Long-term effects of chromium from red mud (bauxite residue) ocean dumping on the benthic environment in South Korea

Between 1999 and 2009, 344,000 m3 of red mud was released into the red mud dumping zone in the East Sea-Byeong ocean dumping site in South Korea. This study aimed to assess the impacts before and after the 2010 red mud dumping ban. We quantified total Cr concentrations by depth from core sediment samples at the red mud dumping station and evaluated benthic communities in 2004, 2009, 2012, 2017, and 2019. At the dumping station DB-085, the Cr content in the upper layer (0–10 cm) exceeded the effect range median criteria in all study years and decreased with time. Geochemical fraction studies using sequential extraction methods from core sediment samples in 2004, 2009, and 2017 showed high ratios of non-residual fractions (anthropogenic inputs), indicating persistent potential long-term risk after the 2010 ban. Additionally, we confirmed that Thyasira tokunagai, an opportunistic and contamination-stress-resistant species, dominated the study station. [Display omitted] •This study examined the impact of red mud dumping on benthic communities in Korea.•Sediment core samples were collected from 2004 to 2019 and examined for Cr content.•Maximum Cr content exceeded ERM standard despite red mud dumping ban in 2010.•BCR SEM analysis showed high non-residual Cr fractions in vertical distribution.•Benthic communities were dominated by the opportunistic species Thyasira tokunagai.