# Insights into PCDD/Fs and PAHs in Biomass Boilers Envisaging Risks of Ash Use as Fertilizers
## 1 Introduction
Despite the low solubility of PCDD/Fs and PAHs, suggesting low environmental availability, it has been shown that leachability of dioxins depends on composition and sorption properties of soils [57]. In fact, [PERSON] and [PERSON] [58] found that the solubility of PCDD/Fs was enhanced by the presence of humic matter. Therefore, the authors concluded that fly ash should not be landfilled with organic wastes in order to prevent leachability of PCDD/Fs [58]. In Europe, some countries have different regulations established for the ash streams that can be applied to soils and different requirements for levels of nutrients and heavy metals allowed, such as the Nord Test Technical Report [59]. POPs are limited in a few countries; in Denmark PAHs control is required only if unburned matter in ashes is higher than 5% with a limit of 3 mg/kg for 9 PAHs [59] and in the Czech Republic the limit is 20 mg/kg [60]. In Sweden there are different limits for carcinogenic and non-carcinogenic PAHs in soils, depending on the soils used sensitivity [61]. In Canada, in addition to the limits for naphthalene and benzo(a)pyrene in wood ashes (4.0 mg/kg for each), PCDD/Fs are also limited to 27 ng TEQ/kg [62]. In Portugal, alternative fertilizers containing sewage sludge and biomass ashes have limits of 6 mg/kg for PAHs, and 100 ng TEQ/kg for PCDD/Fs [63]. In Germany, the regulation for applying fertilizer restricts PCDD/Fs + PCBs to 8 ng TEQ/kg for pasture lands, and 30 ng TEQ/kg for agricultural soils [17]. In Europe, the recent harmonization of EU fertilizers aims at valorizing some wastes as Component Material Categories (CMC) for use as alternative fertilizers [64]. Thermal oxidation materials and derivates, namely ash-based materials, are to be included; in addition to the control of heavy metals, the proposed limit for \(\Sigma_{16}\) PAH is 6 mg/kg and for PCDD/Fs is 20 ng TEQ/kg, respectively [65]. TEQ are the Toxic Equivalents corresponding to the revised WHO\({}_{2005}\) TEQ [66]. Aware of the perilous nature of ashes, frequently obliviated in many studies concerning ash applications as fertilizers, it is important to initiate further practical investigations to determine the PCDD/Fs and PAHs contents and define if the ashes can be used as fertilizers or need a safe disposal. The purpose of this work is to investigate the presence of PCDD/Fs and PAHs in industrial biomass ashes, to distinguish the degree of contamination of different ash streams and evaluate if they comply with the upcoming European Regulation for use of ashes as fertilizers. Also, we wanted to understand the source of POPs in ashes, namely relating with the composition and contamination of the fired biomasses and constitution of ashes. Furthermore, we conducted a literature survey to provide a deeper assessment of the fate of PCDD/Fs and PAHs in biomass combustion and compile up-to-date regulations and programs within the subject. In the experimental part we present chemical data of the residual forest biomass used in four biomass power stations and of various biomass ash streams collected over a year. The distribution of the 17 toxic PCDD/Fs and 16 PAHs measured in biomass and in ash blends is interpreted in view of their constitution. The potential toxicity of ashes is evaluated by calculating TEQs and BaP-EQs, according to various protocols. Also, a sensitivity analysis was performed to understand the impact of management of non-detected (ND) congeners on aggregate quantities used in policy regulation, such as TEQs, \(\Sigma\)PCDD/Fs and \(\Sigma\)PAHs. The ND handling can be critical for environmental risk assessment and evaluation of compliance with limit values.