**3. Movement of persistent molecules in the environment**

The link between bioavailable persistent substances and the spread of these substances in the environment, causing dissemination of hazardous effects, will be discussed in this section. Desorbed or non sorbed molecules are bio-available and can move into the food chain and can also get into ground/surface water or reach the atmosphere through volatilization and are thus be randomly disseminated in the biosphere (Figure 5) [36]. When persistent molecules are adsorbed in the soil they cause less hazardous effects than when they are bioavailable.

**3.1. Movement from soil to water**

processes [46, 47].

through irrigation [51].

**3.2. Movement in the air**

applied amount can be very high [55].

The vertical displacement of substances in the soil can leach from the surface through the unsaturated zone into deeper layers down to ground water [42]. It is well-known that the soil infiltration capacity depends on soil texture characteristics, porosity, and humidity [43]. Soils with a sandy texture are more susceptible to the process of leaching while clay soils have greater pesticide adsorption potential. Leaching can occur in an irregular manner known as preferential flow [44]. This is due to irregularities in the soil that facilitate an easy path for water and pollutants at specific points. These paths can be formed by soil cracks, worm trails, rotten roots, termites, and other biological activities [45]. Soil in which surface layer rich in organic matter was removed by flattened to built roads or courtyard enhance strongly the leaching process [34]. Water consumption from wells exposed to pesticide applications can be very dangerous for humans and cattle. Generally, ground water in the dry season drains to rivers and in the raining period receives water from rivers and pollutants follow these

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Surface water contamination with persistent molecules occurs not only by the drainage processes from ground water but also strongly increases with runoff [48]. When the quantity of rainfall exceeds the soil infiltration capacity, superficial runoffs occur [49]. Runoffs begin with small lamina flows that build up until they form turbulent flows which cause pesticide losses and even gully erosion. This process has been shown to be an important source of pollution in surface waters [50]. Another source of pollution is the discharge of effluents from waste water treatment plants to surface waters [51]. Pollutant molecules can be distributed by rivers and affect different living forms in the water as well as the fauna that use it for drinking. Persistent molecules contaminating these waters are also spread to agriculture products

The sources of POP in the air are pesticide applications, oil combustion, industries and indoors at home. During the application of pesticides a part remains in the air due to drift. Another very important source is volatilization of pesticides from soil or plant surfaces [52]. Pesticide dissipation occurs when the product is being sprayed. Droplets are aerially dispersed and reach non-target areas [53]. The spray drift of pesticides is influenced by the size of the pulverized droplets, application pressure, distance of the pulverizer nozzle to the target and the velocity of the wind during application [54]. By strong volatilization the relative loss of the

These molecules contaminating the air are transported by air currents and redistributed globally, polluting all kinds of ecosystems [56]. Today we may find many such molecules in the Antarctic and in obscure ocean islands [57, 36]. This pollution affects man as well as many animal species [58]. Besides the adsorption capacity that is able to immobilize these molecules, another important variable is the molecular vapor pressure which is influenced by temperature – an increase of 10°C makes these molecules about four times more volatile [59]. This process is much greater in the tropics with higher temperatures than in temperate regions of the world.

**Figure 4.** Restriction access of microorganism in the soil by micropores.

Biodegradable substances, differently from persistent molecules, cannot survive for a long time in the environment. The problem is not only the actual pollution of pesticide applications, which is strongly dependent on the climatic conditions [37, 38] but also the composts with the organic wastes containing POPs that are added to soils [39] as well the inadequate forms in which POPs used to be stored [40, 41].

