Accurate measuring n -octanol/water partition coefficients (log K ow ) of perfluoroalkyl carboxylic acids (PFCAs) using experimental approach has been proven to be very difficult due to their special properties. The ionizable carboxyl groups in PFCAs make their log K ow dependent on pH. In this study, the log K ow values of neutral species of PFCAs (C 4≤n≤14 ) were measured based on reversed-phase high-performance liquid chromatography (RP-HPLC) with the mobile phase pH varying in the range of 1.09–5.00. The relationship between log K ow and retention times was established using some reference compounds (including agrochemicals , polycyclic aromatic hydrocarbons) with known log K ow values, and then validated with alkyl fatty acids, which have similar chemical structures as PFCAs. The apparent log K ow (i.e., log D ow ) of the C 4–14 PFCAs were calculated based on their retention times using the established model, and they displayed a negative linear relationship with the mobile phase pH in the range of 1.09–4.00. Consequently, the log D ow values were converted to the corresponding log K ow values (1.05–7.19) based on the relationship of log D ow = log K ow + p K a – pH. The log K ow increased with perfluorinated carbon chain length with a greater rate for C 4 to C 5 PFCAs than for C 5–14 PFCAs.
Food safety problems caused by pesticide residues have always been a concern for many people. In this study, we investigated the uptake, translocation and subcellular distribution of neonicotinoid insecticides, triazole fungicides, and sulfonylurea herbicides in rice plants ( Oryza sativa L.). The time-dependent uptake kinetics of the three categories of pesticides with different molecular structures fit a first-order one-compartment kinetic model. The neonicotinoids (log K ow −0.66–0.8) were mainly concentrated in the leaves, and the triazoles (log K ow 3.72–4.4) were mainly concentrated in the roots. Neonicotinoid pesticides in the roots were preferentially transported across the membrane through the symplastic pathway; triazole pesticides except for triadimefon and myclobutanil preferentially passed through the symplastic pathway; and sulfonylurea pesticides (log K ow 0.034–2.89) were first transported upward through the apoplastic pathway. In the roots, neonicotinoids, triazoles, and sulfonylurea herbicides were mainly concentrated in the soluble fractions, cell wall and apoplast fractions, respectively. In addition, there was a high positive correlation between the subcellular distribution of pesticides in the roots, stems and leaves. Molecular weight and log K ow jointly affected the enrichment of triazole pesticides in the roots, stems and leaves and the transfer from stems to leaves, while water solubility and log K ow commonly affected neonicotinoids. There was a correlation between pesticide absorption and the molecular structures of pesticides. To develop pesticides with strong uptake and transport capabilities, it is necessary to consider that the electronegativity of some atoms is stronger, the sum of the topological indices of heteroatoms can be large, and the van der Waals volume increases accordingly.
危险品化学品经营许可证（带存储）