Agency for Toxic Substances and Disease Registry
Case Studies in Environmental Medicine (CSEM) 

Trichloroethylene Toxicity
What Are the U.S. Standards for Trichloroethylene Exposure?

Learning Objective

Upon completion of this section, you should be able to:

• identify the OSHA permissible exposure limit (PEL) for TCE and
• identify the EPA’s maximum contaminant level (MCL) for TCE in drinking water.

Introduction

The government has developed regulations and guidelines for TCE. These standards are designed to protect the public from potential adverse health effects.

Workplace Standards

The OSHA permissible exposure limit (PEL) is a time-weighted average (TWA) of 100 ppm, with 300 ppm TCE as a 5-minute maximum peak allowable in any 2-hour period (OSHA 1993).

The National Institute for Occupational Safety and Health (NIOSH) considers TCE a potential occupational carcinogen and recommends an exposure limit of 2 ppm (as a 60-minute ceiling) during the usage of TCE as an anesthetic agent (TCE is no longer used as an anesthetic agent) and 25 ppm as a 10-hour TWA during all other exposures.

The American Conference of Governmental Industrial Hygienists (ACGIH) recommends an 8-hour TWA of 50 ppm and a short-term exposure limit (STEL) of 100 ppm (American Conference of Governmental Industrial Hygienists. 2003).

Biologic exposure indices (BEIs) recommended by ACGIH that might involve either direct or indirect measures of individual worker exposure.

• The TCE metabolite, free trichloroethanol, can be measured in the blood. However, a number of other compounds affect the level of trichloroethanol found in the blood, thereby clouding the clinical significance of this metabolite as an indicator of TCE exposure. Thus, if higher-than-expected blood levels of trichloroethanol are detected, the clinician must consider alternate explanations for the elevated levels (Agency for Toxic Substances and Disease Registry 1997).
• Alternatively, a concentration of 100 milligrams (mg) of trichloroacetic acid per gram of creatinine in urine at the end of the work week reflects the upper biologic limit for TCE exposure. Urinary trichloroacetic acid levels can be increased by the same compounds that affect blood trichloroethanol levels (Agency for Toxic Substances and Disease Registry 1997). Because of large individual variations, a urinary trichloroacetic acid level of 100 mg per gram of creatinine should be used only as a "warning" level or mean for a group of workers (American Conference of Governmental Industrial Hygienists. 2003; Meditext 2004).

Table 1 summarizes current standards and regulations for TCE exposure.

American Conference of Governmental Industrial Hygienists

Air: workplace

50 ppm

100 ppm

Advisory; TLV/TWA^†

Advisory; STEL^‡

National Institute for Occupational Safety and Health

Air: workplace

25 ppm

Recommendation; 10-hour TWA^§; potential carcinogen

Occupational Safety and Health Administration

Air: workplace

100 ppm

300 ppm

Regulation; PEL^¶ over 8-hour workday

Regulation; 5-minute maximum peak in any 2 hour period

Environmental Protection Agency

Air: environment

Not available

Not available

Drinking water

5 ppb

Regulation

^*ppm: parts per million; ppb: parts per billion.

^†TLV/TWA (threshold limit value/time-weighted average): time-weighted average concentration for a normal 8-hour workday or 40-hour work week to which nearly all workers may be repeatedly exposed.

^‡STEL(short-term exposure limit): concentration at which workers can be exposed continuously for a short period of time (usually 15 minutes) without suffering irritation, chronic irreversible tissue damage, or narcosis.

^§TWA (time-weighted average): concentration for a normal 8-hour workday and 40-hour work week is set at a level at which nearly all workers may be repeatedly exposed without adverse effects.

^¶PEL (permissible exposure limit): highest level averaged over an 8-hour workday to which a worker may be exposed. Note: A PEL of 50 ppm was enacted by Occupational Safety and Health Administration in 1989, but that level along with 375 others, was vacated for procedural reasons by the 11th Circuit Federal Court in 1993.

Environmental Standards

Environmental exposures to TCE are generally low and are decreasing because limitations have been imposed on its use as an anesthetic, solvent extractant, fumigant, and dry-cleaning agent.

Air

TCE has a short atmospheric half-life (less than seven days) and is not likely to bioaccumulate in the food chain.

Water

The World Health Organization recommended drinking water limit is 30µg TCE/liter (L) of water (30 ppb). EPA has set a maximum contaminant level (MCL) of 5µg/L (5 ppb) in drinking water (U.S. Environmental Protection Agency 1985).

Although there is no incontrovertible evidence of human health effects associated with exposures to environmental levels of TCE (Brown, Farrar et al. 1990), the issue is not entirely settled. More reliable information is necessary for a final assessment.

Key Points

• OSHA’s current permissible exposure limit is 100 ppm.
• EPA has established a drinking water MCL for TCE of 5 ppb.

Progress Check