As shipping divides into two camps over exhaust gas scrubbers, marine biologists say the issue is more complex than just about the capture of sulphur.

Scientists believe the impact of the use of scrubbers to meet IMO 2020 guidelines remains unclear, but they say there are a number of issues that are often overlooked.

"Whether these effects are positive or negative needs to be studied,"says Sonja Endres, post-doctoral researcher at Germany's Max Planck Institute for Chemistry.