Requirements Technical Debt (RTD) refers to the accumulation of issues, compromises, or incomplete decisions related to the requirements phase of a software development project. When requirements are defined, they are often based on assumptions about the operating environment. Industrial experience indicates that it is often easier to miss an environment behavior than to miss a system specification. This is due to the fact that environment assumptions are rarely documented and evolving as developers build the system. In this paper, we looked at RTD through the lens of environment assumptions. Specifically, we examine and identify instances of RTD caused by environment assumptions using an illustrative example of safety requirements from the literature. We then performed a systematic mapping study to identify tools or models that incorporate environment assumptions in the system development. Our findings demonstrate that environment assumptions act as early indicators of potential issues that may lead to RTD, especially when these assumptions are incomplete or incorrect. From our systematic mapping study, we identify seven models that support effective identification of environment assumptions to mitigate RTD risks. To that end, our study helps fill the gap in the literature by explicitly addressing the role of environment assumptions in the identification of RTD.