The circular economy is based on the maximum use of resources by reducing, reusing, and recycling the elements used. Currently, the items littered most frequently in the world are cigarettes butts (CB) as these debris are freely disseminated in the marine habitat, they are generally difficult to collect and very complex to recycle. Litter CB is a great social problem that generates excessive economic costs and serious environmental problems. CB is also not biodegradable and highly toxic to marine organisms and presents a distinctive mixture of physical and chemical contamination. However, little research has been done on the management and recycling of this dangerous waste. Several proposals have been made to incorporate this waste into high-volume articles of direct production or recycling, but collection logistics are lacking since the current system is inefficient, in addition to the poor environmental behaviour of citizens. This work presents a current synthesis of the CB problem from all its possible aspects in order to have a global vision of the life cycle of the CB, indicating both the known and the gaps in the knowledge of each of them, and intends to give a general outline of the steps to follow to try to end such a worrying problem at the global level.

The effects of certain environmental factors on spatial variation of the mollusc community associated with the alga Halopteris scoparia in Algeciras Bay (southern Spain), located in the Strait of Gibraltar, are studied. Environmental gradients from the exterior to the interior of the bay have been detected, related above all to water movements, solids in suspension, organic content of sediments, and structural complexity of plants. These gradients are seen as differences in the composition of the mollusc communities of the outer zones (Isla de Las Palomas, San Garcma, and Cucareo) and inner ones (Guadarranque and Crinavis). Although the conditions of the inner zone restrict the growth of some groups such as crustaceans and polychaetes, mollusc populations have developed well there in both number and diversity. Species are found exclusively at the exterior of the Bay (include Cingula amabilis, Pisinna glabrata, and Nodulus contortus) and for the interior (Alvania montagui, Alvania rudis, and Rissoa similis), the latter being the most discriminating between the two major zones of the bay. The environmental parameters having the greatest effect on the molluscs associated with Halopteris scoparia are water movement, the morphological characteristics of the substrate, and most importantly the availability of food.