**6.9 Compost and digestate**

*Flame Retardant and Thermally Insulating Polymers*

highest levels [56].

**6.5 Lipid content**

**6.7 Biochar**

**6.8 Sewage sludge**

**6.3 Rhizosphere and mycorrhiza**

**6.4 Specific root and leaf surface**

**6.6 Organic content of the soil**

of wheat was determined as 29–93% of the total plant uptake [25], while BDE-209 accumulation in six different plant species at initial soil levels of 4700 ng g DM−1 ranged 1822–10,933 ng plant−1 with alfalfa showing lowest and maize showing

The release of plant eluates into the mycorrhizal is part of the symbiosis between the plant and the mycorrhizal fungi promoting the plant's uptake of nutrients and the growth of microorganisms in the mycorrhizal area. Its secondary effect of enhanced microbial biodegradation and detoxification of PBDEs in the mycorrhizal area was shown several times in literature. As an example, increased depletion of 470 ng g DM−1 towards 2250 ng g DM−1 was observed for BDE-209

A correlation between accumulation of PBDEs and high specific plant surface was clearly shown for BDE-209 in roots of radish, lettuce and taro [58, 59] and for

The lipid content of a plant, especially of the roots, shows strong effects on PBDE uptake and was successfully evaluated for various mosses, lichens, ryegrass, alfalfa, maize, radish, squash, and pumpkin. A positive correlation between lipid content and PBDE uptake (RCF), as well as a negative correlation in lipid content

Similar to the lipid content an increase in organic content of soil evokes higher PBDE accumulation in the soil and, therefore, reduced PBDE plant uptake [20, 33, 63]. Exemplarily, PBDE uptake in carrots was reduced by 31.5–69.8% and soil-based biodegradation increased by 8.6–28.5% by addition of 1–4 w% of swine manure to the soil fraction [63]. Differentiation between TOC and DOC showed a clear improvement in adsorption of PBDE in the soil matrix at higher TOC levels,

Since biochar is insoluble and thus is considered as a TOC increase of the soil,

As sewage sludge reveals a high TOC content, but also enhanced contamination levels with PBDE or their detoxification and degradation products, sewage sludge is a dominant PBDE exposure pathway. Hence, using contaminated sludges as agricultural fertilizers, increasing concentration levels and accumulation of PBDE in the soil phase and, finally, elevated PBDE plant uptake are observed. However, relevance of this effect strongly depends on the original PBDE contamination levels of the sludge. An overview of PBDE levels in different sewage sludges was

comparing rice plants with and without mycorrhizal fungi [57].

Br2-BDE to Br10-BDE in both pine needles and eucalyptus leaves [60].

and intrinsic PBDE mobility (TF) was observed [19, 22, 61, 62].

whereas no effect was observed in case of increased DOC levels [54].

elevated accumulation of PBDE in the soil phase may occur [64].

**72**

In difference to sewage sludge, the PBDE load of compost and digestates is rather low as confirmed by various studies due to the low contamination levels of the plant educts (leaves, green waste, fruit and food residues). For instance, a broadly based study of biocompost, green waste compost and digestates in Baden-Wuerttemberg showed comparable median concentrations of 13 ng g DM−1, 5.4 ng g DM−1, and 13.7 ng g DM−1 and confirmed to low relevance of these materials as PBDE emissions sources [65].