**Figure 5.** Overview of POP dispersion in the environment of air, water and biosphere.

#### **3.1. Movement from soil to water**

The vertical displacement of substances in the soil can leach from the surface through the unsaturated zone into deeper layers down to ground water [42]. It is well-known that the soil infiltration capacity depends on soil texture characteristics, porosity, and humidity [43]. Soils with a sandy texture are more susceptible to the process of leaching while clay soils have greater pesticide adsorption potential. Leaching can occur in an irregular manner known as preferential flow [44]. This is due to irregularities in the soil that facilitate an easy path for water and pollutants at specific points. These paths can be formed by soil cracks, worm trails, rotten roots, termites, and other biological activities [45]. Soil in which surface layer rich in organic matter was removed by flattened to built roads or courtyard enhance strongly the leaching process [34]. Water consumption from wells exposed to pesticide applications can be very dangerous for humans and cattle. Generally, ground water in the dry season drains to rivers and in the raining period receives water from rivers and pollutants follow these processes [46, 47].

Surface water contamination with persistent molecules occurs not only by the drainage processes from ground water but also strongly increases with runoff [48]. When the quantity of rainfall exceeds the soil infiltration capacity, superficial runoffs occur [49]. Runoffs begin with small lamina flows that build up until they form turbulent flows which cause pesticide losses and even gully erosion. This process has been shown to be an important source of pollution in surface waters [50]. Another source of pollution is the discharge of effluents from waste water treatment plants to surface waters [51]. Pollutant molecules can be distributed by rivers and affect different living forms in the water as well as the fauna that use it for drinking. Persistent molecules contaminating these waters are also spread to agriculture products through irrigation [51].

#### **3.2. Movement in the air**

Biodegradable substances, differently from persistent molecules, cannot survive for a long time in the environment. The problem is not only the actual pollution of pesticide applications, which is strongly dependent on the climatic conditions [37, 38] but also the composts with the organic wastes containing POPs that are added to soils [39] as well the inadequate forms in

which POPs used to be stored [40, 41].

312 Applied Bioremediation - Active and Passive Approaches

**Figure 4.** Restriction access of microorganism in the soil by micropores.

**Figure 5.** Overview of POP dispersion in the environment of air, water and biosphere.

The sources of POP in the air are pesticide applications, oil combustion, industries and indoors at home. During the application of pesticides a part remains in the air due to drift. Another very important source is volatilization of pesticides from soil or plant surfaces [52]. Pesticide dissipation occurs when the product is being sprayed. Droplets are aerially dispersed and reach non-target areas [53]. The spray drift of pesticides is influenced by the size of the pulverized droplets, application pressure, distance of the pulverizer nozzle to the target and the velocity of the wind during application [54]. By strong volatilization the relative loss of the applied amount can be very high [55].

These molecules contaminating the air are transported by air currents and redistributed globally, polluting all kinds of ecosystems [56]. Today we may find many such molecules in the Antarctic and in obscure ocean islands [57, 36]. This pollution affects man as well as many animal species [58]. Besides the adsorption capacity that is able to immobilize these molecules, another important variable is the molecular vapor pressure which is influenced by temperature – an increase of 10°C makes these molecules about four times more volatile [59]. This process is much greater in the tropics with higher temperatures than in temperate regions of the world. Also these losses can affect people, domestic animals, pollinating insects as well as contami‐ nating lakes, rivers, and fish or other aquatic plants and animals. Air pollution is quite difficult to control. Trees and forests can filter the pollution that is spread by horizontal wind but not by rainfall [60]. Air pollutants can move from rural areas to towns and can be present every‐ where. This distribution is determined by the wind and physical barriers such as mountains etc. The challenge is how to reduce this process as much as possible considering that these molecules have been lost for the purpose that they were intended and non target flora and fauna are not able to escape from their hazardous effects efficiently.

tion. The method establishes covalent bonds by UV irradiation only between pollutants containing aromatic structures and the cell component where weak bonding occurs and this covalent form of bonding can resist cell fractionation. Studies with the gram negative soil bacteria *Azospirillum lipoferum*, have shown that dicofol, which is easily hydrolyzed [73] turns persistence by becoming imbedded in the membrane [74]. In this case dicofol was found in the neutral lipids of membranes [75] where it influences the microdomain of membrane bound enzymes, as also occurs with other molecules [76]. This characterizes a non specific mode of action as seen with other molecules that interfere with different membrane bound enzymes

