Physicochemical parameters in relation to Physicochemical parameters in relation to pollutionpollution

What is pollution??

Pollution is defined as the direct or indirect introduction as a result of human activity, of substances, vibrations, heat or noise into the air, water or land which may be harmful to human health or the quality of the environment, result in damage to material property, or impair or interfere with amenities and other legitimate uses of the environment (European Community Water Policy 1996).

What is eutrophication

Eutrophication is caused by pollution of water bodies with nutrients. The high level of nutrients can lead to an excessive growth of algae at the expense of the natural plant and animal community. The source of nutrients may be a variety of point and diffuse sources, including farming, urban waste water and atmospheric deposition.

How can pollution be harmful to human health or to the environment?

By affecting the equilibrium among several vital to living organisms physicochemical parameters such as:

Oxygen and Carbon Dioxide

Phosphorus

Nitrogen

Heavy metals

Discharge, Salinity, Conductivity, TDS,TSS

Important factors affecting river ecosystems:

Discharge is the first factor that controls water chemistry, mainly through dilution.

Discharge is also closely related to the transport of suspended sediment in rivers. Without continuous discharge measurement, fluxes (transport) of sediment and chemicals in rivers cannot be calculated.

A plot of discharge through time is called a hydrograph. The shape of the hydrograph is linked to river size, river regime, and the effects of lakes or groundwater.

Long-term monthly discharges characterize the regime of a river.

Discharge

Oxygen and Carbon DioxideOxygen and Carbon Dioxide

Why is oxygen and carbon dioxide vital to living organisms?They both participate in respiration and photosynthesis

Oxygen participates in many important chemical and biological reactions. It is continually consumed in respiration by plants (autotrophic organisms) and animals (heterotrophic organisms ) and is produced by photosynthesis only when sufficient light and nutrients (P/N) are available.

Ecologically, oxygen is limiting factor for life when it is in low supply. Although abundant in the atmospheric air, its concentration in water (lakes and rivers) is limited.

Very cold water contains less than 5% of the oxygen contained in a similar volume of air. The amount rapidly decreases as the water temperature increases.

Why is that?

Water contains little oxygen due to the relatively low partial pressure of oxygen in the atmosphere and its low solubility.

The lack of oxygen in water (rivers and lakes) relative to air means that it is easily depleted by respiration and decomposition unless continually replenished by air.The amount of dissolved oxygen in an aquatic ecosystem depends on several factors, such as the temperature, the alkalinity, the atmospheric pressure. Augmentation of the values of these parameters causes reduction of the dissolved oxygen. The dissolved oxygen concentration also depends upon the organic load of the water and the photosynthetic organisms.

The short- and long term variations in dissolved oxygen of lakes and rivers give a good measure of their trophic state (oligotrophic and eutrophic). In oligotrophic systems the variation from saturation is insignificant while in eutrophic is significant.Organic matter either from natural sources or from domestic and industrial sewage may result in serious depletion of dissolved oxygen. This is achieved via the augmentation of the number of micro-organisms which use the organic matter as a substrate for decomposition lowering in this way the available oxygen.

When this occurs for a long period of time, most aquatic organisms perish or are replaced by a few specialized organisms tolerant to low oxygen.

Carbon dioxide (CO2) is a product of respiration by both plants and animals, provides the major carbon source for photosynthesis and in most ways shows an inverse relationship to oxygen. It enters freshwater either with diffusion from air or with all the carbonate or bicarbonate compounds, which originate from dissolution of sedimentary rocks, or with respiration.

Its solubility in water is 200 times that of oxygen. When dissolved in water, produces carbonic acid (H2CO3), which dissociates into various fractions (HCO3-, CO3-) depending upon the hydrogen-ion concentration (pH).

The precise levels of each component phase vary both with the temperature and the ionic strength of the river or the lake. The free CO2 necessary to maintain HCO3- in solution is called equilibrium CO2. In highly productive downland rivers or in lakes, where luxuriant growths of macrophytes and microbenthic algae can cause shifts in CO2 concentrations, the carbonate dioxide tends to deviate from atmospheric equilibrium Most plants can utilize only the CO2 for photosynthesis, which can be supplied by diffusion from the air near the surface or from HCO3-, in deeper waters.

