**2. Physical characteristics and their effect on transport pathways and plant uptake**

Because PBDEs show a wide range of molecular weight (328–959 g mol−1), lipophilicity (log KOW = 6–10), and volatility (log KOA = 9–16) [19, 20], BDE congener specific transport and plant uptake mechanisms (soil-air-plant vs. soil–soil moisture-root-plant) are highly different and dependent on specific substance parameters (vapor pressure, Henry coefficient, air-plant partition coefficient, KOW value, KOA value), meteorological parameters (temperature, wind rate, precipitation, temporal rainfall distribution, deposition kinetics of gaseous and particulate BDEs), long range transport, plant specific characteristics (species, lipid content, carbohydrate content, fiber content, foliage morphology, non-lipid plant parts, rind consistency), and rhizosphere factors [18, 21–23]. Under aspects of transport, low brominated BDEs (Br2-Br3) are mainly and medium brominated BDEs (Br4-Br5), depending on the study, are minorly to dominantly distributed as gaseous

**69**

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

**3. Human exposure to PBDE contaminations and uptake**

uptake underlining the relevance as second dominant pathway.

**4. Transformation and detoxification of PBDEs in plants**

While PBDEs in the atmosphere are photolytically transformed by hydroxylation und subsequent transformation to lower brominated congeners or ring closure to the corresponding dibenzofurans [41, 42] and PBDEs in soil and sediments are mainly mineralized by stepwise debromination or detoxified by hydroxylation (OH-BDE) or methoxylation reactions (MeO-BDE) in the rhizosphere, strongly affected by the degree of bromination, concentration of oxygen, organic matter and microorganisms [43], intrinsic PBDEs in plants can be transformed by the same three transformation pathways. Exemplarily, transformation of BDE-28 and BDE-47 in maize was analyzed in detail by Wang et al. [44]. BDE-47 (Br4) was dominantly converted to 6-MeO-BDE-47 (275 ng∙g−1 DM) in the root phase, followed by 5-MeO-BDE-47 (40 ng∙g−1 DM), ∑Br2-BDEs (23 ng∙g−1 DM), ∑Br3-BDEs (20 ng∙g−1

As a result of the presence of gaseous and particulate PBDEs in air, the human PBDE uptake is dominated by inhalation, but the relevance of this pathway is strongly affected by atmospheric PBDE levels. Hites and Sjödin et al. reported concentrations of 5.27–301 pg. m−3 in ambient air and 0.06–67 ng m−3 at indoor air, but increased levels up to 312.1 ng BDE-209 m−3 at a Swedish e-waste recycling site [38, 39]. Average BDE-209 levels of 0.13 ng m−3 (gaseous) and 140 ng m−3 (particulate) were reported by Li et al. in 14 Chinese air samples and total BDE-209 uptake by inhalation was quantified as 3000 ng d−1 (respiration) and 69 ng d−1 (dust uptake), equivalent to 84% of the total daily uptake [40]. This finding was validated by multiple studies. As a consequence, 16% of daily PBDE uptake, and even higher ratios in case of lower ambient PBDE levels, are assigned to dietary

compounds (BDE-15: 100%; BDE-28: 35–60%), while transmission and deposition of higher brominated congeners (Br6-Br10) are obligatorily characterized by adsorption of BDEs on a particulate phase [17, 22–25]. As a result of the particle-bound lower-range transport of the latter PBDEs, the PBDE pattern in soil and plant samples from densely populated regions and near hotspots shows high agreement with the present PBDE emission spectrum, while in sparsely populated regions the PBDE spectrum is dominated by low brominated congeners [7, 23]. Additionally, a significant concentration gradient of ∑PBDEs from both densely populated to sparsely populated regions and from emission sites to adjacent region can be observed [7, 26]. Hence, various studies around the world showed a wide range of PBDE concentrations in dust samples of 4.33–370,000 ng g DM−1 [11, 20, 27–31] with a clear domination of BDE-209 in the range of 69.2–99.6% [11, 20, 25]. Due to the high molar mass and the lipophilicity of high brominated BDEs, plant uptake by the soil–soil moisture-root-plant pathway is of low relevance and restricted to low and medium brominated BDEs (Br2-Br5) like BDE-47, BDE-99 and BDE-100 [21, 32], even though intrinsic transport of BDE-209 was reported by single studies [33–35], but disproved by Wu et al. [36], where plant availability of BDE-209 was quantified as 0.3–0.5% of the initial soil concentration and 99.5–99.7% of BDE-209 are solely adsorbed on the soil matrix and the outer side of the roots. Hence, atmospheric uptake of high brominated BDEs is the dominant pathway, even though BDE-209 reveals a low ratio of 0.1% of the atmospheric

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

PBDE pattern [24, 37].

*Flame Retardant and Thermally Insulating Polymers*

in case of higher degree of bromination [3, 4].

tons were located in sewage sludge [6].

120 pg. g DM−1, and ∑PBDE: 1.7–416 pg. g DM−1) [17, 18].