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The key message is that ecotoxicological effects are not only defined by the intrinsic chemical nature of each compound but also by the interaction of their effects properties within a given environment. Applying the concept of **"Preferential Partition"** helps us to understand conflicting reports about bioaccumulation and the ecotoxicological effects in soils. Bioaccu‐ mulation is the natural process that gradually concentrates non toxic levels of pollutants into

Different side effects have been described for the same pesticide by distinct authors. For example in the nitrogen cycle, some authors reported an inhibition effect of a pesticide while others reported, for the same molecule, an increasing or no effect on the ammonification, nitrification and nitrogen fixation processes. This depends mainly on the differences in the soil used and concentrations applied [79, 80, 77]. **"Preferential Partition"** explains why substances remain in the soil matrix, when they are likely to be bioaccumulated in living forms or move

Non soil bound residues are an essential condition for biodegradation. Persistence occurs mainly when low numbers of or no biodegrading microorganisms are present or most commonly when despite the presence of biodegradation microorganisms, the residues are

Hazardous organic substances that are strongly adsorbed in soil organic matter pose less risk than those with low adsorbance. Sufficient soil organic matter reduces bioavailability and decreases bioaccumulation in the living biosphere but in turn results in persistence with long term pollution in soils [81, 74]. The balance between adsorbed and bioavailable molecules determines the ecotoxicity levels [2] and this is determined by the physic-chemical character‐ istics of the soil as well as the pollutant molecule. This balance is changed by the weathered pollutants in the soil that have a lower bioavailability than the recently applied products [1]. Therefore it is a pitfall to conclude that the hazardous effects are only caused by pesticide

One of the most important sources of pollution in the food chain is soil contaminated with pesticides and other POPs mainly introduced by air deposition. Another way is the direct

through the soil to pollute water resources or are suitable for biodegradation.

such as ATPase [77] and nitrogenase [78].

entrapped and not bioavailable.

concentrations in the soil.

*3.3.3. Plant uptake and food chain up to fauna*

*3.3.2. Ecotoxicological effects in soil living organisms*

toxic levels within a biota causing unpleasant side effects [72].

Air pollution can also begin indoors and then move outdoors. Polybrominated diphenyl ethers (PBDEs) and phthalates among others are some examples. Brominated compounds make up an important group of flame retardants. Some of these products, such as Penta-BDE, seem to show toxicological effects at very low concentrations [61]. PBDEs are structurally similar to thyroid hormones acting as endocrine disruptors via alterations in thyroid hormone homeo‐ stasis [62] and demonstrate neurodevelopmental effects [64]. The most sensitive populations are likely to be pregnant women, developing fetuses, and infants [65].

In recent years, PBDEs have been recognized as significant pollutants of the indoor environ‐ ment [66]. These additives are mixed into plastics and foams but do not form chemical bonds. This makes them much more likely to leach out of goods and products by volatilization. PBDEs are lipophilic compounds [67], and when released into the environment bioaccumulation can occur in living organisms and this is followed by biomagnification in the food chain. Bioac‐ cumulation in wildlife has been reported in numerous studies, even in places with no local sources or industrial production [68] like the Arctic. Due to their high production volume, widespread usage, and environmental persistence, PBDEs have become ubiquitous contami‐ nants in environmental media, biota and humans [69]. As their levels are rapidly increasing in the environment, these chemicals have evolved from 'emerging contaminants' to globallydistributed organic pollutants [70].

#### **3.3. Movement in the food chain**

Movement of persistent molecules in the biosphere toward soil microorganisms, mesofauna and plant uptake will be discussed in this section. Here some aspects of the way in which persistent molecules can be transferred from one life form to other will be emphasized, considering that the overall food chain sequence processes are well known [71].

