Fig. 5. Chemical–biological data-integrative categorization of petroleum substances. Combinatorial integration of physico-chemical and bioactivity data for groupings of petroleum substances in ToxPi was achieved through parameter-specific clustering of assay parameters (a). Four major and equally weighed (= 25%) data clusters reflected eight cardiophysiology phenotypes, three cardiotoxicity and five hepatotoxicity parameters, and two physico-chemical descriptors, i.e. initial and final boiling points. Cluster analysis was performed using the hclust function in r (b). [VHGO = vacuum & hydrotreated gas oils; SRGO = straight run gas oils; OGO = other gas oils; HFO = heavy fuel oils; RAE = residual aromatic extracts].