'Garbage' chemical TCP threatens Valley water --Memo shows Dow knew TCP was useless, but used it anyway 21 Apr 2012 A 1974 memo from Dow Chemical describes several chemicals in a widely used farm fumigant as "garbage." Today, one of those useless chemicals threatens drinking water for more than 1 million people across the San Joaquin Valley. Now linked to cancer, the toxin was waste from a plastic-making process. The fumigant manufacturers, Dow and Shell Oil Co., discovered decades ago that 1,2,3-trichloropropane, or TCP, was not effective against worms called nematodes, according to documents in lawsuits filed by a dozen Valley cities against the companies. But they apparently left it in a fumigant anyway.