#### *3.3.1. Cell bioaccumulation*

How do persistent molecules move into cells in higher concentrations than the surrounding environment [72]? "**Preferential partition**" describes the "choice" of the substance, due to affinity, between cell membranes or components of the environment. As mentioned earlier affinity is characterized mainly by lipophilicity and charge binding. With the photo-binding technique it is possible to identify in which cell component the molecule will preferentially bind. This technique preserves the binding when only weak bonds between the pollutant and cell are available. These weak bonds are not resistant to the harsh conditions of cell fractiona‐ tion. The method establishes covalent bonds by UV irradiation only between pollutants containing aromatic structures and the cell component where weak bonding occurs and this covalent form of bonding can resist cell fractionation. Studies with the gram negative soil bacteria *Azospirillum lipoferum*, have shown that dicofol, which is easily hydrolyzed [73] turns persistence by becoming imbedded in the membrane [74]. In this case dicofol was found in the neutral lipids of membranes [75] where it influences the microdomain of membrane bound enzymes, as also occurs with other molecules [76]. This characterizes a non specific mode of action as seen with other molecules that interfere with different membrane bound enzymes such as ATPase [77] and nitrogenase [78].

#### *3.3.2. Ecotoxicological effects in soil living organisms*

Also these losses can affect people, domestic animals, pollinating insects as well as contami‐ nating lakes, rivers, and fish or other aquatic plants and animals. Air pollution is quite difficult to control. Trees and forests can filter the pollution that is spread by horizontal wind but not by rainfall [60]. Air pollutants can move from rural areas to towns and can be present every‐ where. This distribution is determined by the wind and physical barriers such as mountains etc. The challenge is how to reduce this process as much as possible considering that these molecules have been lost for the purpose that they were intended and non target flora and

Air pollution can also begin indoors and then move outdoors. Polybrominated diphenyl ethers (PBDEs) and phthalates among others are some examples. Brominated compounds make up an important group of flame retardants. Some of these products, such as Penta-BDE, seem to show toxicological effects at very low concentrations [61]. PBDEs are structurally similar to thyroid hormones acting as endocrine disruptors via alterations in thyroid hormone homeo‐ stasis [62] and demonstrate neurodevelopmental effects [64]. The most sensitive populations

In recent years, PBDEs have been recognized as significant pollutants of the indoor environ‐ ment [66]. These additives are mixed into plastics and foams but do not form chemical bonds. This makes them much more likely to leach out of goods and products by volatilization. PBDEs are lipophilic compounds [67], and when released into the environment bioaccumulation can occur in living organisms and this is followed by biomagnification in the food chain. Bioac‐ cumulation in wildlife has been reported in numerous studies, even in places with no local sources or industrial production [68] like the Arctic. Due to their high production volume, widespread usage, and environmental persistence, PBDEs have become ubiquitous contami‐ nants in environmental media, biota and humans [69]. As their levels are rapidly increasing in the environment, these chemicals have evolved from 'emerging contaminants' to globally-

Movement of persistent molecules in the biosphere toward soil microorganisms, mesofauna and plant uptake will be discussed in this section. Here some aspects of the way in which persistent molecules can be transferred from one life form to other will be emphasized,

How do persistent molecules move into cells in higher concentrations than the surrounding environment [72]? "**Preferential partition**" describes the "choice" of the substance, due to affinity, between cell membranes or components of the environment. As mentioned earlier affinity is characterized mainly by lipophilicity and charge binding. With the photo-binding technique it is possible to identify in which cell component the molecule will preferentially bind. This technique preserves the binding when only weak bonds between the pollutant and cell are available. These weak bonds are not resistant to the harsh conditions of cell fractiona‐

considering that the overall food chain sequence processes are well known [71].

fauna are not able to escape from their hazardous effects efficiently.

are likely to be pregnant women, developing fetuses, and infants [65].

distributed organic pollutants [70].

314 Applied Bioremediation - Active and Passive Approaches

**3.3. Movement in the food chain**

*3.3.1. Cell bioaccumulation*

The key message is that ecotoxicological effects are not only defined by the intrinsic chemical nature of each compound but also by the interaction of their effects properties within a given environment. Applying the concept of **"Preferential Partition"** helps us to understand conflicting reports about bioaccumulation and the ecotoxicological effects in soils. Bioaccu‐ mulation is the natural process that gradually concentrates non toxic levels of pollutants into toxic levels within a biota causing unpleasant side effects [72].

