However, previous work by has observed that environmental concentrations of macrolide AAs (ERY, CLR, and AZM) do not positively select for resistance genes . Instead, lowest observable effect concentrations in this study for macrolides were significantly higher than PNECs and the measured environmental concentrations. In this case, it was theorised that PNECs for macrolides could be underestimated when considering combined exposure effects. The same study also demonstrated for CIP, (whilst no significant selection of qnrS was observed), positive selection of intI1 at environmentally relevant concentrations were demonstrated (> 7.8 and <15.6 µg/L). Due to this the authors theorised the likelihood that genes conferring resistance to different antimicrobials may also be co-selected by CIP, due to intI1 association (e.g. sul1 gene is frequently found on the class 1 integrons backbones). Results such as these could potentially indicate AA levels do not drive ARG levels in wastewater. This study has not only highlighted the need for compound specific assessment for selective potential of genes, but also that further research is essential for more informed AA and ARG regulation, for both environmental and public health purposes.