The limiting stage in the solution of carbon dioxide is the hydration-dehydration of carbon dioxide to carbonic acid. This reaction may limit photosynthesis during calm days in high productive waters, where plant demand is greater than free carbon dioxide levels.

Lack of CO2

Additionally, in the case where there is a substantial organic load in a large river, diffusion of CO2 out of river or absorption via photosynthesis can be less than its amount produced via respiration of the microorganisms.

This results in very high partial pressure of the CO2 in the water, which can be even 20 times that of the atmospheric value.

Excess of CO2

In highly productive waters (slow moving rivers with abundant macrophytes) oxygen is elevated and carbon dioxide is reduced during daytime, while the reverse occurs at night. Such changes indicate strong biological control over the concentrations of these gases. In case of absence of such control, oxygen will exhibit the opposite pattern.

There are seasonal and dial variations of both oxygen and carbon dioxide

b) Colloidal suspensions of calcium carbonate produce a lake whitening

a) Benches of limestone or marl are deposited around the edges of the lakes

When the demand for photosynthesis is high in some lakes, precipitation of calcium carbonate occurs in hard waters resulting in two phenomena:

This is caused because there is not enough of the carbonic acid to dissolve the calcium carbonate since it is soon lost after the CO2 uptake by plants.

Precipitation of CaCO3

According to the E.U. Directive concerning oxygen levels in drinkable water, the saturation should be no less than 75%.

The amount of oxygen and carbon dioxide provides a convenient measure of organic production, decomposition and organic enrichment of the water.

Oxygen concentrations can be measured either with the Winkler method, which is a simple oxidation-reduction method, or with an oxygen sensitive membrane probe.

Methodology

Biochemical Oxygen Demand (BOD 5) is also measured in order to evaluate the organic load. BOD is an empirical measurement and focuses on the oxygen required by the microorganisms to decompose the organic load. If the organic load is increased, then the consumed oxygen for its decomposition will also be increased. In rivers, BOD>2,5 mg/l indicate organic enrichment.

Since one of the sources of CO2 in freshwaters is the bicarbonate and carbonate compounds, high concentrations of CO2 can be reflected in the alkalinity and usually are indicative of fertile waters.

Total inorganic carbon is easily measured by titration. CO2 in the water usually does not exceed 10 ml/l. The method used for the determination of its concentration is titrimetric and it is based on its reaction with Na2CO3 or NaOH and the formation of NaHCO3.

Carbon dioxide is less frequently measured

Alkalinity refers to the quantity and kinds of compounds which collectively shift the pH into the alkaline range. Usually it is expressed in mg/l of CaCO3 and its measurement is based on a titrimetric method. Attention: hardness focuses on the measurement of calcium and magnesium salts which are not only carbonate or bicarbonate.

Alkalinity

Within the usual range of pH values of rivers, from 6.4 to 8.3, the HCO3

- is the most common carbonate species found in natural waters.

Concentration of these ions is strongly related to Ca++ concentrations which reflect the weathering of limestones (CaCO3) and dolomites (CaCO3, MgCO3). When these rocks are present the risk of acidification is low.

The distribution of bicarbonate follows the same pattern as that of the Ca++ ion . In streams (<100 km2), HCO3

- concentrations naturally range from 0 to 350 mg L-1, while in major rivers (100 000 km2), the concentration ranges from 10 to 170 mg L-1 .

Alkalinity is closely related to the kinds of aquatic life that will survive in water.

SALINITY

The salt content (salinity) of a water body is one of the main factors determining what organisms will be found there. The density of water is related to the amount of salt dissolved in it.

A hydrometer is used to measure density. The salinity of the water is determined from the density and water temperature.

Note: This measurement is for salt and brackish waters only. For fresh waters measure conductivity instead.

