Berlin, March 2 : Contamination of the North Sea with inorganic and organic pollutants has declined significantly since the 1980s, according to a study published by Germany's Federal Maritime and Hydrographic Agency (BSH). "Monitoring the marine environment shows the extent and efficiency with which legal regulations banning certain pollutants prevent harmful substances from entering the oceans," BSH said on Tuesday. However, the study also found new substances that are harmful to the marine environment. Even small changes in the chemical composition of banned substances could be enough to make them legal again, Xinhua news agency reported citing the governmental agency. The study was conducted by a research group from BSH, the Helmholtz-Zentrum Hereon, and the universities HAW Hamburg and RWTH Aachen. It analysed 90 inorganic and organic pollutants in sediment cores from the North Sea. Based on the samples, "several pollution peaks with high concentrations of various pollutants could be detected in the sediment layers over the past 100 years," BSH said. These included a group of polychlorinated biphenyls (PCB) that were banned in 1979. PCB, toxic organic chlorine compounds, were used as softeners in paints and sealants from 1929 until the ban. According to the study, the sediment load of PCBs was highest in the period just before the ban. /IANS