Because of insufficient data, a GV could not be derived for monochloroacetic acid.

In animal toxicological studies, both the di- and trichloroacetic acids caused increased relative liver weights. The provisional GV for dichloroacetic acid of 0.05 mg/L was derived from an NOAEL of 7.6 mg/kg bw/day using an uncertainty factor of 1000 (extra 10 for possible carcinogenicity) and allocating 20% of the TDI to drinking water. The GV was designated as provisional because the experts were not certain if the GV was technically attainable and "difficulties in meeting a GV must never be a reason to compromiso adequate disinfection."

Only an LOAEL of 178 mg/kg bw/day could be identified in the case of trichloroacetic acid. As a result, an uncertainty factor of 10,000 was used to derive the TDI. Allocating 20% of this TDI to drinking water gives a provisional GV of 0. 1 mg/L.

HalogenatedAcetonitriles, Chloral Hydrate, ChlorinatedPhenols, andMX. These are minor DBPs that are usually present at median concentrations of less than 0.001 mg/L. A summary of the risk assessment of these compounds is also given in Table 3.

For all compounds showing a threshold, the recommended GVs are "provisional" because of the limitation of the database and/or in order not to compromise disinfection. Although little is known about exposure to these compounds from sources other than drinking water, the default value of 10% of the TDI was not used. An allocation of 20% of the acceptable daily intake (ADI) was made in all cases because exposure to these DBPs from other sources is expected to be small. For severas compounds, the available toxicological data were considered insufficient for deriving GVs.

Reaction of aqueous chlorine with phenols leads to formation of mono-, di-, and trichlorophenols. These compounds have strong, disagreeable tastes and odors. The taste threshold for chlorophenols is 0.002 mg/L or less. Therefore, if water containing chlorophenols is free from taste it should not, for all practical purposes, present any risk to health. When excess chlorine is added, additional chlorination occurs, with eventual breakdown of the aromatic ring of phenols to form tasteless and odorless products such as oxalic acid, maleic acid, and carbon dioxide (Morris 1982).