The sea is salty; it has a much higher dissolved solids content than do fresh waters. Salinity is a measure of that saltiness and is expressed in parts impurity per thousand parts water.

The average salinity of the Earth's oceans is 35 parts per thousand, usually written as 35 oo/o.

Sodium and chloride, the components of common table salt (NaCl), contribute the most to the salinity. Since the proportion of chloride in sea water changes little from place to place we can also measure the chloride content, referred to as chlorinity, to estimate the total salinity.

In bays and estuaries we can find a wide range of salinity values, since these are the regions where freshwater and sea water mix. The salinity of these brackish waters is between that of freshwater, which averages 0.5oo/o, and sea water.

Every continent on Earth also has inland lakes that are saline. Some of the more prominent examples are the Caspian Sea in Central Asia, the Great Salt Lake in North America, and several lakes in the Great Rift Valley of East Africa. Some of these are even more saline than sea water.

Waters acquire salinity because rivers carry salts that originated from the weathering, or dissolving, of continental rocks. When water evaporates the salts stay behind, resulting in a buildup of dissolved material. At some point the water becomes saturated with solids, they precipitate out as solids, and the settle out of the water. Whereas the ocean's salinity changes slowly, over many millennia, the salinity of inland waters can change more quickly when rainfall or snowmelt patterns change.

The salt content of a water body is one of the main factors determining what organisms will be found there. Thus fresh waters and saline waters are inhabited by quite different organisms. Plants and animals that live in or use freshwater generally have a salt content inside their cells that is greater than the water they inhabit or use. They tend to give off salts as waste products. Saltwater plants and animals have a salt content equal to or less than the salinity of the surrounding water, and thus have different mechanisms for maintaining their salt balance. In brackish waters we find plants and animals that can tolerate changes in salinity.

Special Considerations for Brackish and Salt Water Sites

For the salinity protocols, you will need to know the times of high and low tide at a location as close as possible to your Hydrology Study Site. You will need to obtain the latitude and longitude of this location. If you can reach this location, the latitude and longitude can be measured using a GPS receiver and following the GPS protocol.

Acidification

The natural acidity of rain water is increased by the presence of sulphur dioxide (SO2) and nitrogen oxides (NOX) which are atmospheric pollutants originating mainly from fossil fuel combustion. These compounds are likely to be carried by winds over long distances from urban, mining, thermo-electric power plants and industrial emission sources.

During rainfall the acidic pollutants are washed out as sulphuric and nitric acids over vast areas and may affect pristine areas located hundreds or thousands of kilometres away from pollutant sources. Acidified waters are characterized by a major decrease in biological density and diversity.

Regional areas at risk from acid rain have been estimated by combining

both the source areas (use of sulphur-bearing coal, major cities, oil refineries, various industries)

and the occurrence of sensitive soils found in wet and humid regions. Most crystalline shields and non-carbonated sedimentary rocks can be considered as being sensitive to acid precipitation.

Conductivity of a water sample is a measure of its ability to carry an electric current. The more impurities (total dissolved solids) in water, the greater its electrical conductivity.

By measuring the conductivity of a water sample, the amount of total dissolved solids in the sample can be determined. To convert the electrical conductivity (microSiemens/cm) of a water sample to the concentration of total dissolved solids (ppm) in the sample, the conductivity must be multiplied by a factor of between 0.54 and 0.96 for natural waters. The value of this factor depends upon the type of dissolved solids. A widely accepted value to use when you are not determining the type of dissolved solids is 0.67.

TDS (ppm) = Conductivity (microSiemens/cm) x 0.67

CONDUCTIVITY

TOTAL DISSOLVED SOLIDS

(TDS) is a measure of the total amount of major ions (plus Silica - SiO2) in water. TDS are naturally highly variable in surface waters and there is no global reference value that can be used to assess a contamination level.

Dissolved salt content is regulated by the weathering of a few key minerals (halite and gypsum , carbonates and silicates, in decreasing order of solubility); therefore, Total Dissolved Solids (TDS) and ionic contents are linked to rock types. Soluble minerals are not found in metamorphic rock shields nor in volcanic rocks where silicates are more weathered. Hence waters tend to be low in TDS. TDS can, however, increase where hydrothermal groundwater inputs occur.