Different side effects have been described for the same pesticide by distinct authors. For example in the nitrogen cycle, some authors reported an inhibition effect of a pesticide while others reported, for the same molecule, an increasing or no effect on the ammonification, nitrification and nitrogen fixation processes. This depends mainly on the differences in the soil used and concentrations applied [79, 80, 77]. **"Preferential Partition"** explains why substances remain in the soil matrix, when they are likely to be bioaccumulated in living forms or move through the soil to pollute water resources or are suitable for biodegradation.

Non soil bound residues are an essential condition for biodegradation. Persistence occurs mainly when low numbers of or no biodegrading microorganisms are present or most commonly when despite the presence of biodegradation microorganisms, the residues are entrapped and not bioavailable.

Hazardous organic substances that are strongly adsorbed in soil organic matter pose less risk than those with low adsorbance. Sufficient soil organic matter reduces bioavailability and decreases bioaccumulation in the living biosphere but in turn results in persistence with long term pollution in soils [81, 74]. The balance between adsorbed and bioavailable molecules determines the ecotoxicity levels [2] and this is determined by the physic-chemical character‐ istics of the soil as well as the pollutant molecule. This balance is changed by the weathered pollutants in the soil that have a lower bioavailability than the recently applied products [1]. Therefore it is a pitfall to conclude that the hazardous effects are only caused by pesticide concentrations in the soil.

#### *3.3.3. Plant uptake and food chain up to fauna*

One of the most important sources of pollution in the food chain is soil contaminated with pesticides and other POPs mainly introduced by air deposition. Another way is the direct surface uptake mainly in leaves during application but also by plant uptake powered by plant evapotranspiration in which persistent molecules dissolved in soil water are moved from roots to shoots. From the roots the pesticides move by translocation to stems and then often a strong bioaccumulation occurs in the leaves [29, 30] or fruits. Crops where pesticides are used intensively are consumed by cattle, humans or wild life. A strong increase the of concentrations of these molecules can occur in this process called biomagnifications as described above (Figure 6).

in a feed material. For meat (including adjunctive fatty tissue), this would mean that in many cases human exposure is very low or even negligible for almost all compounds. The second scenario addresses the accumulation of chemical residues in animal tissues such as liver and kidney with notorious examples including the accumulation of heavy metals, melamine and other nephrotoxins in the kidney, and dioxins and polyhalogenated persistent environmental pollutants (POPs) in the liver and fatty tissues [71]. Persistent molecules increase in each ingestion with the uptake of higher concentrations along the food chain that can result in very poisonous and hazardous concentrations for humans (Figure 6), cattle and wild life. The worst

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The metabolic pathways of digestion in diverse animal species are different. Strict herbivorous species digest soluble fibers in their large caeca (the equivalent of the rumen) with the help of complex microbiological flora. This microbial fermentation may result in the release of bound (plant) toxic products which are often conjugated to sugars (glucosides) in plants and in this form are biologically inactive (or less active) [71]. The morphological and physiological characteristics of the gastro-intestinal tract in farm animal species largely determine the rate of absorption of a contaminant. The internal dose of a toxicant that reaches the post-hepatic circulation, the rate of excretion and subsequently the potential carry over and cumulative potential in tissues need to be considered. The most significant diversity in species is observed at the level of hepatic biotransformation expressed by cytochrome P450 enzymes and their polymorphisms [86]. Diversity can also be observed in all phase of enzymes such as gluta‐ thione-s-transferases, glycine conjugates, UDP-glucuronosyltransferases that are expressed in

The choice of toxicity endpoints may differ between animal health and human risk assess‐ ments. Hence, clinical reports from intoxications in different animals when available may partly provide a basis for hazard characterization whereas other important endpoints maybe applied to human risk assessment as an extrapolation of the dose response from laboratory animal species to humans or using the dose response provided by human epidemiological data [88]. This is typically illustrated with genotoxicity and carcinogenicity data, which are prominent endpoints in human hazard characterization, but which are not commonly used in farm animal health risk assessment considering their relatively short lifespan [71]. The quantitative transfer of a substance from feed to an animal-derived product is commonly expressed as the carry-over rate and serves as a basis to establish maximum tolerable limits

