The Deadliest Catch: Scrubber washwater discharge in ASEAN fishing grounds

When would reducing air pollution become a case of good intentions gone awry? When pollutants once emitted to the atmosphere are simply transferred to marine waters, threatening marine life and the food chain that nourishes humans. This is the dynamic created with the growing use of “scrubbers” to clean up exhaust waste from combusted dirty fuels used on ships. Scrubbed exhaust gases may leave the skies above bright, but they darken marine waters with pollution. Here at ICCT we are studying this vexing problem closely.

The ICCT recently released a first-of-its-kind global analysis of washwater discharge from Exhaust Gas Cleaning Systems (EGCS, or scrubbers) installed on marine vessels. The study shows where and how much scrubber washwater is disposed of worldwide and provides an interactive map for easy visualization of washwater discharges at any geographic scale and location. Member countries of the Association of South-East Asian Nations (ASEAN), including Myanmar, Thailand, Cambodia, Malaysia, Singapore, Indonesia, Laos, Vietnam, Brunei, and the Philippines, sit in one of the most eye-catching hot spots in this map (Figure 1).

Figure 1. Washwater discharge map of the ASEAN region, with discharges ranging from least (light yellow) to greatest (red). (Osipova et al., 2021). For more detail see the interactive version of the map.

This washwater hotspot region is also known for its fishing industry. It is home to four of the top ten leading countries for fish catch—Indonesia, Thailand, Vietnam, and the Philippines—and accounts for some 13 percent of the world’s fish exports. ASEAN is making fisheries one of its 12 priority sectors for promoting regional economic integration, with a focus on, among other priorities, food safety issues. So, we have a major fisheries region that is a leading source of fish exports but also a dumping ground for exhaust wastes. As a seafood lover, I start to wonder if I should worry about my tuna sandwich: afterall, the U.S., where I live, is the world’s largest importer of tuna, much of which likely comes from Southeast Asia. The U.S. is also the second largest importer of shrimp from Vietnam—should I think twice before ordering that as well?

Let’s rewind a little. What is a scrubber and why is its washwater discharge a problem? The new ICCT study explains it well. Scrubbers are installed on marine vessels to remove sulfur dioxides—an air pollutant regulated by the International Maritime Organization (IMO)—from smokestacks. Scrubbers are one option for complying with IMO’s global fuel sulfur limit (effective since January 1st 2020); the other is for ships simply to switch to cleaner but more expensive low-sulfur fuel. The scrubber option is popular: the number of ships with scrubbers rose dramatically between 2015 and 2020, from 243 to more than 4300.

Open-loop scrubbers, the dominant technology, use seawater to treat a vessel’s exhaust gases; they release the waste, known as washwater, back into the ocean. The washwater is warmer and more acidic than surrounding seawater and contains, in varying concentrations, polycyclic aromatic hydrocarbons (PAHs), particulate matter, nitrates, nitrites, and heavy metals including nickel, lead, copper, and mercury. Thus, pollutants once released to the atmosphere are now diverted into the marine environment. These pollutants pose potential harm to fish and humans as they bioaccumulate in the marine food web, including in fish consumed by humans. Although no studies have specifically analyzed the human health risks of consuming seafood exposed to scrubber washwater discharge, and specific studies—in Malaysia in 2009, for example—found that levels of heavy metals were well below tolerable levels set by a joint Food and Agriculture Organization and World Health Organization (FAO/WHO) committee, health authorities often advise consumers to monitor daily fish intake to minimize exposure to these contaminants. Now that scrubbers are adding new pollutants to fishing grounds, the healthfulness of my tuna sandwich is an open question.

The new ICCT study reveals the scale of additional exposure to contaminants found in marine fisheries in the ASEAN region because of scrubber washwater discharges. In total, at least 1 billion tonnes of washwater are dumped in these fishing grounds every year, a full 10% of global discharges. Figure 2 demonstrates the danger. The map overlays areas of washwater discharge with marine fishery grounds managed by the Southeast Asian Fisheries Development Center (SEAFDEC) that includes all 10 ASEAN countries. If the practice of using scrubbers on ships to comply with global air quality regulations continues, more contaminated washwater will be dumped into these waters.

Figure 2. Global washwater discharge overlaid with fishing areas (darkened portion) designated by the Southeast Asian Fisheries Development Center. Source: Shapefile, downloaded from Food and Agriculture Organization of the United Nations (FAO).

Although IMO has published voluntary washwater guidelines for pH, turbidity (as a proxy for heavy metals), and PAHs, discharge limits haven’t been revised since they were established in 2008, when only three scrubbers were in use—compared to the thousands of scrubbers in use today. Some countries and regions have already banned scrubber discharges to protect their waters, including Malaysia in its territorial seas, and in the ports in Indonesia and Singapore. Unfortunately, these bans do not extend to the Strait of Malacca, which is expected to receive the largest concentrations of washwater discharges in the world, according to the ICCT study.

The 16 countries that adopted these restrictive policies as of June 2020 avoided about 4% of total washwater discharged globally. Now more than 30 countries have instituted bans in their ports or national waters. If all 10 ASEAN countries were to follow Malaysia’s example, a total of 156 million tonnes of washwater discharge, or 16% of the region’s total, could be avoided. The rest, released beyond their national waters (including in territorial seas and internal waters), can only be addressed at the international level, through the United Nation’s International Maritime Organization (IMO). Here’s what we think IMO could do:

  • Work with FAO to conduct science-based research on short-term and long-term impacts of washwater discharge on commercial fishing species.
  • Based on the results of such a study, determine whether scrubber discharges should be allowed in these areas. If so, establish more stringent discharge criteria for these areas and other places, such as particularly sensitive sea areas.
  • Prohibit the use of scrubbers as an equivalent fuel sulfur compliance option for new ships under MARPOL and establish a timeline for phasing out scrubbers already installed on existing ships.

Are the fish in ASEAN regions potentially “deadliest catches”? I hope not. As consumers, we are entitled to know the potential risks of washwater discharges on the safety of our seafood. As human beings, we should adopt responsible environmental policies that avoid, reduce, and eliminate pollution—not allow polluters simply to displace air pollution into the ocean.