A Swedish study claims that exhaust gas cleaning systems are harmful to marine life, following a series of scientific reports offering different conclusions on their overall impact.

Both open-loop and closed-loop types pose harm to copepods, a zooplankton vital to the seas' lower food chain, according to a Swedish Environmental Research Institute (SERI) analysis.

"Zooplankton is a crucial link between phytoplankton and higher trophic levels like fish and marine mammals," the 44-page study states.