Many in shipping have bought into open-loop exhaust gas cleaning systems as a safe way to meet the IMO 2020 sulphur emissions rules, and an industry-wide debate last year over their possible harm to marine life has faded from headlines.

But among regulators and scientists, the equipment used to allow ships to continue to use high-sulphur fuel oil after IMO 2020 is the subject of further scrutiny.

The IMO's Marine Environment Protection Committee (MEPC) is now looking at how it can "harmonise" its 2015 guidelines on scrubbers, so that all member states follow the same criteria when assessing the impact that scrubber washwater effluent has on marine life.

Scientists' concerns

It was ordered by the MEPC in 2017 in response to scientists' concerns and undertaken by its pollution prevention and response subcommittee, known as PPR 7.

At last month's MEPC conference in London, the committee unpacked the evidence it had received to date.

Scientific studies and reports filed by leading IMO member states drew very different conclusions, with some claiming scrubber effluent caused ocean contamination and others that it had a negligible impact.

In a nine-page report, the European Union said the discharge's "potential toxicity ... requires careful consideration to avoid irreversible pollution of the marine environment".

It cited a German study that found scrubbers dump "tonnes of toxic heavy metals" into the ocean, and suggested that the revised rules should consider banning the discharge in certain waters.

A 21-page report from Panama highlighted pollutants from scrubber effluent such as heavy metals and coal and tar-laden molecules, polycyclic aromatic hydrocarbons.

"It is also acidic, which can affect ocean chemistry and marine life," it said.

However, a 68-page study by Japan's Ministry of Land, Infrastructure, Transport and Tourism stated that the discharge poses no threat to marine life.

"It was further concluded that risks of discharge water from scrubbers to the marine environment and the marine aquatic organisms are negligible from short and long-term perspectives," it stated.

Warming to scrubbers

Twelve months ago, shipowners appeared divided on scrubbers: some believed the scrubber washwater effluent at the centre of the debate barely affected ocean organisms, others said it might pollute the seas with harmful toxins.

But, in the past year, shipping's acceptance of the exhaust gas cleaning kits appears to have grown, with many deciding that scrubbers offer a safe and savvy option to costly IMO 2020-compliant fuel, until a greener solution comes along.

Giant VLCC owner Euronav was once the most vocal sceptic of scrubbers. It is now among the converted, swooping earlier this month to buy its fourth scrubber-fitted resale from Sinokor Merchant Marine.

Dozens of other owners have spent millions of dollars to retrofit about 4,000 ships.

An eight-page Cruise Line Industry Association report filed to the IMO review said the effluent contributes little or no trace of metals to the ocean, at levels well within IMO standards and discharge limits for land-based factory applications.

Hulda Winnes, project manager and researcher at IVL Swedish Environmental Research Institute (SERI) Photo: SERI

The report was based on a 281-sample study published by classification society DNV GL that claimed the effluent is, in effect, as safe as drinking water.

"Average washwater concentrations also compare favourably to water quality standards with strict criteria," it said.

But many scientists have still to be convinced.

"More studies should be conducted," said Hulda Winnes, project manager and researcher at IVL Swedish Environmental Research Institute.

"The complexity of what happens when the pollutant substances are in the sea, and how they affect marine life is huge, and includes both the complexity of marine life and how the substances spread in the water."

She said the institute is currently conducting an EU-funded study on washwater effluent toxicity.

In June 2019, it published Scrubbers: Closing the Loop — a report that concluded the discharge may pose serious consequences for marine life.

Winnes believes the toxicity of the discharge's "cocktail effect" is of utmost concern.

"The scientific evidence takes time," she said. "This is expected. I think it is very positive that the issue is high on the IMO's agenda."

IMO spokeswoman Natasha Brown told TradeWinds that the current review had recommended the MEPC harmonise its 2015 guidance to consider oceanic conditions and areas.

“Member states have submitted various studies on discharge water from open-loop scrubbers,” she said. “Some say there are potential issues, especially in certain areas or types of water.”

But she added that the IMO does not plan to make any changes to the guidelines at this time, and the current review will run until 2021.