America), and 1600 tons (Japan) [2]. Because of their endocrine-disrupting properties, neurotoxicity, and negative impacts on fertility as well as their high environmental persistence, the use of these mixtures was strictly regulated by the Stockholm Convention of 2001 and finally banned in 2004 (penta-BDEs, octa-BDEs) and severely restricted for BDE-209 in 2019 according to the lower toxicity

As former high-volume chemicals PBDEs are ubiquitous in environment today, but are mainly detectable in soil and dust samples. E-waste sites and waste water sludge were identified as main sources with BDE-209 as dominant congener [5, 6]. Hence, BDE-209 levels of 6.3–12,194.6 ng g DM−1 (dry matter) at a ratio of 35–89.6% of the total PBDE where detected on e-waste recycling sites [7–9], while currently highest ∑PBDE levels of 8.70–18,451 ng g DM−1 were reported for soil at an industrial production site of plastic parts in electrical industry in Changzhou [10]. PBDE levels of 7240–10,469 ng g DM−1, 180–370,000 ng g DM−1, and 270–110,000 ng g DM−1 were also reported as currently highest levels in dust of industrial environment, house dust, and office dust samples in the UK, respectively [11]. In sludge samples of both municipal and industrial waste water treatment plants (WWTPs) in the USA, Turkey, and Hessian (Germany) levels of 85.5 ng g DM−1 up to 2.5 w% of ∑PBDE were reported [12–14]. The annual input of PBDEs into the environment in the USA was quantified as 47.9–60.1 tons, where 24.0–36.0

As WWTP sludge is commonly used as fertilizer in agriculture, PBDE contamination is not restricted to hotspots like e-waste sites, and ubiquitous spread is further increased by gaseous and particulate-based transport of PBDEs. Consequently, soil samples were positively tested towards PBDE contaminations in grassland and forest soils of UK and Norway (∑PBDE: 65–12,000 pg. g DM−1) [15], Western Austria (∑PBDE: 10.4–2744 pg. g DM−1) [16], Germany (BDE-47: <27–505 pg. g DM−1, BDE-209: <156–461 pg. g DM−1) [17], and the Artic (∑12PBDEs ex BDE-209:

Given the widespread distribution of PBDEs in soils, it can be assumed that they are absorbed by plants to a significant extent and are then introduced into humans via the food chain. The following sections are intended to show the factors influencing the plant uptake of PBDEs and their degradation products and to examine in detail the uptake and transport behavior of twelve selected crops. From these data, generally valid relationships for other crops will be derived using simple key

**2. Physical characteristics and their effect on transport pathways and** 

Because PBDEs show a wide range of molecular weight (328–959 g mol−1), lipophilicity (log KOW = 6–10), and volatility (log KOA = 9–16) [19, 20], BDE congener specific transport and plant uptake mechanisms (soil-air-plant vs. soil–soil moisture-root-plant) are highly different and dependent on specific substance parameters (vapor pressure, Henry coefficient, air-plant partition coefficient, KOW value, KOA value), meteorological parameters (temperature, wind rate, precipitation, temporal rainfall distribution, deposition kinetics of gaseous and particulate BDEs), long range transport, plant specific characteristics (species, lipid content, carbohydrate content, fiber content, foliage morphology, non-lipid plant parts, rind consistency), and rhizosphere factors [18, 21–23]. Under aspects of transport, low brominated BDEs (Br2-Br3) are mainly and medium brominated BDEs (Br4-Br5), depending on the study, are minorly to dominantly distributed as gaseous

**68**

parameters.

**plant uptake**

compounds (BDE-15: 100%; BDE-28: 35–60%), while transmission and deposition of higher brominated congeners (Br6-Br10) are obligatorily characterized by adsorption of BDEs on a particulate phase [17, 22–25]. As a result of the particle-bound lower-range transport of the latter PBDEs, the PBDE pattern in soil and plant samples from densely populated regions and near hotspots shows high agreement with the present PBDE emission spectrum, while in sparsely populated regions the PBDE spectrum is dominated by low brominated congeners [7, 23]. Additionally, a significant concentration gradient of ∑PBDEs from both densely populated to sparsely populated regions and from emission sites to adjacent region can be observed [7, 26]. Hence, various studies around the world showed a wide range of PBDE concentrations in dust samples of 4.33–370,000 ng g DM−1 [11, 20, 27–31] with a clear domination of BDE-209 in the range of 69.2–99.6% [11, 20, 25].

Due to the high molar mass and the lipophilicity of high brominated BDEs, plant uptake by the soil–soil moisture-root-plant pathway is of low relevance and restricted to low and medium brominated BDEs (Br2-Br5) like BDE-47, BDE-99 and BDE-100 [21, 32], even though intrinsic transport of BDE-209 was reported by single studies [33–35], but disproved by Wu et al. [36], where plant availability of BDE-209 was quantified as 0.3–0.5% of the initial soil concentration and 99.5–99.7% of BDE-209 are solely adsorbed on the soil matrix and the outer side of the roots. Hence, atmospheric uptake of high brominated BDEs is the dominant pathway, even though BDE-209 reveals a low ratio of 0.1% of the atmospheric PBDE pattern [24, 37].
