To verify chemical suppliers' compliance with environmental standards, you can follow these steps:

1. Review Environmental Certifications
   - Check if the supplier holds relevant certifications such as ISO 14001 (Environmental Management System) or other industry-specific environmental certifications.
   - Verify the validity and scope of these certifications to ensure they cover the supplier's production or service activities.

2. Assess Environmental Management Systems
   - Request documentation on their environmental policies, objectives, and management systems.
   - Evaluate whether the supplier has established procedures to identify, monitor, and manage environmental impacts.

3. Check Compliance with Environmental Regulations
   - Confirm that the supplier is aware of and complies with local and international environmental regulations.
   - Review their compliance records to ensure there are no recent violations or unresolved issues.

4. Conduct On-site Audits
   - Perform or commission an on-site audit to inspect the supplier's facilities and operations. This can include:
     - Facility Inspection: Assess the cleanliness, organization, and safety practices in production areas.
     - Equipment Check: Ensure that environmental control equipment (e.g., waste treatment systems) is operational and well-maintained.
     - Process Observation: Verify that processes comply with environmental standards and regulations.

5. Evaluate Environmental Performance
   - Request records of environmental performance, such as waste management, energy consumption, and emissions.
   - Check for regular monitoring and reporting of environmental data, including compliance with emission limits and waste disposal regulations.

6. Assess Supplier's Environmental Policies and Practices
   - Review their policies on hazardous materials management, waste reduction, and resource efficiency.
   - Evaluate their commitment to sustainable practices, such as using renewable energy sources or recycling programs.

7. Check Historical Compliance Records
   - Investigate the supplier's past environmental performance, including any violations or corrective actions taken.
   - Verify if they have a history of environmental non-compliance and how they have addressed these issues.

8. Engage Third-Party Auditors
   - Consider hiring a third-party auditing firm to conduct a comprehensive environmental compliance audit.
   - These audits can provide an independent assessment of the supplier's environmental practices and compliance status.

9. Monitor Ongoing Compliance
   - Establish a system for ongoing monitoring of the supplier's environmental performance, including regular updates on compliance and any changes in regulations.
   - Require the supplier to provide periodic reports on their environmental management activities.

10. Supplier Training and Improvement
   - Ensure that the supplier's employees receive regular training on environmental regulations and best practices.
   - Encourage continuous improvement in their environmental management systems and practices.

By following these steps, you can effectively verify chemical suppliers' compliance with environmental standards, ensuring that they meet your sustainability goals and regulatory requirements.