Calling it "one of the worst" cases his office has seen, Los Angeles City Atty. James K. Hahn filed 130 misdemeanor charges against the former owners of a Sun Valley plating company, accusing them of illegally dumping cyanide and other dangerous chemicals into the city sewer system. Lawrence Russell Horton, 66, former president of All Valley Plating Co. Inc., and his son, Scott Lawrence Horton, 34, former vice president of the firm, were charged in the complaint filed in Los Angeles Municipal Court. All Valley Plating was cut off from the sewer system July 2, but has since been sold to a new owner who is operating without any problems, city officials said. Hahn said investigators found discharged wastes including cyanide and acids, a mixture that "can produce hydrogen cyanide, which is the poisonous gas used for executions. That kind of dumping can pose a deadly threat to sewer workers, as well as the general public if there is a leak of fumes from the sewer."