Triadic or tetradic multi-tier sustainable supply chain management (MT-SSCM) research emerged recently to reach out towards raw material suppliers and to address their often severe sustainability impacts. This is especially relevant in mineral supply chains (SCs) which consist of a commodity chain upstream and an end-product chain downstream. To comprehensively investigate the reach of MT-SSCM in mineral SCs, the extant Delphi study brought together 44 global authors on sustainability in mineral SCs. They contributed their professional knowledge in three questionnaire rounds, which systematically identify, evaluate and contrast the sustainability challenges in mineral SCs. As a result, a generic mineral SC structure is derived and 17 major sustainability issues are identified. Moreover, the findings reveal that all but two sustainability issues need to be addressed in the upstream SC. As mineral SCs might comprise up to nine tiers, the most impactful tiers lie outside the reach of current MT-SSCM concepts, which are limited to triads or tetrads by the visible horizon or lacking power of the focal firm. We thus propose a cascaded MT-SSCM approach which links the up- and downstream SC parts. Moreover, individual focal firms for each SC part are defined, which build a direct strategic link. This link enables that tailored managerial responses can be cascaded into the respective SC parts, where the individual sustainability issues can best be addressed. This cascaded design represents a novel approach in MT-SSCM which multiplies existing concepts. Moreover, the challenges and opportunities, which the cascaded approach raises for MT-SSCM research are discussed and outlined.

Introduction

Today’s supply chains (SC) connect a wide range of contexts, actors and industries in order to provide a competitive end-product. A firm’s knowledge about the participants of a SC decreases with the physical and cultural distance as well as with the number of tiers between a focal firm and a certain supplier (Carter et al., 2015; Kembro et al., 2017). This is especially relevant for businesses which are sensitive to sustainability, which is typically heavily impacted by the raw material suppliers at the upstream end of the SC (Mena et al., 2013; Schmidt et al., 2017). However, many industries rely on commodity supplies which are produced in considerably different contexts regarding production processes and regulatory frameworks. These commodity supplies often remain outside the visible horizon, i.e., the n-tier suppliers known by the focal firm (Carter et al., 2015). Moreover, one commodity might function as raw material for more than one industry (Schmidt et al., 2017). Mineral commodities, for example, are used by construction, automotive, aviation, jewlry, electronics and packaging industries (Hofmann et al., 2018; Young, 2015). Such industry spanning SCs call for joint concepts in order to implement an effective management of sustainability issues (Seuring & Gold, 2013). Multi-tier sustainable supply chain management (MT-SSCM) thus aims to “reach deeper into the supply chain” (Mena et al., 2013, p. 59) and consequently started to evaluate triadic SCs as the next step upstream (Choi & Wu, 2009). While Mena et al. (2013) proposed ideal structures for triadic SCs, Tachizawa & Wong (2014, p. 651) extended their propositions to “any lower-tier supplier”, thereby moving beyond the second tier. These concepts are currently dominating MT-SSCM research with most studies investigating cases from the food industry (Mena et al., 2013; Grimm et al., 2014) or multiple cases integrating different industries such as electronics, retailing and food (Grimm et al., 2016; Wilhelm et al., 2016a; 2016b). The just outlined MT-SSCM concepts by Mena et al. (2013) as well as Tachizawa and Wong (2014) thus prove applicable for studying entire industries.