Ballast water treatment systems eliminate invasive species, but chemical residues pose a significant risk, lacking proper monitoring in ports.
Ballast water treatment systems are evaluated based on their success in eliminating invasive marine species. However, the chemical residues left behind by these systems are largely overlooked. Despite billions of tons of ballast water being discharged into the seas each year, there is no comprehensive monitoring system in place to track how much bromoform and other disinfection by-products have accumulated in ports.
The focus is on organisms, not chemical residues.
Ballast water treatment technologies have been developed to prevent the spread of invasive organisms carried by ships from one sea to another. The International Maritime Organization's (IMO) Ballast Water Management Convention has also been prepared with this goal in mind.
A ballast water treatment system receives approval if it can effectively eliminate living organisms within the tank. It is deemed sufficient for the ship's discharge to meet the specified organism density limits. However, there is no regular monitoring of the long-term effects that the chemical processes used to kill organisms have on port ecosystems.
Chemical treatment creates new compounds.
Not all ballast water treatment systems use chemicals. Ultraviolet (UV) systems do not add any chemicals to the water, while systems that utilize electrolysis (electrochlorination) produce chlorine from seawater.
This chlorine reacts with bromide and organic matter in seawater after killing the organisms, creating various brominated organic acids. Chemists refer to these substances as 'disinfection by-products' (DBPs).
The IMO is aware of the existence of these compounds. The organization's scientific advisory body, GESAMP, evaluates these substances in the approval processes. However, environmental risk analyses are conducted based on a hypothetical port referred to as 'Model Harbour' rather than real ports.
While inspections focus solely on the amount of free chlorine remaining in the water after treatment, the chemical load accumulated in ports over the years is not accounted for.
The main issue is volume.
According to the research, the problem is not the concentration created by a single ship, but the massive volume of ballast water discharged into the sea each year.
Chemical concentrations in ballast water are measured at the microgram/liter level. In contrast, billions of tons of ballast water are discharged into the sea worldwide each year.
It is estimated that the annual ballast water discharge around Singapore alone is approximately 190 million cubic meters.
Ships are not required to report exactly which ports they discharge their ballast water in.
In the IMO's own documents, global ballast water transfer is mentioned as 3 to 5 billion tons in one section and 10 billion tons in another. There is no common method for measuring the volume of ballast water globally.
Hundreds of tons of bromoform mix into the seas each year.
A review published in the journal Water Research in 2022 directly measured disinfection by-products in treated ballast water.
The study found an average of 247 micrograms/liter of bromoform in ballast water. This value was determined to be about 10 times higher than the levels measured in cooling water and desalination plant effluents by the same researchers.
According to the study, approximately 860 tons of bromoform are released into the marine environment each year as a result of ballast water treatment activities worldwide.
A modeling study published in the journal Ocean Science, which used the European Union's Copernicus Marine Service current data, calculated that approximately 8 to 63 tons of bromine input occurs annually in the area between Singapore and the Pearl River Delta due solely to bromoform from ballast water.
The risk increases in semi-enclosed seas.
Bromoform can mix into the atmosphere over time. While evaporation serves as a significant removal mechanism in open seas, the situation is different in ports where water circulation is weak.
The study cites examples from the Gulf of Fos and the Persian Gulf.
It notes that the same chemical compounds resulting from industrial discharges concentrate around their discharge points in these regions, and some brominated compounds reach levels thousands of times higher in the tissues of marine organisms than in the surrounding water.
Researchers emphasize that the contribution from ballast water has not yet been systematically accounted for in these areas.
Notable findings from Australia.
The Australian Bureau of Agricultural and Resource Economics and Sciences (ABARES) applied the IMO's standard 'Model Harbour' approach to real ports in 2019.
As a result of the modeling, it was determined that dibromoacetonitrile could exceed safe environmental threshold values in Port Hedland, monochloroacetic acid exceeded limit values at all modeling points in Melbourne Port, and dibromoacetic acid levels exceeded threshold levels in the Appleton Dock area.
Although the report recommends that physical water samples be taken in the field, public records do not indicate that such monitoring has been carried out.
'The issue is not treatment, but a lack of monitoring.'
The article does not advocate for the cessation of oxidant-based ballast water treatment. The author emphasizes that the Ballast Water Management Convention has achieved significant success in preventing the transport of invasive species, while the main shortcoming is the failure to track the chemical load that has accumulated in ports over many years.
Currently, detailed modeling studies exist only in Singapore and Australia, while sufficient data regarding the total chemical impact of oxidant-treated ballast water over the years is lacking in ports around much of the world. Therefore, experts highlight the need for long-term environmental monitoring programs, especially in ports with low water renewal rates.
Source: SeaNews Türkiye
