1,2,3,-Trichloropropane

Last Update: August 20, 2009

1,2,3-Trichloropropane (1,2,3-TCP) was used historically as a paint and varnish remover, cleaning and degreasing agent, and a cleaning and maintenance solvent, and more currently as a chemical intermediate (NTP, 2005).  Its use as a pesticide was in formulations with dichloropropenes in the manufacture of D-D, a soil fumigant.  The California Department of Public Health's precursor, the Department of Health Services (CDHS), in its monitoring guidance (PDF), described 1,2,3-TCP as having various industrial uses and historic pesticide uses, with the primary possible contaminating activity appearing to be hazardous waste sites.  

In 1999, the Department established a drinking water notification level for 1,2,3-TCP of  0.005 micrograms per liter (µg/L), the same level as the analytical reporting limit, as described below.  [Certain requirements and recommendations apply if it is detected above this level.]   The 1,2,3-TCP notification level was established after its discovery at the Burbank Operable Unit (OU) — a southern California Superfund site — because of concerns that the chemical might find its way into drinking water supplies.  It was also found in several wells elsewhere in the state.

1,2,3-TCP causes cancer in laboratory animals (US EPA, 1997), which is the basis for the notification level.   It is reasonably anticipated to be a human carcinogen (NTP, 2005).  In 1999, 1,2,3-TCP was added to the list of chemicals known to the state  to cause cancer [Title 22, California Code of Regulations, Section 12000].

Monitoring Requirement and Monitoring Results

In 2001, to obtain information about the presence of 1,2,3-TCP in drinking water sources, we adopted a regulation that included it as an unregulated contaminant for which monitoring is required (UCMR).  For this monitoring, we developed protocols for analytical methods for 1,2,3-TCP at levels comparable to the notification level of 0.005 µg/L.   Monitoring under the UCMR regulation was to have been completed by the end of 2003.  Some water systems continue their monitoring for 1,2,3-TCP.

As of July 1, 2009, detections of 1,2,3-TCE in two or more samples (Excel)were reported in 335 sources, belonging to 86 water systems in 17 counties (see Table 1).  The highest 1,2,3-TCP level reported to date is 57 µg/L, from a Burbank OU well sample taken in 2001.

Though monitoring for 1,2,3-TCP had occurred from 1989 through the 1990s under earlier UCMR regulations, fewer than 20 sources had reported detections.  This likely reflected the less sensitive analytical method available at that time and the reporting limit of 0.5 µg/L.

Future Regulation of 1,2,3-TCP

Given the number of sources with 1,2,3-TCP detections (also see UCMR monitoring results), the Department considered this chemical to be a good candidate for future regulation (i.e., establishment of a drinking water standard, also known as a maximum contaminant level or MCL).  Thus, in July 2004 we requested a public health goal (PHG) from the Office of Environmental Health Hazard Assessment (OEHHA) to begin the early steps of the regulatory process. 

In September 2007, OEHHA released a draft PHG, and in January 2009, a revised draft PHG.  In August 2009, OEHHA established a 0.0007-µg/L PHG for 1,2,3-TCP.

In the absense of an MCL for 1,2,3-TCP, CDPH will continue to use the 0.005-µg/L notification level to provide information to local governing agencies and consumers.

References