 There are several similar and overlapping efforts to define and conceptualize a closed loop lifecycle of product and materials management, with many of these efforts being spearheaded by government agencies, entrepreneurs, scientists and non-governmental organizations.While similar to SMM, these product lifecycle models focus largely on the end-of-life management of materials while SMM focuses on the impacts materials, products and services have on the environment such as eutrophication, acidification, ozone layer depletion, global warming and aquatic toxicity as well as energy and water use.The Product Stewardship Institute defines Product stewardship as