Bioaccumulation is the natural process that gradually concentrates non toxic levels of pollu‐ tants into toxic levels within a biota causing unpleasant side effects [72, 5]. Bioaccumulation involves silent natural processes which stealthily and inevitably affect all biota. Today hazardous substances are ubiquitous, albeit mainly in low concentrations, and for the majority of us they are an unconscious part of our daily diet. The regular intake of sub toxic levels of persistent pollutants can gradually bioaccumulate up to toxic levels and after time produce

bioaccumulation seems to be salmon produced on fish farms [85].

the intestinal wall and in the liver [87].

(MLs) in animal feed and animal-derived foods.

*3.3.5. Chronic toxicology for animals and humans*

chronic effects which today are recognized and understood as such.

**Figure 6.** Human contamination with pesticide moved by food chain.

In order to minimize ecotoxicity we need to restrict the inappropriate use of pesticides and thereby remove them from the food chain and water reserves. **Preferential Partition** presents a concept - tool which is able to estimate what happens to pesticides in crop and fodder plants. In soils with high organic matter content, lipophilic and or charged pesticides are retained in the soil organic matter and the uptake into plants decreases [11, 82, 83]. The reverse occurs in low organic matter sandy soils with low cation exchange capacity CEC. Light textured sandy soils do not adsorb and retain in high amount hazardous products and will both bioaccumulate in living tissues and pollute water resources. In soils of this type, plants strongly adsorb pesticides resulting in enhanced contamination with subsequent phytotoxicity and toxicolog‐ ical effects on fauna [84]. This soil type would be a worst case scenario adequate to be the bench mark for pesticide registration. The pesticides that could be used under these conditions can be used generally in all soils. Registration based on strongly adsorbing soils needs to be avoided because it camouflages the eco-toxicological effects that occur when the pesticide is applied on less adsorbent soils.

#### *3.3.4. Food chain up to fauna*

The food chain sequence is where persistent molecules are first adsorbed by plants which are then consumed by animals that are in turn consumed by predatory species. In the first scenario, the animal serves as a filter with systemic eliminations and the concentration of a xenobiotic that remains present in the consumable product is much lower than the original concentration in a feed material. For meat (including adjunctive fatty tissue), this would mean that in many cases human exposure is very low or even negligible for almost all compounds. The second scenario addresses the accumulation of chemical residues in animal tissues such as liver and kidney with notorious examples including the accumulation of heavy metals, melamine and other nephrotoxins in the kidney, and dioxins and polyhalogenated persistent environmental pollutants (POPs) in the liver and fatty tissues [71]. Persistent molecules increase in each ingestion with the uptake of higher concentrations along the food chain that can result in very poisonous and hazardous concentrations for humans (Figure 6), cattle and wild life. The worst bioaccumulation seems to be salmon produced on fish farms [85].

The metabolic pathways of digestion in diverse animal species are different. Strict herbivorous species digest soluble fibers in their large caeca (the equivalent of the rumen) with the help of complex microbiological flora. This microbial fermentation may result in the release of bound (plant) toxic products which are often conjugated to sugars (glucosides) in plants and in this form are biologically inactive (or less active) [71]. The morphological and physiological characteristics of the gastro-intestinal tract in farm animal species largely determine the rate of absorption of a contaminant. The internal dose of a toxicant that reaches the post-hepatic circulation, the rate of excretion and subsequently the potential carry over and cumulative potential in tissues need to be considered. The most significant diversity in species is observed at the level of hepatic biotransformation expressed by cytochrome P450 enzymes and their polymorphisms [86]. Diversity can also be observed in all phase of enzymes such as gluta‐ thione-s-transferases, glycine conjugates, UDP-glucuronosyltransferases that are expressed in the intestinal wall and in the liver [87].

