September 28 is the deadline for public comments on a U.S. Environmental Protection Agency proposal involving NASA’s request to use ortho-phthalaldehyde, or OPA, to treat coolant fluid in the International Space Station’s internal active thermal-control system. NASA says the treatment would control aerobic and microaerophilic bacteria in the aqueous coolant.
The request concerns a highly specialized operational problem. The station’s thermal-control systems are essential to keeping equipment and crew areas within safe temperature ranges. Microbial growth in a closed-loop system can create maintenance, performance and reliability concerns, particularly when servicing the system in orbit is difficult and costly.
EPA’s public-comment process does not mean the requested exemption has been granted. The agency must review submissions before deciding whether to authorize the specific use. The process reflects the intersection of environmental regulation, spacecraft operations and human-safety requirements.
The issue is also relevant to the future of long-duration spaceflight. As spacecraft remain operational for years and missions extend farther from Earth, operators will need robust methods for managing microbes, corrosion, contamination and system degradation without relying on frequent resupply or ground intervention.
The proposed treatment is narrowly focused on the station’s coolant system and should not be interpreted as a broad change in pesticide policy or an indication of a new crew-health standard. Any final action will depend on EPA’s review and the technical record developed through the docket.
For the space industry, the case shows that routine maintenance questions can become strategic constraints. Life-support and thermal-control systems depend on materials and chemicals that must satisfy both engineering requirements and terrestrial regulatory standards.
Sources: - https://www.govinfo.gov/content/pkg/FR-2026-09-11/pdf/FR-2026-09-11.pdf - https://www.epa.gov/dockets