Despite numerous studies, humic acids are still not a well known fraction of humus substances. This results mainly from the complex structure of these compounds and, in consequence, from the varied chemical and physical properties as well as complex behaviour in connection with other soil substances. On the other hand, humic acids determine key features of soils: fertility, aggregate structure, suitable water-air ratios and microbial conditions. These substances belong to a group of chemical compounds characterised by strong sorption properties. It means that humic acids can interact with different soil substances, including heavy metals, which affects the mobility of cations in the environment.

      The mechanisms of interactions of humic acids with metal ions belong to issues still unclear, complex and not fully explained. It should be stressed that there are a lot of questions, unclear and contradictory opinions in scientific environment related to the reactivity of humic acids, and especially to their interactions with metals. The diversity of interpretations of above phenomena covers such subjects as the way of binding between humic acids and metal ion, type of created bonds, type of structure units of humic acids which take part in interactions, as well as the stability of formed compounds. Additional aspects which complicate studies are varied chemical properties of metal: valence, ionic radius, hydrate ratio, electronegativity as well as varied physicochemical nature of humic acids: different molecular weight, degree of structure transformation, content of aromatic rings, aliphatic chains or functional groups. Simultaneously, it should be added that the form, mobility and reactivity of both humic acids and metal ions in the soil environment strongly depend on pH. Depending on circumstances, created compounds can lead to mobilisation of metals and their leaching from upper parts of soils (which is disadvantageous in the case of fertilisation with microelements), or to the accumulation of heavy metals in soil in the form of insoluble humates, which is dangerous in the case of exceeding the concentrations at which microelements positively influence plants. Moreover, concentration of heavy metals in soils still increases together with the development of the cosmetics, agricultural and chemical industry, whereas methods of neutralisation or removing of heavy metals are still unsatisfactory.

For all these of reasons, the problem of the study of humic acids and their interactions with metals in soil is a very complex matter and difficult for realization. These problems are a still burning and open scientific issue, not only in Poland scale, but also for the entire world, and require additional investigations. Above study also brings up the still actual problem of circulation and remediation of metals in the environment.

Above paper is a comprehensive work about the interaction of metal ions with humic acids. The subject includes interactions with “light” and “heavy” metal ions, simultaneously taking into account its significance in agriculture and plant cultivation. The research problem relates also to the influence of different conditions of the environment, like pH, ionic strength, temperature, humic acids origin or chemical properties of different metals, such as ionic radius, oxidation degree, redox properties, chemical forms. The work includes chapters describing humic acids and metal ions as reactive components of the soil system. The most important characteristics of these components are shown, with emphasis on their sorption abilities. Additionally, the work covers description of the most important factors which can determine reactivity. For selected metals, especially important in soil, some subchapters were prepared and they contain literature review relating to their interactions with humic acids. The final chapters are about selected instrumental techniques, useful in the analysis of interactions of humic acids with metal ions.

       Knowledge about interactions between heavy metals and soil organic matter characterised by varied physicochemical properties should let predict possible consequences of the emission of the metals to the environment. Simultaneously, this knowledge should contribute to development of more effective methods of heavy metal remediation. Such studies can contribute to improvement of soil cultivation, ecological and integrated tillage, and minimising the usage of chemical toxic substances.