Total dissolved solids (TDS) concentrations are generally inversely proportional to river discharge (Q). This relationship is the result of the mixing of more mineralized groundwaters that dominate during baseflow, with more dilute surface runoff waters. This inverse relationship can been seen when seasonal TDS variation is plotted with corresponding discharges.

Relative variations can be quite high: from 30% for rivers with low TDS levels (Sagami, Tennessee) to 200% or even 400% for more saline rivers (Ebro, Murray). TDS can rise proportionately with flow (Q) in arid regions where leaching of salt deposits can occur during the rising stage of the flood.

SALTS AND SALINIZATION OF SURFACE WATERS

Salts are made up of the combination of the chemicals: Sodium (Na+), Potassium (K+), Calcium (Ca++), Magnesium (Mg++), Chloride (Cl-), Sulphate (SO4--), and Bicarbonate (HCO3-). Ions that are positively charged are called cations and those that are negatively charged are called anions . The cations (Ca++, Mg++, Na+, K+) and anions (Cl-, SO4--, HCO3-) are collectively known as major ions.

Concentrations of these major ions are basic descriptors of water quality on which many criteria for water use are based (such as drinking water, agriculture and industrial use).

Calcium, Magnesium and Potassium

Calcium, the most common cation found in surface waters, is mainly a function of geology especially when carbonate or gypsum deposits are present.

Concentrations of magnesium are not strongly influenced by anthropogenic activities and therefore magnesium is not used as an indicator of pollution stress.

In comparison with other continents, European rivers have the highest concentration levels of Ca++. These continental differences are not caused by anthropogenic impacts but by geological influences. At the global scale, natural Ca++ levels range from 0.06 to 210 mg L-1 in streams (<100 km2) and from 2 to 50 mg L-1 in major rivers (100 000 km2); .

Potassium-bearing minerals, mostly feldspar and mica, are abundant but poorly soluble. The natural potassium concentrations in rivers are very low . Even though potassium is affected by fertilizer use, it never reaches levels of concern for water quality. The highest K+ concentrations in these selected European watersheds are found downstream from major mining districts (potash and salt mines) on the Rhine, Weser and Elbe rivers, where concentrations may exceed the 12 mg L-1 guideline for drinking water.

Sodium and Chloride

In most waters sodium and chloride are tightly linked. They both originate from natural weathering of rock and from atmospheric transport of oceanic inputs and from a wide variety of anthropogenic sources. The WHO drinking water guideline for Cl- is 200 mg L-1.

The anthropogenic sources of sodium and chloride are so pervasive that concentrations of sodium and chloride have risen by a factor of 10 to 20 in many rivers.

Since 1889 there has been a five-fold increase in Cl- concentrations at the water intake (Ivry) for the City of Paris .

The background concentration is estimated to be about 5 mg L-1 and originates from marine aerosols. The increases in Cl- concentrations result from anthropogenic activities occurring upstream from this station. Present Cl- concentrations are well below the WHO standard for drinking water (200 mg L-1).

The Rhine River suffers from two major salt sources -- the Alsace potash mines and the Lorraine salt mines, both located in France. The brine from these sites is discharged to the Rhine downstream of Basel and to the Mosel River, respectively. The Alsace source (15 000 tonnes NaCl/day) represents 30 % of the Cl- flux measured at Lobith at the German/Netherlands borders. Other contributions are mostly urban and industrial from the Ruhr area. Since the opening of potash mines, 100 years ago, Cl- levels and fluxes have increased by a factor of 15 to 20. The WHO standard for drinking water has been exceeded, as well as the guideline for greenhouse watering, a very important activity in the Netherlands.

•In industrialized parts of the world chlorine products are some of the most common chemicals used in a wide range of industrial processes and for treatment of drinking water.

