Residents in a coastal region hit by South Korea\'s worst-ever oil spill four years ago are still less healthy than even people living near abandoned metal mines, a study showed Wednesday. In December 2007, some 12,000 tons of crude oil spilled into the seas off Taean, 150 kilometers southwest of Seoul, after a Hong Kong-registered oil tanker collided with a barge owned by Samsung Heavy, blackening beaches and fish farms along the west coast.According to the report on the health of 271 residents in the region based on the test conducted by the Taean Environment Health Center, the urinary concentration of malondialdehyde (MDA) among them was nearly twice the level among people who live near abandoned mines in the country\'s Gangwon and Gyeonggi provinces. MDA is widely used as a biomarker to measure the level of oxidative stress, which results from high levels of toxic by-products from energy production inside cells. The substance itself also can cause mutation and cancer.\"This shows there have been no notable changes from the result of the same test conducted in 2009,\" said Noh Soo-ryun of the health center who wrote the report. \"High levels of such a substance could destroy the body\'s immune system, causing serious diseases including cancer.\"Raising concerns over their long-term impacts, she called for proper measures to improve the residents\' health, vowing continued monitoring by the center.