Fluorescence lifetime measurements of fluoranthene, 1-naphthol, and napropamide in the presence of dissolved humic acid

The binding of hydrophobic organic solutes and nonionic pesticides with dissolved humic substances may significantly influence their behavior and fate in natural systems. The binding of fluoranthene, 1-naphthol, and napropamide [2-(1-naphthoxy)-N,N-diethylpropionamide] by an International Humic Substances Society reference soil humic acid in aqueous solutions was studied using fluorescence quenching and lifetime measurements. The quenching of fluoranthene, 1-naphthol, and napropamide fluorescence by the humic acid was adequately described by the Stern-Volmer equation. The effects of temperature ranging from 283 to 313 K on the quenching ratios was not significant, and the fluorescence lifetimes of these compounds did not shorten as a function of increasing humic acid concentrations