Background: The International Maritime Organization (IMO) has set limits on sulphur content in fuels for marine transport. However, vessels continue to use these residual high-sulphur fuels in combination with exhaust gas cleaning systems (EGCS or scrubbers). Next to high sulphur, combustion of these fuels also results in higher emissions of contaminants including metals and PAHs. In scrubbers, exhaust gases are sprayed with water in order to remove SOx, resulting in acidic washwater with elevated contaminant concentrations discharged in the aquatic ecosystem. The number of vessels with scrubbers is increasing rapidly, but knowledge on washwater quality and impact are limited. Results: The scrubber washwater is found to be acidic with elevated concentrations of, e.g. zinc, vanadium, copper, nickel, phenanthrene, naphthalene, fluorene and fluoranthene. Model calculations on the effects of scrubber discharge under scenario HIGH (20% of vessels, 90th percentile concentrations) on the water quality in harbour docks showed a decrease in pH of 0.015 units and an increase in surface water concentrations for e.g. naphthalene (189% increase) and vanadium (46% increase). Conclusions: The IMO established sulphur regulations to mitigate the impact of high sulphur emissions of the maritime sector. However, the use of open-loop scrubbers as an abatement technology will not reduce their contribution to ocean acidification. In addition, different types of scrubbers discharge washwater that is acutely toxic for aquatic organisms. However, washwater is diluted and the compounds for which a large increase in surface water concentrations was calculated in the Antwerp (Belgium) harbour docks (naphthalene > phenanthrene > fluorene > acenaphthene > vanadium) were not the compounds that already exceed their respective Water Quality Standards (WQS). Nevertheless, the WQS of several 'priority hazardous substances' (Water Framework Directive) are already exceeded in the docks and the Scheldt estuary. Since these hazardous substances are also identified in the washwater, scrubber washwater discharge should be discouraged in coastal waters and estuaries with large ecological value.

Background: The International Maritime Organization (IMO) has set limits on sulphur content in fuels for marine transport. However, vessels continue to use these residual high sulphur fuels in combination with exhaust gas cleaning systems (EGCS or scrubbers). Next to high sulphur, combustion of these fuels also results in higher emissions of contaminants including metals and PAHs. In scrubbers, exhaust gases are sprayed with water in order to remove SOx, resulting in acidic washwater with elevated contaminant concentrations discharged in the aquatic ecosystem. The number of vessels with scrubbers is increasing rapidly, but knowledge on washwater quality and impact are limited. Results: The scrubber washwater is found to be acidic with elevated concentrations of e.g. zinc, vanadium, copper, nickel, phenanthrene, naphthalene, fluorene and fluoranthene. Model calculations on the effects of scrubber discharge under scenario HIGH (20% of vessels, 90th percentile concentrations) on the water quality in harbor docks showed a decrease in pH of 0.015 units and an increase in surface water concentrations for e.g. naphthalene (189% increase) and vanadium (46% increase). Conclusions: The IMO established sulphur regulations to mitigate the impact of high sulphur emissions of the maritime sector. However, the use of open loop scrubbers as an abatement technology will not reduce their contribution to ocean acidification. In addition, different types of scrubbers discharge washwater that is acute toxic for aquatic organisms. However, washwater is diluted and the compounds for which a large increase in surface water concentrations was calculated in the Antwerp (Belgium) harbour docks (Naphthalene > Phenanthrene > Fluorene > Acenaphthene > Vanadium) were not the compounds that already exceed their respective Water Quality Standards (WQS). Nevertheless, the WQS of several ‘priority hazardous substances’ (Water Framework Directive) are already exceeded in the docks and the Scheldt estuary. Since these hazardous substances are also identified in the washwater, scrubber washwater discharge should be discouraged in coastal waters and estuaries with large ecological value.

18Background: The International Maritime Organization (IMO) has set limits on sulphur content in 19 fuels for marine transport. However, vessels continue to use these residual high sulphur fuels in 20 combination with exhaust gas cleaning systems (EGCS or scrubbers). Next to high sulphur, 21 combustion of these fuels also results in higher emissions of contaminants including metals and 22 PAHs. In scrubbers, exhaust gases are sprayed with water in order to remove SOx, resulting in 23 acidic washwater with elevated contaminant concentrations discharged in the aquatic ecosystem. 24The number of vessels with scrubbers is increasing rapidly, but knowledge on washwater quality 25 and impact are limited. 26 Results:The scrubber washwater is found to be acidic with elevated concentrations of e.g. zinc, 27 vanadium, copper, nickel, phenanthrene, naphthalene, fluorene and fluoranthene. Model 28 calculations on the effects of scrubber (20% of vessels) discharge on aquatic systems showed a 29 decrease in pH of 0.015 units and an increase in surface water concentrations for e.g. naphthalene 30 (110% increase) and vanadium (17% increase). 31 Conclusions:The IMO established sulphur regulations to mitigate the impact of high sulphur 32 emissions of the maritime sector. However, the use of open loop scrubbers as an abatement 33 technology will not reduce their contribution to the acidification. In addition, different types of 34 scrubbers discharge washwater that is acute toxic for aquatic organisms. However, washwater is 35 diluted and the compounds for which a large increase in surface water concentrations was 36 calculated (Naphthalene > Phenanthrene > Fluorene > Acenaphthene > Vanadium) were not the 37 compounds that already exceed their respective Water Quality Standards (WQS). Nevertheless, 38 existing WQS exceedances of 'priority hazardous substances' (Water Framework Directive) that 39 are also identified in the washwater indicate that coastal waters and estuaries, often with large 40 3 ecological value, are already under pressure. In these areas the discharge of scrubber washwater 41 should be discouraged. 43International shipping significantly contributes to air pollution and the emissions of SOx, NOx and 60 PM (particulate matter) from marine transport account for an increasing contribution to global 61 anthropogenic emissions 1 . This has a number of environmental consequences 2 , such as ocean 62 acidification 3 and disturbance of climate regulation 4 , and also impacts human health in coastal 63 regions through deteriorated air quality 5, 6 . To mitigate these effects, the IMO (International 64 Maritime Organization) has included annex VI (Prevention of Air Pollution) to the International 65 Convention for the Prevention of Pollution from Ships (MARPOL). This has resulted in a global 66 cap on sulphur (S) in fuel oil of 3.5% (mass percentage) from 2012 and a maximum S content of 67 0.1% in dedicated SOx Emission Control Areas (SECA's) from 2015 onwards 7 . A new stringent 68 global limit on fuel S content ...