Editorial

This special issue of Toxicological & Environmental Chemistry is dedicated to mathematical approaches employed in environmental chemistry, in recognition of the growing number of mathematical interlinks between chemistry, environmental chemistry, and eco/toxicology. Such connections, particularly between chemistry and mathematics, have been recognised as new scientific discipline (Restrepo 2016) for which various definitions have been proposed.

As stated by Klein (2013), mathematical chemistry “entails mathematically novel ideas and concepts adapted or developed for use in chemistry.” The field is different from using routine mathematics for chemical problems, and it also does not deal with the application of complex mathematics in some standardized manner. To the contrary, mathematical chemistry is adapting mathematics — or even developing new mathematics to solve chemical questions.

Being aware of the growing importance of mathematics, not only in chemistry but also in other subjects dealt with in Toxicological & Environmental Chemistry, we have launched a call for papers upon which we received numerous papers. After peer-review, 15 manuscripts were collected which exhibit the diversity of mathematical and statistical approaches currently involved in toxicological and environmental-chemical research. They also demonstrate the world-wide interest in the subject: the articles are authored by scientists from twelve countries: Canada, China, Colombia, Denmark, Germany, Greece, Israel, Italy, Kuwait, Oman, Poland, and Switzerland.

The main subject of several papers in this issue is classification, being of central relevance in chemistry. Here, problems of clustering similar molecular structures are addressed mainly via graph theory employing topological indicators. Such indicators are also useful for prediction of substances' properties by quantitative structure-activity relationship (QSAR) models. Besides the involvement of sophisticated statistics, QSAR approaches are applicable to the finding of relevant predictors and the selection of the best ones and to the development of mathematical tools to attain robust results. QSAR is normally performed for pure substances; here, also the role of impurities and their implications for QSAR related research are addressed. Another aspect covered by some papers is risk evaluation of chemicals, giving rise to two different mathematical branches, one being modelling chemicals in the environment e.g. by dynamic models, the other evaluating chemicals by multi-indicator systems. It is not astonishing that the development of sophisticated dynamic models impacted the development of evaluation tools derived from discrete mathematics, as these models provided many useful indicators for conceiving strategies, for identification of problematic chemicals, or for pointing at endangered environmental areas. From a statistical point of view, Bayesian approaches are also discussed which we consider an important facet in mathematical chemistry although they are not broadly employed for research.

Besides the kind of mathematics considered in this issue, a wide range of applications is presented, from water treatment techniques to medicinal herbal substances, from uranium bioremediation to evaluation of oil and gas well sites. We believe that this special issue contains a range of papers well demonstrating the diversity of mathematics employed and useful for chemical and environmental investigations.