Disinfection By-Products

Monitoring DBPs in the Environment

In December of 1998, the USEPA announced the Stage 1 Disinfectants and Disinfection Byproducts Rule as an amendment to the 1996 Safe Drinking Water Act. This is the first in a series of rules with the purpose of establishing standards that will decrease exposure to potentially hazardous DBPs, while continuing the use of chemical disinfectants that reduce our risk to microbial contaminants.

One of the main purposes of the rule was to establish maximum contaminant levels (MCL) for DBPs. The DBPs contained in this rule are those described above and can be broken into the categories of TTHM (total trihalomethanes) HAAs (haloacetic acids), chlorite and bromate. The testing frequency for these byproducts was also established by this rule. Table 1 below details MCL concentrations and testing frequency as required by the statute. All surface and ground water systems that serve more than 10,000 people must have been in compliance with this rule by January 1, 2002, while similar systems serving fewer than 10,000 people must comply with the rule by January 1, 2004.

Table1

The EPA has approved several methods for environmental testing of DBPs. All of the DBPs have at least one EPA method that has been approved, and some also have approved standard methods. See Table 2 below.

Table 2

Many of the approved methods listed above use gas chromatography to determine the amount of DBPs in a water sample. In this technique, the sample components are separated through interactions with a stationary and gas phase, and then quantitatively and qualitatively analyzed by a detector. The sample is injected into the instrument through a rubber septum and immediately vaporized by the high heat of the injection port. After the sample has been transformed to the gaseous state, it is swept through the instrument by an inert gas called the mobile phase. The sample passes through a column that contains the stationary phase, which is usually an organic liquid that is coated or bonded to the surface of the inside of the column. The sample components are separated based on their affinity for the stationary phase, with the components having the higher affinity staying attached to the bead media inside of the column the longest. The stationary phase is chosen based on the nature of the analytes that are to be separated. As the individual sample components exit the column, they pass through the detector. There are many different kinds of detectors, but the majority will produce an electrical signal as the components exit. This signal is visually seen as a “peak” depending on the time it takes for the sample to exit the instrument. The time that it takes for the component to exit the instrument will distinguish its identity, and the area under the peak will be proportional to the amount present in the sample.

Another technique that is used to determine levels of DBPs is ion chromatography. This technique is very similar to gas chromatography except that the components of the sample are separated based upon the atomic or molecular charge. Ionic groups with an opposite charge of the sample component are bound to the inside of the column and are compensated by small concentrations of counter ions present in the buffer solution. After the sample is added to the instrument, the component of interest takes the place of the weakly bound counter ions. The identity and quantity of the components are determined as in gas chromatography, as the sample is passed through a detector that identifies the compound based upon the residence time within the column.