•In arid and semi-arid areas of the world evapotranspiration leads to an increase in the salt content (salinization) of surface waters and to an increase in the sodium and calcium concentrations. The ratio of sodium to calcium is a key descriptor in water for irrigation.

Sulphate

The sulfate ion (SO4--) is highly variable in surface waters where it is linked to sulphur-bearing minerals. Sulphate has greatly increased in some North American rivers (such as St Lawrence, Mississippi) over the last 100 years resulting from increased industrial and agricultural activities .

When sulphur-bearing minerals are more abundant as in the Great Plains shales, SO4-- levels may exceed the 400 mg L-1 WHO guideline for drinking water.

In comparison, even though natural background levels of SO4-- in the Volga river are among the highest found for large rivers, SO4-- has increased from 50 to 60 mg L-1 since the 1950's. This is due to large-scale human activities, including mining, and oil exploration.

SUSPENDED SOLIDS AND WATER QUALITY

Total Suspended Solids (TSS) is comprised of organic and mineral particles that are transported in the water column. TSS is closely linked to land erosion and to erosion of river channels.

TSS can be extremely variable, ranging from less than 5 mg L-1 to extremes of 30,000 mg L-1 in some rivers. TSS is not only an important measure of erosion in river basins, it is also closely linked to the transport through river systems of nutrients (especially phosphorus), metals, and a wide range of industrial and agricultural chemicals.

In most rivers TSS is primarily composed of small mineral particles. TSS is often referred to as turbidity and is frequently poorly measured. Higher TSS (1000 mg L-1 may greatly affect water use by limiting light penetration and can limit reservoir life through sedimentation of suspended matter. TSS-levels and fluctuations influence aquatic life, from phytoplancton to fish.

TSS, especially when the individual particles are small (< 63µm), carry many substances that are harmful or toxic. As a result, suspended particles are often the primary carrier of these pollutants to lakes and to coastal zones of oceans where they settle.

In rivers, lakes and coastal zones these fine particles are a food source for filter feeders which are part of the food chain, leading to biomagnification of chemical pollutants in fish and, ultimately, in man.

In deep lakes, however, deposition of fine particles effectively removes pollutants from the overlying water by burying them in the bottom sediments of the lake. In river basins where erosion is a serious problem, suspended solids can blanket the river bed, thereby destroying fish habitat.

Time series of instantaneous TSS loads (kg s-1) provides useful information about the physical behaviour of rivers. Because total suspended solids concentration is partly a function of discharge, TSS load increases as discharge increases. In many rivers, the amount of sediment (solids) in transport (the load) can vary over three or more orders of magnitude during the year. The Huag He in China is an example of this relationship.

Typical of most rivers, TSS peak loads occur only during short periods (days), and often are not identified when rivers are sampled on a bi-monthly or monthly basis. This can lead to major errors in calculating sediment transport.

Carbon dioxide, carbonic acid and bicarbonate and carbonate ions form en effective system that resists changes in pH.

Nutrients (forms of P and N)Nutrients (forms of P and N)Nutrients are inorganic materials for life, the supply of which is potentially limiting to biological activity. They occur in various chemical forms of ions or dissolved gases in solution in water.

NitrogenDissolved Inorganic Nitrogen (DIN)NO3- NO2- NH4+Dissolved organic Nitrogen (DON)Particulate Organic Nitrogen (PON)N2

PhosphorusDissolved Inorganic Phosphorus(DIP)PO4

-3

Dissolved Organic Phosphorus (DOP)Particulate Organic Phosphate (POP)Particulate Inorganic Phosphorus (PIP)

Nitrogen

After carbon, oxygen and hydrogen, nitrogen is the most abundant element in living cells. They contain 1-10% total nitrogen by dry weight, which reflects the nitrogen availability of the environment.

Organisms do not use the omnipresent N2 as a source of nitrogen but the NO3.

Only some blue-green algae and bacteria can use the N2 as source of nitrogen via the process of nitrogen fixation. It is the major source of new, usable nitrogen.

The enzyme responsible for this process is called nitrogenase.

