A recent investigation by Lighthouse Reports (https://www.lighthousereports.nl/investigation/an-environmental-crime-in-plain-sight/) has shed light on a problem that is as common as it is potentially disastrous: the discharge into the sea of highly polluting oily wastewater by ships passing through European waters. The NGO SkyTruth, based on satellite data from the European Maritime Safety Agency (Emsa), assumes that there are at least three thousand cases of spills a year. However, the real numbers are unknown and it is very likely that the valuations are underestimated. In fact, on the one hand, satellites do not monitor all European waters every moment and, on the other, it is likely that discharges are carried out at night precisely to evade any checks. The so-called 'bilge water', a polluting mixture, which naturally accumulates on the bottom of boats, of fuel oils, lubricants, cleaning solvents and metals such as lead and arsenic would be spilled. Treating these oily wastewaters to remove pollutants, or discharging them at the port, is expensive. Thus, some ships opt to dump them directly into the sea, where they can pose a serious threat to marine life.
In Europe, spills of oil and other substances are monitored by Emsa through its CleanSeaNet initiative, launched in 2007, precisely for the purpose of analyzing satellite images to detect potential illegal or accidental discharges. In 2020, the agency recorded 7,672 potential spills but received feedback for only a third of these, of which 208 were confirmed as oil slick or its derivatives. And the number of cases actually sanctioned is even lower. SkyTruth calculated how many spills could escape the monitoring system due to gaps in satellite coverage and as a function of how quickly the patches dissipate. The conclusion was that actual spills could be up to ten times more than official ones. Not to mention - as an informant declared - the ease with which it is possible to discharge these waters into the sea. "You can assemble a portable pump in five minutes - he explained - and then quickly remove it if someone comes". Among other things, the paper records on which the quantities of oils transferred on board and processed for proper delivery in ports are noted are easily falsified. "The possibility of finding the culprits also depends a lot on the timing - added IrpiMedia who collaborated in the investigation - within three hours of reporting there is a greater probability of identifying the substances again, but the authorities of the various member states communicate little data on their activities and suggest that it is not always possible to carry out a correct verification".
The risks to the marine ecosystem are mostly unknown but not negligible for this. Indeed, according to the researchers, even in small quantities, waters with traces of hydrocarbons can cause serious damage to marine microorganisms with consequent knock-on effects on all other living beings. Bilge spills tend not to get the same attention as large spills because they are smaller and less visible, but experts say the frequency with which they occur is already having a dramatic effect on marine life. A 2016 study (https://www.nature.com/articles/ncomms11206), conducted precisely on the effects of short-lived oil spills, for example, confirmed "immediate adverse biological effects" on aquatic organisms, including a decline in the number of plankton in the sea, microorganisms at the base of the food chain.