**6.12 Other additives**

Additional additives like graphene, TiO2, Al2O3, Ag, and carbon nanotubes were considered as relevant for BDE-209 uptake in spinach, pumpkin, cucumber, corn and water spinach [36]. Indeed, an increased plant uptake was observed for all of these additives. Combinations of clay minerals like bentonite and oxidizing agents like sodium persulfate have also been positively tested for increased bioavailability of Br3-Br10 – BDEs [69].

## **6.13 Solubilizers**

The addition of surfactant-active additives elevates both mobility of PBDE in the soil matrix and plant uptake as previously described.

### **6.14 Macro- and trace elements**

Apart from undisputed relevance of macro- and trace elements both in the development of the microflora in the rhizosphere and in plant growth, positive effects on the degradation of BDEs were observed in individual cases. Exemplarily, nitrate as additive caused intensified desorption and biodegradation of BDE-99, but might cause inhibition in case of high levels [70, 71].

#### **6.15 Heavy metals**

Presence of elevated concentrations of heavy metals shows ambivalent effects. Metals like Ni or Fe cause an enhanced uptake of PBDE, which was justified by chemical debromination of BDE-209 and enhanced mobilization, uptake and transport of Br8- to Br10-BDEs in the roots and shoots of the plants [64]. Enhanced plant uptake of low brominated BDEs like BDE-47 was also observed (24.76% vs. < 1.5%) [72]. In contrast, reduced BDE-209 uptake of up to 50% by pumpkins was reported after addition of 300 mg Cu kg DM−1 and microbial mineralization was negatively affected at more elevated levels [70, 73]. Similar effects were shown for lead, where BDE-209 uptake was reduced by a factor of 2.9–3.7 by tall fescue at levels up to 1950 mg Pb kg DM−1 [74]. Heavy metal induced effects on PBDE plant uptake are also plant specifics as shown for cadmium, where levels of up to 14,800 ng g DM-1 had no effect on BDE-209 uptake in case of black nightshade, but lifting effects in case of amaranth [75, 76].

In summary, presence of essential heavy metals like iron or copper at adequate concentrations might have a positive effect on PBDE degradation, while nonessential heavy metals at non-toxic levels reveal no effect.

## **7. Predictive mathematical models**

Due to the broad spectrum of food plants, attempts were made to develop simple but sensitive models to predict PBDE plant uptake based on simple chemical

**75**

*Plant Uptake, Translocation and Metabolism of PBDEs in Plants*

about RCF, SCF (shoot concentration factor) or TF.

were reported for the insecticide chlorpyrifor [79].

and root or root and shoot [83].

biomolecules like amino acids.

**8. RCF and TF values of specific crops**

ity bases on three restrictions of lipophilic compounds as follows:

conditions and input variables as distribution equilibria, lipid content, organic matter, and initial PBDE soil-water concentration to achieve predictive statements

While these models provide comparatively good correlations for the RCF, they commonly fail in prediction of the TF, because this value is strongly influenced by intrinsic and atmospheric transport of BDEs in addition to the plant specific uptake of PBDE in the root plexus. Therefore, deviations in the range of two decades can be observed comparing model and real situation [77, 78]. Even after restriction of models to single pollutant situations instead of congener mixtures with variable concentration levels, and after focusing on single and simplified plants like lettuce, where differentiations between shoot and fruit or over the height of the shoot are not applicable, deviations of 25.3–58.2% of the model compared to real situation

Another highly relevant error is caused by incorrect analysis of intrinsic PBDE levels in roots in contrast to adsorptive fractions at the outer root surface affecting quality of environmental data. Hence, Briggs et al. [80] showed a significant decrease in BCF levels and thus RCF values of PBDE starting at a log KOW value of approx. 6.5 (corresponds to a log BCF value of approx. 4.6) after elimination of externally adsorbed congeners (see **Figure 1**). This chart corresponds to Bintein's bilinear model [81], which was confirmed by Meylan et al. [82] for 610 non-ionic pollutants. This negative correlation at high log KOW values and thus high lipophilic-

• **Equilibrium kinetics**: The higher the lipophilicity of a pollutant, the longer it takes to achieve equilibrium state between two phases or compartments. The life span of annual crops might be too short to establish equilibria between soil

strongly lipophilic substances are primarily adsorb onto particles or surfaces. However, for absorptive root uptake of pollutants, a phase transition from soil to the liquid phase as well as from the liquid phase to the intrinsic root is

• **Solubility:** Water solubility decreases with increasing lipophilicity and

• **Membrane permeability and cellular transport mechanisms**: The membrane-based cellular uptake of pollutants takes place by passive permeation [80]. The membrane permeability and thus bioavailability of contaminants is concisely described by Lipinski's 'Law of 5′, stating out low absorption or membrane permeability at log KOW values higher than 5, molecular weight higher than 500, more than 5 hydrogen bond donors and more than 10 (= 2 ∙ 5) hydrogen bond acceptors. The former two requirements are fulfilled even in case of Br4- to Br5 – BDEs. By means of known transport mechanisms into the cell, PBDE plant uptake may be affected by co-transport phenomena of

