Critical evaluation of the microbial turnover to biomass approach for the estimation of biogenic non-extractable residues (NER)

Environmental Sciences Europe

Table 2 Postulated chemical reaction and the Gibbs energy for the studied compounds. O₂ (∆G_f = 0 kJ mol⁻¹) not shown

Compound	∆G_f⁰ kJ/mol	Reaction
2,4-D	− 443.5	C₈H₆O₃Cl₂ + 7.5 O₂ → 8 CO₂ (g) + 2H₂O (l) + 2HCl
Ibuprofen	− 184.0	C₁₃H₁₈O₂ + O₂ → 13 CO₂ + 9 H₂O
Glyphosate	− 1480	C₃H₈NO₅P → 3 CO₂
Glyphosate → AMPA	− 268	C₃H₈NO₅P → CH₆NO₃P + 2 CO₂
Bisphenol S	− 145.4	C₁₂H₁₀O₄S → 12 CO₂ + 5H₂O + (S ignored)
Dodecylphenol	1200	C₁₈H₃₀O → 18 CO₂ + 15 H₂O
DS, DA		same yield taken as for dodecylphenol
Bromoxynil	147.8	C₇H₃Br₂NO + 6 O₂ + OH⁻ → 7 CO₂ + 2 Br⁻ + NH₄⁺
Isoproturon	64.2	C₁₂H₁₈N₂O → 12 CO₂ + 7.5 H₂O + 2 NH₃
MCPA	− 443.8	C₉H₉ClO₃ → 9 CO₂ + 4 H₂O + HCl
Metamitron	414.8	C₁₀H₁₀N₄O → 10 CO₂ + 3 NH₃ (NH₃ disregarded)
Pendimethalin	944.3	C₁₃H₁₉N₃O₄ → 13 CO₂ + 8 H₂O (+ NH₃ + 2NO₂ disregarded)
Sulfadiazine	270.3	C₁₀H₁₀N₄O₂S + 2H₂O → 10 CO₂ + 4 NH₃ + H₂SO₄

Assumptions: N and S keep the oxidation state they have in the parent molecule. In the ∆G_r of pendimethalin and metamitron, formation of NH₃ and NO₃ was disregarded in the calculation of ∆G⁰_r. Furthermore, it was assumed that in the unit gC/gC, DA is dodecylbenzyl trimethylammoniumchloride (DA) and dodecylbenzene sulfonic acid (DS) have the same yield as dodecylphenol, because the functional group is removed in the degradation chain. Glyphosate has two degradation pathways, one leading to complete mineralization, and one where AMPA is formed [16]