In the shipping industry, ballast is the extra weight that is added to large ships, in order to balance their weight and ensure stability during voyage (clearseas, 2021). Often, it is in the form of ballast water, where through the process of ballasting, water from the sea or visiting ports is pumped into the ballast tanks of the ships, thereby adding extra weight to the ship. This water is then discharged when the extra weight is no longer needed (often when cargo is loaded). This process is depicted in Figure 1. 

Figure 1: How ballast water is used to stabilize vessels. (Danfoss, 2022).

According to the International Maritime Organisation, as a result of the practice of ballasting, over 10 billion tonnes of ballast water is transferred around the world annually (International Maritime Organisation, 2019). However, the process of discharging ballast water can be highly pollutive. This is because in the pumping of ballast water, microscopic organisms– bacteria, microbes, pathogens, invertebrates, eggs, cysts, and larvae of various species, are concurrently transferred in (clearseas,2021). Thereafter, should untreated ballast water be discharged into other areas, it can disrupt and threaten local marine environments through the potential release of invasive aquatic nonindigenous species (NIS) (Casas-Monroy et al., 2014). These NIS can compete with native species for limited resources, potentially causing native species to go extinct (Ricciardi et al., 2013; Simberloff et al., 2013). Figure 2 depicts how invasive marine species have been transferred around the world through the discharge of ballast water. These have significant economic costs. Examples of costs incurred include the depletion of fish stock, the higher cost of maintaining NIS-damaged equipment, as well as increased costs from mitigation programs (Coulette et al., 2006). Couletti et al. (2006) have projected the invasion of NIS to cost Canada between Can$13.3 to Can$34.5 billion each year.

Figure 2: Transfer pathways of invasive marine species around the world through discharge of ballast water. (Danfoss, 2022).

Additionally, the release of ballast water possible pathogens and bacteria may also lead to the spread of waterborne diseases (Ruiz et al., 2000). For instance, in July 1992, Vibro cholerae (Bacteria that causes cholera), found in the waters of the USA was determined by the US Food and Drug Administration (FDA) to have been the result of the discharge of ballast water that had their last port in call in South America (McCarthy & Khambaty, 1994). 

In response to environmental concerns relating to the discharge of ballast water, the International Maritime Organisation introduced 2004, the “International Convention for the Control and Management of Ships’ Ballast Water and Sediments”. Under the Convention, all ships will be obligated to put into place a “Ballast Water Management Plan” that involves maintaining a ballast water record book and following established ballast water management procedures that meet specified standards (International Maritime Organization, n.d.).

However, while the convention has been put into force since 2017, its enforcement has been argued to be weak. In Ng et al’s (2018) examination of the ballast waters of six ships docked off the Singapore harbour, they found ballast waters of two of the six ships to not meet the stipulated requirements of the Ballast Water Management Convention, with Enterococci values (indicator of disease-causing bacteria and viruses) more than three times higher than the acceptable limits. In addition, non-toxigenic species of V.chloera, V.parahaemolyticus, and V.culnificus were also detected in at least one of the ships. It is therefore apparent that more can be done to reduce pollution caused by ballast water discharge. 

References 

Casas-Monroy, O., Linley, R.D., Adams, J.K., Chan, F.T., Drake, D.A.R., & Bailey, S.A. (2014). National risk assessment for introduction of aquatic nonindigenous species to Canada by ballast water. Canadian Science Advisory Secretariat. https://waves-vagues.dfo-mpo.gc.ca/library-bibliotheque/352598.pdf

ClearSeas, 2021. Ballast water management: Stopping the spread of invasive species by ships. https://clearseas.org/en/blog/ballast-water-management-stopping-the-spread-of-invasive-species-by-ships/#:~:text=Large%20cargo%20ships%20use%20ballast,into%20a%20new%20marine%20environment.

Colautti, R. I., Bailey, S. A., van Overdijk, C. D. A., Amundsen, K., & MacIsaac, H. J. (2006). Characterised and projected costs of nonindigenous species in canada. Biological Invasions, 8(1), 45–59. https://doi.org/10.1007/s10530-005-0236-y

Danfoss. (2022). How to comply with ballast water regulation. https://assets.danfoss.com/documents/latest/197913/AC290731004318en-000102.pdf

International Maritime Organization. (2019). Ballast water management– the control of harmful invasive species. https://www.imo.org/en/MediaCentre/HotTopics/Pages/BWM-default.aspx

International Maritime Organization. (n.d.). International convention for the control and m management of ships’ ballast water and sediments (BWM). https://www.imo.org/en/About/Conventions/Pages/International-Convention-for-the-Control-and-Management-of-Ships%27-Ballast-Water-and-Sediments-(BWM).aspx

McCarthy, S. A., & Khambaty, F. M. (1994). International dissemination of epidemic Vibrio cholerae by cargo ship ballast and other nonpotable waters. Applied and Environmental Microbiology, 60(7), 2597–2601. https://doi.org/10.1128/aem.60.7.2597-2601.1994

Ricciardi, A., Hoopes, M. F., Marchetti, M. P., & Lockwood, J. L. (2013). Progress toward understanding the ecological impacts of nonnative species. Ecological Monographs, 83(3), 263–282. https://doi.org/10.1890/13-0183.1

Ruiz, G. M., Rawlings, T. K., Dobbs, F. C., Drake, L. A., Mullady, T., Huq, A., & Colwell, R. R. (2000). Global spread of microorganisms by ships. Nature, 408(6808), 49–50. https://doi.org/10.1038/35040695

Simberloff, D., Martin, J.-L., Genovesi, P., Maris, V., Wardle, D. A., Aronson, J., Courchamp, F., Galil, B., García-Berthou, E., Pascal, M., Pyšek, P., Sousa, R., Tabacchi, E., & Vilà, M. (2013). Impacts of biological invasions: What’s what and the way forward. Trends in Ecology & Evolution, 28(1), 58–66. https://doi.org/10.1016/j.tree.2012.07.013