“…For most land application methods, it can be challenging to demonstrate that the applied amendments are being consumed and enhanced degradation of the target compounds is occurring. Recent advances in diagnostic tools (DTs) including compound-specific isotope analysis (CSIA), and molecular biological tools (MBTs) or biomarkers for specific PHCs have improved the ability to assess performance of remedial systems involving biodegradation of PHCs (Griebler et al, 2004;Fischer et al, 2008;Knöller et al, 2008;Batlle-Aguilar et al, 2009;Fischer et al, 2009;Morasch et al, 2011;Braeckevelt et al, 2012;Feisthauer et al, 2012;Thullner et al, 2012;Ponsin et al, 2015;Torrentó et al, 2017;Bouchard et al, 2018a;Shayan et al, 2018;Solano et al, 2018;Wei et al, 2018;Wanner et al 2019). The use of biomarkers relies on the detection and quantification of "signature" metabolites, which are specific to a transformation pathway for a given compound, and/or the detection of mRNA encoding for enzymes involved in the associated biodegradation pathways (Bombach et al, 2010;Laban et al, 2010;Liu et al, 2011;).…”