Under aerobic conditions, avermectin B1a degrades primarily via hydroxylation or oxidation in the C-8a- position, resulting in formation of 8a-hydroxy-avermectin B1a (NOA 448112) and 8a-oxo-avermectin B1a (NOA 448111). At 20 °C, the maximum percentages were 13.4 to 15.7 % of AR for NOA 448112, and 9.1 to 10.3 % for NOA 488111. In one study, it was shown that 8a-hydroxy-avermectin B1a was present as an equilibrium between the hemiacetal ring and the corresponding ring-cleaved aldehyde form, total amount was 20.1 % of AR at ambient temperature. This distinction was not made by the analytical methods used in the other stud- ies. The primary products 8a-hydroxy-avermectin B1a and 8a-oxo-avermectin B1a further degrade via hy- droxylation in the C-4 position to 4,8a-dihydroxy-avermectin B1a (NOA 457464) and 8a-oxo-4-hydroxy- avermectin B1a (NOA 457465). At 20 °C, both compounds reached maximum levels of 9.9 % of AR. The deg- radation pathway is shown in Figure B.8.1.3-1. The maximum percentages of metabolites as presented above, represent the net amount resulting from si- multaneous formation and decline. From the Berkely-Madonna fits, the following "true" formation percent- ages were obtained: 23 and 30 % for NOA 448111 and NOA 448112 (from avermectin B1a), 58 % for NOA 457464 from NOA 448111) and 85 % for NOA 457465 (from NOA 448112). The PECS is calculated applying two methods, using (1) the apparent maximum level and (2) these "true" formation percentages (see Section B.8.3), the PECGW is calculated with the fitted formation percentages (see Section B.8.6.2). The formation of bound residues was 39.1 % of AR after incubation for 91 days at 20 °C and further increased to 44.1 % of AR after 196 days. Mineralisation accounted for 12.4 % of AR after 91 days and reached 27.6 % of AR in another study at the end of a 365-days incubation period.