The number of houses using exhaust gas cleaning systems, better known as "scrubbers", has grown from just three houses in 2008 to more than 4,300 in 2020. Although scrubbers are effective in reducing sulfur dioxide emissions ( SO2) in the air, sulfur and other pollutants removed from the exhaust gases - including carcinogens such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals - are discharged overboard as wash water, also called flush water .