Dense Nonaqueous Phase Liquids (DNAPLs)

Halogenated Alkanes

Ethylene Dibromide

Human Health Toxicity

The general public could be exposed to EDB (also referred to as 1,2-dibromoethane) by the consumption of contaminated groundwater, as well as by inhalation and skin absorption when the water is used for showering. Workers in plants that either manufacture or use EDB in industrial processes might be exposed by inhalation and dermal contact.

EDB is acutely toxic via ingestion, inhalation, and dermal exposure. Formulations containing EDB and EDB in liquid form have been used, often successfully, in suicide attempts. Autopsy investigations of cases of acute EDB poisoning (by ingestion) have reported the causes of death to be massive liver necrosis and kidney failure.

Although known to be acutely toxic, long-term (chronic) exposure to EDB at lower doses than those that cause acute toxicity may be harmful to the human population, and evidence from laboratory animal studies supports this assumption. Two epidemiological studies are available for workers occupationally exposed to this chemical. Both studies suggest that EDB exerts toxic effects on the male reproductive system.

An oral reference dose (RfD)- i.e., an estimate of a daily exposure of the human population that is likely to be without appreciable deleterious effects during a lifetime- is presented in EPA's Integrated Risk Information System (IRIS) summary for 1,2-dibromoethane. The RfD, which is protective of sensitive sub-populations within the general human population, is 9 x 10^-3 mg/kg/day. A reference concentration (RfC) of 9 x 10^-3 mg/m³ for EDB inhaled from ambient air is given by the IRIS Program. This RfC represents an estimate of a daily inhalation exposure of the human population that is likely to be without appreciable risk of deleterious effects during a lifetime.

EDB has been shown to increase the incidence of tumors in both sexes of laboratory rodents by different routes of administration. Tumors occurred at the site of administration and at distant sites. EDB is classified by the IRIS program as "likely to be carcinogenic to humans" and as "reasonably anticipated to be a human carcinogen" by the National Toxicology Program in its eleventh Report on Carcinogens (2005).

IRIS provides an oral slope factor of 2 x 100 (mg/kg/day)^-1, giving an estimate of carcinogenic risk of 2 x 10^-1 µg/L in drinking water for a risk level of one additional case of cancer in 100,000. Also provided is an inhalation unit risk (IUR) of 6 x 10^-4 (µg/m3)^-1, giving an estimate of carcinogenic risk in air of 2 x 10^-2 µg/m³ for a risk level of 1 in 100,000.

Many investigations using both in vivo and in vitro tests have shown EDB to be mutagenic. The compound is directly mutagenic to bacteria and produces chromosomal aberrations in isolated cell systems, such as Chinese hamster ovary cells and isolated human lymphocytes.

The MCL for EDB is .05 ug/L. The regional screening levels (formerly Preliminary Remediation Goals) posted by EPA Region 9 identify risk-based concentrations for EDB for the following common exposure pathways:

Residential soil	3.4 E-02 mg/kg
Industrial soil	1.7 E-01 mg/kg
Residential air	4.1 E-03 ug/m3
Industrial air	2.0 E-02 ug/m3
Tapwater	6.5 E-03 ug/L

References

1,2-Dibromoethane (CASRN 106-93-4)
U.S. EPA, Integrated Risk Information System (IRIS)

1,2-Dibromoethane (Ethylene Dibromide)
Report on Carcinogens, Fourteenth Edition. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program (NTP), 2016

Regional Screening Levels
U.S. EPA Region 9, 2009

Toxicological Profile for 1,2-Dibromoethane
Agency for Toxic Substances and Disease Registry (ATSDR), 2018

Ecological Toxicity

Although a large number of studies have been performed on laboratory rodents to determine the mode of action and the effects of chronic exposure to EDB, there are few studies of its toxicity to wildlife. The existing wildlife studies generally employ aquatic species and are designed to determine the concentration at which EDB could be expected to be acutely toxic. These range-finding investigations are usually LC₅₀ studies. An LC₅₀ is defined as the median lethal concentration- specifically, the concentration of a chemical required to kill 50 percent of the test subjects in a stated time.

Aquatic Toxicity

For the larvae of several aquatic insects- the mayfly (Cloeon dipterum), dragonfly species (Sympetrum frequens and Orthetrum albistylum speciosum), Japanese diving beetle (Eretes sticticus), and the water boatman (Micronecta sedula)- 48-hr LC₅₀ values have been estimated to be >40 mg/L. A 48-hr LC₅₀ of 70 mg/L has been determined for the aquatic invertebrate hydra (Hydra oligactis). EDB exerted an adverse effect on the ability of this invertebrate to regenerate after section. For octopus species Octopus bimaculoides, O. joubini, and O. maya, 48-hr LC₅₀ values of 42.7, 35.3, and 30.6 mg/L, respectively, have been determined. These animals responded to EDB after an exposure of 1 minute. At a concentration of 25 mg/L, chromatophore expansion and locomotor response was lost after 30 minutes, but the animals were able to recover (after 6 hours) if transferred to clean water.

EDB is moderately toxic to juvenile sheepshead minnows (Cyprinodon variegautus) and snook (Centroponus undecimatis), with 48-hr LC₅₀ values estimated at 4.8 and 6.2 mg/L, respectively, and slightly toxic to fingerling bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides), with 48-hr LC₅₀ values estimated in the range of 18 to 25 and 15 to 25 mg/L, respectively. Japanes medaka (Oryzias latipes) developed a variety of cancers when exposed to EDB at concentrations of 6.2 mg/L and 18.58 mg/L for periods of 73 and 97 days.

Terrestrial Toxicity

EDB was employed commercially as a soil and crop fumigant because of its toxicity to soil nematodes and post-harvest insect pests infesting grain, pulses, and citrus fruit. Because evidence suggests that EDB is phytotoxic, the compound typically was used during pre-planting or post-harvest expressly to avoid plant damage.

Many avian studies of EDB toxicity were made in the mid-1950s to early 1960s, when EDB was in use as a crop fumigant. These investigations used domestic fowl, usually chickens (Gallus gallus). Short-term investigations that employed grain with absorbed EDB in amounts ranging from 50 to 320 parts per million (ppm) reported a decrease in egg weight proportional to the level of fumigant. At 320 ppm, egg laying ceased after 6.5 weeks, and at 200 ppm ceased after 8 weeks. Egg laying did not resume when the birds were returned to a normal diet.

A study of bull calves given 2 mg/kg/day EDB from 4 days reported these animals to be of normal health, weight, and libido after 14 to 16 months. Although sperm density was low and motility poor, these changes were reversible.

References

Environmental Health Criteria 177: 1,2-Dibromoethane
Sekizawa, J.
World Health Organization, International Programme on Chemical Safety, 1996

Ethylene Dibromide: Identification, Toxicity, Use, Water Pollution Potential, Ecological Toxicity, and Regulatory Information
Kegley, S.E., B.R. Hill, S. Orme, and A.H. Choi.
PAN Pesticide Database. Pesticide Action Network, San Francisco, CA, 2009