The impact of anaerobic digestate and wood ash amendments on the indigenous 14C-phenanthrene catabolism in soil

Ojo, Adesola S. and Ejileugha, Chisom and Ibeto, Cynthia and Stevens, Carly J. and Semple, Kirk T. (2026) The impact of anaerobic digestate and wood ash amendments on the indigenous 14C-phenanthrene catabolism in soil. Journal of Environmental Management, 405: 129724. ISSN 0301-4797

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Abstract

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment. They are of concern due to their low biodegradability, environmental persistence, and inherent toxic effects on humans. However, PAHs may be degraded in soil under appropriate environmental conditions. This study investigated the impact of nutrient-rich anaerobic digestate (AD) and/or wood-ash (WA) on indigenous catabolism of 9-14C-phenanthrene in soil over a 90-d incubation. The mineralisation kinetics were positively influenced by the amendments, with shorter lag times, faster rates, and higher extents of mineralisation observed in amended soils compared to the unamended soil incubations. Lower amounts of AD (0.173 g, 1.73 g, and 17.3 g kg−1 soil), WA (0.0094 g, 0.094 g, and 0.94 g kg−1 soil), and their combination (AD + WA) showed significantly (P < 0.05) shorter lag times, faster rates, and higher extents of mineralisation when compared to larger amounts of AD (173 g kg−1 soil), WA (9.4 g kg−1 soil), and their combination (AD + WA). The cumulative extents of mineralisation in soils amended with the lower amendment amounts ranged from 52 to 90 % across the 90-d incubation while it ranged from 12 to 49 % in soils amended with the higher AD and/or WA amounts. The negative impact of high amendment amount was higher under WA addition with 9.4 g WA kg−1 soil adversely impacting mineralisation kinetics both singly and in combination with different amounts of AD. These findings demonstrate that optimised application of AD and/or WA can enhance PAH microbial degradation efficiency, but also highlight that excessive amendment application may hinder biodegradation, emphasising the importance of optimising amendment amount in sustainable soil amendment strategies.