Model studies of zinc bonding with humic acid in the presence of UV–VIS–NIR radiation

Model experiments were performed to determine the influence of UV–VIS–NIR radiation on zinc bonded with humic acid (HA). The samples of HA or HA–65Zn radioisotope were overlayed on quartz sand in a glass column and subjected to elution that simulated natural conditions. The zinc concentration was chosen to that occurring in the sewage of the Central Sewage Work in Poznaimage. Zinc was washed with water to simulate the influence of rain. The recovery of injected radiotraces ions in the eluates was found to depend on pH, zinc and HA concentrations and on radiation exposure. The results help to evaluate the migration behavior of zinc in the presence of HA and UV–VIS–NIR radiation. From the first part of the investigation appears that radiation induces a degradation of HA–Zn layer and that the degradation process depends on pH of the environment. A decrease in pH causes an increase in photodegradation and the degree of zinc binding in the humic layer. Simultaneously, the ultra-weak luminescence (UWL) of plants was monitored to estimate the influence of zinc and HA on their development. The results show effects of HA and zinc on UWL and growth of bean and watercress which characterize the rate of plants metabolism and perturbation of their homeostasis. It was observed that high concentrations of zinc ions and HA considerably affect the development process of the plants.