Sustainability policy as Environmental Policy

Answer:

If the sustainability policy meets all requirements of ISO 14001 regarding environmental policy, you can use it as environmental policy. The standard requires for environmental policy the following:
- to be appropriate to the purpose and context of the organization;
- to provide framework for setting environmental objectives;
- to include commitments to protection of the environment, fulfillment of the compliance obligations, continual improvement and other commitments relevant to the context of the organization

For more information, see: How to write an ISO 14001 environmental policy https://advisera.com/14001academy/blog/2019/08/27/key-iso-14001-benefits-to-customers/nowledgebase/how-to-write-an-iso-14001-environmental-policy/

These materials will also help you regarding the environmental policy:
- Free online training ISO 14001:2015 Foundations Course https://advisera.com/training/iso-14001-internal-auditor-course/
- Conformio (online tool for ISO 14001) https://advisera.com/conformio/ "