New shipping pollution regulations introduced earlier this year could harm humans by contaminating fish and crustaceans with toxins, according to an internal report compiled by the International Maritime Organization and obtained by the Guardian.

In the report the IMO, the United Nations agency responsible for regulating shipping, says that there is insufficient “toxicity data” to be able to assess the risk to humans caused by the increased use of exhaust gas cleaning systems, which are also known as “scrubbers”.

These devices reduce the amount of pollution emitted into the air by ships, but the cheapest and most popular models dramatically increase the amount of pollutants pumped directly into the sea.

Shipping companies have spent more than $12bn (£9.2bn) fitting thousands of scrubbers on vessels around the world in order to meet new air pollution standards that were introduced on 1 January 2020.

Some of the pollutants deemed most concerning by experts that are pumped into the sea by scrubbers are polycyclic aromatic hydrocarbons (PAHs), which have been linked to skin, lung, bladder, liver and stomach cancers.

In its report, the IMO says “carrying out a preliminary risk assessment [on the PAH emissions from scrubbers] was not possible considering the available information” and warns that “secondary poisoning (via consumption of seafood) had been mentioned as a likely exposure route for humans”.

Critics say IMO member states should have conducted thorough risk assessments before deciding to allow the use of scrubbers under the new legislation.

Lucy Gilliam, a campaigner for the Brussels-based NGO Transport & Environment, says the IMO should stop the use of scrubbers until it can answer key questions about how discharges may affect health.

“Ships should not be allowed to use scrubbers if the IMO has no idea what the consequences will be for human health and food chain contamination,” she said.

“The surge in scrubber use means that increasing amounts of PAHs will accumulate in sediment over time, and no one knows what the impact on human health will be.

“It is going to have an impact on the food chain and, as things stand, we have no reliable information about when safe threshold limits will be breached.”

Christopher Elliott, a professor at the Institute for Global Food Security at Queen’s University Belfast, believes the effect of bioaccumulation of PAHs in the food chain is a worrying issue.

“Any increase in PAHs at the bottom of the food chain can have a negative impact on human health over the long term, damaging immune systems and potentially increasing susceptibility to cancer,” he said.

Shipping companies have repeatedly said that they have commissioned rigorous studies to test pollutants discharged by scrubbers.

Earlier this year a study commissioned by Cruise Lines International Association (CLIA) Europe, the world’s largest cruise industry trade association, concluded that “exhaust gas cleaning systems have a limited impact on water quality”.

In March last year Carnival, the world’s biggest cruise company, published a study that described scrubbers as “a safe and effective” way of complying with the recently implemented regulations for cleaner air emissions.

The Clean Shipping Alliance, a lobby group for companies that have invested in exhaust gas cleaning technology, says it believes that sufficient research has been conducted and discharges from the devices are safe for marine ecosystems.

“There is well-documented evidence relating to the composition of scrubber washwater,” a spokesperson said.

However, in the IMO’s new internal report it criticises the existing body of research that been published based on analysis of chemical discharge from the devices, saying that some of the existing studies cannot be trusted.

“In a number of reports, no basic information was provided either on the sampling techniques, or on the quality assurance and control of the analytical methods used,” it says.

“Lack of all this information put a great uncertainty on a number of presented results and the quality of the provided data could not be fully judged and trusted.”

Gilliam says many of the existing studies looking at chemical discharges from scrubbers have been done by entities that benefit financially from the use of them.

“In some cases they are commissioning studies by independent groups, but the samples are being collected by their own staff,” she said.

“How do we know exactly where they are taking the sample from, at what time, at what engine load? We don’t have those answers. It can’t be regarded as rigorous, independent, peer-reviewed research.

“We don’t know if this will be a health crisis in 20 or 30 years, because proper research just hasn’t been done.”

A spokeswoman for CLIA said: “Cruise lines are committed to environmental stewardship and have invested more than £16bn in ships with new technologies and cleaner fuels to reduce air emissions and achieve greater energy efficiencies.

“Exhaust gas cleaning systems (EGCS), which are designed to remove 98% of sulphur and well over 50% of particulate matter from exhaust, have been proven safe for maritime environments. Publicly available studies on the long-term impact of discharges from exhaust gas cleaning systems have found minimal environmental impact on water and sediment quality when benchmarked against new European environmental quality standards entering into force in 2021.”

In October, the British Ports Association warned that the use of scrubbers by shipping companies could render some UK ports unusable by contaminating sediment and increasing the cost of dredging.

The IMO is due to discuss future regulation of scrubbers at a meeting starting on Monday.