Humic substances (HSs) are the main component of dissolved organic matter (DOM) in aquatic ecosystems [1,2]. Depending on the source of organic material involved in the humification process, HSs have a variety of molecular structures that differ with their source. Microbial and abiotic degradation of source materials results in a variety of HSs molecular structures, such as acylaromatic, quinoid and aliphatic structures in the core, and amino acid or carbohydrate-like structures and carbonyl-, carboxyl-, phenyl-, and hydroxyl-groups at the periphery [3,4].