**1. Introduction**

Polybrominated diphenyl ethers (PBDEs) have been used for decades as flame retardants in a wide variety of products. Notable among these are building insulations, upholstered furniture, electrical goods, vehicles and aircrafts, foams, textiles, electrical insulations, and a variety of technical plastics such as acrylonitrile-butadiene-styrene copolymers (ABS), high impact polystyrene (HIPS), polybutylene terephthalate (PBT), or plain paper (PAP), where PBDEs were used in concentrations of 5–30 percent by weight. Despite a spectrum of 209 PBDE congeners, only three formulations were of technical relevance, namely pentabromodiphenyl ether (penta-BDEs), octabromodiphenyl ether (octa-BDEs), and perbrominated diphenyl ether (deca-BDE, BDE-209). The global demand (EU demand) of these mixtures in 2001 was about 7500 tons (EU:150 tons), 3790 tons (EU: 610 tons), and 56,100 tons (EU: 7600 tons) [1]. The use of BDE-209 reached its peak in 2003–2006 with 30,000 tons (China), 9600 tons (EU), 5000–10,000 tons (Northern

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

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 tons were located in sewage sludge [6].

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

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 parameters.
