highly unsaturated fatty acid(s) or (a) highly unsaturated fatty acid ethyl ester(s) which has/have been produced using as a feedstock oil, a fat or oil derived from a marine product that contains highly unsaturated fatty acids as constituent fatty acids and which has been reduced in the contents of environmental pollutants; wherein among the dioxins contained, polychlorinated dibenzoparadioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are contained in amounts of less than 0.05 pg-TEQ/g and coplanar polychlorinate biphenyls (Co-PCBs) in amounts of less than 0.03 pg-TEQ/g; wherein said TEQs are calculated based on the toxicity equivalency factors (TEFs) according to WHO; wherein the highly unsaturated fatty acid(s) is/are (a) fatty acid(s) containing at least 18 carbon atoms and at least 3 double bonds; wherein the concentration of the highly unsaturated fatty acid(s) in the sum of fatty acids is at least 80area% as determined by gas chromatography; wherein the polychlorinated dibenzoparadioxins (PCDDs) are selected from the group consisting of 2,3,7,8-tetrachlorodibenzo- p -dioxin, 1,2,3,7,8-pentachlorodibenzo-p-dioxin, 1,2,3,4,7,8-hexachlorodibenzo- p -dioxin, 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin, 1,2,3,7,8,9-hexachlorodibenzo- p -dioxin, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, and octachlorodibenzo- p -dioxin; wherein the polychlorinated dibenzofurans (PCDFs) are selected from the group consisting of 2,3,7,8-tetrachlorodibenzofuran, 1,2,3,7,8-pentachlorodibenzofuran, 2,3,4,7,8-pentachlorodibenzofuran, 1,2,3,4,7,8-hexachlorodibenzofuran, 1,2,3,6,7,8-hexachlorodibenzofuran, 1,2,3,7,8,9-hexachlorodibenzofuran, 2,3,4,6,7,8-hexachlorodibenzofuran, 1,2,3,4,6,7,8-heptachlorodibenzofuran, 1,2,3,4,7,8,9-heptachlorodibenzofuran, and octachlorodibenzofuran; and wherein the coplanar polychlorinate biphenyls (Co-PCBs) are selected from the group consisting of 3,4,4',5-tetrachlorobiphenyl, 3,3',4,4'-tetrachlorobiphenyl, 3,3',4,4',5-pentachlorobiphenyl, 3,3',4,4',5,5'-hexachlorobiphenyl, 2',3,4,4',5-pentachlorobiphenyl, 2,3',4,4',5-pentachlorobiphenyl, 2,3,3',4,4'-pentachlorobiphenyl, 2,3,4,4',5-pentachlorobiphenyl, 2,3',4,4',5,5'-hexachlorobiphenyl, 2,3,3',4,4',5-hexachlorobiphenyl, 2,3,3',4,4',5'-hexachlorobiphenyl, 2,3,3',4,4',5,5'-heptachlorobiphenyl. wherein among the dioxins contained, polychlorinated dibenzoparadioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are contained in amounts of less than 0.05 pg-TEQ/g and coplanar polychlorinate biphenyls (Co-PCBs) in amounts of less than 0.03 pg-TEQ/g; wherein said TEQs are calculated based on the toxicity equivalency factors (TEFs) according to WHO; wherein the highly unsaturated fatty acid(s) is/are (a) fatty acid(s) containing at least 18 carbon atoms and at least 3 double bonds; wherein the concentration of the highly unsaturated fatty acid(s) in the sum of fatty acids is at least 80area% as determined by gas chromatography; wherein the polychlorinated dibenzoparadioxins (PCDDs) are selected from the group consisting of 2,3,7,8-tetrachlorodibenzo- p -dioxin, 1,2,3,7,8-pentachlorodibenzo-p-dioxin, 1,2,3,4,7,8-hexachlorodibenzo- p -dioxin, 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin, 1,2,3,7,8,9-hexachlorodibenzo- p -dioxin, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, and octachlorodibenzo- p -dioxin; wherein the polychlorinated dibenzofurans (PCDFs) are selected from the group consisting of 2,3,7,8-tetrachlorodibenzofuran, 1,2,3,7,8-pentachlorodibenzofuran, 2,3,4,7,8-pentachlorodibenzofuran, 1,2,3,4,7,8-hexachlorodibenzofuran, 1,2,3,6,7,8-hexachlorodibenzofuran, 1,2,3,7,8,9-hexachlorodibenzofuran, 2,3,4,6,7,8-hexachlorodibenzofuran, 1,2,3,4,6,7,8-heptachlorodibenzofuran, 1,2,3,4,7,8,9-heptachlorodibenzofuran, and octachlorodibenzofuran; and wherein the coplanar polychlorinate biphenyls (Co-PCBs) are selected from the group consisting of 3,4,4',5-tetrachlorobiphenyl, 3,3',4,4'-tetrachlorobiphenyl, 3,3',4,4',5-pentachlorobiphenyl, 3,3',4,4',5,5'-hexachlorobiphenyl, 2',3,4,4',5-pentachlorobiphenyl, 2,3',4,4',5-pentachlorobiphenyl, 2,3,3',4,4'-pentachlorobiphenyl, 2,3,4,4',5-pentachlorobiphenyl, 2,3',4,4',5,5'-hexachlorobiphenyl, 2,3,3',4,4',5-hexachlorobiphenyl, 2,3,3',4,4',5'-hexachlorobiphenyl, 2,3,3',4,4',5,5'-heptachlorobiphenyl.