1,2,3,-Trichloropropane

Last Update: December 26, 2007

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 Health Services (CDHS, now CDPH), in its 2001 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.  

Notification Level

The drinking water notification level for 1,2,3-TCP, first established by CDHS in 1999, is 0.005 micrograms per liter (µg/L). Certain requirements and recommendations apply if it is detected above this level.

CDHS established the 1,2,3-TCP notification level 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

In 2001, to obtain information about the presence of 1,2,3-TCP in drinking water sources, CDHS adopted a regulation that included it as an unregulated contaminant for which monitoring is required (UCMR).  For this monitoring, CDHS 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.

Monitoring Results

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.

As of August 2, 2006, 85 water systems in 16 counties reported 1,2,3-TCP detection (Excel)(two or more) in 303 sources. (NOTE: these data are draft - they will change with subsequent updates).  

The highest 1,2,3-TCP level reported to date is 57 µg/L, from a Burbank OU well sample taken in 2001.

Future Plans

Given the number of sources with 1,2,3-TCP detections (also see UCMR monitoring results), this chemical is 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 (PDF) for 1,2,3-TCP of 0.0007 µg/L (OEHHA, 2007)

An MCL for 1,2,3-TCP will likely not be available for several years, so CDPH will continue to use the notification level to provide information to local governing agencies and consumers.

References