The reverse process (reduction of nitrate to gas nitrogen) is also carried out by bacteria at low oxygen levels. It is called denitrification and is very important for the nitrogen budget of an aquatic ecosystem, since it provides these bacteria with oxygen for their respiration.

Nitrogen cycle is complex due to the many chemical states in which it is found and the central role of bacteria in its transformation from one state to another

The sources of the various forms of nitrogen in the water include atmospheric diffusion, runoff, anthropogenic inputs from sewage discharge and agricultural fertilizers.

From all the forms of nitrogen in the water, nitrate (NO3-) is the most common. The supply of nitrate depends on the land-uses of the surrounding watershed.

Nitrate is the most highly oxidized form of nitrogen and is not toxic even in large quantities.

Nitrate ions (NO3-) move easily through soils and and are rapidly lost from the land even in natural drainage systems. This contrasts with ammonium ions which are retained by soil particles.

Natural changes in vegetation caused by fires, floods or artificial cleaning and even moderate environmental disturbances release much more nitrate than ammonia.

According to the European legislation, the higher acceptable concentration of NO3- is 50 mg/l in drinking water.

The second more oxidized form of nitrogen is the nitrite ions (NO2-).

It is often present in small quantities, because it is oxidized to NO3- at high oxygen levels. In anoxic waters it is converted to ammonia.

The less oxidized inorganic form of nitrogen is ammonium ions (NH4+).

It is the form that the plants mainly uptake for their needs.

According to E.U. legislation, its concentration in drinking water should not exceed 0.1 mg/l

The NO3- of the environment is reduced in NO2- by the enzyme nitrate reductase and the NO2- is reduced to ammonium ions by the enzyme nitrite reductase.

NH4+ much more reactive, it is more toxic especially when the environment is alkaline, and it is retained by most soils.It persists in small quantities because it is the main excretory product of aquatic animals.

Its concentration depends on the excretory rates, the plant uptake and the bacterial oxidation and in drinking water should not be greater than 0,5 mg/l.There is a noticed seasonal variation of these forms of nitrogen in lakes:

Concerning NO3+ :

During winter inflow > uptake by algae and is supplemented by some amounts released by the sedimentDuring summer plant uptake > inflow and recycling from the hypolomnio is limited by the thermocline.

Concerning ammonium NH4+ :

Oligotrophic lakes:During spring and summer low values, augmentation in autumn and decrease in winter unless there is an ice-cover. In this case the level of NH4+ is moderate.

Eutrophic lakes:Summer values fluctuate considerably, autumn and winter values are high particularly under ice.

Dissolved Organic Nitrogen

All natural waters contain some DON, which is more abundant in eutrophic than in oligotrophic aquatic ecosystems.

They are excreted like amino sugars by some plants and they are utilized as energy and nitrogen sources.

Phosphorus

Although needed in small quantities, it is one of the most common phytoplankton growth-limiting factor.

That is because:a) Phosphorus containing minerals are sometimes geochemically

scarce and thus the normal supply from rock breakdown is poor

b) There is no gaseous phase so there is no equivalent to nitrogen fixation

c) Phosphorus is tightly bound to soil

The main natural source of phosphorus in aquatic ecosystems is the rock breakdown. It forms compounds with the soil particles and that is why in not easily available.

The form that the algae can use is the PO4-3 , which is called reactive

form.

Dissolved inorganic phosphorus (DIP) is assimilated by plants and microbes into cellular constituents and so transformed into particulate organic phosphorus (DOP).

Cycle of phosphorus

It may be excreted or released by cell lysis directly as DIP or as DOP which is directly broken down to DIP by bacterial activity.

Sorption-desorption reactions act as buffer of DIP

Under aerobic conditions both DIP and DOP may complex with metal oxides and hydroxides to form insoluble precipitates.

This phosphorus is released under anaerobic conditions and since the extent of the anaerobic zones tends to vary seasonally with organic matter loading, the availability of dissolved phosphate varies accordingly.