The choice of toxicity endpoints may differ between animal health and human risk assess‐ ments. Hence, clinical reports from intoxications in different animals when available may partly provide a basis for hazard characterization whereas other important endpoints maybe applied to human risk assessment as an extrapolation of the dose response from laboratory animal species to humans or using the dose response provided by human epidemiological data [88]. This is typically illustrated with genotoxicity and carcinogenicity data, which are prominent endpoints in human hazard characterization, but which are not commonly used in farm animal health risk assessment considering their relatively short lifespan [71]. The quantitative transfer of a substance from feed to an animal-derived product is commonly expressed as the carry-over rate and serves as a basis to establish maximum tolerable limits (MLs) in animal feed and animal-derived foods.

#### *3.3.5. Chronic toxicology for animals and humans*

surface uptake mainly in leaves during application but also by plant uptake powered by plant evapotranspiration in which persistent molecules dissolved in soil water are moved from roots to shoots. From the roots the pesticides move by translocation to stems and then often a strong bioaccumulation occurs in the leaves [29, 30] or fruits. Crops where pesticides are used intensively are consumed by cattle, humans or wild life. A strong increase the of concentrations of these molecules can occur in this process called biomagnifications as described above

In order to minimize ecotoxicity we need to restrict the inappropriate use of pesticides and thereby remove them from the food chain and water reserves. **Preferential Partition** presents a concept - tool which is able to estimate what happens to pesticides in crop and fodder plants. In soils with high organic matter content, lipophilic and or charged pesticides are retained in the soil organic matter and the uptake into plants decreases [11, 82, 83]. The reverse occurs in low organic matter sandy soils with low cation exchange capacity CEC. Light textured sandy soils do not adsorb and retain in high amount hazardous products and will both bioaccumulate in living tissues and pollute water resources. In soils of this type, plants strongly adsorb pesticides resulting in enhanced contamination with subsequent phytotoxicity and toxicolog‐ ical effects on fauna [84]. This soil type would be a worst case scenario adequate to be the bench mark for pesticide registration. The pesticides that could be used under these conditions can be used generally in all soils. Registration based on strongly adsorbing soils needs to be avoided because it camouflages the eco-toxicological effects that occur when the pesticide is

The food chain sequence is where persistent molecules are first adsorbed by plants which are then consumed by animals that are in turn consumed by predatory species. In the first scenario, the animal serves as a filter with systemic eliminations and the concentration of a xenobiotic that remains present in the consumable product is much lower than the original concentration

(Figure 6).

316 Applied Bioremediation - Active and Passive Approaches

**Figure 6.** Human contamination with pesticide moved by food chain.

applied on less adsorbent soils.

*3.3.4. Food chain up to fauna*

Bioaccumulation is the natural process that gradually concentrates non toxic levels of pollu‐ tants into toxic levels within a biota causing unpleasant side effects [72, 5]. Bioaccumulation involves silent natural processes which stealthily and inevitably affect all biota. Today hazardous substances are ubiquitous, albeit mainly in low concentrations, and for the majority of us they are an unconscious part of our daily diet. The regular intake of sub toxic levels of persistent pollutants can gradually bioaccumulate up to toxic levels and after time produce chronic effects which today are recognized and understood as such.

More recently low concentrations have been shown to cause effects such as endocrine disrup‐ tors (EDs) quite different from those observed by high concentrations [89]. EDs are recognized as being partly responsible for a global reduction in male fertility [90], sexual abnormalities [91]), adrenal function disorders [92], human obesity [93] and other metabolic disturbances not to mention similar and worse effects on other living organisms [94, 95]. Recently new evidences have shown the effects of POPs (mainly pesticides) on metabolic disturbances related to obesity [96], insulin resistance promoting diabetes 2 [97] and the association of organochlorine with vitamin D deficiency [98].

results to remove pollutants. The approach in this text is to point out different possibilities with reference to some excellent reviews. The technology used was based on physical, chemical

