The Precautionary Principle and Ship Exhaust Gas Scrubber Discharge Bans
Photo - D. Smith
There is a global debate taking place on whether it is permissible for countries and ports to ban ship exhaust scrubber discharges that are used in order to burn cheaper Heavy Fuel Oil (HFO). Under international law, ships are able to use exhaust gas scrubbers to remove Sulphur from exhaust gases, rather pay for more expensive fuel to meet international fuel Sulphur limits. Pollutants that would have otherwise been emitted into the atmosphere are captured by the Scrubber and discharged into the sea.
The Spring 2026 issue of the American Bar Association’s “Natural Resources & Environment” focuses on “50 Years of RCRA & TSCA” in the United States. While it does not directly address the regulation of ship exhaust gas cleaning systems, it sheds some light on the “Precautionary Principle” that undergirds European domestic bans on ship exhaust gas scrubber discharges.
Issue Editor Robin Kundus Craig, introduces the issue by describing how both the Resource Conservation and Recovery Act (RCRA) and the Toxic Substance Control Act (TSCA) attempted to incorporate a risk-based approach to regulation when these statutes were adopted in 1976. These statutes are far from perfect and reforms are certainly warranted. In contrast to TSCA, the 2007 EU law titled Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) is founded on the Precautionary Principle. “Core to the precautionary principle is the belief that risk prevention is essential in the face of scientific uncertainty. Under REACH, the chemical manufacturer and/or importer bears the responsibility of producing data to support the determination that a chemical is safe for its intended uses. Under old TSCA, the reverse was true: EPA had the burden of proving an existing chemical posed an unreasonable risk before it could act to restrict that substance.” Lynn L. Bergeson and Richard E. Engler, TSCA Chemical Safety – A Sisyphean Journey, 40 Nat. Resources & Env't 4 (Spring 2026).
Keeping the Precautional Principle in mind, consider the potential risks associated with ship exhaust gas scrubber discharges. An open-loop scrubber system sprays large volumes of seawater into the ship’s funnel to capture and remove Sulphur-Dioxide (SO2) from the rising exhaust gases and then discharges the wash water back into the sea. Scrubber wash water discharges can also contain heavy metals (Lead, Mercury, Nickel, and Vanadium) and Polycyclic Aromatic Hydrocarbons (PAHs), which are carcinogenic. Some simply describe the process as turning a ship’s emission funnels upside down so that pollutants go into the sea rather than into the atmosphere. The use of HFO combined with open-loop exhaust gas scrubbers is receiving growing worldwide attention focused on potential adverse environmental impacts. In response to these risks, governments are increasingly banning the use of HFO and/or open-loop scrubbers. Efforts to ban Heavy Fuel Oil (HFO) and open-loop scrubbers accelerated significantly in 2025 and into 2026, transitioning from individual port rules to large-scale regional mandates.
HFO/scrubber users argue that risk assessments aligned with the IMO's voluntary 2022 Guidelines for Risk and Impact Assessments of the Discharge Water from Exhaust Gas Cleaning Systems, MEPC.1/Circ.899 should mandatorily underpin and precede any proposed EGCS restrictions. That is not happening because adequate location-specific risk assessments are often not available. Instead, these nations are exercising their sovereign authority to enact bans based on the “Precautionary Principle” referenced in MEPC.1/Circ.899: “In all aspects of risk and impact assessments the need for evidence-based decision-making should be balanced with the precautionary approach.” The precautionary principle, heavily influenced by the 1992 UN Rio Declaration (Principle 15), dictates that when human activities pose threats of serious or irreversible damage to the environment or human health, lack of full scientific certainty should not prevent taking cost-effective, preventative measures. It shifts the burden of proof to proponents of potentially harmful actions to prove safety, rather than requiring victims to prove harm.
Bergeson and Engler observe that other countries and the State of California have opted to follow the European Parliament and Council utilization of the Precautionary Principle seen in REACH as they adopt domestic laws. They say “the EU’s REACH program quickly became the default gold standard for chemical control legislation and, in comparison, TSCA was increasingly thought to be substandard.”
The Precautionary Principle may be firmly embedded within domestic rulemakings to ban ship exhaust gas scrubber discharges. Whether or not those bans are based upon the Precautionary Principle or peer-reviewed research and/or risk assessments in alignment with the non-mandatory IMO MEPC.1/Circ.899 voluntary guidelines might all be irrelevant if the bans are an exercise of sovereign authority.
With no single global ban from the International Maritime Organization (IMO), the expanding "patchwork" of regional and domestic laws is making HFO and scrubber use difficult on many major cruise routes. The recent rise in fuel prices exacerbates any pressure to maximize the use of cheaper HFO along with scrubbers.
