Contaminated sites, waste management, and green chemistry: new challenges from monitoring to remediation

Human activities suppose a risk of generating contamination of the environment: all of these activities imply the modification of the media, including the landscape, and frequently also the quality of soil, water, and atmosphere in the surroundings. When these affections go further than certain thresholds, we have a contaminated site. Besides, the human activities also imply frequently the accumulation of wastes; even in the simplest way of life, inhabiting caves, the enlargement of the cave for new born humans generates the need of excavation to create a void, extracting materials that need to be accumulated more or less near the cave entrance, generating a residual heap. Nowadays, the management of contaminated sites and of wastes, many of them created or accumulated during many decades, or even centuries, represents an important need, since their extension has not stopped growing, in particular, from the development of the BIndustrial Age.^ However, the task is not easy (nor cheap) to carry out, due to both the diverse nature of the Bcontaminants^ distributed in the environment and to the extension of sites affected by this type of problem. Green chemistry is one of the tools developed to try to get solutions to this type of problems, in many different ways, including the development of chemical process able to mitigate the negative effects that certain contaminants may exert on the soil quality, or in the health of biota affected by such contaminants. But, how can we identify properly Bcontaminated sites^? And how can we identify real risks related with the presence of contaminants or of wastes in the proximity of our industrial sites (or sometimes in urban areas)? Of course, the basis of this is the needed baseline information, meaning what should be the Bnormal^ characteristics of an area considered as not contaminated. This information is not so easy to get; some maps register diverse parameters on the quality of different environmental parameters. As an example, geochemical maps of entire continents, of entire countries, or entire regions are available in commercial basis and/or in the scientific literature. But not all parameters of interest in this sense are always registered on suchmaps. Even the ones that should bemore useful, as the contents in metals which are considered as potentially toxic, may not be appropriate, since maps usually register total contents in those elements and not the portions of those elements susceptible of being incorporated into other environmental compartments: which fraction of the total content is water soluble and so is available for migration from soil to aquatic systems?; which fraction can be uptake by plants? In each case, therefore, it is a real need to identify the regional baseline parameters which may serve as a local reference to identify the areas that should be identified as contaminated, in which the analytical of air, water, or soil quality suppose the real risk of affecting the health of humans, directly or indirectly (by means of direct or indirect transference to the food chain). The present special issue (SI) of Environmental Science and Technology presents a number of studies dealing with some of these aspects, which were presented as scientific contributions to the BThird Energy and Environment Knowledge Week^ (E2KW), held in Paris (France) on 28–29 October 2016. Drawing from selected contributions to this international congress, the SI gathers novel and timely research on contaminated sites, waste management, and green chemistry. A group of papers is focused on environmental quality monitoring. Three additional papers present green chemistry alternatives to mitigate contamination effects and to obtain useful products from agricultural wastes. Finally, two papers are focused on modeling environmental and related processes. The first one aims to improve the estimations of CO2 Responsible editor: Philippe Garrigues