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The first step of POP remediation is to promote desorption [107]. Physical methods need to remove the pollutants from soils or water in order to destroy the molecules completely by burning [107]. This has a high cost as the incinerator plant needs filter systems to eliminate other pollutants such as dioxins. Physical methods such as electro kinetic (EK) remediation technology use a low-level direct current as the ''cleaning agent'', inducing several transport mechanisms (electro-osmosis, electro-migration and electro-phoresis) and electrochemical reactions (electrolysis and electrodeposition). This technology has already proven its value,

Ozon can be used for chemical remediation of pollutants and there are other methods currently being researched [109]. Chemical degradation reactions in the environment depend on water content, pH, temperature and oxygen reduction potential. These conditions are normally not optimum in nature and therefore degradation is frequently low. Physical and chemical remediations are powerful technologies to remediate small areas that have been polluted by industry or transport accidents. For large areas these process are generally considered too

Biological degradation processes are promoted by living organisms such as animals, plants but mainly microorganisms. The advantages of microbes are the ubiquitous distribution in normal and extreme environments, fast biomass growth, easy manipulation and high diversity of catabolic enzymes. Bioremediation using microorganisms compared to the other method‐ ologies can be used in polluted soils and waters and is less expensive than all other methods. Nevertheless the high costs are limitations for large polluted agricultural areas. One of the most powerful approaches is phytoremediation as some plants have a strong capacity to extract pollutants from the soil and incorporate these molecules into their own biomass [29, 30]. Nevertheless in phytoremediation of hydrocarbon pollutants (HCs) the accumulation between roots and shoots is quite low compared to plant-promoted biodegradation in the rhizosphere [110]. Root exudation stimulates microorganisms in the rhizosphere resulting in

Today efforts are being made to identify the most adequate alternative remediation in a framework of possibilities considering parameters that characterize cost-risk tradeoffs and

Two points related to persistent molecules need to be emphasized. The first is the limits of biodegradation of persistent molecules as reported here in which the best microorganism to degrade a given molecule can not be efficient if the molecule is entrapped in the soil. The second point is that there is no technology available to clean the environment considering the large

and biological methods.

expensive.

enhanced mineralization [111].

dispersion of persistent substances.

uncertainty impacts [112].

**5. Conclusions**

especially in contaminated fine-grain soils [108].

The bioaccumulation of POPs by mothers, over many years, exposures the fetus to these pollutants during pregnancy [65]. Despite the difficulty of experimentation with POPs in humans, follicles could be analyzed when "induced reproduction" occurs and results have shown that contamination in the oocyte follicle can reduce human embryo quality with consequences for future generations caused by the harmful effects of these hazard‐ ous chemicals [89, 99].

Clearly, the threat to the environment and human health is reduced when pesticides are not bioavailable and cannot concentrate in the food chain. Food grown in soils where pesticides are strongly adsorbed has lower health risks.

#### *3.3.6. Cell mortality and redistribution of persistent molecules*

The presence of persistent molecules in different forms of life is temporary limited by plant senescence and/or microbial/fauna death. Two possible routes can occur; one following the food chain as described above and the other by a rotting process in which recalcitrant molecules can be released. In plants the rotting process of wood and straw [100] is a complex process in which the twisted lignin/hemicellulose/cellulose fibers follow a cascade where the first step is the "loosing" of the cell wall. This occurs by non enzymatic peroxidation (Fenton reaction) [101] that changes the lignin structure and reduces the barrier effect of the cell wall allowing the second step of enzyme diffusion of ligninase peroxidase, Mn peroxidase and laccase into areas where polysaccharides can be hydrolyzed [102]. Laccase is a phenol oxidase that has the ability to degrade many persistent xenobiotics [103, 104]. Other lignolytic enzymes could be released and are also able to biodegrade many persistent molecules [105, 106].

Nevertheless in this rotting process many recalcitrant substances are not biodegraded or only partially and therefore these molecules follow the normal distribution: adsorption in the soil, free moving molecules that can be removed by runoff, leaching, volatilization and uptake in plants, mesofauna or soil microorganisms [48, 37].
