1,2,3,-Trichloropropane

Last Update: April 3, 2013

In 1999, we established a 0.005-micrograms per liter (µg/L) drinking water notification level for 1,2,3-Trichloropropane (1,2,3-TCP).  This value is based on cancer risks derived from laboratory animals studies (US EPA , 1997).  The notification level is at the same concentration as the analytical reporting limit, as described below.  Certain requirements and recommendations apply if 1,2,3-TCP is detected above its notification level.

The 1,2,3-TCP notification level was established after its discovery at the Burbank Operable Unit (OU) — a southern California Superfund hazarous waste site — because of concerns that the chemical might find its way into drinking water supplies.  It had been found in several drinking water wells elsewhere in the state at that time.  Subsequently 1,2,3-TCP was found in more drinking water sources (see below).

1,2,3-TCP causes cancer in laboratory animals (US EPA, 2009).  It is reasonably anticipated to be a human carcinogen (NTP, 2011), and probably carcinogenic to humans, based on sufficient evidence of carcinogenicity in experimental animals (IARC, 1995).  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].

CDPH's precursor, the Department of Health Services (CDHS), 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.  Its industrial uses, according to NTP (2011), have been as a paint and varnish remover, cleaning and degreasing agent, and a cleaning and maintenance solvent, and as a chemical intermediate.  Its association with past pesticide uses includes its presence in dichloropropenes (as a byproduct/impurity) and  in the manufacture of D-D (a dichloropropane-dichloropropene mixture), used as a soil fumigant (IARC, 1995).

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 November 15, 2011, detections of 1,2,3-TCP in two or more samples (Excel, 1.2MB)were reported in 336 active and standby sources, belonging to 89 water systems in 17 counties (see Table 1). 

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.

Though the UCMR testing is no longer required, CDPH recommends -- when analyses for 1,2,3-TCP are performed -- that water systems' laboratories use the more sensitive analytical methods for 1,2,3-TCP, in order to enable better characterization of the presence of the chemical in drinking water sources.

The water quality monitoring database is available here.

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.

CDPH is currently developing an MCL for 1,2,3-TCP, which is expected to be released for public comment in 2014, as part of the formal regulations adoption process. In the interim, we will continue to use the 0.005-µg/L notification level to provide information to local governing agencies and consumers.

References

US EPA, 2009.. Toxicological Review of 1,2,3-Trichloropropane (PDF)in Support of Summary Information on the Integrated Risk Information System (IRIS), US EPA. September 2009.  IRIS summary is here.