Ratio N/P

This ratio varies widely and indicates which element is likely to limit algal growth. A plant requires a ratio 7:1 by weight or 16:1 by element.

Both N and P can be limiting factors to plant growth.

Nitrogen and phosphorus occur in algal tissue in a remarkably stable ratio of atomic weights of 16:1, termed the Redfield ratio.

It is generally accepted that when N:P ratios fall bellow 16:1 , nitrogen is the limiting factor, whereas if it is higher that 16:1, then phosphorus is lacking.

At N:P ratios between 10:1 and 20:1, joint limitations by both nutrients is likely.

Methodology

Collection of the samples

Filtration

NH4+ : phenate method. Based on the reaction of the ions NH4+ with a phenol which results in the intensely blue indophenol. Absorbance is measured in a spectrophotometer

NO2+: Photometric method based on the red purplr azo dye produced at low pH from the reaction of diazotized sulfanilic acid with NED NO3+: reduced to NO2+ and then followed the process as above.

PO4-3: Ascorbic acid method. Orthophosphate reacts with a

number of reagents forming a substance which is colored blue by the ascorbic acid. Photometric method.

Total phosphorus (dissolved and suspended): no filtration, digestive method to convert all the forms into PO4

-3 and then followed as above.

Heavy metalsHeavy metals

Heavy metals are all the metals that have atomic density more than 6 gr/cm3.

Some of them are very toxic to the flora and fauna such as Pb, Al, Cd, Hg, As, Ni, Cr, Sn, Tl, U, while others are necessary to living organisms in very small quantities such as Fe, Co, Mn, Cu, Se, Zn.

There are several ways according to which heavy metals can enter aquatic ecosystems.

Such are:Industrial wastes, Urban sewage, Precipitation, Runoff

In unpolluted systems, the levels of heavy metals depend on the geochemical background of the area. Heavy metals can be found in the water, in the sediment, in the living organisms

Heavy metals can enter the body of living organisms in two ways:a) Either with direct absorption of the free ions and the simple compounds dissolved in the water through the epithelium, the gills and the digestion tube

b) Or via the food web.

According to the latter way:

Absorption by the digestion tube

Storing in various tissues

Hg, Cd easily stored (liver, gills, skeleton)Zn, Cu not immediately stored (brain, liver)

Augmentation of their concentration after long term exposureBioaccumulation

The term bioaccumulation refers to ability of the living organisms to accumulate heavy metals in their bodies from the environment including both direct absorption from the water and the food web.

Bioconcentration means the accumulation of the heavy metals in the bodies of the living organisms deriving only from the absorption of them from the water.

Bioconcentration factor (CF) is a coefficient which indicates the concentration of a metal in a living organism towards its concentration in the environment

Biomagnification or magnification means that the concentration of heavy metals increase from the lower to the upper levels of the food web

What does bioaccumulation mean?

Biotransference refers to the transference of a heavy metal through successive levels of a food web, while biotransference factor expresses the concentration of the metal in an organism towards the concentration of the same metal in another organism belonging to the directly lower level of the food web.

What are the factors that affect the heavy metal toxicity?

a) The toxicity of the metal itselfb) The cooperative or the competitive presence of other metalsc) The affection of other physicochemical parameters such as

pH which determine the availability of heavy metalsd) The physiological condition of the organisme) The development phasef) Some biological parameters such as the age, the weight, the

length etc.

Hg>Cu>Zn>Ni>Pb>Cd>As>Cr>Sn>Fe>Mn

Very toxic Least toxic

The toxicity causes:

a) Neuropsychological disordersb) Abnormalities in cellsc) Affection of the activity of hormones and enzymesd) Blood parameterse) Mobility of the organismf) Basic functions of the organismg) Development of the organismh) Reproduction

b) Loss of heavy metals along the body surface and the gills

c) Transformation in all the tissues

Metaltheonines: they react with the free metal ions, they store them in specific tissues and from there heavy metals are gradually removed with urea or from the body surface

How can the organisms defend themselves?

a) Excretion of heavy metals with urea or via the digestive tube

Methodology