Following the extensive literature evaluation by Dobslaw et al. [52] twelve crops with the highest documented data density were selected and the occurring RCF and TF values for BDE-47 and BDE-209 were compared. The highest data density regarding the transition of PBDEs from soil to root or from root to plant was available for BDE-209 followed by BDE-47. In contrast to lower brominated

required without adsorptive elimination at the tissue [80, 83]

*DOI: http://dx.doi.org/10.5772/intechopen.95790*

## *Plant Uptake, Translocation and Metabolism of PBDEs in Plants DOI: http://dx.doi.org/10.5772/intechopen.95790*

*Flame Retardant and Thermally Insulating Polymers*

**6.12 Other additives**

of Br3-Br10 – BDEs [69].

**6.14 Macro- and trace elements**

**6.13 Solubilizers**

**6.15 Heavy metals**

case of amaranth [75, 76].

**7. Predictive mathematical models**

and thereby soil remediation was positively investigated.

soil matrix and plant uptake as previously described.

might cause inhibition in case of high levels [70, 71].

by the type of plastic and the temperature level during test conditions as adsorption is an endothermic process. While enhanced accumulation of BDE congeners was observed for polyethylene, polypropylene, polystyrene, and polyamide, low accumulation levels were observed for polyvinylchloride [66–68]. Hence, the hypothetical potential of injection of plastic particles into the soil as sink for PBDE

Additional additives like graphene, TiO2, Al2O3, Ag, and carbon nanotubes were considered as relevant for BDE-209 uptake in spinach, pumpkin, cucumber, corn and water spinach [36]. Indeed, an increased plant uptake was observed for all of these additives. Combinations of clay minerals like bentonite and oxidizing agents like sodium persulfate have also been positively tested for increased bioavailability

The addition of surfactant-active additives elevates both mobility of PBDE in the

Apart from undisputed relevance of macro- and trace elements both in the development of the microflora in the rhizosphere and in plant growth, positive effects on the degradation of BDEs were observed in individual cases. Exemplarily, nitrate as additive caused intensified desorption and biodegradation of BDE-99, but

Presence of elevated concentrations of heavy metals shows ambivalent effects. Metals like Ni or Fe cause an enhanced uptake of PBDE, which was justified by chemical debromination of BDE-209 and enhanced mobilization, uptake and transport of Br8- to Br10-BDEs in the roots and shoots of the plants [64]. Enhanced plant uptake of low brominated BDEs like BDE-47 was also observed (24.76% vs. < 1.5%) [72]. In contrast, reduced BDE-209 uptake of up to 50% by pumpkins was reported after addition of 300 mg Cu kg DM−1 and microbial mineralization was negatively affected at more elevated levels [70, 73]. Similar effects were shown for lead, where BDE-209 uptake was reduced by a factor of 2.9–3.7 by tall fescue at levels up to 1950 mg Pb kg DM−1 [74]. Heavy metal induced effects on PBDE plant uptake are also plant specifics as shown for cadmium, where levels of up to 14,800 ng g DM-1 had no effect on BDE-209 uptake in case of black nightshade, but lifting effects in

In summary, presence of essential heavy metals like iron or copper at adequate

concentrations might have a positive effect on PBDE degradation, while non-

Due to the broad spectrum of food plants, attempts were made to develop simple but sensitive models to predict PBDE plant uptake based on simple chemical

essential heavy metals at non-toxic levels reveal no effect.

**74**

conditions and input variables as distribution equilibria, lipid content, organic matter, and initial PBDE soil-water concentration to achieve predictive statements about RCF, SCF (shoot concentration factor) or TF.

While these models provide comparatively good correlations for the RCF, they commonly fail in prediction of the TF, because this value is strongly influenced by intrinsic and atmospheric transport of BDEs in addition to the plant specific uptake of PBDE in the root plexus. Therefore, deviations in the range of two decades can be observed comparing model and real situation [77, 78]. Even after restriction of models to single pollutant situations instead of congener mixtures with variable concentration levels, and after focusing on single and simplified plants like lettuce, where differentiations between shoot and fruit or over the height of the shoot are not applicable, deviations of 25.3–58.2% of the model compared to real situation were reported for the insecticide chlorpyrifor [79].

Another highly relevant error is caused by incorrect analysis of intrinsic PBDE levels in roots in contrast to adsorptive fractions at the outer root surface affecting quality of environmental data. Hence, Briggs et al. [80] showed a significant decrease in BCF levels and thus RCF values of PBDE starting at a log KOW value of approx. 6.5 (corresponds to a log BCF value of approx. 4.6) after elimination of externally adsorbed congeners (see **Figure 1**). This chart corresponds to Bintein's bilinear model [81], which was confirmed by Meylan et al. [82] for 610 non-ionic pollutants. This negative correlation at high log KOW values and thus high lipophilicity bases on three restrictions of lipophilic compounds as follows:

