The U.S. Environmental Protection Agency (EPA) has prepared this Health Effects Support Document for Dacthal (DCPA) Degradates: tetrachloroterephthalic acid (TPA, or the di-acid degradate) and monomethyl tetrachloroterephthalic acid (MTP, or the mono-acid degradate) to assist in determining whether to regulate TPA and MTP with a National Primary Drinking Water Regulation (NPDWR). The available data on occurrence, exposure, and other risk considerations suggest that, because TPA and MTP do not occur in public water systems at frequencies and levels of public health concern, regulating TPA and MTP will not present a meaningful opportunity to reduce health risk. EPA will present a determination and further analysis in the Federal Register Notice covering the Contaminant Candidate List (CCL) regulatory determinations.