Pb) were measured in phytoplankton, zooplankton, in two species of zoobenthos, and in eight fish species, as well as in the water column and bottom sediments. Results showed that the concentration of Cu and Zn for all organisms was much higher than for other metals, and Cd was the lowest in all species. Generally, heavy metal concentrations in phytoplankton were higher than in zooplankton. In zoobenthos, the concentration in Bellamya sp.(human edible snail) was higher than that in Corbiculidae (bivalve). Metal concentrations had no significant difference between fish species but tended to be higher in predator fish such as Coilia ectenes and Erythroculter ilishaeformis than in herbivorous fish. The level of measured metals in Taihu fish was moderate-low compared with that of fresh water fishes from international results. Spatially, metal concentrations in organisms were higher in the north and west Taihu lake but lower in south and east lake and this appears to be related to river inputs that are heavily influenced by anthropogenic activities. The bio-concentration factor (BCF) for all aquatic organisms in the food chain indicated that it was generally highest in planktons, followed by zoobenthos, and lowest in fish. Health risk assessment and comparison with national and international standards showed that consumption of aquatic products from the lake was generally safe but fishermen were a higher risk group especially through dietary intake of Bellamya sp.

Temporal and spatial trends in heavy metal concentrations in the marine mussel Mytilus edulis from the Western Scheldt estuary (The Netherlands)

Since the first North Sea Conference (1984, Bremen), all countries bordering the North Sea made commitments to reduce discharge of hazardous substances into the North Sea. From Belgium and The Netherlands, large reductions (upto 90) in heavy metal emissions from land-based sources have been reported between 1985 and 2000. Recently, some studies in the Western Scheldt estuary (WS) have shown that total metal concentration in the water, sediments and suspended particles have decreased compared to levels in the 70s. However, data on aquatic organisms is still very limited and it is therefore difficult to confirm whether the reductions in pollution input and generally improving water quality in the WS have a corresponding impact on the levels of heavy metals in aquatic organisms. The current study measured metal concentrations in the soft tissues of mussels, Mytilus edulis (known to be good indicators of environmental metal pollution) during the period 1996–2002. Spatial (salinity and pollution gradients), temporal and seasonal variations were also studied. Results showed a down-stream decreasing trend for the metals studied (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) during all sampling campaigns. There was also a significant seasonal effect on tissue metal concentrations, with a peak observed around spring in both WS and the nearby less polluted Eastern Scheldt (ES). On temporal trends, a clear drop of metals in mussels was observed in the early 80s coinciding with the start of the efforts to reduce chemical pollution input into the North Sea. Since those early reductions, metal concentrations in mussels generally remained unchanged upto mid 90s. However, in recent times metal concentration in mussels have increased significantly, for example Cd in 2002 was almost 10 times the values in 1983 and similar to levels seen during the peak in the 70s. Other metals also increased in the 90s also reaching levels seen in the 70s. As there is no indication of recent increase in metal input into the estuary, we suggest that increased metal concentrations observed in mussels in recent years especially in the upper estuary are most likely a result of changes in physical and chemical speciation and metal bioavailability. Such changes may be caused by changes in some water quality parameters in the estuary (i.e. increased dissolved oxygen, concentration of organic matter), resulting in conditions that favour releases of sediment-bound metals into the water column. The relationship between metal content and season showed very similar annual profiles in the polluted WS and less polluted ES. Thus, seasonal variations in metal concentrations appear to be largely controlled by biological processes, while total body burdens are dependent on environmental levels and bioavailability.

Long term studies on heavy metals in aquatic organisms from the River Odra mouth area

Contents of Hg, Cd, Pb, Cu, and Zn were determined within 1984-1988 in plankton, zebra mussel (Dreissena polymorpha), roach (Rutilus rutilus), bream (Abramis brama), and pikeperch (Lucioperca lucioperca) from different parts of the Rira Odra mouth area. Mercury was determined with CV AAS and assays of the remaining metals were carried out with flame AAS. In terms of their heavy metal contents, the organisms studied can be ordered in the following way: plankton &gt; mussel &gt; fish. A downstream decrease in heavy metal content was observed in the plankton. Mercury contents in fish decreased downstream, too. Mercury, copper, and zinc contents in fish were species-dependent, the highest contents being recorded in roach. Heavy metal dynamics in the plankton over the 5 years of study seems to evidence a gradual reduction in mercury and zinc and an increase in cadmium and lead. However, the changes were not reflected in contents of the metals in fish. No definite trend could be revealed in Hg, Cd, Pb, Cu, and Zn dynamics in roach, bream, and pikeperch, nor a clear-cut pattern could be found with respect to the author&prime;s results published earlier.

Genetic adaptation to heavy metals in aquatic organisms: A review

Natural populations in polluted areas are possibly subjected to selective pressures for an increased resistance to toxicants. This can result in the evolution of resistance, which may have important implications for decisions regarding safe ambient toxicant levels. By reviewing the evolution of resistance to heavy metals in aquatic organisms, we aimed to determine if all populations negatively affected by toxicants do adapt to them. If the published literature accurately represents the situation in polluted areas (i.e. negative results having an equal chance of being published), it can be concluded that most, but not all, populations in polluted areas do have an increased resistance. But it can usually not be determined if such an increased resistance has a genetic basis. There is less evidence for the evolution of resistance in metazoans (especially fish) than in micro-organisms. Additional information strongly indicates that many populations fail to survive in polluted environments. It thus seems dangerous to relax water quality criteria on the assumption that all populations in polluted environments will evolve an increased resistance. But the fact that the evolution of resistance to environmental pollutants does seem to occur in some populations in polluted environments warrants taking that possibility into consideration when evaluating the results of bioassays and monitoring programs.

Decrease in cadmium concentration in a Cd-contaminated fish by short-term exposure to EDTA.

Heavy metals, especially cadmium in aqueous environments, are accumulated in aquatic plants and animals. There are many reports which refer to the toxicity and accumulation of heavy metals in aquatic organisms. Experiments on the elimination in fish in which heavy metals have accumulated, and have led to the postulate that the protein of the fish combine with metals relatively loosely. Accordingly, the present experiment studied the effects of short periods of fresh-water and EDTA treatment in removing heavy metals from Cd-contaminated fish.

主要貝類の生長度と重金属濃度との関係

It is important to clarify the concentration of heavy metals in aquatic organisms under normal condition in order to evaluate heavy metal pollution in environmental sea water from the change of heavy metal contents in the organisms. For this purpose the normal levels of a few heavy metals in the cultured scallops, oysters and abalones were determined from the relationship between the body weight and the concentration of heavy metals. The results obtained showed that the concentration of each heavy metal in the soft parts increased with the increase of body weight. The relationship was especially significant in the mid-gut gland including stomach of scallops. These results suggest the existance of a characteristic pattern of heavy metal accumlation for each species, and the pattern observed in the mid-gut gland of scallops together with that in the soft parts may be available as a biological index for the evaluation of heavy metal pollution in environmental sea water.